Thermal pressure sensor for measuring a pressure of a fluid

Abstract

In one aspect, the invention relates to a pressure sensor for measuring a pressure of a fluid. The pressure sensor comprises a detection chamber within which a thermal sensor is arranged. The thermal sensor comprises a heating element for providing a thermal field and a sensor component for detecting a temperature response of the thermal sensor. The heating element is designed to be controlled in an oscillating manner at at least one frequency. The pressure of the fluid can be determined on the basis of the temperature response of the thermal sensor. The thermal sensor is positioned on a support membrane which is held by a support structure and extends over a cavity. Furthermore, there is an aperture which allows for pressure compensation between the cavity and an interior region of ​​the detection chamber. In further aspects, the invention relates to a method for measuring a pressure of a fluid and to a use of the pressure sensor according to the invention for monitoring.

Description

[0001] THERMAL PRESSURE SENSOR FOR MEASURING THE PRESSURE OF A FLUID

[0002] DESCRIPTION

[0003] The invention lies in the technological field of thermal pressure sensors.

[0004] In one aspect, the invention relates to a pressure sensor for measuring the pressure of a fluid. The pressure sensor comprises a detection chamber within which a thermal sensor is arranged. The thermal sensor comprises a heating element for providing a thermal field and a sensor component for detecting a temperature response of the thermal sensor. The heating element is designed to be controlled in an oscillating manner at at least one frequency. The pressure of the fluid can be determined based on the temperature response of the thermal sensor. The thermal sensor is positioned on a support membrane, which is held by a support structure and extends over a cavity. Furthermore, an aperture is present, which enables pressure equalization between the cavity and an interior region of the detection chamber.

[0005] In further aspects, the invention relates to a method for measuring a pressure of a fluid and a use of the pressure sensor according to the invention for monitoring a pressure of a fluid.

[0006] Background and state of the art

[0007] Microsystems technology is now used in many applications to manufacture compact, mechanical-electronic devices. The resulting microelectromechanical systems (MEMS) are extremely compact (in the micrometer range) while simultaneously offering excellent functionality and ever-decreasing manufacturing costs.

[0008] Microsystem technology can also be used to provide pressure sensors, enabling compact pressure measurement in various research and application areas.

[0009] Various measurement principles are known for measuring pressure. Javed, Ali Shah & Mansoor (2019) provides an overview of known measurement principles for determining pressure.

[0010] In particular, mechanical pressure sensors are known, which are usually based on the deflection of a membrane. The deflection can be detected, for example, by a piezoresistive, piezoelectric, capacitive, or optical effect.

[0011] A corresponding piezoresistive pressure sensor comprises, for example, one or more strain gauges arranged on a membrane and interconnected, for example, via a Wheatstone bridge circuit. When pressure is applied, the membrane and the strain gauges buckle. The deformation of the strain gauges causes a change in the electrical resistance. The change in resistance, or the associated voltage change, allows a conclusion to be drawn about the pressure.

[0012] In capacitive pressure sensors, a pressure-dependent deflection of a diaphragm is capacitively detected. For this purpose, a rigid backplate is provided, which, like the deflectable diaphragm, exhibits electrical conductivity. A change in the pressure acting on the deflectable diaphragm changes the distance between the diaphragm and the backplate. The change in distance can be detected as a change in electrical capacitance. Since the change in distance between the diaphragm and the backplate corresponds to the pressure acting on the diaphragm, the capacitive measurement can be used to determine the pressure.

[0013] Optical pressure sensors, which detect the pressure-dependent deflection of a membrane using optical means, are also common. In this case, light is usually emitted from a light source onto a deflectable membrane. The light reflected by the membrane is detected by a detector. The membrane is in fluid communication with an environment for which the pressure is to be measured. When pressure is applied to the membrane, a corresponding curvature occurs, which can be detected by a change in the reflection of the light.

[0014] Furthermore, various designs of piezoelectric pressure sensors are known in the prior art that utilize the piezoelectric effect for pressure measurement. In this case, a piezoelectric material is connected to one or more electrodes. The deformation of the piezoelectric material due to pressure results in a voltage generation that can be measured using one or more electrodes.

[0015] Thermal pressure sensors represent another alternative to conventional mechanical pressure sensors for measuring pressure. Thermal pressure sensors measure the change in a thermodynamic or thermal quantity due to the influence of pressure. Pressure can be determined using various thermal quantities.

[0016] An example thermal pressure sensor is described in Ohji et al. (2011). The thermal pressure sensor comprises a metal-based membrane that acts as a heat sink. Furthermore, the metal membrane can be deflected as a result of pressure. Above the metal membrane is a rigid nitride membrane on which a heating element is positioned. The heating element is designed as a heating resistor, which also acts as a sensor. When pressure is applied to the metal membrane, the distance to the nitride membrane decreases. To create a heat field, the heating resistor is impacted with an electric current. If the distance between the nitride membrane and the metal membrane or heat sink is reduced, the temperature at the heating element drops. This makes it possible to draw conclusions about the applied pressure based on the temperature measurement at the heating resistor.

[0017] US 6393919 B1 discloses a thermal pressure sensor having a similar structure to the previously described thermal pressure sensor. The thermal pressure sensor comprises a heat-insulating membrane, which may comprise, for example, silicon nitride. The membrane is positioned on a base material. Furthermore, a heat-sensitive resistance layer is present on the membrane, which functions as a heating element and sensor component. Furthermore, the thermal pressure sensor comprises a deflectable diaphragm for sensing pressure. The deflectable diaphragm extends along a cylindrical body. Furthermore, spacers are provided so that a spatial gap exists between the heat-insulating membrane and the diaphragm, which are positioned opposite one another. The heating resistor is electrically connected to a control unit so that power or an electric current can be applied to the heating resistor to generate heat.When pressure is applied to the diaphragm, heat flows between the diaphragm and the heat-insulating membrane. This flow depends on the deflection of the diaphragm, which in turn depends on the applied pressure. By measuring the variation in temperature, resistance, and / or other electrical variables at the heating resistor, the deflection of the diaphragm and, consequently, the pressure can be determined. One embodiment includes a second heat-sensitive resistance layer. The second heat-sensitive resistance layer is positioned such that it is applied opposite a fixed end of the diaphragm. This is intended to record a reference signal that is largely independent of the applied pressure.

[0018] US 6619130 B1 describes a thermal pressure sensor constructed similarly to the pressure sensor of US 6393919 B1. The pressure sensor also comprises a deflectable diaphragm, which is located on a cylinder and serves to record the pressure of a measuring fluid. A heat-insulating membrane is mounted opposite the diaphragm, on which a heat-sensitive resistance layer is located as a thermal sensor. The pressure of the measuring fluid can be determined by the deflection of the diaphragm based on a variation in heat flow. In one embodiment, the thermal pressure sensor additionally has a second chamber, a second diaphragm, and a second heat-sensitive resistance layer. No pressure is transmitted to the second diaphragm, so it is not deflected. The second heat-sensitive resistance layer is mounted opposite the second diaphragm to provide a reference signal.

[0019] The thermal pressure sensors described in US 10436665 B2 and US 6619130 B1 measure the changing distance of the heat sink in the measuring chamber and thus the heat dissipation from the heating element. The sensitivity of these sensors, in turn, depends on the mechanical properties of the membrane or diaphragm.

[0020] Another well-known approach to thermal pressure sensors is so-called Pirani sensors. Pirani sensors exploit the fact that, within certain limits, the thermal conductivity of gases is pressure-dependent. In particular, Pirani sensors exploit the fact that the thermal conductivity of a gas depends essentially linearly on the pressure within a certain pressure range. For this purpose, a Pirani sensor can comprise a wire, synonymously also called a heating wire, which is positioned inside a tube and heats up when a current is applied. This is also referred to as a static pressure measurement. The pressure dependence of the thermal conductivity of the gas heated by the heating wire can be characterized by the so-called Knudsen number Kn. The Knudsen number is defined as Kn = A / l, where A denotes the mean free path and I the characteristic length, where the characteristic length is a value that depends on the structural orThe Knudsen number is a dimensionless parameter that can describe the behavior of a gas within specific pressure ranges. At high pressures and Kn«1, the gas flow can be considered a continuum flow. At low pressures and Kn»1, the gas flow can be considered a molecular flow. Pirani sensors should preferably operate in the molecular regime, since only within this regime is there an essentially linear relationship between pressure and the thermal conductivity of the gas.

[0021] Various micro-Pirani sensors, i.e. Pirani sensors based on MEMS, are known in the prior art. These are usually statically controlled, i.e. they comprise a heating element that is driven by a direct current. The sensitivity of a micro-Pirani sensor is proportional to the area of ​​the heating element and also depends on the gap through which the gas is to flow, which exists between a heating element for heating the gas and a heat sink. A smaller gap allows the measurement to be shifted to higher pressures. The small gap reduces a characteristic path length and thus keeps the Knudsen number significantly greater than 1 even at higher pressures. However, the formation of a smaller gap between a membrane on which the heating element is positioned and a heat sink is difficult to achieve due to surface tension and sticking effects.Khosraviani & Leung (2007) propose a micro-Pirani sensor with a gap spacing of 25 nm. However, its fabrication proves to be complex.

[0022] Often, the static excitation of thermal pressure sensors, such as micro-Pirani sensors, limits the pressure range to be measured. For example, a static measurement can only be performed at < 100 mbar (see Zhang & Laser (2018)). Against this background, there are also isolated approaches in the state of the art for thermal pressure sensors that utilize dynamic excitation, i.e., a heating element is controlled by an oscillating signal.

[0023] Zhang & Laser (2018) discloses a micro-Pirani sensor capable of detecting even higher pressure values. The micro-Pirani sensor is implemented using SOI technology from MEMSCAP. Two resistors are connected in series via a half-Wheatstone bridge circuit. Specifically, a pulse signal is applied to the bridge circuit. Based on the temperature response, the pressure of a gas passing through the wires that provide the thermal field is determined.

[0024] Legendre et al. (2015) describes a pressure sensor that uses a 1 mm long polysilicon wire as a heating element. Oxide layers are applied to the front of the wire, while a nitride layer is applied to the underside. The sensor structure is located above a substrate cavity that has openings to allow the passage of a gas. The wire is dynamically controlled to measure a transient temperature response to a pressure.

[0025] US 8047711 B2 discloses a measuring system that also serves to measure the pressure of a fluid. The system comprises a sensor element that includes a thermocouple and can generate a thermoelectric voltage. Furthermore, the measuring system comprises a first circuit configured to output pulses to the sensor element. A second circuit is provided to measure a thermoelectric voltage at the sensor element. Heating pulses are activated when the thermoelectric voltage is below a lower threshold. Furthermore, the heating pulses are deactivated during a cooling period when the thermoelectric voltage exceeds an upper threshold. The duration of the heating period, cooling period, or the sum of the two time periods is determined in order to determine the pressure of the fluid based on this.

[0026] US 2012 / 0118060 A1 discloses a barometric heat conduction sensor. The barometric heat conduction sensor is based on a thin film that is thermally separated from a substrate above a cavity. The thin film can be designed, for example, as a cantilever, but designs as a diaphragm are also possible. The thin film preferably comprises various thin film layers that have different expansion coefficients. A heater and a thermocouple are attached to the (front) thin film of the cantilever, while another thermocouple is positioned on the (rear) thin film of the cantilever. The heater is controlled with an intermittent square-wave signal. Controlling the heater causes a recurring bending of the cantilever. The vibration or bending is intended to cause air flow or convection of the ambient gas.As a result, the thermocouple (at the rear end of the cantilever) is cooler than the thermocouple at the front end of the cantilever. The temperature difference depends on the barometric pressure of the ambient gas, which should make it possible to measure pressures of 1 atm or higher. The performance or sensitivity of the sensor depends on the thermal expansion coefficient and mechanical material properties (Young's modulus) and dimensions (length-to-thickness ratio), the mechanical clamping of the cantilever, the frequency, and the power of the excitation (resonance behavior). Due to the vibration of the cantilever, there is no defined distance to the heat sink. Slits in the thin film are intended to reduce heat conduction to the substrate. In other embodiments, a cap is placed above the thin film, with holes also provided in the cap. The cap is intended to provide protection for the sensor.

[0027] JP 2007147344 A relates to a Pirani sensor comprising a thin film with two sections or two thin film sections. The first thin film section has a heater and a first temperature sensor, while the second thin film section comprises a second temperature sensor. The heater is controlled with a rectangular pulse. Between the thin film sections, there is a slit, which acts as a thermal resistor, so that heat transfer occurs via the gas. The first and second thin film sections are preferably formed by a 10 μm thick silicon layer, on which the heater and temperature sensor are provided. Furthermore, the Pirani sensor comprises a substrate and a cover, which are present as components of an SOI substrate. Slits formed by a DRIE process are present on the cover.The cover serves in particular as a defined heat sink and significantly influences heat conduction at higher pressures in the range of approximately 1 bar. Above the second thin film, there is a heat sink with a bulge or protrusion to create a narrow gap between the heat sink and the second thin film, on which the temperature sensor is located. Since the heated second thin film is cooled by heat transfer to the heat sink via the narrow gap, depending on the vacuum, the vacuum or pressure should be measured with high sensitivity without saturating the temperature response in the low vacuum range. Due to the gap, with a small distance of approximately 200 nm, the Knudsen number should be greater than 1 even for an atmospheric pressure of approximately 1 bar. At higher pressures, however, the mean free path of the gas is so small that the required gap dimensions can no longer be manufactured.The ability to achieve a defined distance to the heat sink with small gap dimensions thus limits the pressure measuring range and the usability of the structure at higher pressures.

[0028] US 10436665 B2 describes arrangements for a Pirani sensor and a micro-Pirani sensor. In the Pirani sensor, a filament heating element is mounted below the measuring element. The filament heating element generates heat, which is emitted to the measuring element. The radiated heat compensates for at least part of the heat lost from the measuring element through thermal radiation. A similar structure is described for micro-Pirani sensors. By evaluating the heat transfer from the measuring elements to the fluid, a pressure is to be determined, among other things. The ambient temperature is measured, and a compensation signal for the measuring elements is selected based on the measured ambient temperature. By applying a compensation signal, heat loss through thermal conduction and thermal radiation is to be compensated, thus achieving increased sensitivity for the sensor, whereby low pressures down to approximately 10 -6mbar can be measured. Oscillating excitation of the heating elements is not disclosed.

[0029] Thermal pressure sensors have advantages over mechanical pressure sensors in that they generally do not require movable or additional evaluation structures, which allows for a simpler structural design. However, known micro-Pirani sensors in particular are usually limited in their ability to measure higher pressures or require complex manufacturing to achieve good sensitivity even for higher pressures by reducing the gap spacing and / or increasing the heating surface. Thermal pressure sensors with dynamic excitation sometimes offer improvements in their measuring range. However, there is still a need for improvements. For example, the sensitive structures are often directly exposed to the fluid, which can lead to cross-sensitivities due to the influence of flows or changes in fluid composition.High pressures can also damage fragile components of known thermal pressure sensors, such as a membrane on which the heating element is positioned. The object of the invention is to achieve this.

[0030] The object of the invention is to provide a pressure sensor that eliminates the disadvantages of the prior art. In particular, the object of the invention is to provide a thermal pressure sensor that is characterized by a wide measuring range combined with high sensitivity and a compact design.

[0031] Summary of the invention

[0032] The object of the invention is achieved by the independent claims. Further advantageous embodiments of the invention are disclosed in the dependent claims.

[0033] In a first aspect, the invention relates to a pressure sensor for measuring a pressure of a fluid comprising a detection chamber within which a thermal sensor is arranged, wherein the thermal sensor comprises a heating element for providing a thermal field and a sensor component for detecting a temperature response of the thermal sensor as a function of an influence of the fluid on the thermal field, characterized in that the heating element is designed to be controlled in an oscillating manner at at least one frequency and the pressure of the fluid can be determined on the basis of the temperature response of the thermal sensor, wherein the thermal sensor is positioned on a carrier membrane which is held by a carrier structure and extends over a cavity and wherein an aperture enables pressure equalization between the cavity and an interior region of the detection chamber.

[0034] The pressure sensor according to the invention advantageously eliminates the disadvantages of conventional Pirani sensors. As explained above, the detectable pressure range of Pirani sensors is often limited, which means that pressure measurements are typically carried out at well below 1 bar. At higher pressures, however, saturation occurs, making it difficult or even impossible to determine the pressure. The measuring principle of Pirani sensors is based on the dependence of thermal conductivity on pressure. At very low Knuden number values, thermal conductivity is independent of pressure. In order to make Pirani sensors more sensitive even at high pressures, it is known to reduce the gap between a heating element and a heat sink and / or to increase the surfaces facing the heat sink. However, this results in more complex processing and may lead to a loss of mechanical stability.

[0035] The disadvantages of known Pirani sensors, which are based on a static measuring principle, are advantageously eliminated by the pressure sensor according to the invention. In particular, with an oscillating control of the heating element, which in the context of the invention can be understood as a dynamic excitation, the temperature response depends significantly on the volumetric heat capacity. The volumetric heat capacity, in turn, exhibits a pressure dependence that does not saturate at high pressures. Instead, there is advantageously an almost linear relationship between the volumetric heat capacity and the acting pressure (see Fig. 2). Because the pressure sensor according to the invention does not exhibit saturation at or within a certain pressure range, the pressure can therefore be measured over a significantly larger measuring range.In particular, pressure measurements for pressures significantly above 1 bar are also possible, making the pressure sensor suitable for measuring pressure in gas tanks, for example. In particular, pressures significantly above 1 bar, such as 10 bar or even 100 bar or more, can also be measured. The extended measuring range also broadens the fields of application.

[0036] In particular, a substantially linear relationship between the temperature response, for example, between an inverse of an amplitude and / or a phase of the temperature response, and the pressure can be advantageously used to allow a conclusion to be drawn about the pressure of the fluid. It may also be preferred that other mathematical variables that can be derived from the temperature response be used to determine a pressure. These include, in particular, an amplitude, a phase, their inverses, and / or combinations thereof.

[0037] In preferred embodiments, a calibration measurement is first performed for this purpose. Preferably, for an oscillating control according to the invention, a temperature response, in particular an amplitude and / or phases of a temperature response, is recorded for a series of measurements of known pressures, which would preferably be expected during use of the pressure sensor.

[0038] By means of the calibration measurement, a relationship between a quantity derivable from the temperature response, for example a phase and / or amplitude of the pressure, can be determined for the pressure sensor. According to the invention, it was advantageously found that, with an oscillating excitation, a quantity derivable from the temperature response, for example a phase and / or an inverse of an amplitude, exhibits a substantially linear relationship over a wide measuring range and, in particular, does not saturate. With knowledge of a corresponding calibration curve, the pressure can thus be easily deduced during subsequent use of the pressure sensor by measuring a specific temperature response (or, for example, its phase and / or amplitude).

[0039] Furthermore, the pressure sensor according to the invention has a simple, compact, and robust design. Unlike known Pirani sensors, it is not necessary to make structures such as the heating element of a pressure sensor larger in order to optimize sensitivity and / or the measuring range. Instead, the pressure sensor according to the invention enables reliable measurements of the pressure of a fluid even with compact dimensions.

[0040] A further advantage of the pressure sensor according to the invention is that it can be provided by means of simple processing. In particular, the pressure sensor can be manufactured using simple and proven methods of semiconductor technology and / or microsystem technology. The provision of complexly structured components to reduce a gap distance in known Pirani sensors is advantageously not necessary. Instead, the thermal pressure sensor can comprise a flat carrier membrane on which the thermal sensor is positioned and which extends over a cavity. Due to an oscillating excitation provided according to the invention, the Knudsen number advantageously does not limit the possible measuring range. In this respect, it is not necessary to reduce a gap size by providing complex structures.Instead, there is a high degree of flexibility regarding the dimensioning of the carrier membrane as well as the cavity in order to achieve a desired compact design while maintaining a high measuring range.

[0041] A further advantage of the pressure sensor according to the invention lies in the provision of a detection chamber and in the fact that the pressure sensor has an aperture to enable pressure equalization between the cavity and an interior region of the detection chamber. The detection chamber of the pressure sensor advantageously initially represents mechanical protection, for example, for the thermal sensor. Furthermore, it prevents the thermal sensor from seeing, for example, a fluid flow, which could lead to anemometric heat dissipation and forced convection and falsify the measurement results. Instead, the detection chamber separates an inner region in which the thermal sensor is located from an outer region of an environment in which the fluid is located and whose pressure is to be detected.

[0042] The detection chamber can preferably be a closed or open detection chamber. In both cases, it is ensured that an external pressure in the environment of the detection chamber propagates into the interior, so that the internal pressure in the detection chamber essentially corresponds to the external pressure. In the case of a closed detection chamber, this is achieved by a deflectable membrane. In the case of an open detection chamber, the introduction of one or more targeted openings leads to a corresponding equalization of the pressure within the detection chamber, advantageously, however, without any fluid flow also penetrating the interior of the detection chamber and influencing the thermal measurement.

[0043] In the pressure sensor according to the invention, a change in the pressure of the fluid leads to a change in the pressure of the fluid within the detection chamber. The fluid within the reference chamber can be the fluid to be measured, particularly in an open detection chamber, or a reference fluid within the detection chamber, particularly in a closed detection chamber. A change in the fluid surrounding the reference chamber leads to a compression or decompression of the fluid (measured fluid or reference fluid). The compression or decompression is reflected in the temperature response of the thermal sensor, on the basis of which the pressure can be determined.

[0044] The thermal sensor itself is located within the detection chamber on a support membrane, which in turn is located above a cavity. Such a design advantageously allows for a particularly sensitive measurement of the volumetric heat capacity of the fluid (and thus indirectly of the pressure) within the detection chamber. The provision of an aperture for pressure equalization between the cavity and the interior of the detection chamber advantageously prevents mechanical deformation of the support membrane itself. While such pressure-dependent deformation of a membrane is essential for mechanical pressure sensors, it can lead to inaccurate measurement results in the case of a thermal measurement principle, since, for example, distances between a heating element and / or temperature sensor as a sensor component can change.The introduction of a corresponding aperture, for example by introducing the aperture into the carrier membrane, effectively prevents this.

[0045] Furthermore, the introduction of an aperture supports an expansion of the measuring range of the pressure sensor according to the invention to higher pressures. Thus, pressure equalization prevents the carrier membrane from bulging or deflecting under the influence of high pressures to such an extent that damage occurs. In particular, it advantageously prevents a possible tear in the carrier membrane and / or other damage to components of the pressure sensor. Consequently, the introduction of an aperture for pressure equalization can provide a pressure sensor with particularly long-term stability.

[0046] The pressure sensor according to the invention serves in particular to determine the pressure of a fluid by detecting a temperature response of the thermal sensor as a function of the influence of the fluid on a heat field generated by a heating element. Since the pressure measurement is based on a thermal measuring principle, the pressure sensor according to the invention is also referred to as a thermal pressure sensor. The pressure can be determined in particular by an amplitude of the temperature response and / or a phase difference (synonymously also just phase) between the temperature response and a control signal for an oscillating control of the heating element. In this case, the temperature response is preferably dependent on the frequency. The term "thermal" in the thermal sensor as a component of the pressure sensor also clarifies in particular that the pressure sensor is based on a thermal measuring principle, i.e.a thermodynamic quantity (of the fluid) is determined, from which a pressure can be determined.

[0047] The thermal sensor comprises a heating element and a sensor component. The heating element serves to provide a heat field that spreads out from the heating element. According to the invention, the control of the heating element is oscillating, so that the provision of the heat field emanating from the heating element is also oscillating. The term “oscillating” preferably means that periodic heating is caused emanating from the heating element. Thus, there are alternating phases in which heating and cooling take place. The corresponding phases are preferably caused by an oscillating control signal for the heating element. Preferred control signals for oscillating control of the heating element can preferably be described by a function that is selected, for example, from a group comprising a harmonic function (such as, for example,a sine and / or cosine function), a rectangular function, a pulse function, a triangular function, and / or a sawtooth function, without being limited thereto. In the context of the invention, the oscillating control can comprise one or more frequencies. In particular, the frequency can change during an oscillating control. For example, it may be preferred for the oscillating control to be carried out using a frequency that changes over time, as is the case, for example, with a chirp signal as the control signal.

[0048] The heating element can preferably be controlled with one frequency or with a plurality of frequencies across a frequency range. The latter enables, in particular, a frequency scan. A frequency scan can be used to determine a spectrum of a frequency-dependent temperature response. A frequency scan preferably refers to the control of the heating element and the reading of a temperature response across multiple frequencies within a frequency range, for example, from 10 mHz to 10 kHz, preferably 1 Hz to 1 kHz. The oscillating control can preferably have a constant amplitude, with only the frequency being increased. A corresponding frequency scan advantageously allows a frequency-dependent temperature response, in particular its amplitude and / or phase relationship to the exciting signal, to be determined across a broad frequency range, thus enabling a more meaningful analysis of the fluid.

[0049] The temperature response preferably relates to a measurement signal from the thermal sensor that changes as a result of the heating of the fluid by the heating element. In other words, the temperature response relates to the ability of the thermal sensor to detect a temperature change resulting from the generation of a thermal field by the heating element. The sensor component preferably refers to the structural component of the thermal sensor that is designed to record the temperature response. The sensor component can preferably be formed by a temperature sensor. It can also be preferred for the sensor component to be formed by the heating element itself. In other words, the temperature response preferably comprises an effect of a fluid on the thermal sensor upon corresponding oscillating excitation or control of the heating element.The temperature response preferably corresponds to an oscillating measurement signal whose frequency is preferably predetermined by the oscillating control of the heating element, whereby the temperature response can have a different phase and / or amplitude. However, the temperature response can also be evaluated at other frequencies, for example, integer multiples of the exciting frequency (so-called higher harmonic signals). The temperature response can preferably be an oscillating electrical signal whose amplitude can be described by an electrical voltage and / or an electrical current. The temperature response can also preferably relate to a thermal variable that can be read by the sensor component, such as a temperature.

[0050] The thermal sensor is installed in a detection chamber to record the temperature response. The detection chamber preferably refers to a component of the thermal pressure sensor, which has a casing and a cavity. Components such as the thermal sensor, the support membrane, and the support structure are installed in the cavity. A section of the casing of the detection chamber preferably serves to hold the support structure. The fluid to be measured is operatively connected to the detection chamber. The operative connection here preferably refers to a possible propagation of an (external) pressure of the fluid to be measured into the interior of the detection chamber.

[0051] The casing of the detection chamber preferably initially enables a substantial spatial separation of the pressure sensor from the environment. The fluid whose pressure is to be measured is preferably located in the environment of the detection chamber. For an operative connection for transmitting pressure between the thermal pressure sensor and the fluid in the environment, it may be preferred for the detection chamber to be an open or closed pressure chamber. In an open detection chamber, there is preferably an opening in the detection chamber so that there is a direct fluid connection between the detection chamber and the environment. The opening is preferably sufficiently large to ensure rapid pressure equalization. On the other hand, the opening is preferably sufficiently small that flows in the environment of the detection chamber have no or only a reduced influence on the measurement by the thermal sensor.In the case of an open detection chamber, not only the pressure between the interior of the detection chamber and its surroundings is equalized, but also the composition of the fluid, so that essentially the same fluid is present inside the detection chamber and its surroundings.

[0052] In a closed detection chamber, however, media separation is possible. In this case, an effective connection for pressure transmission is preferably provided by a pressure equalization membrane. In the event of a change in the pressure of the fluid surrounding the detection chamber, the pressure equalization membrane undergoes a deflection until the pressure inside the detection chamber and the surrounding area are identical. The deflectable pressure equalization membrane thus preferably ensures that, even in a closed detection chamber that does not provide for fluid exchange with the surrounding area, the pressure inside the detection chamber always follows the external pressure of the fluid being measured.

[0053] The support membrane represents a component which serves to position the thermal sensor. The support membrane extends along a support structure above or over a cavity. The support membrane is preferably designed to be flat, i.e. it preferably has a length and / or width which is many times greater than its thickness. The thickness here refers to an extension along an axis which is essentially orthogonal to a length and / or width of the support membrane. For example, the length and / or width can be greater than the thickness by a factor of 1.5, 2.5, 10, 100, 1,000 or more. The thickness of the support membrane is preferably between 0.1 - 20 pm, preferably between 0.2 - 10 pm, particularly preferably between 0.5 - 5 pm, most particularly preferably between 0.5 - 2 pm.The membrane can preferably also be regarded as an insulating element which reduces heat conduction resulting from the heating element, so that the accuracy of the measurement can be improved.

[0054] The membrane is preferably held by a support structure. The support structure is preferably a frame structure which is essentially formed by a continuous outer border in the form of side walls of a remaining flat area. The frame structure is preferably stable and rigid. In the case of a square frame shape, the individual side areas which preferably essentially form the frame structure are in particular referred to as side walls. The support membrane is preferably held by at least two side areas of the support structure. The support structure can preferably be formed from a wafer or substrate using structuring processes proven in the prior art, for example for providing a cavity on the support structure over which the support membrane extends.

[0055] The support membrane is preferably firmly connected to the support structure and is preferably located immobile above the cavity of the support structure. In this respect, it is preferably provided that the support membrane essentially does not vibrate, in particular not for the purpose of measurements. The pressure is thus essentially measured using an immobile support membrane that is stationary with respect to the support structure. Compared to approaches such as US 2012 / 0118060 A1, in which a cantilever is excited to vibrate in order to cause convection of the ambient gas, this represents a simpler and more robust design. Components of the thermal sensor (e.g. the heating element for providing the thermal field or the sensor component for detecting a temperature response of the thermal sensor) can also be stably applied to a stationary membrane.This leads to greater long-term stability and reduces interference and cross-sensitivity.

[0056] The cavity preferably denotes a recess in the support structure, which defines a hollow space. The membrane is preferably held by the support structure in such a way that it extends over the cavity and defines an upper boundary of the cavity. The cavity is thus preferably located below the thermal sensor. The support structure can preferably comprise one or more cavities. A cavity can preferably extend continuously through the support structure, so that the height of the cavity preferably corresponds substantially to the height of the support structure. However, it can also be preferred for the cavity to be introduced into the support structure in such a way that it has a lower height than the height of the support structure.

[0057] Terms such as substantially, approximately, about, approx., etc. preferably describe a tolerance range of less than ± 20%, preferably less than ± 10%, particularly preferably less than ± 5%, even more preferably less than ± 2%, and especially less than ± 1%, and always include the exact value. Similarly, preferably describes quantities that are approximately equal. Partially, preferably describes at least ± 5%, particularly preferably at least ± 10%, and especially at least ± 20%, in some cases at least ± 40%.

[0058] Since the support structure, membrane, and cavity are located within the detection chamber, the cavity represents a partial volume of the hollow space of the detection chamber. Furthermore, the detection chamber comprises an interior region, which comprises a volume formed, in particular, by the hollow space minus the cavity. The interior of the detection chamber is, in particular, as explained above, operatively connected to an environment of the detection chamber. Preferably, the interior is either in fluid communication with the environment of the detection chamber via an opening (open detection chamber) or a pressure equalization membrane enables the transfer of an external pressure into the interior (closed detection chamber).

[0059] An aperture enables pressure equalization between the cavity and an interior of the detection chamber. The aperture preferably refers to an opening through which a fluid connection is formed between the cavity and the interior of the detection chamber. The aperture is preferably incorporated in the support membrane. However, it can also be preferred for one aperture to be present in the support structure. Through the fluid connection, a fluid can therefore spread from the cavity into the interior or vice versa. In the case of an open detection chamber, the fluid can be the fluid whose pressure is being measured. In the case of a closed detection chamber, it can also be preferred for the fluid to be a reference fluid that is enclosed within the detection chamber.The aperture functions in particular to equalize the pressure between the cavity on the support structure and the interior of the detection chamber, thus ensuring that the pressure within the cavity and the interior is equalized. As explained above, the introduction of an aperture improves measurement accuracy by avoiding pressure-dependent deformation of the membrane, and also increases operational suitability even at high pressures by reducing the risk of pressure-induced damage to the support membrane. Preferably, one or more apertures can be present, for example, on the support membrane and / or on the support structure. In a cross-section, the aperture can preferably have a round shape or a slit shape. A (minimum) length and / or width of an aperture can be, for example, 0.1 pm to 20 pm.

[0060] In a preferred embodiment, the pressure sensor comprises an electronic circuit and / or is data-connected to an electronic circuit, wherein the electronic circuit is configured to oscillate the heating element and / or to determine the pressure of the fluid based on the temperature response of the thermal sensor.

[0061] For the purposes of the invention, an electronic circuit preferably refers to a combination of individual electrical or electromechanical elements in a functional arrangement. The electronic circuit preferably allows data or electrical signals to be sent, received, and / or processed.

[0062] In preferred embodiments, the electronic circuit can also be configured to process the temperature response recorded by the sensor component. Processing data preferably means that the electronic circuit is configured to perform computational operations and / or computational steps, for example, with the recorded temperature response of the sensor component.

[0063] An electronic circuit therefore preferably functions as a computing unit, which preferably acts as a data processing unit, processing data recorded by the heating element or a preferred temperature sensor. Likewise, the electronic circuit can preferably assume the functions of a control unit, exciting the heating element to oscillate at at least one frequency.

[0064] Preferred electronic circuits include, without limitation, an integrated circuit (IC), an application-specific integrated circuit (ASIC), a programmable logic circuit (PLC), a field-programmable gate array (FPGA), a microprocessor, a microcomputer, a programmable logic controller, and / or another electronic circuit that is preferably programmable. The electronic circuit may preferably also include a memory unit. A memory unit allows the backup and / or intermediate storage of data. Non-limiting examples of memories, preferably semiconductor memories, are volatile memories, (RAM) memories, or non-volatile memories, such as ROM memories, EPROM memories, EEPROM memories, or flash memories, and / or other memory technologies.The term "computing unit" preferably refers to any device or unit that can be configured to perform computing operations. The computing unit is preferably, for example, a processor, a processor chip, a microprocessor, and / or a microcontroller, which is preferably configured to evaluate the modulation of the thermal field. The computing unit can also preferably be a programmable circuit board. The computing unit can also preferably comprise a computer-usable or computer-readable medium, such as a hard disk, random access memory (RAM), read-only memory (ROM), flash memory, etc.

[0065] Method steps for determining the pressure of the fluid, as described herein, are preferably carried out by the electronic circuit or computing unit. The phrase "configured to" preferably means that computer code and / or software is installed on the electronic circuit or computing unit to carry out the method step, for example, to check the extent to which a modulation of the heat field was induced and which fluid parameters were decisive for this. The computer code and / or software for evaluating the modulation of the heat field can be written in any programming language or a model-based development environment, e.g., in C / C++, C#, Objective-C, Java, Basic / VisualBasic, MATLAB, Simulink, StateFlow, Lab View, and / or Assembler.

[0066] The computer code and / or software, which is preferably installed on the electronic circuit or processing unit, in particular to evaluate the modulation of the thermal field, can be considered technical features because a direct physical effect of the thermal sensor, for example, the supply of a control signal for a heating element or the detection of a temperature response by the sensor component, is utilized. Functional descriptions of the computer code and / or software can therefore be considered preferred and defining embodiments of the invention.

[0067] The electronic circuit can preferably be positioned within the detection chamber. It can also be preferred for the electronic circuit to be located outside the detection chamber and to have a data connection with the thermal sensor. A data connection preferably means that data, for example, data from the sensor component and / or data for controlling the heating element, can be sent, received, and / or processed. The data connection can be provided, for example, by an electrical connection. A data connection can also preferably be provided through the exchange of electromagnetic waves, for example, via WLAN, Bluetooth, etc.

[0068] In a further preferred embodiment, the pressure sensor is characterized in that the temperature response comprises a measurement signal comprising an amplitude and / or a phase, such that the pressure of the fluid can be determined based on the amplitude and / or the phase, wherein the amplitude and / or the phase preferably depends on a volumetric heat capacity, which is dependent on the pressure. The temperature response preferably refers to a measurement signal of the thermal sensor that changes as a result of the oscillating control of the heating element. With an oscillating control of the heating element, an open detection chamber results in an oscillating heating of the fluid, which is fluidically connected to the pressure sensor from the environment. With a closed detection chamber, an oscillating control of the heating element results in an oscillating heating of the reference fluid.Therefore, the temperature response can be characterized as describing the ability to detect a temperature change of the fluid or the reference fluid.

[0069] Due to the oscillating control of the heating element, the temperature response is also, in particular, an oscillating signal. Therefore, the temperature response can be described, in particular, by an amplitude and / or phase. The amplitude and / or phase of the temperature response can, in turn, be used to determine the fluid pressure. It may also be preferable to consider an inverse of the amplitude or phase for pressure determination. The relationship between the temperature response and the pressure can, in particular, be approximately described by a linear relationship.

[0070] As explained in more detail below and illustrated in Fig. 2, in the case of an oscillating excitation of the heating element, the amplitude and / or the phase of the temperature response depends on a volumetric heat capacity, which is dependent on the pressure, so that the pressure can preferably be determined by determining the volumetric heat capacity.

[0071] The volumetric heat capacity preferably describes the amount of energy that must be added to a unit volume of the fluid (or a reference fluid) in the form of heat to cause a temperature increase of 1 degree Celsius. The SI unit of volumetric heat capacity is J / m³. 3 * K. The volumetric heat capacity can preferably also be determined by the product of density and specific heat capacity of the fluid (or a reference fluid).

[0072] Preferably, the pressure p can be described by a function g that depends on a plurality of parameters, for example, the thermal resistance Rth and the heat capacity Cth. The thermal resistance preferably denotes a measure of the temperature difference that arises in an object when a heat flow (heat per time period) passes through it. The heat capacity denotes the ratio of the heat supplied to an object and the resulting temperature increase. The thermal resistance Rth and the heat capacity Cth depend in particular on the composition of the fluid and / or the reference fluid, the temperature and / or the pressure. Furthermore, however, material properties of the components of the thermal pressure sensor, such as the material properties of a carrier membrane, a heating element or a temperature sensor, can also influence the thermal resistance and the heat capacity. Such influences can also be referred to as parasitic effects.Additional influencing factors may include the chamber volume or the general packaging of the thermal pressure sensor. In this respect, the heat capacity can also be understood as the "thermal mass" of the system. The function g, in turn, can also depend on parameters such as the frequency, the voltage for the control signal of the heating element, and the power. Therefore, the pressure p can preferably be described by the function g as follows: p = g (Rth (composition, temperature, pressure), Cth (composition, temperature, pressure), frequency, excitation voltage, power).

[0073] A concrete representation of the function g depends on the structural design of the pressure sensor, in particular with regard to the geometry, such as the dimension and / or the number of apertures and / or the distance between the heating element and a preferred temperature sensor for detecting the temperature response.

[0074] Preferably, the temperature response is proportional to a square root of the pressure. For low pressure values, the function g can be approximated by a linear function.

[0075] In a further preferred embodiment, the pressure measurement by the pressure sensor can be approximated by a first-order low-pass filter. The amplitude of the temperature response ATAC and the phase 0 can be described as TAC = p / ^((1 / Rth) 2 + (2 nf Cth) 2 )

[0076] 0 = - arctan (2 TT f Rth Cth).

[0077] The thermal resistance depends in particular on the thermal resistance of the fluid or reference fluid Rth, fluid and on the parasitic thermal resistance Rth, parasitic, while the heat capacity depends on the heat capacity of the fluid or reference fluid Cth, fluid and Cth, parasitic (see Fig. 1 ). The parasitic quantities refer to components that do not result from the fluid itself, but rather, for example, from components of the pressure sensor. For example, undesired heat conduction can occur through the carrier membrane on which the heating element is positioned. This heat conduction is preferably kept low anyway (for example, through the design of the aperture, the material, etc.), but should be taken into account for a particularly comprehensive measurement.

[0078] The design of the sensor advantageously enables a broad range of pressure values ​​to be measured. While prior art Pirani sensors, for example, are generally only sensitive in the mbar range and saturate above a certain range, e.g., 1 mbar, the sensor according to the invention can also read significantly higher pressure values. Advantageously, the sensor can be used to measure pressures above 10 bar, 20 bar, 50 bar, 100 bar, or more without saturation occurring. This also further distinguishes the sensor according to the invention from prior art approaches such as US 2012 / 0118060 A1 or JP 2007147344 A, which, according to their own statements, can perform measurements down to approximately 1 bar using alternative designs.

[0079] In particular, a substantially linear relationship between the temperature response and the pressure can be advantageously used to infer the pressure from the temperature response. Thus, a substantially linear relationship between an inverse of the amplitude and / or phase of the temperature response and the pressure can preferably be used (see Fig. 2).

[0080] In a further preferred embodiment, the pressure sensor is characterized in that the pressure sensor further comprises a means for determining a thermodynamic material property, preferably a thermal conductivity, a volumetric thermal conductivity, a density, and / or a composition of the fluid, so that the determined thermodynamic material property and / or composition of the fluid can be taken into account for determining the pressure.

[0081] A thermodynamic material property can relate to one or more parameters selected from a group comprising a temperature, a moisture content, a thermal conductivity, a heat capacity, and in particular also a volumetric heat capacity. The composition of the fluid preferably refers to the chemical composition of the fluid, i.e. the chemical composition and influences a thermodynamic material property. In this respect, in the context of the invention, the determination of a thermodynamic material property can also mean the determination of a composition of the fluid, or vice versa. Preferably, the determination of a thermodynamic material property and / or a composition is used for or in the sense of a compensation measurement, which in particular takes pressure-independent influences on the measured data into account. An example thermodynamic material property for this is thermal conductivity.

[0082] The further means may, for example, be in the form of a reference sensor that determines one or more thermodynamic material properties.

[0083] A reference sensor preferably refers to an additional sensor that can measure another parameter relevant for determining the fluid pressure. As explained above, the determination of pressure is usually dependent on a multitude of parameters. One or more reference sensors can advantageously determine one or more of these parameters, thus simplifying the determination of pressure based on the temperature response of the thermal sensor. The reference sensor can preferably be used in both a closed and an open detection chamber and can determine, for example, a fluid composition or a temperature.

[0084] The additional means can preferably also be provided by the design of the pressure sensor itself. For example, in a closed detection chamber, the reference fluid located within the detection chamber is known, so no separate sensor is required to determine the composition of the reference fluid.

[0085] As explained above, the temperature response, in particular the function with which the pressure can be determined, depends on a large number of parameters. The additional means can advantageously be used to determine one or more parameters which, in addition to a change in pressure, can influence the measurement results, so that their consideration enables a more precise conclusion to be drawn about the pressure of the fluid. For example, it may be preferable to carry out a pressure measurement which is dependent on one or more thermodynamic material properties, for example also the composition of the fluid. By taking into account the thermodynamic material property and / or the composition of the fluid, a more precise determination of the pressure can take place, which takes into account any changes in the thermodynamic material properties.

[0086] In particular, a compensation measurement can be performed, which, for example, ensures that a reliable pressure measurement can continue even if thermodynamic material properties and / or the composition of the fluid should change. The additional means can preferably involve a reference sensor configured for this purpose or an evaluation of different frequencies of the temperature response, as explained in more detail below.

[0087] In a further preferred embodiment, the thermal pressure sensor is characterized in that the temperature response comprises at least a first frequency and a second frequency, wherein the first frequency is smaller than the second frequency and allows an assignment with regard to a thermodynamic material property, preferably a thermal conductivity.

[0088] As described above, the oscillating control of the heating element results in the temperature response being an oscillating signal. The temperature response can have one or more frequencies, i.e. in particular a first frequency and a second frequency. The first frequency and second frequency therefore form frequency components of the temperature response. Preferably, the first frequency is lower than the second frequency. In particular, the first frequency and the second frequency can differ by a factor of at least 2, 3, 4, 5, 6, 7, 8 or more. The lower frequency, i.e. the first frequency, can preferably enable an assignment of a thermodynamic material property of the fluid. Preferably, in the range of the first frequency, the measurement signal can essentially depend on a thermodynamic material property (or composition of the fluid) and be independent of the pressure.This makes it possible to determine the thermodynamic material property without having to take into account the influence of pressure or the influence of pressure on the thermodynamic material property.

[0089] For a first frequency, which is particularly low and, for example, essentially corresponds to a constant component of the temperature response (at 0 Hz), the temperature response preferably depends on the thermal conductivity and has no pressure dependence. The thermal conductivity preferably represents a thermodynamic material property, which allows simple conclusions to be drawn about a fluid composition. If the fluid whose pressure is to be determined is, for example, a gas mixture whose components A and B are known, the components of A and B can generally be easily determined by measuring the thermal conductivity of the fluid as a gas mixture. For this purpose, only the thermal conductivity of the individual components of A and B must be known and taken into account accordingly.In this respect, an evaluation of the temperature response at a first (low) frequency (preferably close to 0 Hz) represents a further example of a means for determining a thermodynamic material property, preferably a thermal conductivity, and / or a composition of the fluid, so that the determined thermodynamic material property and / or composition of the fluid can be taken into account for determining the pressure. Advantageously, in the described embodiment, no separate sensor components are required for this purpose; instead, a temperature sensor can determine the thermodynamic material property and thus indirectly a composition of the fluid based on a temperature response at a first (low) frequency, preferably essentially 0 Hz.

[0090] Preferably, the temperature response at a second frequency, which is higher than the first frequency, depends not only on a thermodynamic material property (such as thermal conductivity), but also in particular on a pressure. The temperature response at a second (higher) frequency can in particular correspond to a temperature response at the frequency of the control of the heating element, thus a so-called 1-omega signal. Likewise, the temperature response can be evaluated at preferably integer higher multiples of the control frequency. As explained above, it was recognized according to the invention that with an oscillating control, the temperature response (preferably at a control frequency or a higher harmonic thereof) has a dependence on the volumetric heat capacity, which depends on the pressure.

[0091] By determining the temperature response at a first and second frequency, whereby the temperature response at the first frequency depends essentially on a thermodynamic material property, while the temperature response at the second frequency has a pressure dependence (which may additionally depend on a thermodynamic material property), a particularly precise measurement of the pressure is possible.

[0092] In particular, the measurement results for the pressure can be compensated with respect to a cross-sensitivity with regard to the fluid composition, which, as explained above, can be determined via a thermodynamic material property such as thermal conductivity.

[0093] In a further preferred embodiment, the pressure sensor is characterized in that the first frequency has a value of substantially 0 Hz and / or the second frequency has a value greater than 0 Hz or is 1-OMEGA, 2-OMEGA or 3-OMEGA.

[0094] The range from essentially 0 Hz is preferably also referred to as the direct current signal or DC component. The measuring range preferably corresponds to a temporally constant component of the temperature response during an oscillating excitation of the heating element. The signal can also be referred to as an O-OMEGMA or O-Omega signal. The designations 1-OMEGA, 2-OMEGA, and 3-OMEGA of the temperature response preferably refer to multiples of the frequencies of the oscillating activation of the heating element. Thus, the OMEGA signals (or Omega signals) preferably describe harmonic components of the temperature response. For example, if the heating element is excited sinusoidally at f = 100 Hz with an amplitude of +1-5 V (volts), the temperature response also displays higher-order harmonic signals. The 2-Omega signal describes the temperature response at f = 200 Hz, the 3-Omega signal at f = 300 Hz, etc.

[0095] It may be preferred that the frequency for the control signal of the heating element for oscillating excitation be selected in the range of the cutoff frequency of the thermal sensor. The cutoff frequency preferably corresponds to a characteristic frequency at which an amplitude of the frequency-dependent temperature response drops, in particular to a predetermined value depending on the context of the measurement. The cutoff frequency can preferably be the frequency above which the temperature response has dropped to approximately 1 / A / 2 times the maximum temperature response. The latter preferred option for determining the cutoff frequency preferably corresponds to a drop of approximately 70% of a maximum value of the temperature response. Above the cutoff frequency, a measurement is possible with only reduced sensitivity.In terms of measurement technology, the cutoff frequency therefore refers in particular to a maximum frequency with which the heating element can (still) be controlled and a sufficient amplitude of a temperature response can be measured, which allows the pressure of the fluid to be measured.

[0096] Furthermore, the signal-to-noise ratio (SNR) is particularly important. If, for example, the excitation frequency is set too high, the signal change will be lost in the noise, and a reliable measurement will no longer be possible.

[0097] Preferably, the temperature response is evaluated for an 0-omega signal and an omega signal for higher frequencies. As explained above, the temperature response of the 0-omega signal can depend on a thermodynamic material property, e.g., thermal conductivity, which also depends on the composition of the fluid and is not, or only to a lesser extent, dependent on pressure.

[0098] An evaluation of the dynamic temperature response for a 1-omega, 2-omega, or 3-omega signal of the temperature response preferably represents functions that depend both on the thermodynamic material properties or composition of the fluid and, in particular, on the pressure. The evaluation of the temperature response for an 0-omega and a 1-omega, 2-omega, or 3-omega can be used to obtain a measurement signal for the pressure in which the fluid composition can be taken into account or compensated for in determining the pressure. Such evaluations of the temperature response for the preferential receipt of a pressure signal that has been compensated for the actual composition of the fluid can preferably be obtained by the electronic circuit configured for this purpose.

[0099] As explained above, in preferred embodiments, the pressure sensor can comprise a means for determining a thermodynamic material property, preferably a thermal conductivity, a volumetric thermal conductivity, a density, and / or a composition of the fluid, so that the determined thermodynamic material property and / or composition of the fluid can be taken into account for determining the pressure. In a further preferred embodiment, the pressure sensor is characterized in that the pressure sensor comprises a reference sensor, wherein the reference sensor is configured to determine an environmental parameter, such as humidity and / or temperature.Using a humidity sensor and / or an additional temperature sensor to determine the ambient temperature, other parameters that may influence the pressure measurements can be considered or compensated for, in addition to the thermodynamic material properties and / or fluid composition. Environmental parameters refer in particular to physical quantities that are independent of the fluid and characterize external influences on the fluid and / or the pressure sensor, such as external temperature and / or humidity fluctuations. Taking these parameters into account using appropriate reference sensors results in a more precise determination of the pressure.

[0100] In a further preferred embodiment, the thermal pressure sensor is characterized in that the heating element is an electrical heating element, preferably a heating resistor.

[0101] The heating element preferably refers to the component of the thermal sensor from which the heat field or heat flow emanates by releasing heat energy. An electric heating element preferably refers to a heating element capable of converting electrical energy into heat energy, which in the context of the invention is used as a heat field and transferred to the sensor component, preferably the temperature sensor. In an electric heating element, the heat energy or heat field is preferably generated by using an electrically conductive material through which an electric current flows and which is heated by Joule heat. A heating resistor has proven particularly suitable for this purpose, comprising in particular metallic alloys or highly doped polysilicon, which do not melt and / or oxidize even at the particularly high temperatures they can reach.

[0102] In a further preferred embodiment, the thermal pressure sensor is characterized in that the sensor component is formed by a temperature sensor, wherein the temperature sensor is preferably selected from a group comprising a thermocouple, a thermopile, and / or a diode and / or a thermistor. Preferably, multiple temperature sensors can be present to obtain multiple temperature responses, so that a differential signal can preferably be obtained across the multiple temperature responses. A preferred arrangement of the thermal sensor comprises a heating element mounted between two temperature sensors.

[0103] The temperature sensor is preferably a component of the thermal sensor capable of measuring the thermal field, in particular the modulation of the thermal field by the fluid, i.e., the influence of the fluid on the thermal field. A temperature sensor, as a preferred sensor component, is capable of determining the influence of the fluid on the thermal field through a temperature measurement.

[0104] A thermistor preferably refers to a component comprising an electrical resistance whose value changes reproducibly with temperature. Thermistors are divided into thermistors and cold thermistors based on their temperature behavior. A thermistor has a negative temperature coefficient and is able to conduct electrical current better when hot than when cold. A cold thermistor has a positive temperature coefficient and is able to conduct electrical current better when cold than when hot. In the context of the invention, a thermistor or a cold thermistor can preferably be used as a thermistor. Using a thermistor, conclusions about a modulation of the thermal field and thus at least one material property of the fluid can be determined in a simple and precise manner based on a changing electrical resistance.

[0105] A thermocouple preferably refers to an arrangement comprising a pair of electrically conductive materials that are connected to one another at one end and allow a conclusion to be drawn about the measured temperature due to the thermoelectric effect. Electrical energy is provided when there is a temperature difference along the arrangement. A thermopile refers to an element that has multiple thermocouples. The thermocouples of the thermopile are preferably connected electrically in series and thermally in parallel.

[0106] The measuring point of the thermocouple or thermopile is referred to as the hot end or hot junction and forms one end of a thermocouple. The other end, analogously referred to as the cold end or cold junction, represents a reference junction used to determine a temperature difference. Preferably, an electronic circuit and / or a processing unit for processing the temperature measurement is connected to the cold junction.

[0107] A diode can also function as a temperature sensor and thus as a preferred sensor component. This can be exploited, for example, by the fact that the forward voltage of a diode changes essentially linearly with temperature. The higher the temperature, the lower the forward voltage, and vice versa. Accordingly, the change in the forward voltage can be used to draw conclusions about a change in temperature.

[0108] In a further preferred embodiment, the heating element itself functions as a sensor component, i.e., a sensor component can preferably be provided by the heating element itself without a temperature sensor being used as a sensor component. The effect of the heating element as a sensor component can, for example, be enabled in the same way as the 3-omega method known from the prior art. In the 3-omega method, a thermal property, such as thermal conductivity, is determined. A heating element itself is used as a temperature sensor and is fed with an oscillating control signal. Due to the fed-in power, the temperature of the heating element changes at the same frequency as the control signal. The amplitude and the phase shift compared to the fed-in power depend on the thermal conductivity and the frequency.The temperature oscillations lead to resistance oscillations in the heating element, which can be described, among other things, by a resistance amplitude, which in turn depends on a temperature coefficient of the electrical resistance of the heating element. From this, the voltage across the heating element can be calculated by applying Ohm's law. This voltage contains a component with three times the frequency (3 μJ) and a corresponding amplitude proportional to the temperature amplitude of the heating element.

[0109] In a further preferred embodiment, the thermal pressure sensor is characterized in that the pressure sensor comprises a closed detection chamber within which a reference fluid and the thermal sensor are enclosed.

[0110] A closed detection chamber refers to a detection chamber that is preferably hermetically sealed from its environment. In particular, a closed detection chamber means that no fluidic connection can occur between the detection chamber and the environment, i.e., it is not possible for a fluid to be exchanged between the detection chamber and the environment. In particular, a closed detection chamber prevents foreign substances from the environment from entering the detection chamber. At the same time, the enclosed reference fluid is prevented from escaping from the detection chamber. The thermal sensor and the reference fluid are encapsulated within the closed detection chamber.

[0111] The reference fluid is preferably introduced into the closed detection chamber at a predetermined pressure. Thus, the reference fluid creates an internal pressure within the closed detection chamber. An operative connection between an interior of the closed detection chamber and an environment is preferably mediated by a pressure equalization membrane, as explained in more detail below, which ensures that the internal pressure of the detection chamber adjusts to the external pressure of the fluid to be measured in the environment of the detection chamber.

[0112] In a closed detection chamber, the reference fluid and the fluid whose pressure is to be measured are separate from one another. The fluid to be measured can also be referred to as the measuring fluid in the context of the invention. The provision of a closed detection chamber is advantageous if the pressure of corrosive fluids, for example liquids or corrosive gases, is to be determined. On the other hand, the provision of a closed detection chamber can ensure that the composition of the medium in the vicinity of the thermal sensor is precisely controlled or known. As explained above, knowledge of or monitoring the composition of the fluid medium in the vicinity of the thermal sensor leads to more precise pressure measurement, since cross-sensitivity of the pressure-dependent measurement signal to a thermodynamic material property or composition of the fluid medium can be taken into account or compensated for.

[0113] The reference fluid preferably refers to a fluid, preferably a gas, which is introduced within the closed detection chamber and is preferably designed to transmit the pressure of a fluid outside the detection chamber to the thermal sensor. In other words, the reference fluid preferably transmits an external pressure of a fluid from the environment of the detection chamber to the thermal sensor in such a way that the external pressure can be determined based on a measurement of the internal pressure of the reference fluid by means of the thermal sensor.

[0114] The transfer of external pressure to the reference fluid can, for example, occur by changing the geometry of the detection chamber (e.g., by deflecting a pressure compensation membrane). In the case of higher external pressure, the pressure compensation membrane bulges inward, compressing the reference fluid, preferably a reference gas, until the internal pressure has adjusted to the external pressure. The oscillating heating of the reference fluid (at an internal pressure that essentially corresponds to the external pressure) is achieved via the oscillating control of the heating element, as explained above. As a result of a recorded temperature response during an oscillating control, the pressure of the reference fluid can advantageously be determined (preferably based on a volumetric heat capacity), which essentially corresponds to the external pressure of the fluid.The internal pressure of the reference fluid is measured analogously to the determination of a fluid pressure in the case of an open detection chamber, as explained elsewhere herein. In this respect, statements regarding an advantageous determination of a pressure in a (measurement) fluid, for example, due to a substantially linear relationship between a temperature response and a pressure in an oscillating control, apply analogously to a reference fluid.

[0115] In the preferred closed detection chamber, the properties of the reference fluid are advantageously known, in particular the composition of the reference fluid.

[0116] Therefore, it is preferably not necessary to determine the composition of the reference fluid through additional measurements.

[0117] Furthermore, it is advantageously possible to adjust the pressure sensitivity based on the properties of the reference fluid, i.e., to select a reference fluid, preferably a gas, whose thermodynamic properties exhibit a preferably high dependence on pressure. This allows the internal pressure of the reference fluid (which corresponds to the external pressure of a fluid to be measured) to be measured particularly sensitively.

[0118] Furthermore, a closed detection chamber is advantageous in that it also allows the pressure of aggressive fluids to be measured, i.e., fluids that could have an adverse effect upon direct contact with the thermal sensor, for example, due to a corrosive effect. Media separation between the fluid and reference fluid ensures that the thermal sensor is always surrounded by a non-aggressive reference fluid, thus ensuring a long service life.

[0119] In a preferred embodiment, the reference fluid is a gas, preferably selected from a group comprising air, hydrogen, carbon dioxide, helium, neon, argon, krypton, xenon, sulfur hexafluoride and / or nitrogen.

[0120] The preferred fluids mentioned are suitable as reference fluids because they are mostly inert and cannot exert any damaging influence on the thermal sensor. Furthermore, they suitably transmit external pressure into the interior of the detection chamber and, due to their preferably high pressure sensitivity, can be used well for measuring pressure using the described oscillating control. Thus, for the preferred reference gases, a substantially linear relationship between the pressure and a variable derived from the temperature response (e.g., a phase and / or an inverse of the amplitude) could be determined. Therefore, determining pressure based on a temperature response with oscillating control is particularly precise over a wide measuring range for the reference gases mentioned.

[0121] In a further preferred embodiment, the pressure sensor is characterized in that the pressure sensor comprises a closed detection chamber and a pressure compensation membrane, wherein a change in the pressure of the fluid causes a deflection of the pressure compensation membrane, which leads to a pressure change of the reference fluid, which can be detected by the thermal sensor.

[0122] The pressure equalization membrane is preferably present as a partial section of the closed detection chamber, in particular as a partial section of the self-contained casing of the closed detection chamber. The pressure equalization membrane preferably refers to a membrane that can be deflected as a result of a pressure difference between an external environment of the detection chamber and an interior of the detection chamber in order to equalize an internal pressure in the detection chamber to the external pressure. If, for example, the pressure of the fluid outside the detection chamber decreases, the pressure equalization membrane can bulge outwards, so that the volume of the closed detection chamber changes (here: increases) as a result of the deflection of the pressure equalization membrane. This changes the internal pressure of the reference fluid in the closed detection chamber.The pressure change of the reference fluid depends on the magnitude of the deflection of the pressure compensation membrane, which in turn depends on the magnitude of the change in the pressure of the fluid that caused the deflection of the pressure compensation membrane.

[0123] Advantageously, a sensitive pressure measurement of the fluid is achieved, which is the sensitivity or deflectability of the pressure compensation membrane. With mechanical sensors, for example, it is necessary for a pressure compensation membrane to undergo a sufficiently large deformation at a pressure to be determined in order to enable a measurement. In the context of the invention, the extent of deflection of the pressure compensation membrane is not critical. Preferably, only such a deflection of the pressure compensation membrane is necessary that essentially the same pressure is reached inside the detection chamber as in the surroundings of the detection chamber. The pressure compensation membrane should therefore undergo a deflection through which the pressure can be transmitted from the surroundings into the interior of the detection chamber to the reference fluid.

[0124] The pressure equalization membrane is preferably sufficiently thin to be deflected as a result of a pressure change in the environment. The pressure equalization membrane can preferably have a thickness of 0.1 - 1,000 μm, preferably of 0.5 - 500 μm, particularly preferably of 1 - 300 μm, most particularly preferably between 5 - 200 μm. The pressure equalization membrane can preferably be folded, corrugated, or substantially flat, i.e., without any unevenness. Furthermore, it is preferred that the pressure equalization membrane TI is elastic, i.e., can return to an initial position, in particular after a deflection as a result of a pressure effect from the fluid in the environment.

[0125] In a further preferred embodiment, the pressure sensor is characterized in that the pressure sensor comprises an open detection chamber which has at least one opening for fluid communication between an interior region of the detection chamber and an environment.

[0126] The terms fluid communication, fluid connection, or fluidic connection can be used synonymously within the meaning of the invention. An open detection chamber is characterized by a fluidic connection to the environment, so that the fluid from the environment can spread into the pressure sensor, and conversely, the fluid from the pressure sensor can also flow back into the environment. The environment preferably refers to the area outside the detection chamber, i.e., any space located outside the detection chamber. The fluidic connection between the environment and the detection chamber is preferably provided by an opening.

[0127] The opening designates a non-closed area of ​​the detection chamber. In particular, the opening is present in the casing of the detection chamber. Preferably, the opening is an interruption in the casing of the detection chamber, so that in an open detection chamber, there is no continuous, self-contained course of the casing of the detection chamber. Preferably, multiple openings can also be present. If an opening is introduced into the detection chamber, in the context of the invention, this is preferably referred to as an open detection chamber. The opening of the open detection chamber is present in addition to the aperture to provide pressure equalization between the cavity and the (remaining) interior of the detection chamber.

[0128] Advantageously, particularly high pressures can be measured using an open detection chamber. With a closed detection chamber, the measuring range can be limited by the maximum deflection of the pressure compensation membrane. Such a limitation is advantageously not present with an open detection chamber. For example, pressures of more than 10 bar, 50 bar, 100 bar, 200 bar, or more, such as those found in gas tanks, can be reliably detected. This ensures long-term functional capability, since even at such high pressures, there is little or no risk of damage to the structural components of the pressure sensor.Any disadvantages of an open detection chamber compared to a closed variant with regard to a lack of control over the composition of the fluid in the environment of the thermal sensor can be effectively compensated by means for monitoring and / or determining a thermodynamic material property and / or composition of the fluid.

[0129] In a further preferred embodiment, the pressure sensor comprises a fluid line attached to the opening. The fluid line can advantageously enable a more controlled fluid exchange. The fluid line can preferably be attached to the detection chamber as a tube or hose. In a further preferred embodiment, the pressure sensor is characterized in that the support membrane comprises a material selected from a group comprising silicon nitride, silicon dioxide, and / or polyimide.

[0130] The preferred materials for the carrier membrane have proven advantageous in that, in addition to their excellent design options as a carrier membrane, they also offer thermal insulation, thus reducing or eliminating heat conduction caused by the carrier membrane. Consequently, one or more of the preferred materials mentioned efficiently utilize the heat field emanating from the heating element to produce oscillating heating. The heat conduction resulting from the carrier membrane is advantageously reduced, thus reducing heat loss, thus ensuring optimal use of the heat field.

[0131] In a further preferred embodiment, the pressure sensor is characterized in that the carrier membrane has at least one membrane aperture which forms the aperture for pressure equalization and / or the carrier structure has a carrier aperture which forms the aperture for pressure equalization.

[0132] Accordingly, several options are advantageously available to enable the aperture to equalize pressure between the cavity and the interior of the detection chamber. In preferred embodiments, one or more membrane apertures are attached to the membrane, which serve to equalize pressure, i.e., apertures attached to the membrane. It may also be preferred to have one or more support apertures in the support structure.

[0133] It has proven particularly advantageous to attach one or more apertures to the membrane for pressure equalization between the cavity and the interior of the detection chamber, i.e., as membrane apertures. Firstly, their installation involves less effort in terms of process technology. Furthermore, in addition to pressure equalization, a membrane aperture can also reduce parasitic heat transport through the membrane. Reducing heat conduction through the membrane advantageously enables improved, and in particular more sensitive, measurement of the fluid pressure, since the thermal field is essentially used to measure the fluid pressure and can be detected by the sensor component, preferably one or more temperature sensors.A high degree of perforation (=open area / total area) is preferred to reduce parasitic heat conduction, but the degree of perforation should preferably be selected such that sufficient mechanical stability of the support membrane is still ensured. In preferred embodiments, the degree of perforation can be, for example, 2% to 70%.

[0134] In a further preferred embodiment, the pressure sensor is characterized in that the thermal sensor comprises a heating element and a temperature sensor mounted on the support membrane, wherein the support membrane has at least one membrane aperture. As explained above, the membrane aperture forms an aperture for pressure equalization.

[0135] There are various variants for positioning the membrane aperture. In a preferred embodiment, the membrane aperture is not arranged between the heating element and the temperature sensor. Instead, the membrane aperture is laterally spaced from the temperature sensor and / or the heating element. It may also be preferred to have multiple membrane apertures laterally spaced from the temperature sensor and / or heating element. In particular, one or more membrane apertures can border the heating element and the temperature sensor on the membrane. For example, two membrane apertures can be present, with one membrane aperture laterally spaced from the heating element and another aperture laterally spaced from the temperature sensor.

[0136] Preferably, the heating element and the temperature sensor itself can be positioned close to each other, for example, with a distance of less than 20 pm, preferably less than 10 pm, 5 pm, or less. The distance refers to the external dimensions of the components and is largely determined by the manufacturing tolerances, which are determined, for example, by a resolution during lithography or an offset during mask alignment. This embodiment ensures essentially direct heat loss to the fluid or reference fluid in the environment of the thermal sensor (see Fig. 17).

[0137] It may also be preferred for the membrane aperture to be incorporated into the membrane in such a way that it is located between the heating element and the temperature sensor. This creates a spatial separation between the temperature sensor and the heating element, allowing for a longer heat transfer from the heating element to the temperature sensor via the fluid or reference fluid. By spatially separating the heating element and the temperature sensor by means of an intermediate membrane aperture, a higher sensitivity can advantageously be achieved (see Fig. 18).

[0138] Furthermore, it may be preferable to combine the two previously mentioned preferred variants with regard to the positioning of a membrane aperture with regard to the arrangement of the heating element and the temperature sensor. For example, it may be preferable to mount a first temperature sensor in close proximity to the heating element (without a membrane aperture in between), while a second temperature sensor is located further away on the membrane and separated from the heating element by a membrane aperture. By measuring the temperature response using two sensors, which are also located on different areas of the membrane, cross-sensitivities during pressure measurement can be further reduced. For example, the more closely spaced temperature sensor will generally be more susceptible to parasitic heat conduction across the membrane and can thus be used to compensate for this effect.

[0139] In a preferred embodiment, the pressure sensor is characterized in that the thermal sensor comprises a heating element and a first temperature sensor and a second temperature sensor for differential temperature measurement, wherein the at least one membrane aperture is preferably located between the heating element and the first temperature sensor and / or the second temperature sensor. The first temperature sensor and the heating element can preferably be positioned particularly close to one another. A membrane aperture can preferably be arranged between the heating element and the second temperature sensor.

[0140] Preferably, the different spacing of the temperature sensors can be used to compensate for cross-sensitivities of the pressure measurement for heat conduction across the membrane and / or global temperature fluctuations. For example, it may be preferable to monitor the function of the heating element using a temperature sensor in the immediate vicinity of the heating element. Furthermore, the setup can preferably more precisely measure a direct heat transfer from the heating element (via the fluid) to a temperature sensor with a differential measurement.

[0141] For this purpose, it may also be preferable to vary the distance between the first temperature sensor and the heating element, so that a greater distance from one another may also be preferable. Furthermore, it may also be preferable to have a first membrane aperture between the first temperature sensor and the heating element, and a second membrane aperture between the heating element and the second temperature sensor. A plurality of membrane apertures can advantageously further reduce heat conduction caused by the carrier membrane.

[0142] Furthermore, it is advantageous that a differential measurement can be performed by using multiple thermal sensors or multiple temperature sensors. A differential measurement preferably comprises the formation of a combination signal. A combination signal preferably comprises a measurement signal formed from the respective temperature responses of at least two sensor components, preferably two temperature sensors. A combination signal for a differential measurement can be formed by one or more of the arithmetic operations of the at least two temperature responses. The arithmetic operations are preferably selected from a group comprising subtraction, addition, multiplication, and / or division.

[0143] By forming a combination signal, ie by performing a differential measurement, a particularly precise measurement of the pressure of the fluid can advantageously be carried out, which, for example, enables compensation for global temperature fluctuations and / or parasitic heat conduction across the membrane.

[0144] For this purpose, it may be preferable to perform further mathematical operations on the combination signal in order to be able to determine the pressure of the fluid, for example a fast Fourier transform.

[0145] For the two or more temperature sensors, it is generally possible to evaluate both DC components of a temperature response (0-omega signal) and also multiple harmonic AC components (1-omega signal, 2-omega signal, 3-omega signal, etc.). In this respect, the provision of a plurality of temperature sensors allows for particularly precise pressure measurement, which can calculate out or take into account a wide variety of errors or disturbances (such as temperature fluctuations of the thermal sensor, fluctuations in the fluid composition, etc.). In a further preferred embodiment, the pressure sensor is characterized in that the pressure sensor has at least one detection chamber, which is preferably formed by an SMD housing, a THT housing, in particular a TO housing, or a wafer stack or a wafer-level package, wherein the wafer stack or a wafer-level package preferably comprises at least one base wafer and one cap wafer.As explained in more detail herein, it may also be particularly preferred to provide two or more detection chambers.

[0146] An SMD housing (SMD, English: surface mounted device) preferably comprises a housing body with a housing top, a housing bottom, and housing side walls, wherein the housing side walls extend from the housing bottom to the housing top. The housing further preferably comprises a lead frame structure configured to electrically and mechanically connect the housing to a base plate, wherein the housing bottom preferably faces the base plate. The lead frame structure comprises one or more external connections, preferably connecting lines, which serve to electrically connect the thermal sensor. In particular, the external connection, preferably connecting lines, can be located on the housing bottom. An SMD housing is advantageously suitable for the electrical and mechanical connection of various circuit carriers, in particular conventional flat printed circuit boards.Furthermore, installation on curved circuit boards is also advantageously possible.

[0147] A THT package (THT, English: through-hole technology) also has a bottom and top of the package, as well as side walls that form the housing shell, extending from the bottom to the top. A THT package has one or more electrical connections that penetrate one or more components of the housing shell. This allows them to be attached to base plates, such as circuit boards, and enables a particularly robust connection.

[0148] A preferred THT package is a TO package. TO packages (transistor outlines) comprise a base and a cap and offer an advantageous design. One or more connecting leads, for example 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, or more, are preferably attached to the base of a TO package. These connecting leads enable electrical contact between a base plate, such as a circuit board, and the thermal sensor. TO packages offer a wide range of electrical contacting options, particularly by having at least one connecting lead. Advantageously, TO packages can be directly integrated into other sensor systems, for example. They also enable fast and high data transmission rates through appropriate connecting lead(s). Furthermore, they are sufficiently compact, allowing for simple mechanical installation options.In addition, TO packages can be purchased in large quantities with consistent dimensions and / or components.

[0149] A wafer stack or a wafer-level package is preferably formed from at least two wafers, but can also comprise 3, 4, 5, 6, 7, 8, 9, 10, 15, 20, 50 or more wafers. In particular, a wafer stack or a wafer-level package can be formed by a bottom wafer and a cap wafer. The bottom wafer can preferably comprise the support structure. The wafers can be connected to one another both horizontally and vertically in two or more layers, thus forming a three-dimensional configuration. It is also preferred that further layers, such as one or more oxide layers, are located between the wafers of a wafer stack or a wafer-level package. In a wafer stack or a wafer-level package, a lateral region, i.e., an edge region, of one of the at least two wafers is preferably applied with a connecting agent, via which the connection between the at least two wafers is enabled.Preferably, at least one wafer, preferably two wafers, in a wafer stack or a wafer-level package can have a cavity, so that the at least one cavity creates a larger space in order to be able to place the thermal sensor.

[0150] The aforementioned preferred variants for one or more detection chambers have proven advantageous because their design can be implemented using simple and known means of the prior art. Furthermore, the preferred variants are suitable for both closed and open detection chambers.

[0151] Preferably, one or more connecting lines are present on the preferred housing types mentioned in order to enable an electrical contact option to a circuit carrier, preferably a printed circuit board. The electronic circuit can be located on the base plate, for example, wherein the electronic circuit can preferably be used to control the heating element and / or evaluate the temperature response of the sensor component. For this purpose, it can be preferred that the electronic circuit is connected to the thermal sensor, preferably via electrical connection connections. The electrical connection can preferably be selected from a group comprising a connection pad, a conductor track, a conductor track strip, a bonding wire, a solder connection, an electrically conductive adhesive, a bump and / or a through-hole.

[0152] In a further preferred embodiment, the pressure sensor is characterized in that the pressure sensor comprises at least a first detection chamber and a second detection chamber, wherein the first detection chamber is designed such that an external pressure change of the fluid causes an internal pressure change within the first detection chamber, while a second detection chamber is designed such that an external pressure change of the fluid does not cause an internal pressure change within the second detection chamber, so that a differential measurement of temperature responses of the thermal sensors in the first detection chamber and second detection chamber can be carried out to determine the pressure of the fluid.

[0153] The preferred embodiment described above is characterized in that the thermal sensors of the first detection chamber and the second detection chamber detect the same temperature changes under changing ambient conditions. The internal pressure change preferably refers to a pressure change within the detection chamber itself. The internal pressure change can preferably relate to a pressure change in a reference fluid enclosed within the detection chamber. The internal pressure change can also occur in an open detection chamber that has a fluidic connection to the environment. The second detection chamber is preferably closed, so that there is no fluid communication with the environment.Preferably, the second detection chamber has a rigid casing so that the casing of the second detection chamber does not deform due to a change in the pressure of the ambient fluid, thus preventing any internal pressure change. Consequently, in the event of an external pressure change, an internal pressure change occurs in the first detection chamber, while no internal pressure change occurs in the second detection chamber. This advantageously compensates for the influence of environmental parameters, such as temperature, on a pressure measurement. The temperature change will affect both measurements equally.If a combination signal is preferably formed, for example a difference between the temperature response of the thermal sensors in the respective detection chambers, the combination signal is not dependent on global temperature fluctuations, but reflects a pressure change particularly reliably.

[0154] In preferred embodiments in which the pressure sensor comprises at least a first detection chamber and a second detection chamber, increased signal accuracy can advantageously be achieved. For example, drift related to the ambient temperature and / or fluid composition can be compensated.

[0155] In the preferred embodiments with multiple detection chambers comprising at least one additional second detection chamber, one can therefore also speak of the provision of an additional compensation chamber. Taking into account the measurement signals from both detection chambers—a first pressure-sensitive detection chamber and a second pressure-insensitive (compensation) detection chamber—changes in temperature and / or changes in fluid composition can be efficiently taken into account during pressure determination, as explained in more detail below.

[0156] Preferably, a thermal sensor is present in each of the first detection chamber and the second detection chamber. While a first thermal sensor in the first detection chamber allows the measurement of a first temperature response, the second thermal sensor in the second detection chamber allows the detection of a second temperature response. Since only the first detection chamber and not the second detection chamber is designed so that an external pressure change of the fluid causes an internal pressure change within the first detection chamber, the differential measurement of the temperature responses of the first and second thermal sensors in the respective detection chambers allows compensation for factors that can influence the pressure measurement results.

[0157] Preferred embodiments of a detection chamber with a thermal sensor, which were disclosed herein for a pressure sensor with at least one detection chamber, preferably also apply to the first detection chamber with the first thermal sensor, which is designed such that an external pressure change of the fluid causes an internal pressure change within the first detection chamber. Preferably, features of these embodiments also largely apply to the second detection chamber with a second thermal sensor, with the exception that the second detection chamber is designed such that an external pressure change of the fluid does not cause an internal pressure change within the second detection chamber.

[0158] Preferred embodiments of a thermal sensor disclosed herein for a pressure sensor with at least one detection chamber also preferably apply analogously to a pressure sensor with two (or more) detection chambers.

[0159] The structure of the first and second thermal sensors can therefore preferably be analogous to the structure of a thermal sensor, which has been described in connection with embodiments of the pressure sensor with at least one detection chamber.

[0160] Preferably, the first and second thermal sensors also comprise a heating element for providing a thermal field and a sensor component for detecting a temperature response of the thermal sensor. Furthermore, the two thermal sensors are preferably each positioned on a carrier membrane, which is held by a support structure and extends over a cavity.

[0161] Preferably, in the first detection chamber, in which an external pressure change results in a change in the internal pressure, there is an aperture for pressure equalization between the cavity and an interior region of the detection chamber. The aperture for pressure equalization in the first detection chamber can be provided, for example, as a membrane aperture, i.e., an aperture on the membrane, and / or as a support aperture, i.e., an aperture in the support structure.

[0162] Furthermore, it may be preferred that such an aperture for pressure equalization within the second detection chamber, in which an external pressure change does not cause an internal pressure change, is not incorporated. However, it may also be preferred that an aperture for pressure equalization between the cavity and the interior of the second detection chamber is also present in the second detection chamber, for example, as a membrane aperture (aperture on the membrane) and / or as a support aperture (aperture on the support structure).

[0163] However, an opening or aperture for pressure equalization between the first and second detection chamber is preferably not provided.

[0164] For the provision of a first detection chamber in which an internal pressure change occurs and a second detection chamber in which no internal pressure change occurs, several preferred embodiments of the detection chamber can advantageously be considered.

[0165] In a preferred embodiment, the pressure sensor is characterized in that the first detection chamber is formed by an open detection chamber having fluid communication with an environment and the second detection chamber is formed by a closed detection chamber.

[0166] The closed second detection chamber is preferably designed so that an external pressure change of the fluid does not cause an internal pressure change within the second detection chamber. For this purpose, the casing of the second detection chamber is preferably rigid and, in particular, does not include a deflectable pressure equalization membrane.

[0167] In an open detection chamber, an internal pressure change occurs immediately due to a pressure change in the ambient fluid through fluid communication between the detection chamber and the ambient. It may be preferred for the first detection chamber and the second detection chamber to be formed by a single or two separate SMD packages. It may also be preferred for the first detection chamber and the second detection chamber to be formed by a single or two separate THT packages, in particular TO packages. Furthermore, it may be preferred for the first detection chamber and the second detection chamber to be formed by a wafer stack.

[0168] In a further preferred embodiment, the pressure sensor is characterized in that the first detection chamber is formed by a closed detection chamber which comprises a pressure compensation membrane, wherein an external pressure change of the fluid causes a deflection of the pressure compensation membrane, which leads to an internal pressure change of a reference fluid within the first detection chamber, which can be detected by the first thermal sensor, and the second detection chamber is formed by a closed detection chamber which is designed such that an external pressure change of the fluid does not cause an internal pressure change within the second detection chamber (cf. Fig. 21 ).

[0169] Thus, the first detection chamber can be formed by a closed detection chamber having a deflectable pressure equalization membrane as explained above. A change in the pressure of the ambient fluid causes a deflection of the pressure equalization membrane, resulting in an internal pressure change. The second detection chamber can preferably be formed by a closed detection chamber that does not have a pressure equalization membrane, i.e., is preferably characterized by a rigid casing. As a result, no internal pressure change occurs in the second detection chamber.

[0170] Here, too, it may be preferred for the first detection chamber and the second detection chamber to be formed by a single or two separate SMD housings. An SMD housing is advantageously suitable for the electrical and mechanical connection of a large number of circuit carriers, for example in conventional printed circuit boards. Furthermore, it may also be preferred for the first detection chamber and the second detection chamber to be formed by a single or two separate THT housings, in particular TO housings. THT housings advantageously enable a particularly robust connection. TO housings can advantageously be integrated directly into other sensor systems, for example, and allow a fast and high data transmission rate via corresponding connecting line(s). Furthermore, it may be preferred for the first detection chamber and the second detection chamber to be formed by a wafer stack.A wafer stack is particularly quick and easy to prepare due to the applicability of standardized processes. Furthermore, the deflection of the pressure compensation membrane can be optimized in the case of a closed detection chamber. For example, the pressure compensation membrane can be arranged above or next to the thermal sensor.

[0171] To achieve an internal pressure change in the first detection chamber, it may therefore be preferred that an opening is provided on the first detection chamber or that a pressure equalization membrane is provided on the first detection chamber. In the preferred case of an opening on the detection chamber, an external pressure change has a substantially direct effect on an internal pressure change in the first detection chamber. With a preferred pressure equalization membrane, an external pressure change leads to a deflection of the pressure equalization membrane. As a result of the deflection of the pressure equalization membrane, an internal pressure change occurs in the first detection chamber. With an opening on the detection chamber, there is additional fluid communication with the environment, whereas with a pressure equalization membrane, there is no fluid communication with the environment.However, from a functional point of view, the orifice and the pressure equalization membrane are similar in that an external pressure change is translated into an internal pressure change.

[0172] In a further preferred embodiment, the pressure sensor is characterized in that the pressure sensor comprises a first detection chamber and a further detection chamber, wherein the first detection chamber is designed such that an external pressure change of the fluid causes an internal pressure change within the first detection chamber and there is no fluid communication between the first detection chamber and an environment, while a second detection chamber is designed such that an external pressure change of the fluid causes an internal pressure change within the second detection chamber and there is fluid communication between the second detection chamber and the environment, so that preferably a differential measurement of temperature responses of the thermal sensors in the first detection chamber and second detection chamber can be carried out to determine the pressure of the fluid (cf. Fig. 22).

[0173] A change in the pressure of the fluid within an environment leads to an internal pressure change in the first detection chamber. The first detection chamber preferably has no fluid connection to the environment. A first thermal sensor within the first detection chamber thus detects an external pressure change, but not a change in the composition of the fluid, should this change. Within the second detection chamber, a pressure change in the fluid can also be detected by an internal pressure change. Because there is fluid communication, i.e. a fluid connection between the environment and the second detection chamber, a second temperature sensor within the second detection chamber advantageously detects a change in the fluid composition.By generating a corresponding combined signal from the temperature responses of the thermal sensors in the first and second detection chambers, any fluctuations in the composition of a fluid can be advantageously eliminated or compensated for. Since both detection chambers are equally affected by a global temperature fluctuation, any temperature influence on the pressure measurement can also be compensated for.

[0174] Different designs can be implemented to provide first and second detection chambers that meet the above-mentioned requirements. In a preferred embodiment, the first detection chamber is formed by a closed detection chamber having a pressure equalization membrane. The second detection chamber is preferably formed by an open detection chamber that allows fluid communication with the environment. A change in the pressure of the fluid in the environment causes the pressure equalization membrane of the first detection chamber to deflect, so that an internal pressure change adjusts the pressure inside the first detection chamber to the external pressure. The opening also adjusts the pressure in the second detection chamber. At the same time, the opening also allows fluid communication with the environment.

[0175] The first detection chamber and the second detection chamber can preferably be formed by a single or two separate SMD packages. Preferably, the first detection chamber and the second detection chamber can be formed by a single or two separate THT packages, in particular TO packages. Furthermore, it may be preferred for the first detection chamber and the second detection chamber to be formed by a wafer stack.

[0176] In a further preferred embodiment, the pressure sensor is characterized in that the pressure sensor comprises at least a first thermal sensor and a second thermal sensor, wherein a solid body is introduced as a reference substance only below the second thermal sensor, so that different temperature responses can be detected by the first thermal sensor and the second thermal sensor.

[0177] Preferably, a pressure change of the fluid can be determined based on different dependencies of the temperature responses of the first and second thermal sensors on the pressure. The second thermal sensor is preferably located on the second membrane, below which the reference substance is located as a solid. The first membrane, on which the first thermal sensor is located, comprises at least one, preferably two or more apertures through which diffusion of the fluid is enabled, preferably into a cavity located underneath. The preferred embodiment described is particularly well suited for taking a pressure measurement using a differential signal. The fluid is heated by the oscillating control of the first and second heating elements, with the fluid flowing around both the first and the second thermal sensor.While a solid body serves as a reference substance beneath the second thermal sensor, the first thermal sensor is preferably surrounded exclusively by the fluid to be measured or a reference fluid (in the case of a closed detection chamber). Preferably, the reference substance, as a solid body, differs from the fluid to be measured (or a reference fluid in a closed detection chamber) in at least one thermal property. Accordingly, it is preferred that the reference substance behaves differently than the fluid (or reference fluid) in at least one property as a result of a temperature change caused by the heating element.

[0178] When the temperature increases or the pressure changes, the density of the fluid (or a reference fluid) changes, whereas the density of the solid reference substance changes only slightly or not at all. A change in pressure, in turn, leads to a change in the volumetric heat capacity of the fluid (or a reference fluid), which influences the temperature response to the activation of the first heating element. In particular, the volumetric capacity of the fluid (or a reference fluid) that has diffused through the at least one aperture below the first thermal sensor changes. However, the volumetric heat capacity of the reference substance, which is present as a solid below the second heating element, changes little or only slightly.Thus, the pressure sensor, together with the first temperature sensor, detects a change in the volumetric heat capacity, while the second thermal sensor detects no or only a minor change in the volumetric heat capacity, particularly for the reference body. A differential signal from the temperature responses of the first and second thermal sensors thus allows for a particularly precise measurement of the pressure change.

[0179] It may be preferable to install the first and second thermal sensors on or in a single detection chamber or in multiple detection chambers.

[0180] For example, it may be preferred that the first thermal sensor and the second thermal sensor are positioned on a membrane that extends along a support structure having two cavities. A first cavity is located below the first thermal sensor. Through the membrane apertures, which are located in the region of the first thermal sensor, i.e., above the first cavity, a transition of the fluid (or a reference fluid) for pressure equalization is possible. The second thermal sensor is preferably also located on the membrane. Below the second thermal sensor, there is preferably a second cavity, within which the solid body is preferably introduced as a reference substance (cf. Fig. 23A).

[0181] It may also be preferred for the preferred embodiment described above to be formed by a wafer stack. The preferred wafer stack may comprise a bottom wafer and a cap wafer. The wafer stack forms a single detection chamber. The cap wafer may preferably comprise one or more openings. The first thermal sensor and the second thermal sensor may be attached to the preferred bottom wafer. The bottom wafer and the cap wafer are preferably connected to one another at lateral regions, thereby forming the wafer stack. The openings enable the fluid to flow around the first and second thermal sensors. The first thermal sensor may, for example, be located above a first cavity and the second thermal sensor above a second cavity, with the solid body serving as a reference substance within the second cavity (cf. Fig. 23B).

[0182] Furthermore, the preferred embodiment described above can be provided by an SMD housing or THT housing, in particular also a TO housing, within which the first and second thermal sensors are located. The first thermal sensor is preferably located on a first support membrane, which is located on a first support structure having a cavity. The second thermal sensor is preferably located on a second support membrane, which is located on a second support structure having a cavity and within which the solid body is located as a reference substance. The housing preferably has an opening through which the fluid can flow around the first and second thermal sensors (cf. Fig. 23C).In a further aspect, the invention relates to a method for measuring a pressure of a fluid comprising the following steps: a) providing a pressure sensor (comprising a detection chamber within which a thermal sensor is arranged, wherein the thermal sensor comprises a heating element for providing a thermal field and a sensor component for detecting a temperature response due to an influence of the fluid on the thermal field, wherein the thermal sensor is further positioned on a support membrane which is held by a support structure and extends over a cavity and wherein an aperture enables pressure equalization between the cavity and an interior region of the detection chamber, b) oscillating control of the heating element with at least one frequency, c) determining the pressure of the fluid on the basis of the temperature response of the thermal sensor as a function of the influence of the fluid on the thermal field.

[0183] The average person skilled in the art will recognize that technical features, definitions and advantages described for the pressure sensor according to the invention and for its preferred embodiments equally apply to the method for measuring a pressure of a fluid, and vice versa.

[0184] The pressure sensor according to the invention advantageously eliminates the disadvantages of conventional Pirani sensors. As explained above, the detectable pressure range of Pirani sensors is often limited, which means that pressure measurements are typically carried out at well below 1 bar. At higher pressures, however, saturation occurs, making it difficult or even impossible to determine the pressure. The measuring principle of Pirani sensors is based on the dependence of thermal conductivity on pressure, whereby at very low Knuden number values, thermal conductivity is independent of pressure. In order to make Pirani sensors more sensitive even at high pressures, it is known to reduce the gap between a heating element and a heat sink or to increase the surface area. However, this results in more complex processing and may lead to a loss of mechanical stability.

[0185] The disadvantages of known Pirani sensors, which are based on a static measuring principle, are advantageously eliminated by the pressure sensor according to the invention. In particular, with an oscillating control of the heating element, which in the context of the invention can be understood as a dynamic excitation, the temperature response depends significantly on the volumetric heat capacity. The volumetric heat capacity, in turn, exhibits a pressure dependence that does not saturate at high pressures. Instead, there is advantageously an almost linear relationship between the volumetric heat capacity and the acting pressure (see Fig. 2). Because the pressure sensor according to the invention does not exhibit saturation at or within a certain pressure range, the pressure can therefore be measured over a significantly larger measuring range.In particular, pressure measurements for pressures significantly above 1 bar are also possible, which means the pressure sensor can also be used to measure the pressure in gas tanks, for example. In particular, pressures significantly above 1 bar, such as 10 bar, 100 bar, or more, can also be measured. The extended measuring range also leads to an expansion of the fields of application.

[0186] A further advantage lies in the provision of a detection chamber and in the fact that the pressure sensor has an aperture to enable pressure equalization between the cavity and an interior region of the detection chamber. The detection chamber of the pressure sensor advantageously provides mechanical protection, for example, for the thermal sensor. Furthermore, it prevents the thermal sensor from seeing, for example, a fluid flow, which could lead to anemometric heat dissipation and forced convection, which could falsify the measurement results. Instead, the detection chamber separates an inner region, in which the thermal sensor is located, from an outer region of an environment in which the fluid is located and whose pressure is to be measured.

[0187] In a further aspect, the invention relates to a use of the pressure sensor according to the above-described for monitoring a pressure of a fluid.

[0188] The average person skilled in the art will recognize that technical features, definitions and advantages described for the pressure sensor according to the invention and for its preferred embodiments and for the method equally apply to the use of the pressure sensor for monitoring a pressure of a fluid, and vice versa.

[0189] In many applications, pressure is a relevant parameter that should be reliably measured and monitored.

[0190] For example, tanks containing a gas or liquid can be monitored. The use of a pressure sensor is particularly useful when a critical fluid and / or a particularly high pressure is enclosed. For example, it can be used to monitor a tank in which hydrogen is stored. Hydrogen is viewed in the state of the art as the energy carrier of the future, as it can also be used as a fuel, particularly in the automotive sector. Hydrogen is intended to replace fossil fuels in particular, as the combustion of hydrogen does not produce any climate- and / or environmentally harmful exhaust gases. However, hydrogen is a particularly reactive gas, which means that constant monitoring of the hydrogen pressure in the respective containers or tanks is desirable.

[0191] By using the compact pressure sensor according to the invention with an advantageous measuring range extending to high pressures of more than 10 bar, 50 bar, 100 bar, or more, a continuous and reliable measurement of hydrogen can be advantageously performed through pressure measurement or pressure monitoring. The detection of a pressure change could, for example, indicate that a leak has occurred and hydrogen is escaping, resulting in a change in the pressure within the tank.

[0192] This can advantageously be detected using a pressure sensor, allowing appropriate measures to be initiated quickly. For monitoring such high pressures, it may be preferable to use an open detection chamber to avoid limitations imposed by a pressure equalization membrane. Furthermore, the pressure sensor can advantageously be used to monitor the pressure of a fluid, regardless of whether the fluid is a gas or a liquid, for example, by ensuring media separation through a closed detection chamber.

[0193] The application can also be implemented in the consumer sector, where pressure monitoring of a fluid can also be relevant.

[0194] The aspects of the invention will be described below by way of example with reference to figures, without being limited to these figures.

[0195] Figures

[0196] Short description of the characters

[0197] Fig. 1 Comparison between a pressure measurement from the prior art and by means of the pressure sensor according to the invention.

[0198] Fig.2 Representation of a measurement signal which has a substantially linear

[0199] Relationship between temperature response and pressure in an oscillating control is illustrated.

[0200] Fig. 3 Diagram illustrating the pressure measurement using the pressure sensor according to the invention.

[0201] Fig. 4-8 Schematic representation of preferred embodiments of a pressure sensor according to the invention comprising a closed detection chamber.

[0202] Fig. 9-14 Schematic representation of preferred embodiments of a pressure sensor according to the invention comprising an open detection chamber.

[0203] Fig. 15 Schematic representation of a preferred measuring principle for determining the pressure by evaluating the temperature response at a first and second frequency

[0204] Fig.16 Schematic representation of preferred embodiments of a

[0205] Pressure sensor or its thermal sensor using different MEMS technologies.

[0206] Fig. 17-20 Schematic representation of preferred embodiments for attaching one or more membrane apertures as well as preferred positioning of a heating element and temperature sensor(s) on a carrier membrane.

[0207] Fig. 21-22 Schematic representation of preferred embodiments in which a differential signal for a pressure measurement is formed.

[0208] Fig. 23 Schematic representation of a preferred embodiment of a pressure sensor according to the invention comprising a solid as a reference substance. Detailed description of the figures

[0209] Fig. 1A shows an electrical circuit diagram illustrating the functional principle of a static pressure measurement, which is carried out in particular using known Pirani sensors. Furthermore, Fig. 1A shows a measurement curve that can be recorded using a Pirani sensor.

[0210] Pirani sensors are used to measure pressure by exploiting the fact that, within certain limits, the thermal conductivity of gases is pressure-dependent. In particular, Pirani sensors exploit the fact that the thermal conductivity of a gas depends essentially linearly on the pressure within a certain pressure range. For this purpose, a Pirani sensor can comprise a wire, synonymously also called a heating wire, which is positioned inside a tube and heats up when a current is applied. The pressure dependence of the thermal conductivity of the gas heated by the heating wire can be characterized by the Knudsen number Kn, which is defined as the ratio of the mean free path and the characteristic length. At low pressures and Kn»1 (also at Kn>1 ), the flow of the gas can be regarded as a molecular flow.Pirani sensors should preferably operate in the molecular regime, since only within this regime is there an essentially linear relationship between pressure and the thermal conductivity of the gas. At Kn<1, however, saturation occurs, where the thermal conductivity remains constant. Therefore, inference about pressure is not possible outside the molecular regime.

[0211] The electrical circuit diagram in Fig. 1 A illustrates the dependence of pressure measurement in the case of a static excitation and evaluation of a temperature response using known Pirani sensors. The temperature response and excitation are compared with the application of an electrical voltage U across a resistor Ro, resulting in a power P = U*l = U 2 *Ro' 1 results.

[0212] Both the parasitic heat flows (e.g. heat conduction across the membrane) and the heat flows to be measured to the fluid or gas can be represented in the model by thermal resistances, which preferably correspond to a thermal conductivity, and capacitive components, which preferably correspond to a volumetric heat capacity.

[0213] In the case of a static measurement of the equilibrium state, the thermal resistances Rth (parasitic thermal resistance Rth, parasitic and resistance of the fluid Rth, gas) dominate the temperature response. The capacitive components, in particular a parasitic heat capacity and / or volumetric heat capacity (parasitic heat capacity Cth, parasitic and volumetric heat capacity of the fluid or gas Cth, gas), are not captured in a static measurement. Instead, a static measurement can preferably capture a thermal conductivity, which only exhibits a pressure dependence for high Knudsen numbers (or low pressures).

[0214] Fig. 1 B shows a circuit diagram illustrating a pressure measurement using the pressure sensor according to the invention. In a first approximation, the pressure measurement using the pressure sensor according to the invention can be described by a first-order low-pass filter. In analogy to electrical quantities, the thermal field or the heat provided by the heating element can be compared to an electrical charge. The heat capacity Cth corresponds to an electrical capacitance, the electrical current corresponds to a heat flow (heat per time), the thermal conductivity k (or A) corresponds to an electrical conductivity, and the thermal resistance Rth to an electrical resistance. The parasitic quantities refer to components that do not result from the fluid itself, but rather, for example, relate to heat conduction through other components of the thermal pressure sensor, such as a membrane.

[0215] Here, the thermal resistance depends in particular on the thermal resistance of the fluid or reference fluid Rth, gas, and on the parasitic thermal resistance Rth, parasitic, while the heat capacity depends on the heat capacity of the fluid or reference fluid Cth, fluid and Cth, parasitic. In the circuit diagram, Rth, gas and Rth, parasitic are connected in parallel and form the thermal resistance Rth. The thermal resistance of the fluid (here, the gas) depends on the thermal conductivity k. Therefore, the following applies:

[0216] Rth — Rth, parasitic | | Rth, gas — Rth, parasitic Rth, gas / (Rth, parasitic "*■ Rth, gas).

[0217] Furthermore, in the circuit diagram, CRth, gas, and Cth, are parasitically connected in parallel to each other and form the thermal capacity Cth. The capacity of the fluid (here the gas) depends on the volumetric heat capacity cv, which in turn depends on the pressure P. Therefore, the following applies:

[0218] Cth— Cth, parasitic | | Cth, gas (CV(p)) — Cth, parasitic "*■ Cth, gas

[0219] The thermal resistance of the gas is

[0220] Rth, Gas = AI / k,

[0221] While the heat capacity of the gas

[0222] Cth, Gas = A2* cv(p) applies,

[0223] Where Ai and A2 are geometric factors that affect the geometric design of the pressure sensor.

[0224] In particular, with an oscillating control of the heating element, which can be considered a dynamic excitation in the context of the invention, the temperature response depends significantly on the capacitive components and thus on the volumetric heat capacity. Advantageously, the volumetric heat capacity—in contrast to thermal conductivity—is pressure-dependent, which does not saturate at high pressures. This advantageously allows the pressure sensor to cover a larger measuring range.

[0225] The circuit diagram shows a first-order low-pass filter. The amplitude of the temperature response ATAC and the phase can be described in a first approximation as

[0226] ATAC = p / l / Rth) 2 + (2 TT f Cth) 2 )

[0227] 0 = - arctan (2 TT f Rth Cth), where f denotes the frequency, so that the pressure p of the fluid can be determined from this.

[0228] Fig. 2 shows a representation of a measurement signal which illustrates a substantially linear relationship between the temperature response, in particular between an inverse value of an amplitude and / or a phase of the temperature response, and the pressure in an oscillating control according to the invention.

[0229] The schematic illustration is based on various measurements.

[0230] For example, for nitrogen as a fluid, a substantially linear relationship between phase and pressure was observed with an oscillating heating element control (60 Hz and peak voltage 4 V). The phase increased with a substantially constant gradient of approximately 1.97 bar from approximately 90° to approximately 94° over a pressure range of approximately 0.4 bar to approximately 2 bar.

[0231] Similarly, for argon, an essentially linear relationship between a phase and the pressure was found, with the phase increasing in a range from approximately 0 bar to approximately 8 bar with a constant increase of approximately 1.67 bar from 98° to approximately 116°.

[0232] The lack of saturation and the preferably linear increase, for example of a phase or an inverse of an amplitude, enables a simple conclusion to be drawn about a pressure in the case of an oscillating control of a heating element and corresponding evaluation of a temperature response.

[0233] In preferred embodiments, a calibration measurement can first be performed for this purpose. Preferably, for an oscillating control according to the invention, a temperature response, in particular an inverse value of an amplitude and / or phase of a temperature response, is recorded for a series of measurements of known pressures, which would preferably be expected in the context of the use of the pressure sensor.

[0234] By means of the calibration measurement, a relationship between a quantity derived from the temperature response, for example a phase and / or amplitude of the pressure, can be determined for the pressure sensor. According to the invention, it was advantageously found that, with an oscillating excitation, a quantity derived from the temperature response, for example a phase and / or an inverse of an amplitude, exhibits a substantially linear relationship over a wide measuring range and, in particular, does not saturate. With knowledge of a corresponding calibration curve, the pressure can thus be easily deduced during subsequent use of the pressure sensor by measuring a specific temperature response (or, for example, its phase and / or amplitude).

[0235] Fig. 3 shows a diagram for carrying out the pressure measurement using a pressure sensor according to the invention. The pressure sensor has a detection chamber which can be closed or open. A change in the pressure of the fluid in an environment, i.e. Pextem, can be reflected in a change in the mechanical properties of the thermal pressure sensor, for example in the form of a pressure change within the detection chamber (package). The influence on the detection chamber depends on the fluid properties (gas properties if the fluid (or reference fluid) is a gas) and the conditions within the detection chamber. The fluid in the environment, which has an active connection in the sense of pressure transfer with the detection chamber, leads in particular to a change in the internal pressure within the detection chamber Pintern.The periodic heating of the fluid (or reference fluid) is achieved by oscillating the heating element. The temperature response (Asignal) in turn changes due to a change in the internal pressure within the detection chamber, which results from the effect of the ambient fluid on the thermal pressure sensor. The recorded temperature response can then be used to determine the pressure of the ambient fluid.

[0236] Fig. 4 shows a preferred embodiment of a pressure sensor 1. The pressure sensor 1 comprises a closed detection chamber 9, within which a reference fluid 19 and a thermal sensor 3 are enclosed. The pressure sensor 1 further comprises a pressure compensation membrane 21. A change in the pressure of the fluid causes a deflection of the pressure compensation membrane 21, which leads to a pressure change in the reference fluid 19. The pressure change in the reference fluid 19 can, in turn, be detected by the thermal sensor 3. The thermal sensor 3 is positioned on a support membrane 39. The support membrane 39 is held by a support structure 25 and extends over a cavity 27.

[0237] The transfer of an external pressure to the reference fluid 19 is reflected in a change in the geometry of the detection chamber 9 through a deflection of a pressure compensation membrane 21. In the case of a higher external pressure, the pressure compensation membrane 21 bulges inward, compressing the reference fluid 19 until the internal pressure has adjusted to the external pressure. The oscillating heating of the reference fluid 19 (at an internal pressure that essentially corresponds to the external pressure) is achieved via the oscillating control of the heating element. As a result of a recorded temperature response during an oscillating control, the pressure of the reference fluid 19 can advantageously be determined (preferably based on a volumetric heat capacity), which essentially corresponds to the external pressure of the fluid.

[0238] In the closed detection chamber 9, the properties of the reference fluid 19 are advantageously known, in particular its composition.

[0239] It is therefore not necessary to determine or monitor the composition of the reference fluid 19 through additional measurements. Furthermore, a closed detection chamber 9 is advantageous in that the pressure of aggressive fluids can also be measured, i.e. fluids that could have an adverse effect on direct contact with the thermal sensor, for example due to a corrosive effect. By separating the fluid and reference fluid 19, it can be ensured that the thermal sensor 3 is always located in an environment of a non-aggressive reference fluid and therefore has a long service life. Figs. 5-8 show further preferred embodiments of pressure sensors 1 which comprise a closed detection chamber 9. These have a different design with regard to the detection chamber 9.

[0240] Fig. 5 shows a preferred embodiment of the pressure sensor 1, in which the closed detection chamber 9 is formed by an SMD housing 11. An SMD housing 11 comprises a housing body with a housing top, a housing bottom, and housing side walls, wherein the housing side walls extend from the housing bottom to the housing top. The housing further preferably comprises a lead frame structure configured to electrically and mechanically connect the housing to a base plate, wherein the housing bottom faces the base plate. The lead frame structure comprises connecting lines 17, which serve to electrically connect the thermal sensor 3. The connecting lines 17 are located on the housing bottom. An SMD housing 11 is advantageously suitable for the electrical and mechanical connection of a large number of circuit carriers, for example conventional printed circuit boards.Furthermore, installation on curved circuit boards is advantageously possible.

[0241] The reference fluid 19 and the thermal sensor 3 are enclosed within the closed detection chamber 9. A pressure compensation membrane 21 is attached to the detection chamber 9. A change in the pressure of the fluid leads to a deflection of the pressure compensation membrane 21. This results in a pressure change in the reference fluid 19, which can be detected by the thermal sensor 3. The thermal sensor 3 is located on a support membrane 39, which extends over the cavity 27 of the support structure 25.

[0242] The pressure sensor 1 further comprises a reference sensor 31. A reference sensor 31 preferably means an additional sensor by which a further parameter relevant for determining the pressure of the fluid can be measured. In most cases, the determination of the pressure depends on a large number of parameters. One or more reference sensors 31 can advantageously determine one or more of these parameters, so that the pressure can be determined more precisely based on the temperature response of the thermal sensor 3. The reference sensor 31 can be used to determine a thermodynamic material property and / or a composition of the fluid. Likewise, the reference sensor 31 can also be used to detect or monitor environmental parameters such as humidity and / or temperature.

[0243] Fig. 6 shows a further preferred embodiment of the pressure sensor 1, in which the closed detection chamber 9 is formed by a TO housing 13. The TO housing 13 comprises a base and a cap and offers an advantageous design. Connecting lines 17 are attached to the base of the TO housing 13, which enable electrical contact between a base plate, such as a circuit board, and the thermal sensor 3. The TO housing 13 offers a wide range of electrical contact options, particularly by having at least one connecting line 17. The TO housing 13 can advantageously be directly integrated into other sensor systems, for example. In addition, the TO housing 13 allows for fast and high data transmission rates through corresponding connecting lines 17. Furthermore, the TO housing 13 is sufficiently compact, so that simple mechanical installation options are also available.In addition, TO packages 13 can be purchased in large quantities with consistent dimensions and / or components. Analogous to the embodiment of Fig. 5, the pressure sensor 1 comprises a pressure compensation membrane 21. A change in the pressure of the fluid in the vicinity of the pressure sensor 1 causes a deflection of the pressure compensation membrane 21. This leads to a pressure change in the reference fluid 19, which can be detected by the thermal sensor 3. The thermal sensor 3 is located on a carrier membrane 39, which extends over the cavity 27 of the carrier structure 25. A reference sensor 31 can be used to detect additional parameters that must be considered when determining the pressure.

[0244] Fig. 7 shows a further preferred embodiment of the pressure sensor 1, in which the closed detection chamber 9 is formed by a wafer stack 15. The wafer stack 15 comprises a bottom wafer 14 and a cap wafer 12. The cap wafer 12 is connected to the bottom wafer 14 at lateral regions. The bottom wafer preferably comprises the support structure 25, which comprises a cavity 27. The support membrane 39, on which the thermal sensor 3 is located, extends above the cavity 27. The cap wafer 12 comprises the pressure compensation membrane 21. A change in the pressure of the fluid in the environment of the pressure sensor 1 results in a deflection of the pressure compensation membrane 21. This leads to a pressure change in the reference fluid 19, which can be detected by the thermal sensor 3. The reference fluid 19 is located in the cap wafer 12 and in the cavity 27 of the bottom wafer 14. The pressure sensor 1 may further comprise a reference sensor 31.

[0245] A wafer stack 15 provides advantageous space, for example, to optimize the deflection of the pressure compensation membrane 21. Furthermore, optimal design options are possible for the placement of the thermal sensor 3, in particular a heating element and a temperature sensor. In particular, the at least one cavity 27 can create a larger space for placing the thermal sensor 3.

[0246] Fig. 8 shows a further preferred embodiment of the pressure sensor 1 with a closed detection chamber 9, which, analogous to Fig. 7, is formed by a wafer stack 15 comprising a base wafer 14 and a cap wafer 12. However, in the embodiment shown, the thermal sensor 3 and the pressure compensation membrane 21 can advantageously be mounted on the same wafer.

[0247] Fig. 9 shows another preferred embodiment of a pressure sensor 1. The pressure sensor 1 comprises an open detection chamber 9, which has an opening 29 for fluid communication between an interior of the detection chamber 9 and the environment. An open detection chamber 9 is characterized by a fluidic connection to the environment, so that fluid from the environment can spread into the pressure sensor 1 and, conversely, the fluid from the pressure sensor 1 can also flow back into the environment.

[0248] The pressure change of the fluid can be detected by the thermal sensor 3. The thermal sensor 3 is positioned on a support membrane 39. The support membrane 39 is held by a support structure 25 and extends over a cavity 27. Particularly high pressures can advantageously be measured using an open detection chamber 9. In a closed detection chamber, the measuring range, in particular, can be limited by a maximum deflection of the pressure compensation membrane. Such a limitation is advantageously not present in an open detection chamber 9. For example, pressures of more than 10 bar, 50 bar, 100 bar, or more, as can occur in gas tanks, can be reliably detected.This ensures long-term functionality, since even at such high pressures, there is little or no risk of damage to structural components, such as a fragile pressure equalization membrane, of the pressure sensor 1. Any disadvantages of an open detection chamber 9 compared to a closed version, with regard to a lack of control over the composition of the fluid in the vicinity of the thermal sensor 3, can be effectively compensated for by means for monitoring and / or determining a thermodynamic material property and / or composition of the fluid.

[0249] Figs. 10-14 show further preferred embodiments of pressure sensors 1 comprising an open detection chamber 9. These have a different design with regard to the detection chamber 9.

[0250] Fig. 10 schematically illustrates another preferred embodiment of the pressure sensor 1, in which the open detection chamber 9 is formed by an SMD housing 11. An opening 29 is provided on the SMD housing 11. The thermal sensor 3 is positioned on the support membrane 39. The support membrane 39 is held by the support structure 25 and extends over the cavity 27. Furthermore, connecting lines 17 are present on the SMD housing 11. The detection chamber 9 comprises a reference sensor 31, which is incorporated within the SMD housing 11. The connecting lines 17 are located on the underside of the housing.

[0251] Fig. 11 shows another preferred embodiment of the pressure sensor 1, in which the open detection chamber 9 is formed by a TO housing 13. The TO housing 13 comprises a base and a cap and offers an advantageous design. Connecting leads 17 are attached to the base of the TO housing 13, enabling electrical contact between a circuit carrier, such as a printed circuit board, and the thermal sensor 3.

[0252] Fig. 12 shows a further preferred embodiment of the pressure sensor 1, in which the open detection chamber 9 is formed by a TO housing 12. The opening 29 is located at the base of the TO housing 13. The opening 29 is located below a cavity 27, over which the support membrane 39 extends and on which the thermal sensor 3 is attached. A fluid line 19 is located at the opening 29. Fluid communication with the environment is enabled through the fluid line 19. A reference fluid 19 is present in the interior of the detection chamber 9. The fluid line 19 can advantageously enable a more controlled fluidic exchange. The fluid line 19 can preferably be attached to the detection chamber 9 as a pipe or a hose. Furthermore, connecting lines 17 are attached to the TO housing 13. In addition, a reference sensor 31 is located within the TO housing 13.

[0253] Fig. 13 serves to schematically illustrate another preferred embodiment of the pressure sensor 1, in which an open detection chamber 9 is formed by a wafer stack 15 comprising a bottom wafer 14 and a cap wafer 12. The bottom wafer 14 comprises a support structure 25. A support membrane 39 is attached to the support structure 25 and extends over a cavity 27. The thermal sensor 3 is positioned on the support membrane 39. Several openings 29 are attached to the cap wafer 12, which openings enable fluid communication with the environment of the pressure sensor 1. Furthermore, the pressure sensor 1 comprises a reference sensor 31.

[0254] Fig. 14 shows another preferred embodiment of a pressure sensor 1 comprising an open detection chamber 9. The detection chamber 9 is formed by a wafer stack 15 comprising a bottom wafer 14 and a cap wafer 12. The bottom wafer 14 comprises a support structure 25. The support membrane 39 is mounted on the support structure and extends over the cavity 27. The thermal sensor is positioned on the support membrane 39. The openings 29 for fluid communication with the environment of the pressure sensor 1 are mounted on the bottom wafer 14.

[0255] Fig. 15 shows a preferred measuring principle in which the temperature response is evaluated at two frequencies in order to allow a conclusion to be drawn about a pressure.

[0256] Oscillating the heating element results in the temperature response also being an oscillating signal and can have one or more frequencies. A first frequency and a second frequency can form frequency components of the temperature response, with the first frequency being lower than the second frequency.

[0257] For a first frequency, which is particularly low and, for example, essentially corresponds to a constant component of the temperature response (at 0 Hz), the temperature response preferably depends on the thermal conductivity and has no pressure dependence. The thermal conductivity preferably represents a thermodynamic material property, which allows simple conclusions to be drawn about a fluid composition. If the fluid whose pressure is to be determined is, for example, a gas mixture whose components A and B are known, the components of A and B can generally be easily determined by measuring the thermal conductivity of the fluid as a gas mixture. For this purpose, only the thermal conductivity of the individual components of A and B must be known and taken into account accordingly.

[0258] The temperature response at a second frequency, which is higher than the first frequency, preferably depends not only on a thermodynamic material property (such as thermal conductivity), but also, in particular, on pressure. The temperature response at a second (higher) frequency can, in particular, correspond to a temperature response at the frequency of the heating element's activation, thus a so-called 1-omega signal. Likewise, the temperature response can be evaluated at preferably integer multiples of the activation frequency.

[0259] Preferably, the first frequency f1 thus provides a measurement signal or a function of a thermodynamic material property of a fluid or its composition. The second frequency f2 (greater than 0 Hz), on the other hand, preferably provides a measurement signal or a function that depends on a thermodynamic material property of a fluid or its composition and the pressure. Both signals can be combined with each other using an electronic circuit or electronics to obtain a fluid-compensated pressure signal related to a composition.

[0260] Fig. 16 AC schematically show preferred embodiments of a pressure sensor 1 or its thermal sensor 3 using different MEMS technologies.

[0261] In all embodiments shown, an aperture 37 enables pressure equalization between the cavity 27 and an interior region of the detection chamber 9. The pressure sensor 1 comprises a detection chamber 9, within which a thermal sensor 3 is arranged. The thermal sensor 3 comprises a heating element for providing a thermal field. Furthermore, the thermal sensor 3 comprises a sensor component for detecting a temperature response of the thermal sensor as a function of the influence of the fluid on the thermal field. The heating element is designed to be controlled in an oscillating manner at at least one frequency, so that the pressure of the fluid can be determined based on the temperature response of the thermal sensor 3. The thermal sensor 3 is positioned on a support membrane 39, which is held by the support structure 25 and extends over a cavity 27.

[0262] The cavity 27 of Fig. 16A can preferably be obtained by etching from a front side and extend not continuously, but through a partial region of the support structure 25. Fig. 16B illustrates an embodiment in which a cavity 27 is provided by back-side etching and extends completely through the support structure 25. Fig. 16C illustrates an embodiment in which a thermal sensor 3 is provided on a support membrane 39 above a flatter cavity 27 by means of surface micromechanics.

[0263] Fig. 17A and B show a preferred introduction of membrane apertures 37 on a support membrane 39 extending over a cavity 27 of the support structure 25. Fig. 17A shows a cross-sectional view, while Fig. 17B illustrates a top view of the pressure sensor 1.

[0264] The membrane apertures 37 form the apertures for pressure equalization between the cavity 27 and the interior of the detection chamber. It has proven particularly advantageous to incorporate one or more apertures for pressure equalization between the cavity 27 and the interior of the detection chamber into the support membrane 39, i.e., as membrane apertures 37. This advantageously further reduces the parasitic influence of the support membrane, i.e., in particular, the heat conduction resulting from the support membrane 39 can be further reduced.

[0265] The thermal sensor 3 comprises a heating element 5 and a temperature sensor 7, which are positioned close to each other and are located between two laterally spaced membrane apertures.

[0266] Fig. 17C shows a circuit diagram of direct heat transfer to the fluid of the preferred embodiment according to Fig. 17 A and B, wherein the temperature sensor 7 and a heating element 5 are positioned close to each other and the temperature sensor 7 is used to determine the temperature response T1 of the heating element 5. Figs. 18A and 18B show another preferred embodiment of a pressure sensor 1 and another option for attaching the membrane aperture 37. Fig. 18A shows a cross-sectional view, while Fig. 18B shows a top view.

[0267] The pressure sensor 1 comprises a support structure 25 with a cavity 27. The support membrane 39, on which the thermal sensor 3 is positioned, extends above the cavity 27. The thermal sensor 3 comprises a heating element 5 and a temperature sensor 7. The membrane aperture 37 is located between the heating element 5 and the temperature sensor 7. This allows for a longer heat transfer from the heating element 5 to the temperature sensor 7 through the fluid or reference fluid, thus achieving greater sensitivity.

[0268] Fig. 19 shows further preferred embodiments of the pressure sensor 1 as well as possible designs of the aperture for pressure equalization between the cavity 27 and the interior of the detection chamber 9. Fig. 19A shows a cross-sectional view, while Fig. 19B shows a plan view.

[0269] Fig. 19A and B show a combination of the two previously described variants from Figs. 17 and 18 with regard to the positioning of the membrane aperture 29 with regard to the arrangement of the heating element 5 and the temperature sensor 7. The thermal sensor 3 comprises a heating element 5 as well as a first temperature sensor 7 and a second temperature sensor 7. The first temperature sensor 7 and the heating element 5 are positioned particularly close to one another. However, a membrane aperture 37 is arranged between the heating element 5 and the second temperature sensor 7. By measuring the temperature response using two temperature sensors 7, which are also located on different areas of the carrier membrane 39, cross-sensitivities during a pressure measurement can be further reduced.For example, the more closely spaced temperature sensor 7 will generally have a higher susceptibility to parasitic heat conduction via the carrier membrane 39 and can thus be used to compensate for this effect.

[0270] Fig. 19C shows a circuit diagram illustrating a pressure measurement using the preferred embodiments of a pressure sensor according to the invention shown in Figs. 19 A and B. The temperature sensor 7 in the immediate vicinity of the heating element 5 detects the temperature response T1, while a temperature sensor 7 separated by an aperture 37 measures the temperature response T2.

[0271] Fig. 19D shows an embodiment of the pressure sensor 1 according to Fig. 19A and B, in which a distance between the first temperature sensor 7 and the heating element 5 (between which there is no aperture) has been increased.

[0272] Fig. 19E shows a preferred embodiment of the thermal pressure sensor 1 according to Fig. 19c, in which a further membrane aperture 37 has been introduced between the first temperature sensor 7 and the heating element 5.

[0273] Fig. 19F shows a further preferred embodiment of a thermal pressure sensor 1 with two temperature sensors 7, without a membrane aperture. Pressure equalization for this pressure sensor 1 occurs through a support aperture (not shown). Figs. 20A-B serve to schematically illustrate further preferred embodiments of the pressure sensor 1. The pressure sensor comprises a support structure 25, on which the support membrane 39 is attached. Located on the support membrane 39 is a thermal sensor 3, which comprises a heating element 5 and a temperature sensor 7. In Fig. 20A, the heating element 5 and the temperature sensor 7 are positioned particularly close to one another on the support membrane 39. In Fig. 20B, the heating element 5 and the temperature sensor 7 are spaced apart by a greater distance.

[0274] Fig. 21A-C show preferred embodiments of a pressure sensor 1 that performs a differential measurement for determining a pressure. The pressure sensors 1 comprise a first detection chamber 9a and a second detection chamber 9b. The first detection chamber 9a is designed such that an external pressure change of the fluid causes an internal pressure change within the first detection chamber 9a. The second detection chamber 9b is designed such that an external pressure change of the fluid does not cause an internal pressure change within the second detection chamber 9b, so that a differential measurement of temperature responses of the thermal sensors 3 in the first detection chamber 9a and second detection chamber 9b can be carried out to determine the pressure of the fluid.

[0275] The preferred embodiment shown is characterized in that the thermal sensors 3 of the first detection chamber 9a and the second detection chamber 9b detect the same temperature changes under changing ambient conditions. Consequently, an internal pressure change occurs in the first detection chamber 9a, while no internal pressure change occurs in the second detection chamber 9b. Advantageously, this allows the influence of temperature on the pressure measurement to be compensated. This enables a further more sensitive measurement of the fluid pressure.

[0276] The internal pressure change can relate to a pressure change of a reference fluid 19 enclosed within the detection chamber 9a. The internal pressure change can also occur in an open detection chamber that has a fluidic connection to the environment. The second detection chamber 9b is closed, so that there is no fluid communication with the environment. The second detection chamber 9b preferably has a rigid casing, so that the casing of the second detection chamber 9b does not undergo any deformation as a result of a pressure change of the fluid in the environment, so that no internal pressure change can occur. Consequently, in the event of an external pressure change, an internal pressure change occurs in the first detection chamber 9a, whereas no internal pressure change occurs in the second detection chamber 9b. Advantageously, this allows the influence of environmental parameters, such as temperature, on a pressure measurement to be compensated for.The temperature change will affect both measurements equally. If a combined signal, for example, a difference between the temperature response of the thermal sensors in the respective detection chambers 9a, 9b, is preferably generated, the combined signal is not dependent on global temperature fluctuations but rather reflects a pressure change particularly reliably. Several preferred configurations for the detection chambers can advantageously be considered for providing a first detection chamber 9a, in which an internal pressure change occurs, and a second detection chamber 9b, in which no internal pressure change occurs.

[0277] In the illustrated embodiment of the pressure sensor 1 in Fig. 21A, the first detection chamber 9a includes an opening 29 for fluid communication with the environment. The second detection chamber 9b is formed by a closed detection chamber 9b, which does not have a pressure compensation membrane. The first, open detection chamber 9a and the second, closed detection chamber 9b are formed by a single SMD housing 11. Connecting lines 17 for an electrical contacting option are provided on the SMD housing 11.

[0278] In the illustrated embodiment of the pressure sensor 1 in Fig. 21B, the first and second detection chambers 9a and 9b are closed. However, the first detection chamber 9a comprises a pressure compensation membrane 21, so that an external pressure change due to deflection of the pressure compensation membrane 21 leads to an internal pressure change of the reference fluid 19 within the first detection chamber 9a. The internal pressure change can be detected by the first thermal sensor 3. The second detection chamber 9b is formed by a closed, rigid detection chamber 9b, which is designed so that an external pressure change of the fluid does not cause an internal pressure change within the second detection chamber 9b. The detection chambers 9a, 9b are formed by a single SMD housing 11.

[0279] In the preferred embodiment of the pressure sensor 1 shown in Fig. 21C, the first detection chamber 9a and the second detection chamber 9b are formed by two separate TO housings 13. The first detection chamber 9a has an opening 29 for fluid communication with the environment. The second detection chamber 9b is closed and provided with a rigid housing without a pressure equalization membrane.

[0280] Fig. 21D shows a further preferred embodiment of the pressure sensor 1 for differential measurement to determine pressure. The first detection chamber 9a and the second detection chamber 9b are provided as separate TO housings 13. The first detection chamber 9a is formed by a closed detection chamber comprising a pressure equalization membrane 21 to transmit an external pressure change of the fluid to an internal reference fluid 19. The second detection chamber 9b is formed by a closed detection chamber, which is designed so that an external pressure change of the fluid does not cause an internal pressure change within the second detection chamber 9b.

[0281] In the preferred embodiment shown in Fig. 21E, the first detection chamber 9a and the second detection chamber 9b are formed by a wafer stack 15 comprising a bottom wafer 14 and a cap wafer 12. The second detection chamber 9b comprises a pressure equalization membrane 21. As a result, an external pressure change in the environment leads to an internal pressure change in the reference fluid 19. The internal pressure change can be detected by the second thermal sensor 3. In the first detection chamber 9a, no internal pressure change is caused by an external pressure change. In the preferred embodiment of the pressure sensor 1 according to Fig. 21F, the first detection chamber 9a and the second detection chamber 9b are also formed by a wafer stack 15. The wafer stack 15 comprises a bottom wafer 14 and a cap wafer 12. The first detection chamber 9a has openings 29 for fluid communication with the environment.The second detection chamber 9b, on the other hand, is closed and is not designed to allow an external pressure change of the environment to be transmitted to the interior of the detection chamber 9b.

[0282] Fig. 22A-C show preferred embodiments of a pressure sensor 1 comprising a first detection chamber 9a and a second detection chamber 9b, wherein the first detection chamber 9a is designed such that an external pressure change of the fluid causes an internal pressure change within the first detection chamber 9a, and there is no fluid communication between the first detection chamber 9a and the environment. The second detection chamber 9b, on the other hand, is designed such that an external pressure change of the fluid causes an internal pressure change within the second detection chamber 9b, and there is fluid communication between the second detection chamber 9b and the environment, so that a differential measurement of temperature responses of the thermal sensors 3 in the first detection chamber 9a and the second detection chamber 9b can be carried out to determine the pressure of the fluid.

[0283] Advantageously, the preferred embodiment of the pressure sensor 1, which is shown in Fig. 22A-C, can compensate for the influence of temperature and the influence of the fluid or its composition.

[0284] A change in the pressure of the fluid within an environment leads to an internal pressure change in the first and second detection chambers 9a and 9b. However, the first detection chamber 9a has no fluid connection to the environment. A first thermal sensor 3 within the first detection chamber 9a thus sees an external pressure change, but not a change in the composition of the fluid, should this change. Within the second detection chamber 9b, a pressure change in the fluid can also be detected by an internal pressure change. Because there is fluid communication, i.e. a fluid connection between the environment and the second detection chamber 9b, a second temperature sensor 3 within the second detection chamber 9b advantageously sees a change in the fluid composition.By forming a corresponding combined signal from the temperature responses of the thermal sensors 3 of the first and second detection chambers 9a, b, any fluctuations in the composition of a fluid can be advantageously eliminated or compensated. Since both detection chambers are equally affected by a global temperature fluctuation, a temperature influence on the pressure measurement can also be compensated.

[0285] In Fig. 22A, the first detection chamber 9a is formed by a closed detection chamber having a pressure equalization membrane 21. The second detection chamber 9b is formed by an open detection chamber 9b with an opening 29. The first detection chamber 9a and the second detection chamber 9b are formed by an SMD housing 11. Connecting lines 17 for electronic contacting are located on the SMD housing 11.

[0286] In Fig. 22B, the first detection chamber 9a and the second detection chamber 9b are formed by two separate TO housings 13. Connecting lines 17 are arranged on the TO housings 13 for electrical contact with the thermal sensors 3. The first detection chamber 9a is formed by a closed detection chamber with a pressure equalization membrane 21. The second detection chamber 9b is formed by an open detection chamber 9b with openings 29.

[0287] In Fig. 22C, the first detection chamber 9a and the second detection chamber 9b are formed by a wafer stack 15 comprising a bottom wafer 14 and a cap wafer 12. The first detection chamber 9a comprises a pressure equalization membrane 21. The second detection chamber 9b is formed by an open detection chamber to which openings 29 are attached.

[0288] Fig. 23A-C show further preferred embodiments of the pressure sensor 1 comprising a first and a second thermal sensor 3, wherein a solid body is introduced as a reference substance 41 only below the second thermal sensor 3. This allows a pressure change of the fluid to be determined based on different dependencies of the temperature responses of the first and second thermal sensors 3 on the pressure.

[0289] The fluid is heated by the oscillating control of the first and second heating elements, with the fluid flowing at least partially around both the first and the second thermal sensor 3. While a solid body acts as a reference substance beneath the second thermal sensor 3, the first thermal sensor 3 is preferably surrounded exclusively by the fluid to be measured (or a reference fluid). For this purpose, there are membrane apertures 37 in the carrier membrane 39, through which the fluid can diffuse into a cavity 27 beneath the first thermal sensor. The reference substance, as a solid body, differs from the fluid to be measured (or a reference fluid) in at least one thermal property. While a change in pressure, in particular, leads to a change in the volumetric heat capacity of the fluid (orof a reference fluid), the volumetric heat capacity of the reference substance 41, which is present as a solid exclusively below the second thermal sensor 3, changes hardly or only insignificantly.

[0290] Thus, the pressure sensor 1 essentially detects a change in the volumetric heat capacity of the fluid with a first thermal sensor 3, while the second first thermal sensor 3 detects no or only an insignificant change in the volumetric heat capacity for the solid as a reference substance. A differential signal of the temperature responses for the first and second thermal sensors 3 thus allows for particularly precise pressure measurement.

[0291] In Fig. 23A, the pressure sensor 1 comprises two detection chambers 9a, 9b. The first and second thermal sensors 3 are positioned on a support membrane 39, which extends along a support structure 25 with two cavities 27. Below the first thermal sensor 3 is a first cavity 27. Through the membrane apertures 37, which are located in the region of the first thermal sensor 3, i.e., above the first cavity 27, a transfer of the fluid for pressure equalization is possible. The second thermal sensor 3 is also located on the support membrane 39. Below the second thermal sensor 3 is a second cavity 27, within which the solid body is introduced as a reference substance 41.

[0292] In Fig. 23B, the pressure sensor comprises a detection chamber 9, which is formed by a wafer stack 15 comprising a bottom wafer 14 and a cap wafer 12. The cap wafer 12 comprises a plurality of openings 29. The first thermal sensor 3 and the second thermal sensor 3 are attached to the bottom wafer 14. The openings 29 enable the fluid to flow around the first and second thermal sensors 3. The first thermal sensor 3 is located above a first cavity 27, and the second thermal sensor 3 is located above a second cavity 27, with the solid body serving as reference substance 41 being located within the second cavity 27.

[0293] In Fig. 23C, the pressure sensor 1 comprises a detection chamber 9 formed by an SMD housing 11. The SMD housing 11 comprises an opening 29 through which the fluid can flow past a first thermal sensor 3 and a second thermal sensor 3. The first thermal sensor 3 is located on a first support membrane 39, which is located on a first support structure 25 having a cavity 27. The second thermal sensor 3 is located on a second support membrane 39, which is located on a second support structure 25 having a cavity 27 and within which the solid body as reference substance 41 is located.

[0294] List of reference symbols

[0295] I Pressure sensor

[0296] 3 Thermal sensor

[0297] 5 Heating element

[0298] 7 Sensor component, preferably temperature sensor

[0299] 9 Detection chamber

[0300] 9a First detection chamber

[0301] 9b Second detection chamber

[0302] II SMD housing

[0303] 12 cap wafers

[0304] 13 TO housings

[0305] 14 bottom wafers

[0306] 15 wafer stacks

[0307] 17 Connection cable

[0308] 19 Reference fluid

[0309] 21 Pressure equalization membrane

[0310] 25 Support structure

[0311] 27 Cavity

[0312] 29 Opening

[0313] 31 Reference sensor

[0314] 33 Fluid line

[0315] 35 liquid

[0316] 37 aperture

[0317] 39 Carrier membrane

[0318] 41 Reference substance

[0319] Bibliography

[0320] Javed, Yaser, Mohtashim Mansoor, and Irtiza Ali Shah. "A review of principles of MEMS pressure sensing with its aerospace applications." Sensor Review 39.5 (2019): 652-664.

[0321] Zhang, Ming, and Nicolas Llaser. "Exploiting a micro pirani gauge for beyond atmospheric pressure measurement." IEEE Transactions on Circuits and Systems II: Express Briefs 65.10 (2018): 1450-1454.

[0322] Legendre, Olivier, et al. "Pressure sensing method based on the transient response of a thermally actuated micro-wire." Sensors and Actuators A: Physical 221 (2015): 115-122.

[0323] Ohji, Hiroshi, et al. "A new pressure sensor measured by heat transfer." SENSORS, 2002 IEEE. Vol. 2. IEEE, 2002.

[0324] Khosraviani, Kourosh, and A. M. Leung. "Extreme narrow gap surface micromachined pirani pressure sensor." TRANSDUCERS 2007-2007 International Solid-State Sensors, Actuators and Microsystems Conference. IEEE, 2007.

Claims

PATENT CLAIMS 1. A pressure sensor (1) for measuring a pressure of a fluid, comprising a detection chamber (9) within which a thermal sensor (3) is arranged, wherein the thermal sensor (3) comprises a heating element (5) for providing a thermal field and a sensor component (7) for detecting a temperature response of the thermal sensor (3) as a function of an influence of the fluid on the thermal field, characterized in that the heating element (5) is designed to be controlled in an oscillating manner at at least one frequency and the pressure of the fluid can be determined based on the temperature response of the thermal sensor (3), and wherein the thermal sensor (3) is positioned on a support membrane (39) which is held by a support structure (25) and extends over a cavity (27), and wherein an aperture (37) enables pressure equalization between the cavity (27) and an interior region of the detection chamber (9).

2. Pressure sensor (1) according to the preceding claim, characterized in that the pressure sensor (1) comprises an electronic circuit and / or is data-connected to an electronic circuit, wherein the electronic circuit is configured to control the heating element (5) in an oscillating manner and / or to determine the pressure of the fluid on the basis of the temperature response of the thermal sensor (3).

3. Pressure sensor (1) according to one or more of the preceding claims, characterized in that the pressure sensor (1) further comprises a means for determining a thermodynamic material property, preferably a volumetric heat capacity, a density, a thermal conductivity and / or a composition of the fluid, so that the determined thermodynamic material property and / or composition of the fluid can be taken into account for determining the pressure.

4. Pressure sensor (1) according to one or more of the preceding claims, characterized in that the temperature response comprises at least a first frequency and a second frequency, wherein the first frequency is smaller than the second frequency and allows an assignment with regard to a thermodynamic material property, preferably a thermal conductivity.

5. Pressure sensor (1) according to one or more of the preceding claims, characterized in that the sensor component is formed by a temperature sensor (7), wherein the temperature sensor (7) is preferably selected from a group comprising a thermocouple and / or a thermopile.

6. Pressure sensor (1) according to one or more of the preceding claims characterized in that the pressure sensor comprises a closed detection chamber (9) within which a reference fluid (19) and the thermal sensor (3) are enclosed.

7. Pressure sensor (1) according to one or more of the preceding claims, characterized in that the pressure sensor (1) comprises a closed detection chamber (9) and a pressure compensation membrane (21), wherein a change in the pressure of the fluid causes a deflection of the pressure compensation membrane (21), which leads to a pressure change of the reference fluid (19) which can be detected by the thermal sensor (3).

8. Pressure sensor (1) according to one or more of the preceding claims, characterized in that the pressure sensor (1) comprises an open detection chamber (9) which has at least one opening (29) for fluid communication between an interior region of the detection chamber (9) and an environment.

9. Pressure sensor (1) according to one or more of the preceding claims, characterized in that the pressure sensor (1) comprises a reference sensor (31) for determining an environmental parameter, wherein the reference sensor (31) is preferably a humidity sensor and / or an additional temperature sensor.

10. Pressure sensor (1) according to one or more of the preceding claims, characterized in that the carrier membrane (39) has at least one membrane aperture which forms the aperture (37) for pressure equalization or the carrier structure (25) has a carrier aperture which forms the aperture (37) for pressure equalization.

11. Pressure sensor (1) according to one or more of the preceding claims, characterized in that the pressure sensor (1) comprises at least a first detection chamber (9a) and a second detection chamber (9b), wherein the first detection chamber (9a) is designed such that an external pressure change of the fluid causes an internal pressure change within the first detection chamber (9a), while the second detection chamber (9b) is designed such that an external pressure change of the fluid does not cause an internal pressure change within the second detection chamber (9b), so that a differential measurement of temperature responses of the thermal sensors (3) in the first detection chamber (9a) and the second detection chamber (9b) can be carried out to determine the pressure of the fluid.

12. Pressure sensor (1) according to one or more of the preceding claims, characterized in that the pressure sensor comprises a first detection chamber (9a) and a second detection chamber (9b), wherein the first detection chamber (9a) is designed such that an external pressure change of the fluid causes an internal pressure change within the first (9a) detection chamber and there is no fluid communication between the first detection chamber (9a) and an environment, while the second detection chamber (9b) is designed such that an external pressure change of the fluid causes an internal pressure change within the second detection chamber (9b) and there is fluid communication between the second detection chamber (9b) and the environment, so that a differential measurement of temperature responses of the thermal (3) sensors in the first detection chamber (9a) and second detection chamber (9b) can be carried out to determine the pressure of the fluid.

13. Pressure sensor (1) according to one or more of the preceding claims, characterized in that the pressure sensor (1) comprises at least a first thermal sensor (3) and a second thermal sensor (3), wherein a solid body is introduced as a reference substance (41) only below the second thermal sensor (3), so that different temperature responses can be detected by the first thermal sensor (3) and second thermal sensor.

14. A method for measuring the pressure of a fluid, comprising the following steps: a) providing a pressure sensor (1) comprising a detection chamber (9) within which a thermal sensor (3) is arranged, the thermal sensor (3) comprising a heating element (5) for providing a thermal field and a sensor component (7) for detecting a temperature response due to an influence of the fluid on the thermal field, the thermal sensor (3) further being positioned on a support membrane (39) which is held by a support structure (25) and extends over a cavity (27), and an aperture (37) enabling pressure equalization between the cavity (27) and an interior region of the detection chamber (9), b) oscillating control of the heating element (5) with at least one frequency, c) determining the pressure of the fluid on the basis of the temperature response of the thermal sensor (3) as a function of the influence of the fluid on the thermal field.

15. Use of the pressure sensor according to one or more of the preceding claims 1 - 13 for monitoring a pressure of a fluid, preferably a gas.

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