Hot fluid flow sensor

Abstract

We disclose in this article a fluid and heat conduction sensor, comprising: a semiconductor substrate, which includes an etched portion; a dielectric region, which is located on the semiconductor substrate, wherein the dielectric region includes at least one dielectric film located above the etched portion of the semiconductor substrate; and a heating element, which is located within the dielectric film. The dielectric film includes one or more discontinuities located between the heating element and the edge of the dielectric film.

Description

Technical Field

[0001] The present disclosure relates to a microelectromechanical sensor, and in particular but not exclusively, to a fluid flow sensor having a heater formed within a discontinuous dielectric film to sense the properties of a fluid flow or the composition of a fluid based on thermal conductivity. Background Art

[0002] Thermal fluid flow sensors utilize the thermal interaction between the sensor itself and the fluid. Depending on the physical phenomenon governing the interaction, flow sensors can be classified into the following three categories:

[0003] (i) An anemometer that measures convective heat transfer caused by a fluid flow passing over a heated element;

[0004] (ij) A calorimetric sensor that detects the asymmetry of the temperature distribution generated by a heated element and caused by forced convection of a fluid flow; and

[0005] (iii) A time-of-flight (ToF) sensor that measures the time elapsed between the application and sensing of a thermal pulse.

[0006] A review of thermal fluid flow sensors has been published in (B. Van Oudheusden, “Silicon flow sensors”, Control Theory and Applications, IEE Proceedings D, 1988, pp. 373 - 380; B. Van Oudheusden, “Silicon thermal flow sensors”, Sensors and Actuators A: Physical, Vol. 30, pp. 5 - 26, 1992; N. Nguyen, “Micromachined flow sensors - A review”, Flow measurement and Instrumentation, Vol. 8, pp. 7 - 16, 1997; Y.-H. Wang et al., “MEMS-based gas flow sensors”, Microfluidics and nanofluidics, Vol. 6, pp. 333 - 346, 2009; J.T. Kuo et al., “Micromachined Thermal Flow Sensors - A Review", Micromachines, Vol. 3, pp. 550 - 573, 2012). Further background can also be found in US6460411 to Kersies et al.

[0007] In "Integrated silicon anemometer" by A. Van Putten and S. Middelhoek, Electronics Letters, Vol. 10, pp. 425 - 426, 1974, and "An integrated silicon double bridge anemometer" by A. Van Putten, Sensors and Actuators, Vol. 4, pp. 387 - 396, 1983, resistor - based anemometers were integrated on a chip within a Wheatstone bridge configuration. "Integrated flow friction sensor" by B. Van Oudheusden and J. Huijsing, Sensors and Actuators, Vol. 15, pp. 135 - 144, 1988, presented a heat - flow sensor calibrated for friction measurements, where thermocouples other than the heating resistor and the ambient - temperature - monitoring transistor were integrated on the chip. "Monolithic integrated direction - sensitive flow sensor" by J. H. Huijsing et al., Electron Devices, IEEE Transactions on, Vol. 29, pp. 133 - 136, 1982, "Integrated - circuit bipolar transistor array for fluid - velocity measurements" by W. S. Kuklinski et al., Medical and Biological Engineering and Computing, Vol. 19, pp. 662 - 664, 1981, Platzer's US3992940, and "A novel CMOS flow sensor with constant chip temperature (CCT) operation" by T. Qin - Yi and H. Jin - Biao, Sensors and actuators, Vol. 12, pp. 9 - 21, 1987 are examples of transistor - based anemometers. A drawback of the previously mentioned cited literature is that these sensors have high power consumption, low sensitivity, and slow dynamic response of the sensors.

[0008] In "Silicon gas flow sensors using industrial CMOS and bipolar IC technology" by D. Moser et al., Sensors and Actuators A: Physical, Vol. 27, pp. 577 - 581, 1991, an array of seven npn transistors was used as a heating element and suspended on a crystalline silicon cantilever beam for effective thermal isolation. The temperature on the beam was measured with a common pn diode. When driving the heater with a constant power, the voltage across 19 silicon / aluminum thermocouples (with the hot junctions on the beam and the cold junctions on the substrate) was related to the gas flow rate. The device was mechanically brittle and vibration - sensitive.

[0009] Similarly, in "A sensor based on silicon technology for turbulence measurements" by L. Lofdahl et al., Journal of Physics E: Scientific Instruments, Vol. 22, p. 391, 1989, a heating resistor and a heater temperature - sensing diode integrated on a cantilever beam were proposed. Polyimide was used as the thermal isolation material between the beam and the substrate, which affected the mechanical strength of the beam.

[0010] In "An integrated sensor for invasive blood - velocity measurement" by R. Kersjes et al., Sensors and Actuators A: Physical, Vol. 37, pp. 674 - 678, 1993, a polysilicon heater driven with a constant heating power and a first diode for heater temperature monitoring were placed on a silicon membrane. A second diode was placed on the substrate to monitor the ambient temperature. A similar sensor was proposed in "A liquid velocity sensor based on the hot - wire principle" by A. Van der Wiel et al., Sensors and Actuators A: Physical, Vol. 37, pp. 693 - 697, 1993, where, to improve the temperature sensitivity of the sensor, more transistors were connected in series in a diode configuration. Using silicon as the membrane material led to high power consumption, low sensitivity, and slow dynamic response of the sensor.

[0011] In US6460411 by Kersjes et al., a silicon membrane perforated through slits in a thermal insulation material was proposed, but the manufacturing process is more complex.

[0012] A CMOS flow sensor including a heating element and a plurality of thermocouples is disclosed in US20160216144A1. The thermocouples provide an additional heat dissipation path within the membrane, thereby increasing power consumption, reducing sensitivity, and slowing down the dynamic response of the sensor.

[0013] In "An integrated mass flow sensor with on-chip CMOS interface circuitry" by E. Yoon and K. D. Wise, Electron Devices, IEEE Transactions on, Vol. 39, pp. 1376 - 1386, 1992, a multi-measurement flow sensor was proposed. However, the manufacturing process is not fully compatible with CMOS, so it is more expensive than a fully CMOS-compatible process.

[0014] "Multi-range silicon micromachined flow sensor" by N. Sabaté et al., Sensors and Actuators A: Physical, Vol. 110, pp. 282 - 288, 2004, proposed a multi-range flow sensor that uses nickel resistors as temperature sensors and positions the nickel resistors at different distances from a nickel resistor heater. Nickel is not a standard CMOS material, so the sensor manufacturing process is more expensive than a fully CMOS-compatible process.

[0015] In G. De Graaf and R. F. Wolffenbuttel, "Surface-micromachined thermal conductivity detectors for gas sensing", 2012 IEEE International Instrumentation and Measurement Technology Conference Proceedings, pp. 1861 - 1864, a structure including a heater for temperature control and two thermopiles embedded in a dielectric perforated membrane for sensing was proposed. The membrane is obtained by front-side etching of vias that have no effect on the operating behavior of the device. However, this process does not compensate for the influence of convection.

[0016] US20180143051A1 proposes a structure using four resistors in a full-bridge configuration, where at least one external element not affected by the current is coupled to any of the previous elements. This design requires complex circuitry for readout and uses large resistors to increase the output signal, which severely damages the insulation provided by the membrane.

[0017] Conventional flow sensors based on hot wires embedded in a membrane are known. Efforts have also been made to quantify the composition of fluids by using heat conduction sensors.

[0018] Figure 1 A cross-section of a prior art level flow sensor based on a heating element and a self-sensing element is shown. Figure 2 A top view of a prior art level flow sensor based on a heating element and a self-sensing element is shown. The device has a substrate 1 that can be based on a semiconductor material such as silicon, a membrane containing one or more dielectric layers 2, and a heater 3. The membrane is defined by using dry etching or wet etching techniques, with back etching (as shown) or front etching. When fluid passes over the top of the membrane 4, the heater 3 cools due to heat convection losses. This can be simply measured by correlating the change in the resistance of the heater with the flow rate, velocity, volume, or mass flow rate. The heater 3 is connected externally through connectors and pads 5 (as Figure 2 shown). Optionally, the heater can be maintained at a constant temperature or constant resistance mode by modifying the power supplied to the heater element. In this case, the change in power due to the flow rate, velocity, volume, or mass flow rate can be measured. Summary of the Invention

[0019] Currently available sensors have at least the following disadvantages:

[0020] · High power consumption, low sensitivity, and slow dynamic response of the sensor;

[0021] · Mechanical brittleness and vibration sensitivity;

[0022] · Reduction in the mechanical strength of the sensor support structure;

[0023] · Complex manufacturing processes;

[0024] · Manufacturing processes that are not fully compatible with CMOS; and

[0025] · Expensive manufacturing processes.

[0026] The device of the present disclosure is superior to prior art level devices for at least the following reasons:

[0027] · Thermal isolation of the heated element reduces power consumption, increases sensitivity, and provides a fast dynamic response of the sensor;

[0028] · Compared with beam structures, the mechanical brittleness and vibration sensitivity of the membrane structure are reduced;

[0029] · Suitable dielectric materials for the dielectric membrane improve the mechanical strength of the membrane;

[0030] · Suitable dielectric materials for the dielectric membrane reduce power consumption, improve sensitivity, and provide a fast dynamic response of the sensor;

[0031] · The discontinuities within the membrane reduce power consumption, sensitivity, and dynamic response issues; and

[0032] · These devices are fully compatible with CMOS and can therefore be fabricated using a fully CMOS-compatible process.

[0033] The currently disclosed sensors (referred to as flow and heat conduction sensors) are capable of (i) measuring convective heat transfer caused by a fluid flow passing over a heated element; and / or (ii) measuring the composition of a fluid based on the different thermal conductivities of each component of the fluid flow.

[0034] The various aspects and preferred features are set forth in the appended claims.

[0035] According to a first aspect of the present disclosure, there is provided a flow and heat conduction sensor comprising: a semiconductor substrate including an etched portion; a dielectric region located on the substrate, wherein the dielectric region includes at least one dielectric membrane located above the etched portion of the semiconductor substrate; and a heating element located within the dielectric membrane, wherein the dielectric membrane includes at least one groove region located between the heating element and an edge of the dielectric membrane.

[0036] The edge of the dielectric membrane may refer to the outer peripheral edge of the dielectric membrane, in other words, may refer to the region where the dielectric membrane abuts or joins the semiconductor substrate. The area of the dielectric region above the semiconductor substrate may refer to the area of the dielectric region outside the dielectric membrane.

[0037] The groove region may be located between the heating element and an edge of the dielectric membrane spaced apart from the heating element in the direction of flow. In other words, the groove region may be spaced apart from the heating element along an axis defined by the direction of flow passing through the sensor.

[0038] The dielectric region may include a dielectric layer or multiple layers including at least one dielectric layer. The heating element may be fully or partially embedded within the dielectric membrane. At least one groove region may include one or more discontinuous regions where the thickness of the dielectric membrane is discontinuous or varies with respect to the average dielectric membrane thickness or the most common dielectric membrane thickness.

[0039] Generally speaking, the dielectric film region can be positioned adjacent to the etched portion of the substrate. The dielectric film region corresponds to the region of the dielectric area above the etched cavity portion of the substrate. Each dielectric film region can be above a single etched portion of the semiconductor substrate.

[0040] The groove region or discontinuity in the dielectric film interrupts (or partially interrupts) the thermal conduction path of the solid through the dielectric film. This in turn means that the thermal path will be achieved more through the fluid above the groove (by conduction and convection) or through the cavity space formed by the groove (mainly by fluid conduction). In both cases (i.e., the heat above or within the cavity space), heat dissipation will be achieved according to the thermal conductivity of the fluid.

[0041] The groove region can be a hole (perforation) through the dielectric film. This would be advantageous because it obstructs the thermal conduction path of the solid through the dielectric film, which means that heat conduction will occur through the hole (mainly by conduction) or above the hole (by conduction and convection), thus helping to measure the composition of the fluid based on the different thermal conductivities of each component of the fluid flow.

[0042] The heating element can be driven with DC (direct conduction) power / voltage / current or with AC (alternating conduction) power / voltage / current. To reduce power loss and optimize the operating speed, the heating element can be driven in pulses (e.g., square pulses or sine pulses).

[0043] The sensor can be a heat conduction flow sensor incorporated in a MEMS structure that includes a heating element and at least one other sensing element capable of separately detecting fluid flow performance (such as flow velocity, volumetric flow rate, mass flow rate) and the composition of the fluid based on differences in the thermal conductivity, specific heat capacity, dynamic viscosity, density (and other thermomechanical properties, hereinafter simply referred to as thermal properties) of different components of the fluid. The flow performance can be associated with the pressure difference within the system. Therefore, the sensor can separately detect different pressure differences caused by the flow and different pressure differences caused by the composition of the flow based on differences in the thermal conductivity, specific heat capacity, dynamic viscosity, density (and other thermomechanical properties, hereinafter simply referred to as thermal properties) of different components of the fluid.

[0044] The measured pressure difference spans across the two ends of the sensor, or can be measured as the pressure difference across the two ends of the ports of the sensor package. The flow through the sensor package is related to the pressure difference across the two ends of the sensor package. The sensor can be characterized / calibrated for (one or more) known flows or (one or more) known pressure differences, or both. Then, the sensor can be used to measure the flow or the pressure difference or both based on the characterized / calibrated results.

[0045] The disclosed sensors can be applicable to various gases and liquids, but we specifically refer to carbon dioxide (CO2), methane, and hydrogen because these specific gases have significantly different thermal conductivities from that of air. Although we specifically refer to thermal conductivity as the thermomechanical property used to distinguish fluids, the disclosed devices can also utilize any other thermomechanical property. The disclosed devices can be used, for example, in breathalyzers that can simultaneously measure flow and CO2 concentration. The disclosed devices can also be used in other healthcare, fluid, consumer, environmental, or smart home applications.

[0046] The sensor can include a flow and heat conduction sensor, which includes: a semiconductor substrate, a dielectric membrane, a heating element embedded in the membrane that can itself be used as a sensing element, a sensing element or pair of sensing elements for sensing flow properties (such as flow rate, flow velocity, mass flow rate, or volume flow rate of the flow, or a quantity derived as a result of a pressure difference such as a differential pressure of the flow), at least one hole passing through the membrane, and other sensing elements or a pair of other sensing elements for sensing the composition of the fluid and the concentration of the components of the fluid based on the difference in the thermal conductivity of the components of the fluid, whereby (depending on the area, number (if more than one), and location) at least one groove (which can be a hole) is designed and arranged to enhance the sensitivity and selectivity to the concentration of the components of the convection.

[0047] The sensitivity and accuracy to the convection composition (e.g., the percentage or ppm value of CO2 in air) can be significantly improved by the presence of the holes passing through the membrane and / or by the flow itself. A higher flow rate or flow velocity allows for strengthening the signal for distinguishing fluids (or components of the fluid) with different thermal conductivities. This is because the heat loss generated by the heater through the flow itself is both conductive and convective in nature, and convection (the movement of fluid atoms with the flow) helps to enhance the heat conduction process through the fluid rather than through the solid membrane. As a result, since more heat conduction occurs through the fluid rather than through the solid dielectric membrane, the differential signal generated due to the presence of a fluid or fluid component (CO2) having a thermal conductivity different from that of a reference fluid or another component of the fluid (such as air) can be enhanced.

[0048] The flow sensor can be incorporated within the same device or chip, and optionally within the same membrane, a heat conduction sensor based on at least one temperature sensing element. The device is capable of simultaneously sensing the properties of the fluid flow, such as velocity, mass, volume, shear stress, or a derived output (such as differential pressure), as well as the composition of the flow (e.g., whether the fluid (in this case a gas) has a certain percentage / ppm of CO2, hydrogen, or methane in air).

[0049] There can be at least one hole through the membrane for connecting the upper side of the membrane to the lower side of the membrane via the fluid to be sensed. The at least one hole also breaks the heat conduction path through the solid dielectric membrane, forcing more heat to dissipate through the environment via convection and conduction. Since the heat conduction loss (through the solid membrane) is reduced, the presence of the at least one hole also helps to reduce the power consumption of the device (at the same heater temperature). In addition, the presence of at least one hole results in a reduced thermal mass of the membrane, thus reducing the time required to heat and cool the heater.

[0050] The at least one hole can be used to enhance the sensitivity / selectivity to a component of a fluid or a fluid (e.g., air with a CO2 concentration) whose thermal conductivity is different from that of a reference fluid or another component of the fluid (e.g., air).

[0051] Different hole arrangements and specific designs are provided for enhancing the sensitivity to a component of a fluid or a fluid (e.g., air with a CO2 concentration) whose thermal conductivity is different from that of a reference fluid or another component of the fluid (e.g., air).

[0052] At least one arrangement of different holes and different sensing elements is provided for providing a differential signal indicating the concentration of a specific component of a fluid (e.g., the concentration of CO2) in a reference fluid (air) between two sensing elements (i.e., a pair of sensing elements). The provided differential signal can be proportional to such a concentration. The sensing elements can refer to temperature sensing elements, and they can be in the form of resistance temperature detectors, diodes, transistors, or thermopiles, or a series or parallel array of these elements, or a combination of these elements. For example, the differential signal can be a voltage difference caused by a temperature difference across a pair of sensing elements.

[0053] The arrangement of different holes (or groove regions) can be symmetrically placed around the heater.

[0054] The heater temperature can be adjusted by applying different power levels to increase the sensitivity and selectivity to different fluid components based on the thermal conductivity of the fluid components varying with temperature.

[0055] The heater can operate in a pulsed mode (e.g., driven with a square wave, sine wave, pulse width modulation wave, pulse density modulation, etc.) or a continuous mode. The pulsed mode has the advantages of reduced power consumption, reduced electromigration, and improved device reliability / lifetime, as well as improved fluid performance sensing ability, etc.

[0056] At least one groove region can be arranged asymmetrically with respect to the axis defined by the heating element. In use, this allows the use of the differential signal between two sensing elements to sense different components of the fluid in the absence of flow or in a static flow situation.

[0057] The holes can have an asymmetric design within the membrane. The arrangement of the different holes can be asymmetrically placed within the membrane.

[0058] The heating element can be configured to operate as a sensing element, for example, by sensing a change in resistance due to a temperature change. The heating element can operate simultaneously as a heating element and a sensing element. The heating element is electrically equivalent to a resistor. The thermal conductivity of most heater materials (tungsten, titanium, platinum, aluminum, polysilicon, single crystal silicon) varies with temperature. This variation is mainly linear and is characterized by the TCR (temperature coefficient of resistance). The TCR can be positive or negative, but most metals have a positive and stable TCR, which means that the resistance of these metals increases with increasing temperature. When current flows through the heating element, the heating element gets hot, thereby heating the membrane surrounding the heating element. If the heater operates at the same power, when a fluid flows over the heater, due to convection, the fluid cools the heater, thereby changing the resistance of the heater (for a heater with a positive TCR, the resistance decreases). The heater can also be driven in a constant resistance or constant temperature mode and can correlate the change in power required to keep the heater resistance or heater temperature the same in the presence of flow. The sensor can be capable of measuring the performance of the flow, such as flow rate, flow velocity, mass flow rate, or volume flow rate, or a derived output (such as a pressure difference) and the composition of the flow. The device can be configured to measure the performance of the flow, such as flow rate, flow velocity, mass flow rate, or volume flow rate, or a derived output (such as a pressure difference), by sensing a change in temperature, a change in voltage when a constant current is supplied to the device, or by sensing a change in power when the heater is operated in a constant temperature or constant resistance mode.

[0059] Optionally, the flow or the pressure difference can be measured by employing sensing elements (such as temperature sensing elements or temperature sensors), which are placed on either side of the heater within the same dielectric membrane and which can optionally be used as a differential pair. The differential pair can be formed by an upstream sensing element and a downstream sensing element. The device can be arranged to measure the composition of the flow and the performance of the flow by providing at least one hole or discontinuity in the membrane and by employing at least one other sensing element or a pair of sensing elements (such as temperature sensing elements or temperature sensors). Optionally, the holes or discontinuities can be placed such that they have a lesser effect on the differential signal between the sensing elements for measuring the performance of the flow, while they have a more significant effect on the differential signal between the sensing elements for measuring the composition of the flow.

[0060] At least one groove region can include one or more holes. The holes can refer to holes, perforations, or slits that extend through the entire height or depth or thickness of the dielectric membrane. This forms a fluid flow path and provides a fluid connection between the region above the membrane and the region below the membrane.

[0061] At least one of the one or more holes may include an elongated slit extending towards an opposite edge of the dielectric film. The elongated slit may not fully extend to the edge of the dielectric film, or either side of the elongated slit may be completely isolated from the dielectric film. The elongated slit increases the thermal isolation across the width of the dielectric film of the device. Optionally, the elongated slit may extend in the same direction as the one or more heating elements and / or sensing elements. The elongated slit may be, for example, rectangular, square, or semi-circular.

[0062] The one or more holes may include an array of perforations. The perforations may include individual holes that are significantly smaller than the width of the dielectric film of the device. The array of perforations may extend substantially across the width of the device.

[0063] At least one recessed area may include a partial recess within the dielectric film. The partial recess or groove may extend from the top surface of the dielectric film or may extend from the bottom surface of the dielectric film. The partial recess may extend partially through the height or depth or thickness of the dielectric film. At least one perforation may be in the form of a groove formed from the top surface or the bottom surface but not penetrating the other surface.

[0064] An interruption may refer to a gap in the film from the top surface to the bottom surface. An interruption may also refer to a groove or a local hole formed from the top surface or the bottom surface (in the case of an inverted film) and not penetrating the other surface, but this is less effective in terms of thermal performance. The advantage of such local holes is that they may have a smaller impact on the mechanical strength of the film and in some cases they may be easier to fabricate. Additionally, such local holes may be used to hermetically seal the bottom side of the film or to prevent flow from penetrating beneath the film.

[0065] At least one recessed area may have a zigzag shape. In other words, the interruption may have a non-standard shape, such as a bellows shape or a corrugated shape formed by a series of regularly undulating curves, bent lines, or zigzag lines.

[0066] The sensor may also include one or more other sensing elements. There may be one other sensor element or there may be more than one other sensing element. One or more other sensing elements may be combined with the heating element operating as a sensing element to measure a parameter.

[0067] One or more other sensing elements may include at least a pair of sensing elements located on opposite sides of the heating element. The at least a pair of sensing elements may include an odd number of sensing elements or may include multiple pairs of sensing elements. One or more other sensing elements may be laterally spaced from the heating element and located on a first side of the heating element, and one or more other sensing elements may be laterally spaced from the heating element and located on a second side of the heating element, where the first side and the second side are opposite sides of the heating element.

[0068] At least one groove region may be located between the first other sensing element of at least one pair of sensing elements and the heating element, and at least one other groove region may be located between the second other sensing element of at least one pair of sensing elements and the edge of the membrane. This thermally isolates the first other sensing element from the heating element and thermally isolates the second other sensing element from the semiconductor substrate around the edge of the membrane. Thus, the heat difference between the first other sensing element and the second other sensing element is more sensitive to changes in the concentration and composition of the gas. This asymmetric arrangement of the discontinuities can sense different components of the fluid using the differential signal between the two sensing elements, even in the absence of flow or in the case of static flow.

[0069] One of the first other sensing element or the second other sensing element may be located upstream of the flow relative to the heating element, while the other of the first other sensing element or the second other sensing element may be located downstream of the flow relative to the heating element. This allows for the measurement of the performance, variables, or parameters of the convective flow.

[0070] At least one discontinuity may be laterally placed within the membrane between the heater and a sensing element (e.g., a hot wire located in the middle of the membrane) on one side of the heater, and another of the at least one discontinuity may be laterally placed within the membrane between the sensing element and the edge of the membrane on the other side of the heater. Possibly, the two discontinuities or a set of discontinuities may have similar surface areas. Optionally, the two sensing elements may be the same in size and lateral distance from the heater and may be fabricated in the same manufacturing process (e.g., during the CMOS steps before membrane etching).

[0071] The sensor may include at least two thermopiles, namely at least one upstream thermopile and at least one downstream thermopile with respect to the direction of the flow, and at least one hole is laterally placed between one of the thermopiles and the heater.

[0072] At least one hole or discontinuity may be laterally placed within the dielectric membrane between the heater and one sensing element. At least one other hole or discontinuity may be laterally placed within the dielectric membrane between another temperature sensing element and the edge of the membrane.

[0073] The sensor may sense static flow or no-flow condition (zero flow rate) based on the change of the heater resistance with temperature, or based on a pair of matched sensing elements laterally placed at the same distance from the heater, or based on thermopiles symmetrically placed around / across the heater. At least one other sensing element or a pair of additional sensing elements or additional heater / sensing elements may be used to measure the concentration of different components of the fluid based on the different thermal conductivities of the different components of the fluid.

[0074] The flow / heat transfer sensor can also measure a "no-flow state", i.e., a zero-flow state, a static flow, or a negligible flow. This can be done by measuring the signal between two matching sensing elements symmetrically placed on either side of the heater. A zero-flow state can also be inferred to have a zero pressure difference. Optionally, the zero-flow state (or zero pressure difference) can be identified by measuring the change in the resistance of the heater with respect to a previously calibrated value (baseline value) of the resistance applied to the heater to maintain a constant resistance / power, or the change in the power with respect to a previously calibrated value (baseline value). The sensitivity and selectivity of the composition of the convection are enhanced by using additional sensing elements, and symmetric or asymmetric holes, and / or additional heaters as described in the previous embodiments.

[0075] At least one groove region can be located between the heating element and at least one of one or more other sensing elements. For example, this can include wires extending across the membrane, and / or a thermopile on a dielectric membrane with cold junctions located on the membrane.

[0076] At least one of one or more other sensing elements can be configured to measure the difference across the heating element. For example, at least one other sensing element can be used to measure the change in temperature across the heating element. At least one thermopile can be placed symmetrically around / across the heater, and the voltage difference between the ends of the thermopile can indicate the performance of the flow, while the sign of the voltage can indicate the direction of the flow.

[0077] At least one of one or more other sensing elements can be configured to measure the difference between the dielectric membrane and the dielectric region above the semiconductor substrate. For example, the thermopile can be arranged such that the hot junctions of the thermopile are on the dielectric membrane and the cold junctions of the thermopile are on the dielectric region above the semiconductor substrate (i.e., outside the dielectric membrane region).

[0078] Two thermopiles can be arranged on either side of the heating element, with the hot junctions of both thermopiles on the dielectric membrane and the cold junctions outside the dielectric membrane region. Since the two sets of cold junctions located outside the dielectric membrane will be at substantially the same temperature, the difference between the two hot junctions can be used to measure the change in temperature across the heating element. The cold junctions of at least two thermopiles can be placed outside the membrane and physically or electrically connected together.

[0079] At least one groove region can be located between at least one of one or more other sensing elements and the edge of the dielectric membrane. This reduces the heat conduction through the dielectric membrane between the sensing element and the edge of the dielectric membrane. Thus, the temperature of the sensing element is more dependent on the concentration and composition of any fluid present in at least one discontinuity between the sensing element and the edge of the dielectric membrane.

[0080] One or more other sensing elements may include a resistive temperature detector, a diode, or a thermopile. The thermopile may be used to measure the temperature difference between the dielectric film and the dielectric region above the substrate, or may be used to measure the temperature difference across the heating element. Compared with the thermopile, the diodes and detectors reduce the heat loss of the semiconductor substrate because they are entirely located on or within the dielectric film. One type of sensing element may be used or a combination of different types of sensing elements may be used.

[0081] The sensing element may be temperature sensitive and may be any one of a resistive temperature detector, a bolometer, a diode, a transistor, or a thermopile, or an array of these elements in series or parallel, or a combination of these elements.

[0082] The sensing element may also be made of a thermopile. The thermopile includes one or more thermocouples connected in series. Each thermocouple may include two different materials that form a junction at a first region of the film, while the other ends of the two different materials form a junction at a second region of the film or in a heat sink region (substrate outside the film region), and each thermocouple is electrically connected to an adjacent thermocouple or pad for external readout. The thermocouple material may include metals such as aluminum, tungsten, titanium, or a combination of these metals, or any other metal available in the process. Optionally, the thermocouple material may include thermocouples based on n-type and p-type silicon or polysilicon, or a combination of metals and semiconductors. The position of each junction of the thermocouple, as well as the number and shape of the thermocouples, may be any desired position, number, and shape for adequately mapping the temperature profile on the film to achieve a specific performance.

[0083] The selection of the temperature sensing element, the shape, position, and number of the heating element, and the selection of the number or area of the holes in the film may produce a temperature profile and / or map the temperature profile on the film, thereby achieving specific performance, and may produce a sensing ability with multiple directions, multiple ranges, and multiple performances. For example, a flow sensor may be designed to sense the flow rate and the direction of the flow, or the flow rate, the direction of the flow, and the composition of the flow, based on any other combination of thermal conductivity or flow performance.

[0084] The sensing element formed within the dielectric film may be configured as a temperature resistive detector (TRD) or a bolometer, a diode, a transistor, or an array of transistors or diodes for enhancing sensitivity and selectivity.

[0085] The sensing element can be used in a differential manner to (i) sense flow properties such as flow velocity, flow rate, volume or mass flow rate, or a derived quantity (such as pressure difference) (by measuring the signal difference between an upstream sensing element and a downstream sensing element); and / or (ii) sense the composition of the flow based on the difference in thermal conductivity between different components of the fluid (for example, the thermal conductivity of hydrogen is much higher than that of air; the thermal conductivity of CO2 is lower than that of air).

[0086] The pores within the membrane can be placed at specific locations and can be used to enhance the differential signal between the sensing elements to more accurately detect the composition of the fluid. Additionally, the heater temperature can be modulated to different levels by electrical pulses to increase selectivity and detect the coexistence of more than one component of the flow with different thermal conductivities. For example, by adjusting the temperature of the heater and based on the fact that the thermal conductivities of these gases (CO2 and air) vary differently with increasing temperature, the concentrations (percentage / ppm) of hydrogen and CO2 in the air flowing over the surface of the sensor can be detected simultaneously.

[0087] The heater or heating element can also be used as a temperature sensing device. Then, the heat exchange between the heater and the fluid can be measured by the change in the resistance of the heater itself, and this heat exchange is associated with at least one property of the fluid (such as flow velocity, flow rate, mass flow rate or volume flow rate of the flow, the applied wall shear stress, pressure difference, pressure, temperature, direction).

[0088] Additional sensing elements and pores or discontinuities through the membrane can be placed at specific locations to achieve discrimination (or differentiation) of the fluid. For example, the flow sensor can sense whether the fluid is in gaseous form or liquid form, or the sensor can distinguish between different fluids (such as between air and CO2), or in the case where the fluid is a mixture, the sensor can measure the mixture ratio by adjusting the temperature level of the heater or by operating the heater in a pulsed mode and measuring the flight time of the sensing elements placed at specific locations. Qualitative information (such as liquid or gaseous form) and quantitative information (such as gas concentration) of the fluid properties can be obtained.

[0089] The sensor can be configured to operate as a flow sensor or a pressure difference sensor. The sensor can be configured to measure or sense the properties of a fluid flow. Optionally, the sensor can be configured to measure the properties of the fluid when there is no fluid flow or a static flow.

[0090] The sensor can include a first pair of other sensing elements and a second pair of other sensing elements, wherein the differential signal between the first pair of other sensing elements can be configured to measure the properties of the flow, and wherein the differential signal between the second pair of sensing elements can be configured to measure the properties of the components of the flow composition.

[0091] The sensor may include two pairs of sensing elements, where the differential signal between one pair of sensing elements is used to extract the performance of the flow, such as flow rate, flow direction, flow velocity, or mass flow rate or volumetric flow rate of the flow, and the differential signal between the other pair of sensing elements is used to detect different components of the fluid and their concentrations based on the different thermal conductivities of different components of the fluid.

[0092] By using the differential signal between two sensing elements, different components of the fluid can be sensed based on the different thermal conductivities of different components of the fluid.

[0093] In use, the heating element may extend in a direction perpendicular to the direction of the flow through the sensor. The heating element may not be at an exact right angle to the direction of the flow, but may extend in a diagonal direction or at an acute angle with respect to the direction of the flow, provided that one component of the extending portion of the heating element is perpendicular to the flow. Optionally, the heating element may be substantially perpendicular to the flow through the sensor, or may be arranged at an angle within 10° with respect to the direction perpendicular to the flow through the sensor.

[0094] The sensor may include other heating elements, and in use, the other heating elements may extend in a direction parallel to the direction of the flow through the sensor. The heating element may not be exactly parallel to the direction of the flow, but may extend in a diagonal direction or at an acute angle with respect to the direction of the flow, provided that one component of the extending portion of the heating element is parallel to the flow. The other heating element may be perpendicular to the heating element, or may be positioned at an acute angle with respect to the heating element. Optionally, the heating element may be substantially parallel to the flow through the sensor, or may be arranged at an angle within 10° with respect to the direction of the flow through the sensor.

[0095] Additional or other heaters or heating elements may be incorporated within the same dielectric film, where the two heaters may be operated under pulsed conditions at different times, and the additional heater is used to enable the detection of different components of the fluid and their concentrations based on the different thermal conductivities of different components of the fluid.

[0096] Optionally, one or more other heaters may be placed on or within the dielectric film towards the edge of the film. This may be referred to as a film edge heater. Towards the edge of the dielectric film may be defined as within the dielectric film region but closer to the edge of the dielectric film than the center of the dielectric film. By driving with a suitable current / voltage / power, the additional film edge heater can be maintained or held at a constant temperature regardless of the ambient temperature or the temperature of the main heater. The additional film edge heater can provide an improved signal-to-noise ratio for the measurement of the flow and the composition of the flow, and can provide enhanced immunity to ambient temperature variations. The temperature of the additional film edge heater may exceed the ambient temperature and be lower than the temperature of the main heater.

[0097] The additional membrane edge heater can be in the form of a hot wire, circular or spiral.

[0098] The sensor can also include one or more other sensing elements configured to measure differential signals on other heating elements. The other sensing elements can be at least a pair of other sensing elements positioned laterally spaced apart from each other on either side of the other heating elements. The other sensing elements can be aligned with the direction of the fluid flow through the device and / or extend in a direction parallel to the direction of the fluid flow through the device. The other sensing elements can not be precisely parallel to the direction of the flow, but can extend in a diagonal direction or at an acute angle with respect to the direction of the flow, provided that a component of the extension of the other sensing elements is parallel to the flow. The temperature difference between the laterally spaced other sensing elements around the other heating element can be less dependent on the flow rate and performance, but more dependent on the gas concentration and composition.

[0099] The first heater can be in the form of a hot wire and can be orthogonal to the direction of the flow, and the additional heater can be in the form of a hot wire and can be aligned with the direction of the flow.

[0100] At least one additional heater (hot wire or hot plate) can be provided, which can be operated to distinguish the presence and parameters of the flow or the pressure difference and composition of the flowing fluid. The heater can be operated in a pulsed mode at different times. One heater can be operated to sense the performance of the flow (such as flow rate, flow velocity, mass flow rate or volume flow rate) by measuring the resistance of the heater in the presence of the flow, or by monitoring the temperature / power of the sensing element or the differential signal of a pair of sensing elements, and the second heater can be used to enable the detection of the composition of the fluid.

[0101] Optionally, the first heater including the hot wire and / or the sensing element has a direction orthogonal to the direction of the flow to enhance the sensitivity to the flow rate / flow velocity, while the second heater is aligned with the direction of the flow to be less affected by the flow rate / flow velocity and instead measures the composition of the fluid.

[0102] The two heaters can be made of different metal layers (such as aluminum, tungsten, copper, titanium, platinum, etc.) available in a manufacturing process (such as a CMOS process).

[0103] A pair of sensing elements and holes or discontinuities can be provided around the second heater to enhance the detection of the convective component. At least one hole can be laterally disposed in the membrane between the second heater and the sensing element on one side of the second heater, and another of the at least one hole can be laterally disposed in the membrane between the sensing element and the edge of the thin film on the other side of the second heater. The two holes or a set of holes can have similar surface areas. The two sensing elements can be the same in size and lateral distance from the heater and can be fabricated in the same manufacturing process (e.g., a CMOS step before membrane etching).

[0104] The first heater can be a hot wire made of the first metal (metal 1) of the CMOS process, the second heater can be a hot wire disposed in the membrane and orthogonal to the first heater, and the second heater can be made of a different metal layer (e.g., metal 2) so that the two heaters are not electrically connected (shorted).

[0105] The sensing element or elements can be one or more thermopiles. Optionally, at least one sensing element in the form of a thermopile can be symmetrically disposed around or across the two heaters. The hot junctions of at least one sensing element can be placed on one side of the first heater, while the cold junctions can be placed on the other side of the first heater, both the hot and cold junctions being at a distance from the heater and the edge of the membrane within the membrane. The heater can be operated in a pulsed mode at different times. The first heater perpendicular to the flow direction is operated to sense the performance of the flow, such as flow rate, flow velocity, mass flow rate, or volume flow rate, by measuring the voltage drop across the thermopile, while the second heater aligned with the flow can be operated to sense the composition of the flow by measuring the voltage drop across the thermopile. The temperature of the first heater and / or the second heater can be adjusted to improve the measurement accuracy and increase the sensitivity / selectivity to different components of the convection. Holes can be provided to reduce heat loss and enhance the sensitivity / selectivity to different components of the convection. Optionally, the holes can be asymmetrically placed to provide a larger differential signal across the thermopile, thereby further enhancing the sensitivity / selectivity to different components of the convection.

[0106] The temperature of the heater can be adjusted, and the voltage difference between the ends of the thermopile at different temperatures can be evaluated relative to a reference value, and the voltage difference between the two ends represents the composition of the flow.

[0107] Optionally, at least one sensing element in the form of a thermopile can be placed symmetrically around or across the heater. The hot junction of the at least one sensing element can be located on one side of the heater, and the cold junction can be located on the other side of the heater, with both the hot and cold junctions being a certain distance from the edge of the membrane within the membrane. The holes can be placed asymmetrically or symmetrically within the membrane in the space between the at least one thermopile and the edge of the membrane. The voltage difference between the hot and cold junctions (proportional to the temperature difference) represents the performance of the flow. The temperature of the heater can be adjusted, and the thermopile voltage (voltage drop between the hot and cold junctions) can be evaluated relative to calibration data to indicate the composition of the flow. The composition of the flow can also be related to the measured value of the resistance of the heater. Optionally, other sensing elements (such as additional resistance temperature detectors or other thermopiles) can be provided to enhance the sensitivity / selectivity to different components of the flow. The holes can be placed laterally and asymmetrically around these additional sensing elements to further improve the sensitivity / selectivity to different components of the flow.

[0108] The temperature sensing element can be formed as a long element that can be aligned with the first heater or an additional / second heater, depending on whether the main purpose of the temperature sensing element is to sense the performance of the flow (such as flow rate or velocity), or whether the main purpose of the temperature sensing element is to sense the composition of the flow and the concentration of different components of the flow respectively.

[0109] The dielectric membrane can be circular or other shapes with rounded corners (circular corners with a rounded shape), and at least one groove region can have an arc shape. The heating element and the sensing element can also have an arc shape. The center of the circle where the arc is located can correspond to the center of the circular membrane. This increases the use of the membrane area and improves the thermal performance.

[0110] The sensor can also include a flow mechanism configured to provide or control the flow through the sensor. For example, if a flow with a known velocity is provided, the sensor can be used to measure another variable more accurately or precisely (such as the composition or concentration of the flow). The sensor can measure a flow with a known velocity but use this information to determine other performances, so the sensor may not operate purely or strictly as a flow sensor. Optionally, the sensor can be configured to operate as a differential pressure sensor.

[0111] The flow mechanism can include at least one additional heater configured to generate a temperature gradient across the sensor. The heater can be located outside the sensor within the manifold, or can be one or more heaters located on the same dielectric membrane or a different membrane but monolithically integrated with the sensor.

[0112] The sensor may include a flow-forming device or a flow mechanism (such as a microfan, a micropump, or a microvalve) to generate and / or manipulate a flow at the surface of the sensor, so as to be able to more accurately measure the concentrations of different components of the flow based on the different thermal conductivities of the different components of the flow. The flow mechanism may be capable of generating or manipulating a flow (e.g., a micropump or an additional heater generates a temperature gradient and a flow via thermophoresis or thermal diffusion near the flow / heat conduction sensor).

[0113] The flow mechanism or the flow-forming device may be used to enhance the signal / accuracy of the composition of the existing flow. For example, in a normal static flow, it is difficult to detect CO2 at a low ppm value (e.g., 500 ppm at an accuracy of 100 ppm) because the signal provided by the heat conduction sensor may be hidden in the noise level. To enhance / enlarge the signal, a device that allows for easier or more accurate detection by enhancing the differential signal between two sensing elements over a period of time may be used to generate a flow. The flow sensor may be used to calibrate or measure the flow generated on the surface of the sensor.

[0114] The flow itself may be used to enhance the signal / accuracy detection of the fluid. A micropump for generating a fluid flow, or at least one additional heater embedded in the same membrane or on different membranes within the same substrate or placed externally, may be used to generate a temperature gradient to generate a flow, or to enhance the detection of the convective component by using the different thermal properties (thermal conductivity, heat convection, heat time) of the flow components. Such a device may also be integrated with an ASIC and / or placed within a manifold.

[0115] An additional heater may be provided within the same system or the same package or the same device or the same membrane to generate a temperature gradient, and a flow is generated at the surface of the sensor via thermal diffusion, so as to be able to more accurately measure the concentrations of different components of the flow based on the different thermal conductivities of the different components of the flow.

[0116] A flow mechanism or flow forming device can be used to enhance the signal / accuracy of other gas sensors (such as gas sensors based on metal oxides, electrochemical reactions, or catalytic reactions). Taking a gas sensor as an example, the flow can help enhance the binding of gas molecules to the metal oxide or the diffusion of gas molecules into the metal oxide, and thus improve the sensitivity to the gas or enhance the detected signal of the gas. An example can be a volatile organic compound or nitrogen dioxide or carbon monoxide sensor. The flow forming device can enhance the reaction of the gas with the metal oxide layer deposited on the dedicated electrode, where the dedicated electrode is placed on the membrane above the heater or near the heater. A flow sensor adjacent to or monolithically integrated with the gas sensor can be used to accurately measure the flow. A gas sensor array can be set up to enhance selectivity, and different flow rates can be used to optimize the sensitivity to each gas. The flow forming device can be the same flow forming device as described above (e.g., a micropump, a microfan, or a device based on an additional heater).

[0117] Optionally, the flow sensor can be integrated with the gas sensor on the same membrane to save space and reduce costs. In this case, the flow sensor and the gas sensor can operate under pulsed conditions. In one pulse, the flow sensor is activated and can measure the flow rate and the performance of the flow, while in another pulse, the gas type and concentration can be detected and measured.

[0118] Optionally, the flow sensor can also include a heat conduction sensor and be integrated with at least one metal oxide, catalytic, or electrochemical gas sensor in the same system / package or chip. The flow sensor can measure the flow rate, the heat conduction sensor can measure gases (such as CO2 or hydrogen) based on the difference in thermal conductivity between these gases and air, and the gas sensor can measure other gases (such as NO2, CO, or volatile organic compounds). The gas sensor can also measure hydrogen and in this way help the heat conduction sensor distinguish the presence of CO2 and hydrogen.

[0119] The sensor can also include an application-specific integrated circuit (ASIC) coupled to the sensor. The ASIC can be positioned below the sensor using, for example, die stacking technology. Optionally, the ASIC can be positioned at other locations. The ASIC can be connected to the sensor using wire bonding and pads, or using through-silicon vias (TSVs) that extend through the semiconductor substrate.

[0120] The ASIC can be provided on the same system or the same package or chip to provide circuitry to drive the sensor, read out signals from the sensor, and process the signals from the sensor. The ASIC can be placed in a stacked die configuration below the sensor, and the sensor and the ASIC can be placed within a manifold.

[0121] Analog / digital circuits can be integrated on a chip. The circuits can include IPTAT, VPTAT, amplifiers, analog-to-digital converters, memories, RF communication circuits, timing blocks, filters, or any other device for driving a heating element, reading from a temperature sensing element, or electronically manipulating a sensor signal. For example, it has been demonstrated that heating elements driven in a constant temperature mode can improve performance, and heating elements with on-chip devices implementing such a driving method will represent a significant advancement over state-of-the-art flow sensors. The known 3ω driving method can be implemented by an on-chip device, or by any other driving method (such as those requiring a constant temperature difference and time-of-flight to achieve specific performance (e.g., power consumption, sensitivity, dynamic response, range, flow performance detection, etc.)). In the absence of on-chip circuitry, when applying such a circuit block to a flow sensor having one or more features described in any of the foregoing embodiments, the present disclosure also encompasses off-chip implementations of such a circuit block. Such off-chip implementations can be realized in an ASIC, or by separate components, or by a hybrid of these two approaches.

[0122] The device can be packaged using a metal TO-type package and a ceramic, metal, or plastic SMD (surface mount device) package. The device can also be directly packaged on a PCB, or packaged using a flip-chip method. The device can also be embedded in a substrate, such as a substrate that is a customized version of one of the foregoing packaging methods, a rigid PCB, a semi-rigid PCB, a flexible PCB, or any other substrate, such that the device surface is flush with the substrate surface. The package can also be a chip or wafer-level package formed, for example, by wafer bonding.

[0123] The device can also be assembled within a manifold that provides an inlet, an outlet, and a predetermined channel through which a fluid flow is generated. The manifold provides protection for the device and allows for easier and more controllable measurement of the flow or fluid composition. The ASIC or an external readout circuit can also be placed in the same manifold in a lateral or die-stacked configuration.

[0124] The flow sensor can have through-silicon vias (TSVs) to avoid bond wires in the vicinity of the sensitive area of the device that may affect the readings of the flow sensor. Advantageously, a flow sensor with TSVs can be capable of using 3D stacking technology. For example, the flow sensor chip can be located on top of the ASIC, thereby reducing the size of the sensor system.

[0125] The semiconductor substrate can be silicon, and the dielectric film can be mainly formed of oxide and nitride materials, and the heater is made of a metal such as tungsten, titanium, copper, aluminum, gold, platinum, or a combination of these metals, or made of a semiconductor such as highly doped n-type silicon or p-type silicon or polysilicon, and the heater has a meandering shape, a spiral shape, or a hot-wire shape.

[0126] The starting substrate can be any semiconductor, such as silicon, silicon-on-insulator (SOI), silicon carbide, sapphire, or diamond. In particular, the use of silicon is advantageous as it ensures high-volume manufacturing capabilities, low cost, and high reproducibility of the sensor. The use of a silicon substrate also enables the use of on-chip circuitry, thereby enhancing sensor performance and facilitating system integration. Such on-chip circuitry can be implemented by using analog signal blocks, digital signal blocks, or mixed-signal blocks placed outside the dielectric film.

[0127] A dielectric film or a multi-layer film can be formed by back-etching the substrate using deep reactive ion etching (DRIE), which produces vertical sidewalls and thus enables reduction of the sensor size and cost. However, the back-etching can also be accomplished by using anisotropic etching, such as KOH (potassium hydroxide) or TMAH (tetramethylammonium hydroxide), which results in slanted sidewalls. Dielectric layers that can be formed within the film by oxidation or oxide deposition can be used as an etch stop during the DRIE or wet etching process. The film can also be formed by front etching or a combination of front etching and back etching, thereby producing a suspended film structure supported only by two or more beams. The film can be circular, rectangular, or rectangular with rounded corners for reducing stress in the corners, but can also be of other shapes. Additionally, holes can be formed within the film to reduce heat dissipation through thermal conduction through the dielectric film and to increase heat loss through thermal convection and thermal conduction in the regions below and above the film and optionally in the path of the fluid (above the film). Optionally, the holes or interruptions can be fabricated by front etching after the film is formed.

[0128] The dielectric film can include silicon dioxide and / or silicon nitride. The film can also include one or more spin coatings on glass, as well as a passivation layer on one or more dielectric layers. The use of materials with low thermal conductivity (e.g., dielectric) enables significant reduction of power consumption and an increase in the temperature gradient within the film, thereby directly benefiting sensor performance (e.g., sensitivity, frequency response, range, etc.). A temperature sensing element or heater made of a material such as single-crystal semiconductor, polycrystalline semiconductor, or metal can be suspended or embedded within the dielectric film.

[0129] The film can also have other structures made of metal or other conductive materials or other materials with higher mechanical strength. These structures can be embedded within the film, or can be above or below the film, to design the thermo-mechanical properties of the film (e.g., rigidity, temperature profile distribution, etc.), and / or to design the hydrodynamic interaction between the fluid and the film. More generally, these structures can also be outside the film and / or used for bridging between the inside and outside of the film.

[0130] The sensed fluid can be a gas, and the gas can consist of air and a component of interest, which can be any one of CO2, methane, hydrogen, or other gases having a thermal conductivity different from that of air.

[0131] The substrate can include: more than one etched portion; a dielectric region located on the substrate, where the dielectric region includes a dielectric film above the region of each etched portion of the substrate. At least one film can include any combination of the above features. The second film can have more holes or discontinuities, larger area holes or discontinuities, or holes or discontinuities at different positions. A differential signal between a sensing element on the first film and a sensing element placed on the second film can be measured to detect the composition of the fluid and the flow properties of the fluid.

[0132] The flow / heat conduction sensor can also operate under static flow (zero flow rate / flow) and be used to detect the presence of a specific component of the fluid. The flow sensor element can detect the absence of flow, while at least one additional sensing element (or a pair of sensing elements operating in a different manner) can detect the composition of the flow (e.g., CO2 ppm in air).

[0133] The flow / heat conduction sensor can be configured to be calibrated by using one or more flow measurements with only clean air having a known flow rate. Optionally or additionally, the flow / heat conduction sensor can be calibrated by using a zero flow measurement. The advantage of using flow measurements is that overall calibration can preferably be performed without the need for specific calibration in a gas (with a known gas concentration - e.g., CO2 concentration). Alternatively, one or more differential pressure measurements and / or zero differential pressure measurements can be used to calibrate the flow / heat conduction sensor.

[0134] The flow / heat conduction sensor can be used in applications such as from consumables (such as personal care products or white goods), smart energy (e.g., HVAC, gas metering), and industrial automation (e.g., leak testing, dispensing, analytical instruments) to medical (e.g., breath analyzers, spirometry, capnometry, respirators, inhalers, drug delivery) and fluid dynamics research (e.g., turbulence measurement, flow attachment). Interestingly, the sensor is also capable of being applied to harsh environments (from cryogenic conditions to ambient temperatures up to 300 °C), such as the environments of boilers, automobiles, space, etc.

[0135] According to another aspect of the present disclosure, there is provided a fluid sensing device, including: a flow sensor housing; and a sensor as described above located within the flow sensor housing. The flow sensor housing can include an inlet and an outlet, and a fluid flow path for guiding the fluid flow through the sensor. The sensor can be encapsulated within a packaging housing or manifold having an inlet, an outlet, and channels, thereby providing a more accurate measurement of the flow.

[0136] According to yet another aspect of the present disclosure, a method of manufacturing a sensor is provided, the method comprising: forming at least one dielectric film on a semiconductor substrate including an etched portion, wherein the dielectric film is over a region of the etched portion of the semiconductor substrate; forming a heating element within the dielectric film; and forming at least one groove region within the dielectric film, the at least one groove region being located between the heating element and an edge of the dielectric film.

[0137] The manufacturing method may include: forming at least one dielectric film on a substrate including an etched portion, wherein the dielectric film is over a region of the etched portion of the substrate; forming at least one hole through the dielectric film, forming a heater and one or more sensing elements to sense flow properties such as flow rate, volumetric flow rate, and mass flow rate, and sensing the composition of a fluid based on different thermal properties of the fluid components. BRIEF DESCRIPTION OF THE DRAWINGS

[0138] Some embodiments of the present disclosure will now be described only by way of example and with reference to the accompanying drawings, in which:

[0139] Figure 1 A cross-section of a prior art level flow sensor based on a heating and self-sensing element is shown;

[0140] Figure 2 A top view of a prior art level flow sensor based on a heating and self-sensing element is shown;

[0141] Figure 3 A cross-section of a sensor according to an embodiment of the present disclosure is schematically shown;

[0142] Figure 4 Schematically shown is an Figure 3 embodiment of the present disclosure

[0143] Figure 5 A cross-section of a sensor according to an embodiment of the present disclosure having a discontinuous portion with an asymmetric arrangement within the dielectric film is schematically shown;

[0144] Figure 6A Schematically shown is an Figure 5 embodiment of the present disclosure

[0145] Figure 6B Schematically shown is an Figure 5 embodiment of the present disclosure having a three-dimensional (3D) top view of a sensor with a discontinuous portion having an asymmetric arrangement within the dielectric film;

[0146] Figure 6C Schematically shown is Figure 5Top view of a sensor with an additional heater at the edge of the membrane;

[0147] Figure 7 Schematically shows a top view of a sensor having only one discontinuity within a dielectric membrane according to an alternative embodiment of the present disclosure;

[0148] Figure 8 Schematically shows a top view of a sensor using a heater as a sensing element according to an alternative embodiment of the present disclosure;

[0149] Figure 9 Schematically shows a cross - section of a sensor having additional sensing elements upstream and downstream of a heating element according to an alternative embodiment of the present disclosure;

[0150] Figure 10A Schematically shows according to an embodiment of the present disclosure Figure 9 a top view of a sensor;

[0151] Figure 10B Schematically shows according to an embodiment of the present disclosure a sensor similar to Figure 9 the sensor shown in but having additional discontinuities;

[0152] Figure 11 Schematically shows a top view of a sensor according to an alternative embodiment of the present disclosure similar to the sensor shown in FIG. 6 and having an array of smaller holes within the dielectric membrane;

[0153] Figure 12 Schematically shows a top view of a sensor having holes of non - standard shape with a symmetric arrangement according to an alternative embodiment of the present disclosure;

[0154] Figure 13 Schematically shows a top view of a sensor according to an alternative embodiment of the present disclosure similar to the sensor shown in FIG. 6 and having holes of non - standard shape arranged within the dielectric membrane;

[0155] Figure 14 Schematically shows a top view of a sensor with an additional heater according to an alternative embodiment of the present disclosure;

[0156] Figure 15 Schematically shows according to an alternative embodiment of the present disclosure a sensor similar to Figure 14 the sensor shown in and having holes with an asymmetric arrangement within the dielectric membrane;

[0157] Figure 16 Schematically shows a top view of a sensor having thermopiles placed upstream and downstream of a heating element according to an alternative embodiment of the present disclosure;

[0158] Figure 17 Schematically shows a top view of a sensor similar to that shown in Figure 16 and having a single hole upstream of the heating element;

[0159] Figure 18 Schematically shows a top view of a sensor having a circular membrane and a heater, hole, and thermopile of corresponding shape according to an alternative embodiment of the present disclosure;

[0160] Figure 19 Schematically shows a top view of a sensor similar to that shown in Figure 18 and having symmetrically arranged holes;

[0161] Figure 20 Schematically shows a top view of a sensor having four holes and four thermopiles according to an alternative embodiment of the present disclosure;

[0162] Figure 21 Schematically shows a top view of a sensor similar to that shown in Figure 20 and having asymmetrically arranged holes;

[0163] Figure 22 Schematically shows a top view of a sensor having one thermopile placed across the heating element according to an alternative embodiment of the present disclosure;

[0164] Figure 23 Schematically shows a top view of a sensor similar to that shown in Figure 22 and having a single hole downstream of the heating element;

[0165] Figure 24 Schematically shows a top view of a sensor similar to that shown in Figure 22 and having two additional thermopiles;

[0166] Figure 25 Schematically shows a top view of a sensor having a thermopile and a resistance temperature detector according to an alternative embodiment of the present disclosure;

[0167] Figure 26 Schematically shows a top view of a sensor having a second heating element perpendicular to the first heating element according to an alternative embodiment of the present disclosure;

[0168] Figure 27 Schematically shows a top view of a sensor similar to that shown in Figure 26 and having symmetrically arranged holes;

[0169] Figure 28 Schematically shows a top view of a sensor similar to that shown in Figure 27 and having an asymmetrically arranged hole downstream of the heating element;

[0170] Figure 29 Schematically shows a cross-section of a sensor according to an alternative embodiment of the present disclosure having a flow mechanism for controlling or generating a fluid flow;

[0171] Figure 30 Schematically shows a cross-section of a sensor according to an alternative embodiment of the present disclosure having a flow heater for controlling or generating a temperature gradient;

[0172] Figure 31 Schematically shows a cross-section of a sensor according to an alternative embodiment of the present disclosure having an integrated additional heater for controlling or generating a temperature gradient;

[0173] Figure 32 Schematically shows a cross-section of a sensor according to an alternative embodiment of the present disclosure having an ASIC placed below the sensor;

[0174] Figure 33 Schematically shows a cross-section of a sensor according to an alternative embodiment of the present disclosure having trenches or partial grooves in a dielectric film; and

[0175] Figure 34 Schematically shows a cross-section of a sensor chip located within a flow sensor housing according to an alternative embodiment of the present disclosure. DETAILED DESCRIPTION

[0176] Some examples of the disclosed device are given in the drawings.

[0177] List of Reference Numerals:

[0178] 1. Semiconductor substrate (e.g., silicon)

[0179] 2. Dielectric film (e.g., oxide and nitride)

[0180] 3. First heater or heating element - hot wire (e.g., tungsten, platinum, titanium)

[0181] 4. Etched region defining the film

[0182] 5. Bias track

[0183] 6. Sensing element

[0184] a. Upstream

[0185] b. Downstream

[0186] c. Distant upstream

[0187] d. Distant downstream

[0188] 7. Pores or grooves in the membrane

[0189] a. Upstream

[0190] b. Downstream

[0191] c. Distant upstream

[0192] d. Distant downstream

[0193] e. Upstream near the heater

[0194] f. Downstream near the heater

[0195] 8. Second heater or heating element

[0196] 9. Thermopile

[0197] a. Upper left

[0198] b. Lower left

[0199] c. Upper right

[0200] d. Lower right

[0201] 10. Hot plate

[0202] 11. Additional heater on the discrete micro hot plate

[0203] 12. Membrane of the discrete micro hot plate

[0204] 13. ASIC (or readout circuit, conversion circuit, and drive circuit)

[0205] 14. Bonding wire

[0206] 15 and 16. Bonding pads

[0207] 17. Package base

[0208] 18. Package sidewall

[0209] 19. Package lid

[0210] 20. Flow mechanism

[0211] 21 and 22. Flow heater

[0212] 30. Heater at the membrane edge

[0213] 91. Thermal contact of the central thermopile

[0214] 92. Cold contact of the central thermopile

[0215] Figure 3 Schematically shows a cross-section of a sensor according to an embodiment of the present disclosure and Figure 4 schematically shows Figure 3 a top view of the sensor of

[0216] The device has a semiconductor substrate 1, a dielectric layer or dielectric region 2 suspended on or above an etched region defining a dielectric membrane 4, and a heater or heating element 3. The heating element extends in a direction substantially perpendicular to the direction of the flow through the sensor. When the flow passes above the top of the membrane 4, the heater 3 is cooled due to heat convection losses.

[0217] In this embodiment, there are two temperature sensing elements 6a (upstream) and 6b (downstream) symmetrically placed on opposite sides of the heater. Since the heating element itself can be used as a sensing element, these two temperature sensing elements can be considered as other sensing elements. These two sensing elements can be made of the same material as the heater (e.g., tungsten, polysilicon, platinum, aluminum), or can be made of different materials with a stable and relatively high temperature coefficient of resistance (TCR). Optionally, diodes or thermopiles can be used for the sensing elements. The two sensing elements can measure the difference across the heating element.

[0218] Interrupted portions or recessed regions (holes in this embodiment) 7a and 7b passing through the membrane (optionally processed by front-side etching) are placed symmetrically. The holes minimize the thermal path through the solid dielectric membrane, thus forcing more heat to dissipate through the environment via convection and conduction (mostly via convection and conduction above the membrane), but some heat will still dissipate via heat conduction through the space formed by the holes or the space below the membrane (in the case where holes are provided). Due to the reduced total heat loss, the presence of the holes also helps to reduce the power consumption of the device (for the same heater temperature). In addition, due to the reduced thermal mass of the membrane, the holes help to reduce the thermal response time (increase the heating speed of the heater when supplied with an electrical power pulse). In this embodiment, the holes are elongated slits extending towards the opposite edges of the dielectric membrane.

[0219] The change in the resistance of heater 3 is associated with flow rate, flow velocity, volumetric flow rate, or mass flow rate. Optionally, heater 3 can be maintained in a constant temperature or constant resistance mode by modifying the power supplied to the heater element. In this case, the change in power due to flow rate, flow velocity, volumetric flow rate, or mass flow rate can be measured. In the presence of flow, the temperature of 6b (downstream sensing element) is higher than the temperature of 6a (upstream sensing element). The temperature difference between 6b and 6a increases with an increase in flow rate (or flow velocity). In an example of sensing the CO2 concentration in air, given the fact that the thermal conductivity of CO2 is lower than that of air, less heat is dissipated through the environment, which results in a smaller increase in the temperature between 6b and 6a for a given flow rate. The change in the temperature difference between the two temperature sensing elements 6b and 6a can be correlated with the CO2 concentration in air based on the given flow rate (which can be measured by heater 3 itself).

[0220] If there is a certain concentration of hydrogen in the air, the opposite effect will occur. Hydrogen has a higher thermal conductivity than air, so for a given flow rate, the increase in the temperature between 6b and 6a is greater.

[0221] Depending on the temperature sensing elements employed, the temperature difference can be converted into a voltage difference or a resistance difference. For a diode supplied with a constant current, or for a thermopile, a voltage difference is appropriate. For a resistive temperature detector (RTD), various readout techniques can be used, such as using a meter bridge or using a current mirror and sensing the voltage difference to measure the change in resistance.

[0222] However, since the change in the temperature of the two sensing elements due to the composition of the flow (e.g., CO2 in air) is relatively low compared to the change in temperature of the two sensing elements caused by the flow through convection, the sensitivity of this arrangement may be limited.

[0223] Figure 5 A cross-section of a sensor according to an embodiment of the present disclosure having a discontinuous portion with an asymmetric arrangement within a dielectric film is schematically shown. Figure 6A Schematically shown is Figure 5 a top view of the sensor, and Figure 6B schematically shown is Figure 5 a three-dimensional (3D) top view of the sensor.

[0224] Optionally, an asymmetric design is proposed and shown in Figure 5 , 6A and 6B. This asymmetric design can improve the sensitivity to the composition of convection (in the case where the components of the flow have different thermal conductivities) by achieving a greater differential change in temperature between the two sensing elements.

[0225] In this embodiment, at least one hole 7a can be laterally placed within the membrane 4 between the heater 3 and the upstream temperature sensing element 6a on one side of the heater 3, and at least one other hole 7b can be laterally placed within the membrane between the downstream temperature sensing element 6b and the edge of the membrane 4 on the other side of the heater 3. In this embodiment, the two holes 7a and 7b or a set of holes have similar surface areas, but they can also have different surface areas. In this embodiment, the two sensing elements 6a and 6b are the same in terms of size and the lateral distance from the heater, and can be manufactured using the same manufacturing process, such as during the CMOS steps before membrane etching.

[0226] Here, when the heater 3 is powered on, even in air (or a static flow), 6b operates at a higher temperature than 6a. If CO2 is present, since the thermal conductivity of CO2 is less than that of air, the temperatures in 6a and 6b will be even more different (e.g., 6b will become hotter than 6a). The reason is that 6a is isolated from the heater by the hole (due to the presence of CO2, the thermal conductivity of the hole is low), and there is no hole between 6a and the edge of the membrane at ambient temperature. This means that 6a will become colder than in the case of normal air (with less CO2). For 6b, the opposite argument can be made. There is no hole separating 6b from the heater, but there is a hole between 6b and the edge of the membrane. In the presence of a higher level of CO2, the thermal conductivity of the hole becomes low, causing the temperature in 6b to increase.

[0227] In this arrangement, the temperature difference (the differential signal between 6b and 6a) between the two sensing elements 6b and 6a is proportional to the CO2 concentration. For the case of normal air, there is an offset between 6b and 6a. This can be corrected externally through an auto - zeroing technique or simply taken into account in the read - out circuit.

[0228] By monitoring the change in temperature at a constant power, the flow rate or velocity can be measured by the heater itself. Optionally, the heater 3 can be maintained in a constant - temperature or constant - resistance mode by modifying the power supplied to the heater element. In this case, the change in power due to the flow rate, velocity, volumetric flow rate, or mass flow rate can be measured.

[0229] The heater 3 can also be temperature - regulated to increase selectivity. To distinguish different components of a fluid (e.g., air, hydrogen, methane, CO2), the heater 3 can be powered to different temperatures, and the results can be evaluated relative to calibrated data or a look - up table stored in a storage device (on - chip device or external device). The thermal conductivities of these gases (i.e., CO2, hydrogen, and methane) vary with temperature, and the variation for each gas present is different.

[0230] Figure 6C shows a top view of a sensor similar to Figure 5 but having an additional heater 30 at the edge of the membrane 30. The heater 30 can be maintained at a constant temperature higher than the ambient temperature but lower than the temperature of heater 3, and the heater 30 helps to keep the sensor response the same regardless of changes in the ambient temperature. The heater can be designed differently, for example, it can be a 2-wire heater in a direction parallel or perpendicular to the flow, or a 4-wire heater in each direction. The heater can also be an annular heater on a rectangular or circular membrane.

[0231] Figure 7 Schematically shows a cross-section of a sensor having only one discontinuity within a dielectric membrane according to an alternative embodiment of the present disclosure. Figure 7 Shows an alternative asymmetric design of the design shown in FIG. 6. In this embodiment, only one hole is provided between the upstream sensing element and the heater. As described in the previous embodiment, 6b is hotter than 6a, and the temperature difference between 6b and 6a can indicate the CO2 or hydrogen concentration. This structure is simpler than the structure shown in the embodiment of FIG. 6, but the sensitivity may be greatly reduced.

[0232] Figure 8 Schematically shows a top view of a sensor using a heater as a sensing element according to an alternative embodiment of the present disclosure. Figure 8 Shows a design in which there is more than one hole, and the only sensing element is the sensing element formed by the heater itself. The flow rate or velocity can be measured by monitoring the change in the temperature of the heater at a constant power. Optionally, the heater 3 can be maintained in a constant temperature or constant resistance mode by modifying the power supplied to the heater element. In this embodiment, the user can measure the change in power due to the flow rate, velocity, volumetric flow rate, or mass flow rate.

[0233] Then, the temperature of the heater 3 is adjusted to detect the composition of the flow (CO2 concentration in the air) relative to a set of calibrated data.

[0234] Since this design has no additional sensing elements, this design is the simplest, but it has lower sensitivity and selectivity to the flow composition of the flow.

[0235] Figure 9 Schematically shows a cross-section of a sensor having other sensing elements upstream and downstream of a heating element according to an alternative embodiment of the present disclosure, and Figure 10A Schematically shows Figure 9 the top view of the sensor of Figure 5 and the design shown in FIG. 6.

[0236] In this embodiment, when compared with the sensor shown in FIG. 6, two additional sensing elements (referred to as 6c and 6d) are formed on either side of the heater (i.e., at the upstream (6a) and downstream (6b) positions). Since there are no holes between the heater and these sensing elements, the differential signal between 6b and 6a is proportional to the flow rate and is less affected by the composition of the flowing stream. The hole 7a is laterally placed within the membrane 4 between the sensing element 6a and the sensing element 6c (at the upstream position), and the hole 7b is laterally placed within the membrane between the sensing element 6d and the edge of the membrane 4 on the other side of the heater 3 (at the downstream position).

[0237] Here, when the heater 3 is energized, even in air (or when there is no flow), 6d operates at a higher temperature than 6c. If CO2 is present, since the thermal conductivity of CO2 is less than that of air, the temperatures in 6d and 6c will be more different (e.g., 6d will become hotter than 6c). In this arrangement, the temperature difference between the two sensing elements 6d and 6c (the differential signal between 6d and 6c) is proportional to the CO2 concentration. As previously described, the flow rate or fluidity can be measured by the temperature difference between 6b and 6a or by the change in the resistance / power of the heater. By combining the readout results from the heater 3 and the sensing elements 6a and 6b, the directionality of the flow can also be inferred.

[0238] This particular design can also be used to measure the "no-flow" (or zero-flow, or static-flow) state. In this case, due to symmetry, the signal difference (e.g., temperature difference or voltage difference or resistance difference) between the sensing elements 6b and 6a should be zero. However, in normal air (or no-flow) conditions, there will still be an offset between 6d and 6c. This can be corrected to zero by the readout circuit for normal air. When CO2 is present, even if no flow is generated, the differential signal difference (quantified as a temperature difference or voltage difference or resistance difference) between 6d and 6c increases linearly with the CO2 concentration. This can be helpful for measuring the CO2 concentration in air, for example, for air quality applications.

[0239] Figure 10B A top view schematically shows an alternative sensor according to an embodiment of the present disclosure that is similar to the sensor shown in Figure 9 but has additional discontinuities. FIG. 10b shows a design similar to FIG. 10a, where there are two additional holes 7e and 7f on either side of the heater 3. These additional holes provide greater thermal isolation between the elements 6a and 6b, thus resulting in higher measurement sensitivity.

[0240] Figure 11A top view of a sensor similar to that shown in FIG. 6 and having an array of smaller holes or perforations within a dielectric membrane, according to an alternative embodiment of the present disclosure, is schematically shown. Figure 11 A design similar to that of FIG. 6, but with a plurality of small holes 7a and 7b formed upstream and downstream, respectively. This design helps to ensure that the strength of the membrane is not damaged during manufacturing or during operation. In the case where the fluid is a liquid (rather than a gas), this design also helps to prevent the liquid from being trapped beneath the membrane. The small holes (e.g., having a diameter in the micrometers) can also be more easily processed during the manufacture of the device and do not damage the inner layer of the membrane due to, for example, over-etching. The geometric arrangement in the form of one or more rows of holes reduces heat conduction through the membrane, but does not significantly affect the mechanical stability and manufacturability of the membrane structure. The presence of the holes equalizes the pressure on both sides of the membrane and allows for a greater membrane deflection to minimize strain in the membrane, thereby improving the long-term reliability of the device. These holes also avoid the formation of a pressure difference between the top and bottom of the membrane, which may cause device failure during encapsulation / assembly. The elongated slits of any other embodiment can be interchanged with the small holes or perforations of this embodiment.

[0241] Figure 12 A top view of a sensor having holes of non-standard shapes with a symmetric arrangement, according to an alternative embodiment of the present disclosure, is schematically shown. Figure 12 A symmetric design is shown, where the holes and the sensing elements can have different shapes (non-standard shapes). In the embodiment shown, the sensing element has a zigzag shape and the holes have a corresponding matching shape. This design increases the length of the sensing element, thereby improving the accuracy and simplicity of signal processing. The matching shape of the holes helps to reduce heat loss through the membrane.

[0242] Figure 1 3 A top view of a sensor similar to that shown in FIG. 6 and having non-standard shaped holes arranged within a dielectric membrane, according to an alternative embodiment of the present disclosure, is schematically shown. Figure 13 The design example in Figure 12 has sensing elements and holes of the same shape as those shown in Figure 13 but uses an asymmetric arrangement similar to that shown in FIG. 6. This design can further improve sensitivity, and the sensing element has a higher resistance due to its zigzag shape, which may be more advantageous for the readout circuit.

[0243] Figure 14 A top view of a sensor having an additional heater, according to an alternative embodiment of the present disclosure, is schematically shown. Figure 14shows a symmetric design with an additional / other heater or heating element (hot wire) 8 to distinguish between the presence of a flow, flow parameters, and the composition of the fluid. The other heating element extends in a direction parallel to the direction of the flow through the sensor. The two heaters 3 and 8 can be operated in pulse mode at different times. Heater 3 can be operated to sense flow parameters (such as flow rate, flow velocity, mass flow rate, or volumetric flow rate) by measuring the resistance of heater 3 in the presence of a flow (alternatively, by monitoring the temperature / power of a sensing element, or the differential signal of a pair of sensing elements (not shown)), and the second heater 8 can be used to detect different fluid components (flow composition). The first heater 3 containing the hot wire has a direction orthogonal to the direction of the flow to enhance sensitivity to flow rate / flow velocity, while the second heater is aligned with the direction of the flow such that it is less affected by the flow rate / flow velocity and is thus used to measure the composition of the fluid. The two heaters can be made of different metal layers (such as aluminum, tungsten, copper, titanium, platinum, etc.) available in a manufacturing process (e.g., CMOS process). A pair of sensing elements and holes can be provided around the second heater to enhance the detection of fluid components. In Figure 14 the holes are symmetrically placed around the two heaters.

[0244] Figure 15 Schematically shows a top view of a sensor similar to the one shown in Figure 14 and having holes with an asymmetric arrangement within a dielectric film. Figure 15 Also shown are two heater arrangements having a similar range of heater arrangements as described in the embodiment shown in Figure 14 In this embodiment, the sensing elements 6a, 6b are parallel to the other heating element 8 due to the direction of the flow. Figure 15 An asymmetric design is proposed in

[0245] Figure 16 to increase the sensitivity to the detection of fluid components. When heater 8 is operated, 6a will be hotter than 6b, and the temperature difference between 6a and 6b will be proportional to the CO2 concentration. Assuming that heater 8 and sensing elements 6a and 6b are aligned with the flow, due to the flow rate, the temperature difference between 6a and 6b will be significantly less than the temperature difference between 6a and 6b in those structures where heater 8, sensing elements 6a and 6b are placed perpendicular to the direction of the flow. In this regard, this particular design provides high sensitivity to the composition of the flow and is capable of more effectively distinguishing temperature changes caused by the flow or the concentration of fluid components with different thermal conductivities.

[0245] Figure 16 Schematically shows a top view of a sensor according to an alternative embodiment of the present disclosure having thermopiles placed upstream and downstream of a heating element. Figure 16Shows a symmetric design with a heater 3 and two holes 7a and 7b. Thermopiles 9a and 9b are placed upstream and downstream in the flow direction. A thermopile is a relative temperature sensor that can sense the temperature difference between a hot junction and a cold junction without any external power source and convert the temperature difference into a voltage change. The hot junctions of 9a and 9b are placed closer to holes 7a and 7b respectively, while the cold junctions are placed outside the film above the semiconductor substrate. Thus, each thermopile measures the temperature difference between the dielectric film and the dielectric region above the semiconductor substrate. Assuming that the cold junctions will remain at the same temperature, the differential voltage signal between the hot junctions of thermopiles 9b and 9a depends on the thermal conductivity of the fluid.

[0246] Each of the thermopiles shown includes one or more thermocouples connected in series. Each thermocouple is formed by bonding two different materials (e.g., two metals, two semiconductors, one metal and one semiconductor) together. The thermocouple material can include metals such as aluminum, tungsten, titanium, or a combination thereof, or any other metal available in the process. Optionally, the thermocouple material can include thermocouples based on n-type and p-type silicon, or polysilicon, or a combination of metal and semiconductor. The voltage across the thermopile is proportional to the temperature difference between the hot and cold junctions, the Seebeck coefficient of the thermocouple, and the number of thermocouples connected in series.

[0247] Figure 17 Schematically shows a top view of a sensor similar to that shown in Figure 16 and having a single hole upstream of the heating element. Figure 17 Shows an asymmetric design with only one hole 7a placed upstream in the flow direction. The temperature of the hot junction of 9a will be lower than the temperature of the hot junction of 9b. This imbalance will increase as the concentration of the fluid component with a lower thermal conductivity (e.g., the concentration of CO2 in air) increases. Compared with the symmetric design shown in Figure 16 , this arrangement provides higher sensitivity to the composition of the convection.

[0248] Figure 18 Schematically shows a top view of a sensor according to an alternative embodiment of the present disclosure having a circular film and a heater, hole, and thermopile of a corresponding arcuate shape, and Figure 19 Schematically shows a top view of a sensor similar to that shown in Figure 18 and having symmetrically arranged holes.

[0249] Figure 18 and Figure 19Asymmetric and symmetric devices are shown respectively having a circular membrane and corresponding matching shaped heaters 10, holes 7a and 7b, and thermopiles 9a and 9b. The heater 10 is a micro hotplate, and in this case, the heater 10 is powered through the metal tracks 5. The advantage of these arrangements is better use of the membrane area and higher thermal performance, but their design is more complex than Figure 16 and Figure 17 the designs shown in

[0250] Figure 20 A top view of a sensor having four holes and four thermopiles according to an alternative embodiment of the present disclosure is schematically shown; and Figure 21 A top view of a sensor similar to the sensor shown in Figure 20 and having asymmetrically arranged holes is schematically shown.

[0251] Figure 20 and 21 (respectively) show different symmetric and asymmetric designs using four holes and four thermopiles. By using the differential signal and the total signal between different thermopile groups, the performance of the flow (such as flow rate or velocity) and the composition components of the flow can be distinguished based on the difference in thermal conductivity between different components of the flow. For example, referring to the embodiment in Figure 21 , assuming that the temperatures of the cold junctions of all thermopiles are the same, then T9a + T9c - (T9b + T9d) can obtain the performance of the flow, while T9c + T9b - (T9a + T9d) can obtain a signal based on the thermal conductivity of different components of the fluid. T9x represents the temperature of the hot junction of the 9x thermopile. It should be noted that the signal is measured as a voltage difference and depends on the Seebeck coefficient and the number of thermocouples connected in series in each thermopile.

[0252] To minimize the influence caused by different cold junction temperatures, the cold junctions of all thermopiles shown in Figures 15 to 21 can be electrically or thermally connected together by metallization on the outer side or the edge of the membrane. The cold junctions of all these thermopiles can be grounded and used as a reference potential.

[0253] Figure 22 A top view of a sensor having a thermopile placed across the heating element according to an alternative embodiment of the present disclosure is schematically shown. Figure 22Another embodiment is shown in which the thermopile 9 is placed symmetrically around / across the heater 3. Here, the heater is shown as a hot wire placed perpendicular to the direction of the flow. The hot junctions 91 of the thermopile can be on one side of the heater 3, and the cold junctions 92 can be on the other side of the heater, both at a position within the membrane 4 at a certain distance from the edge of the membrane. The holes 7a and 7b can be placed symmetrically within the membrane in the space between the thermopile and the edge of the membrane. The thermopile measures the temperature difference across the heating element. The voltage difference (proportional to the temperature difference) between the hot junction 91 and the cold junction 92 represents the performance of the flow. The temperature of the heater 3 can be adjusted, and the thermopile voltage (the voltage drop between the hot junction 91 and the cold junction 92) can be evaluated relative to calibrated data to indicate the composition of the flow. This can also be related to the measured value of the resistance of the heater 3.

[0254] Figure 23 A top view schematically shows a sensor similar to that shown in Figure 22 and having a single hole downstream of the heating element. Figure 23 Shows a structure similar to that shown in Figure 22 except that the holes are placed asymmetrically. Here, a single hole is shown in the downstream position.

[0255] This helps to enhance the sensitivity / selectivity to different components of the convection. If there is a higher concentration of CO2, the hot junction 91 will be hotter than, for example, when only normal air is present in the flow. The temperature of the heater 3 can be adjusted, and the thermopile voltage (the voltage drop between the hot junction 91 and the cold junction 92) can be used to distinguish the performance of the flow and the composition of the flow and / or enhance the sensitivity / selectivity to the composition of the flow (e.g., the concentration of CO2 or hydrogen in the air).

[0256] Figure 24 A top view schematically shows a sensor similar to that shown in Figure 22 and having two additional thermopiles. Figure 24 Shows a structure similar to that shown in Figure 23 and having two additional thermopiles (9a is the upstream thermopile and 9b is the downstream thermopile) placed on either side of the heater, with the cold junctions of both thermopiles placed outside the membrane. The operation of this embodiment is similar to that of Figure 7 . The first thermopile 9 can be used to measure the direction of the flow and the performance of the flow (such as the flow rate or velocity), while the voltage difference between the hot junctions of the upstream thermopile and the downstream thermopile can be used to measure the concentration of different components of the flow. Similar to Figure 23Compared with the prior designs in [reference], this design has more parameters to measure, but is also more complex and may generate additional heat loss through the thermopile itself.

[0257] Figure 25 A top view of a sensor having a thermopile and a resistance temperature detector according to an alternative embodiment of the present disclosure is schematically shown. Figure 25 It shows a combined design where the sensing element is a thermopile 9 and two resistance temperature detectors or diodes (one is an upstream resistance temperature detector or diode 6a and one is a downstream resistance temperature detector or diode 6b). Since the device does not have additional thermopiles for heat to dissipate through them, the heat loss of this device is lower than Figure 23 the device shown in [reference]. In addition, the asymmetric arrangement of the holes 7a and 7b helps to increase the sensitivity / selectivity of the convective components (in a manner similar to the effect described for the embodiment shown in FIG. 6).

[0258] Figure 26 A top view of a sensor having a second heating element perpendicular to the first heating element according to an alternative embodiment of the present disclosure is schematically shown. Figure 26 It shows a dual - heater design, where the first heater 3 is placed perpendicular to the direction of the flow, and the second heater 8 is placed in a direction aligned with the direction of the flow. These two heaters are not physically or electrically connected and can be made of different metal layers, for example. The thermopile 9 (also made of a layer different from heaters 3 and 8) can be placed symmetrically around or across the two heaters. The hot junction 91 can be placed on one side of the first heater 3, and the cold junction 92 can be placed on the other side of the first heater 3, at a position within the membrane at a certain distance from the edges of the heaters and the membrane. The heaters can be operated in a pulsed mode at different times. The first heater 3 perpendicular to the direction of the flow can be operated to sense the performance of the flow (such as flow rate, flow velocity, mass flow rate, or volume flow rate) by measuring the voltage drop across the thermopile, while when the heater 3 is turned off, the second heater 8 aligned with the flow can be operated to sense the composition of the flow by measuring the voltage drop across the thermopile. The temperature of the first heater 3 and / or the second heater 8 can be adjusted to improve the measurement accuracy and the sensitivity / selectivity to different components of the convection.

[0259] Figure 27 A top view of a sensor similar to Figure 26 the sensor shown in [reference] and having symmetrically arranged holes according to an alternative embodiment of the present disclosure is schematically shown. Figure 27Shows two heater designs with symmetrically designed holes (i.e., holes 7a and 7c upstream, and holes 7b and 7d downstream). Here, the holes are provided to reduce heat loss, reduce thermal mass, and enhance the sensitivity / selectivity of different components of convection.

[0260] Figure 28 Schematically shows a top view of a sensor similar to that shown in Figure 27 and having holes with an asymmetric arrangement downstream of the heating element. In Figure 28 , the holes (7b, 7d, 7m, and 7n) are placed asymmetrically (shown here in the downstream position) to provide a greater differential signal for the thermopile (compared to the design in Figure 27 ), thereby further enhancing the sensitivity / selectivity of different components of convection.

[0261] Figure 29 Schematically shows a top view of a sensor according to an alternative embodiment of the present disclosure having a flow mechanism 20 for controlling or generating a fluid flow. In Figure 29 , a flow forming device 20 (e.g., a micropump, a microfan, or an additional heater that generates a temperature gradient and flow through thermophoresis or thermal diffusion) is provided near the flow / heat conduction sensor to generate or manipulate the flow. The flow forming device 20 can also be a valve-type device. The valve-type device can be fully closed to put the system in a zero-flow state, can be partially closed to reduce the flow rate of the flow, or can be kept fully open without manipulating the flow. In the case where the valve-type device is fully closed, a pressure will be generated across the valve-type device such that when the valve-type device is opened, a flow will be generated with a flow rate proportional to the pressure generated across the valve-type device when it was closed. The device 20 can be used to enhance the signal / accuracy indicating the components present in the flow (based on the difference in thermal conductivity of different components of the flow enhanced by convection through the flow). For example, the flow can enhance the differential signal between the sensing elements 6b and 6a, thereby providing information about the components of the flow. The flow rate can be calibrated by evaluating the change in the resistance of the heater 3.

[0262] Figure 30 Schematically shows a cross-section of a sensor according to an alternative embodiment of the present disclosure having a flow heater for controlling or generating a temperature gradient. In Figure 30In [the figure], we show two additional heaters 21, 22, which can be in the form of MEMS micro hotplates and are placed within the channel and optionally formed within the manifold. The two additional heaters 21, 22 can electrically be in the form of coils wound around the flow channel. The flow heaters serve as flow mechanisms. Flow heaters 1 and 2 operate at different temperatures and create a controllable temperature gradient in the channel, thereby creating flow at the surface of the flow / heat conduction sensor. As in the previous case, the flow can enhance the differential signal between 6b and 6a, thereby providing information about the composition of the flow. The flow rate can be calibrated by evaluating the change in the resistance of heater 3.

[0263] Figure 29 and 30 The design shown in [the figure] is particularly useful in a no-flow or static environmental state. The no-flow state can be detected by a flow sensor or by using a device similar to the device in FIG. 10. To enhance the accuracy of detecting different components in the flow and their associated concentrations, the flow-forming device (as in Figure 29 [the figure]) or the flow heater (as in Figure 30 [the figure]) can be turned on. These devices can be used to more accurately sense the percentage / ppm of CO2 in static air. The temperature of heater 3 can also be adjusted to increase selectivity. To distinguish different components of the flow (e.g., air, hydrogen, methane, CO2), heater 3 can be energized to different temperatures, and the results can be evaluated relative to calibrated data or a look-up table stored in a storage device (on-chip device or external device).

[0264] Figure 31 Schematically shows a cross-section of a sensor with an integrated additional heater for controlling or generating a temperature gradient according to an alternative embodiment of the present disclosure. Figure 31 Shows the type of integrated micro hotplate with a specially designed heater that can be used to generate a temperature gradient, generate heat diffusion, and thus generate flow. Heater 11 can be energized to a high temperature (optionally higher than the temperature of the heater for sensor 3), thereby generating and manipulating the flow. The integrated micro hotplate using heater 11 can be monolithically integrated with the flow / heat conduction sensor, and similar elements can be used for the heater and the membrane. Membrane 12 can be adjacent to sensor membrane 4 (as shown), or a single membrane can be used for the two heaters (not shown). Flow can be generated within a predefined channel formed as part of a manifold or sensor housing.

[0265] Figure 32 Schematically shows a cross-section of a sensor with an ASIC placed below the sensor according to an alternative embodiment of the present disclosure. Figure 32Shows an arrangement in which the ASIC 13 is placed below the flow / heat conduction sensor (using stacked die technology). The ASIC can be used to drive the sensor, read out signals, and process signals. The ASIC can include analog blocks and digital blocks, such as:

[0266] Current and voltage drivers

[0267] Current mirrors

[0268] Voltage proportional to absolute temperature (VPTAT);

[0269] Current proportional to absolute temperature (IPTAT);

[0270] Switches, multiplexers, decoders, filters, amplifiers, analog-to-digital converters, timing blocks, RF communication circuits, memories, and / or

[0271] Means for driving and / or reading out from heating elements and / or temperature sensing elements; and / or

[0272] Means for electronically manipulating sensor signals; and / or

[0273] Means for enabling / disabling sensor elements.

[0274] In Figure 32 the die stack configuration shown, the ASIC is connected to the sensor via line 14 by using bond wires and pads on the sensor 15 and the ASIC 16.

[0275] Figure 33 Schematically shows a cross-section of a sensor having trenches or partial grooves in a dielectric film according to an alternative embodiment of the present disclosure. Figure 33 Shows a structure similar to the structure shown in FIG. 6, where the holes do not need to connect the top and bottom surfaces of the membrane. 7a and 7b are shown as trenches or partial grooves formed from the top surface into the membrane. 7a and 7b provide a similar function to the holes shown in other embodiments, and partial grooves can be used instead of holes in any embodiment.

[0276] In fact, in all embodiments, the discontinuity can refer to a gap (hole) in the membrane from the top surface to the bottom surface. The discontinuity can also refer to a trench formed from the top surface or the bottom surface (in the case of using an inverted membrane) and not penetrating the other surface, but this is not as effective in terms of thermal performance. The advantage of such local holes (trenches or partial grooves) is that they have less impact on the mechanical strength of the membrane, and in some cases they may be easier to fabricate. In addition, such local holes can be used to hermetically seal the bottom side of the membrane or prevent flow from penetrating below the membrane.

[0277] Figure 34 A sensor chip located within a flow sensor housing according to an alternative embodiment of the present disclosure is shown. Figure 34 A flow sensor chip within a flow sensor housing or a small chamber such as a manifold is shown. The housing includes a base 17 to which the chip is attached by an adhesive, a die attach, or solder. There is also an encapsulation wall 18 and a lid 19. The lid has an inlet and an outlet to communicate the flow. The base 17 and the wall 18 may be made of a PCB (printed circuit board) type material, while the lid 97 may be a molded plastic. Other materials based on epoxy resin, resin may also be used.

[0278] Those skilled in the art will understand that in the foregoing description and the appended claims, positional terms such as "above", "overlapping", "below", "lateral", etc. are described with reference to conceptual diagrams of the device (such as diagrams showing standard cross-sectional stereograms and diagrams shown in the drawings). These terms are used for ease of reference but are not intended to be limiting in nature. Thus, these terms should be understood to be with respect to the device in the orientation shown in the drawings.

[0279] Although the present disclosure has been described in accordance with the above preferred embodiments, it should be understood that these embodiments are illustrative only and the claims are not limited to these embodiments. Those skilled in the art will be able to make modifications and alternatives in accordance with the present disclosure, and these modifications and alternatives are considered to fall within the scope of the appended claims. Each feature disclosed or illustrated in this specification may be incorporated into the present disclosure individually or in any suitable combination with any other feature disclosed or illustrated herein.

Claims

1. A flow and heat conduction sensor, comprising: A semiconductor substrate, the semiconductor substrate including an etched portion; A dielectric region located on the semiconductor substrate, wherein the dielectric region includes at least one dielectric film located above the etched portion of the semiconductor substrate; A heating element located within the dielectric film; and A pair of temperature sensing elements located within the dielectric film and on opposite sides of the heating element; Wherein the dielectric film includes at least one groove region between the heating element and the edge of the dielectric film; A first region located between the heating element and a first temperature sensing element of the pair of temperature sensing elements; wherein the first region includes at least one groove region; A second region located between the heating element and a second temperature sensing element of the pair of temperature sensing elements; wherein the second region includes a continuous portion of the dielectric film between the heating element and the second temperature sensing element; and Wherein the at least one groove region is arranged asymmetrically with respect to an axis defined by the heating element, thereby introducing a temperature difference between the first temperature sensing element of the pair of temperature sensing elements and the second temperature sensing element of the pair of temperature sensing elements; wherein the differential signal between the pair of temperature sensing elements is configured to determine the properties, composition, or concentration of the fluid based on the thermal conductivity of the fluid.

2. The sensor according to claim 1, wherein, The heating element is configured to operate as a temperature sensing element.

3. The sensor according to claim 1, wherein, The at least one groove region includes one or more holes, or is made up of one or more holes.

4. The sensor according to claim 3, wherein At least one of the one or more holes includes an elongated slit extending towards an opposite edge of the dielectric film.

5. The sensor according to claim 3, wherein The one or more holes include an array of perforations.

6. The sensor according to claim 1 or 2, wherein At least one of the at least one groove region is partially recessed within the dielectric film.

7. The sensor according to claim 1, wherein, At least one of the pair of temperature sensing elements is configured to measure the temperature difference between the dielectric film and the dielectric region above the semiconductor substrate.

8. The sensor according to claim 1, wherein, At least one groove region is located between at least one of the pair of temperature sensing elements and the edge of the dielectric film.

9. The sensor according to claim 1, wherein, The pair of temperature sensing elements includes a resistance temperature detector, a diode, or a thermopile.

10. The sensor according to claim 1 or 2, wherein the pair of temperature sensing elements is a first pair of temperature sensing elements, and the sensor further includes another pair of temperature sensing elements, which is a second pair of temperature sensing elements, and Among them, The differential signal between the first pair of temperature sensing elements is configured to measure flow performance or pressure difference, and Wherein the differential signal between the second pair of temperature sensing elements is configured to measure the performance of the components of the flow.

11. The sensor according to claim 1 or 2, wherein, In use, the heating element extends in a direction perpendicular to the direction of the flow passing through the sensor.

12. The sensor according to claim 1, comprising other heating elements, and wherein, In use, the other heating element extends in a direction parallel to the direction of the flow passing through the sensor.

13. The sensor according to claim 1, including other heating elements placed towards the edge of the dielectric film, Among them, In use, the other heating element is maintained at a constant temperature during operation of the sensor, and wherein the constant temperature of the other heating element is higher than the ambient temperature and lower than the temperature of the heating element.

14. The sensor according to claim 12 or 13, further comprising another pair of temperature sensing elements configured to measure a differential signal across the other heating element.

15. The sensor according to claim 1 or 2, wherein, The dielectric film is circular or has rounded corners, and wherein the at least one groove region has an arcuate shape.

16. The sensor according to claim 1 or 2, wherein, The sensor is configured to be calibrated using any one of the following: A measured value in a zero flow state; One or more measured values at a known flow rate; A measured value at zero pressure difference; and / or One or more measured values at a known pressure difference.

17. The sensor according to claim 1 or 2, further comprising: A flow mechanism configured to provide or control flow through the sensor, and optionally wherein the flow mechanism includes at least one additional heater configured to create a temperature gradient across the sensor; and / or An application specific integrated circuit (ASIC) coupled to the sensor.

18. An influenza sensing device, comprising: A flow sensor housing; And The sensor according to claim 1 or 2 located within the flow sensor housing.

19. A method of manufacturing a sensor, the method comprising: Forming at least one dielectric film on a semiconductor substrate including an etched portion, wherein the dielectric film is over the region of the etched portion of the semiconductor substrate; Forming a heating element within the dielectric film; Forming a pair of temperature sensing elements located within the dielectric film and on opposite sides of the heating element; Forming at least one groove region within the dielectric film, the at least one groove region being located between the heating element and an edge of the dielectric film; Wherein the dielectric film includes: A first region between the heating element and a first temperature sensing element of the pair of temperature sensing elements; wherein the first region includes at least one groove region; A second region between the heating element and a second temperature sensing element of the pair of temperature sensing elements; wherein the second region includes a continuous portion of the dielectric film between the heating element and the second temperature sensing element; and Wherein the at least one groove region is arranged asymmetrically about an axis defined by the heating element so as to introduce a temperature difference between the first temperature sensing element of the pair of temperature sensing elements and the second temperature sensing element of the pair of temperature sensing elements; wherein a differential signal between the pair of temperature sensing elements is configured to determine a property, composition or concentration of the fluid based on the thermal conductivity of the fluid.

Images