Gas Sensors

Abstract

The invention shows a gas sensor 5 having a sensor element 10, a measuring chamber 15 and an emitter element 20. The sensor element 10 has a MEMS diaphragm 25 which is arranged in a first substrate region 40. The measuring chamber 15 is also designed to accommodate a measurement gas 50.

Description

[0001] This application is a divisional application of the invention patent application with application date of March 25, 2016, application number 201610174975.5 and invention name “Gas Sensor”. Technical Field

[0002] The present invention describes a gas sensor with a MEMS diaphragm. The embodiment shows a PAS (Photo Acoustic Sensor) module using a MEMS (Micro Electro Mechanical System) multi-die solution. Background Art

[0003] MEMS devices, also known as micro-electromechanical systems, are often used as sensors, such as acceleration sensors, pressure sensors or acoustic wave sensors (microphones). All these MEMS devices have a movable element, such as a diaphragm or a cantilever, wherein the movement of the movable element, for example due to pressure changes or acceleration, can be detected capacitively. Thus, a common variant of a MEMS device comprises a movable electrode as the movable element and a fixed electrode, which is opposite to the movable electrode, so that a change in the distance between the two electrodes (caused by the movement of the movable element) can lead to a change in capacitance.

[0004] Gas sensor systems to date utilize components with dimensions in the millimeter to centimeter range. As a result, components such as infrared emitters have a relatively large thermal mass, whereby high powers are required to operate the gas sensor. This makes the system sluggish and only allows very small duty cycles. Thus, the possibilities for fast calibration and fast measurements are limited. Summary of the invention

[0005] Therefore, there is a need to create an improved solution for a gas sensor.

[0006] This need is achieved by the subject matter of the independent claims. Developments according to the invention are defined in the dependent claims.

[0007] The exemplary embodiment shows a gas sensor, which comprises a sensor element, a measuring chamber and an emitter element. The sensor element has a MEMS diaphragm, wherein the MEMS diaphragm is arranged in a first substrate region. In addition, the measuring chamber is configured to accommodate a measurement gas. The emitter element is configured to emit electromagnetic radiation, wherein the electromagnetic radiation passes through a radiation path starting from the emitter element and having the measuring chamber. In addition, the emitter element and the sensor element are arranged fixedly to each other, i.e., for example, mechanically connected to each other.

[0008] For example, miniaturized gas sensors advantageously utilize a combination of components produced using MEMS technology. These components can be connected in a so-called wafer stack or substrate stack (wafer or substrate stack) and form emitters and sensors, which in turn can be connected to one another. The gas sensor can be, for example, a PAS sensor (photoacoustic sensor) that utilizes the photoacoustic effect.

[0009] The photoacoustic effect is a physical effect that utilizes photoacoustics. The effect describes the conversion of light energy into acoustic energy (sound). If a propagation medium, such as a gas, is irradiated with light, part of the light energy is absorbed (absorbed) by the medium and converted into heat energy. By heat conduction, this energy is distributed in the medium after a finite time and a minimum temperature rise occurs in the medium. By heat transport, in particular, an expansion of the volume occurs. If the medium is irradiated with a sequence of light flashes or, in general, with pulses of electromagnetic radiation, periodic heating and cooling result. This constant alternation of volume expansion and contraction is the source of sound. This can be structure-borne sound in solids or normal sound in gases.

[0010] Advantages result from the very small dimensions of the entire sensor system, which allows a very small thermal mass of the sensor system to be achieved. This reduces the power consumption and allows high switching speeds, which results in very high duty cycles and thus a long overall life. The higher switching speeds also result in shorter measurement cycles of the measurement, which allows a greater number of measurements to be performed within the same time. The gas sensor thus meets the highest quality requirements and has a prolonged life compared to conventional gas sensors.

[0011] The embodiment shows a gas sensor, which includes a sensor element, a measuring chamber and an emitter element. The sensor element has a MEMS diaphragm and a reference chamber, the reference chamber having a reference fluid therein, wherein the MEMS diaphragm is arranged in a first substrate region and the cavity of the reference chamber is arranged in a second substrate region. The first and second substrate regions are sealed and connected to each other. The measuring chamber is configured to accommodate a measuring gas. The emitter element is configured to emit electromagnetic radiation, wherein the electromagnetic radiation passes through a radiation path starting from the emitter element having a measuring chamber and a reference chamber, wherein the measuring chamber is spatially separated from the reference chamber by a layer transparent to electromagnetic radiation. In addition, the emitter element and the sensor element are mechanically connected to each other. An embodiment with a reference chamber and a reference gas present therein is advantageous because the pressure measurement is carried out in a closed and known reference volume, and thus a greater number of implementation options are available. The background is: the possibility of fully or partially selective variable adjustment of the MEMS diaphragm or the sensor element to the measuring gas or the avoidance of cross-sensitivity. In this way, if the reference gas is pure and there is no "interfering gas", the sensor element only reacts to the absorption wavelength of the reference gas. If interfering gases are present, cross-sensitivities may occur where the absorption wavelengths of the reference gas (or measurement gas) and the interfering gas overlap. Thus, for example, in the case of CO2 measurement, there is a cross-sensitivity to moisture at a wavelength of approximately 2.2 μm, since the absorption bands of carbon dioxide and water overlap there.

[0012] The exemplary embodiment shows that the MEMS diaphragm is designed to convert the energy of the electromagnetic radiation present in the reference chamber into an output signal. This conversion is performed, for example, in that the MEMS diaphragm is designed to have a deflection depending on the current energy of the electromagnetic radiation. This is advantageous because the electromagnetic radiation excites the reference fluid to increased oscillations, and thus the increased particle movement or increased pressure in the reference chamber can be measured by the MEMS diaphragm or a sensor formed using the MEMS diaphragm.

[0013] According to an embodiment, the emitter element is designed to emit electromagnetic radiation in a pulsed manner at a frequency of typically greater than 0.1 Hz or greater than 0.5 Hz or greater than 1 Hz. This is advantageous because an increased number of measurements can thus be performed in the same time. In addition, the measurement density is thus increased, for example in the case of continuous measurements, wherein changes in the measurement gas are thus detected more quickly in the measurement chamber.

[0014] In addition, an embodiment shows an emitter element comprising a first and a second substrate region, wherein the first substrate region has an emitter unit which is designed to emit electromagnetic radiation. The second substrate region has a cavity which is designed to minimize the thermal mass of the emitter element. This is advantageous because the already described fast switching times of the emitter element can thus be achieved. In addition, unnecessary heating of the sensor is reduced. A warming up of the sensor can lead to a faster degradation. A cooling device of the gas sensor for dissipating excess heat can thereby be dimensioned to be smaller or completely eliminated.

[0015] Furthermore, the sensor or the MEMS diaphragm is preferably outside the direct optical path of the electromagnetic radiation emitted by the emitter in order to reduce the heating of the MEMS diaphragm due to the direct electromagnetic radiation. A further embodiment shows a gas sensor with a shadow mask, which is arranged in the radiation path, wherein the shadow mask is designed to reduce the direct electromagnetic radiation of the emitter element onto the MEMS diaphragm. This is advantageous because degradation of the MEMS diaphragm is thereby delayed, since the MEMS diaphragm is exposed to a significantly smaller portion of the electromagnetic radiation. In addition, the pressure balance chamber located behind the MEMS diaphragm is heated by the electromagnetic radiation with less intensity, whereby the sensitivity or accuracy of the gas sensor is ensured over a prolonged period of time.

[0016] According to a further embodiment, the emitter element and the sensor element are arranged in a projection plane extending laterally to the emitter element and the sensor element. In this case, the emitter element and the sensor element are arranged in a housing which is designed to reflect electromagnetic radiation from the emitter element onto the sensor element. This arrangement is advantageous because an extremely flat gas sensor can be realized in this way. In this case, the measuring chamber of the gas sensor can be designed as a cavity in the housing. It is also advantageous if the first substrate region of the sensor element and the first substrate region of the emitter element are implemented on the same substrate and / or the second substrate region of the sensor element and the second substrate region of the emitter element are implemented on the same substrate. This is advantageous because the manufacturing steps involving the same substrate plane in the sensor element and in the emitter element can be implemented in one manufacturing step. The manufacturing of the gas sensor is thus simplified, thereby achieving an increase in productivity.

[0017] According to a further embodiment, the emitter element and the sensor element are arranged in a projection plane extending in the thickness direction to the emitter element and the sensor element, wherein the second substrate region of the sensor element is connected to the emitter element in a sealed and closed manner. This is advantageous because a minimum overall structural size of the gas sensor is achieved in this way. In this case, the cavity in the emitter element and / or the cavity between the emitter element and the sensor element can form a measuring chamber. If the measuring chamber is integrated in the emitter element, the gas sensor has a minimum height in the thickness direction. If the cavity is formed between the emitter element and the sensor element, the emitter element can be spatially separated from the measured gas, thereby avoiding a possible increased degradation of the sensor element due to the measured gas.

[0018] In addition, exemplary embodiments show gas sensors in which the contacts of the emitter element and the sensor element are led to a common substrate plane by means of through-substrate contacts (TSV, through-semiconductor vias) in the emitter element and the sensor element and are implemented on a main surface area of ​​the gas sensor accessible from the outside. This is advantageous because the contacts of the gas sensor are thus implemented only at one location of the gas sensor and the contacting is thus simplified.

[0019] In addition, an embodiment describes that the contacts of the emitter element and the sensor element are implemented laterally at the surface area of ​​the emitter element and the sensor unit, wherein the circuit board is arranged parallel to the thickness direction of the emitter element and the sensor element and contacts the contacts implemented laterally. This is advantageous because the sensor can be arranged on the circuit board, for example, without additional contact material and electrically connected to the circuit board.

[0020] According to a further embodiment, the emitter element has an emitter unit for emitting electromagnetic radiation, which emitter unit is an infrared emitter.

[0021] Further embodiments show gas sensors in which the MEMS membrane forms a micromechanical capacitive sensor. The micromechanical capacitive sensor is, for example, a microphone. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The preferred embodiments of the present application are described below with reference to the accompanying drawings.

[0023] Figure 1a shows a schematic side view of a gas sensor;

[0024] Figure 1b shows a schematic side view of a gas sensor having a reference chamber;

[0025] Figure 1c The emitter element and the sensor element are shown Figure 1aSchematic side views of gas sensors in different arrangements;

[0026] Figure 2a A schematic diagram showing an emitter element and a sensor element used in a gas sensor is shown in cross-section;

[0027] Figure 2b shows a schematic diagram of an emitter element and a sensor element used in a gas sensor according to an embodiment having a reference chamber;

[0028] Figure 2c A schematic diagram showing an emitter element and a sensor element used in a gas sensor according to another embodiment;

[0029] Figure 2d shows a schematic diagram of an emitter element and a sensor element in an alternative embodiment with a reference chamber;

[0030] Figure 2e shows a schematic diagram of an emitter element with a perforated counter electrode at the top;

[0031] Figure 3 shows a schematic diagram of a gas sensor in a housing, wherein an emitter element and a sensor element are arranged side by side;

[0032] Figure 4a shows a schematic diagram of a gas sensor according to one embodiment, wherein an emitter element and a sensor element are stacked in a thickness direction;

[0033] Figure 4b shows a schematic diagram of a gas sensor according to an embodiment with a reference chamber, wherein emitter elements and sensor elements are stacked in the thickness direction;

[0034] Figure 4c Shown with Figure 4b Schematic diagram of a gas sensor with a reference chamber in various embodiments;

[0035] Figure 5a shows a schematic diagram of a gas sensor according to an embodiment with exemplary contacts of the gas sensor;

[0036] Figure 5b shows a schematic diagram of a gas sensor according to an embodiment having a reference chamber and exemplary contacts of the gas sensor;

[0037] Figure 5c shows a schematic diagram of a gas sensor according to various embodiments having a reference chamber and exemplary contacts of the gas sensor;

[0038] Figure 5dA schematic diagram of a gas sensor according to an embodiment with different contacts of the gas sensor is shown. DETAILED DESCRIPTION

[0039] In the following description of the figures, identical or identically acting elements are provided with the same reference numerals, so that their description in different exemplary embodiments is interchangeable with one another.

[0040] Figure 1a A gas sensor 5 is shown, which has a sensor element 10, a measuring chamber 15 and an emitter element 20. The sensor element 10 has a MEMS diaphragm 25, which is arranged in a first substrate region 40. The measuring chamber 15 is designed to accommodate a measurement gas 50. In addition, according to one embodiment, the sensor element 10 and the emitter element 20 can have a sealed connection, so that a sealed measuring chamber 15 is formed. This can extend the service life of the emitter element 20 or the entire gas sensor, because it is operated in a protective atmosphere. The same effect can also be achieved by a housing surrounding the gas sensor. The MEMS diaphragm forms, for example, a micromechanical capacitive sensor, such as a microphone. The micromechanical capacitive sensor is designed to capacitively measure the deflection of the MEMS diaphragm relative to a counter electrode (not shown).

[0041] in addition, Figure 1a An emitter element 20, for example an infrared emitter, is shown, which can be implemented as a MEMS element, which is designed to emit electromagnetic radiation 55. The electromagnetic radiation 55 passes through a radiation path 60, which, starting from the emitter element 20, has a measuring chamber 15. In addition, the emitter element 20 and the sensor element 10 are mechanically connected to each other. A hermetically sealed connection is optional, since enclosing the measurement gas in a volume, for example, can also be achieved by Figure 3 The housing shown is implemented. In addition, there is also an embodiment in which the enclosure of the measuring gas is optional. If the measuring gas is not present in the closed volume, it is advantageous to implement the measuring gas or the measuring volume as an acoustic high pass so that the photoacoustic signal of the measuring gas acts on the MEMS diaphragm and avoids scattering into the free space. Therefore, the acoustic high pass makes it possible to perform continuous measurements when the measuring gas is in the free space. In other words, when the sensor element is implemented as a high pass, pressure changes can be measured in the case of a non-enclosed volume or reference volume of the detector. Therefore, continuous measurement can be achieved, for example, using a closed detector or by configuring the detector as a high pass. The described embodiment is a gas sensor that can be constructed very small, because the gas sensor is not implemented in the embodiment with a reference chamber described below.

[0042] Improved measurement results can be achieved by isolating the thermal transition from the emitter element 20 via the measuring gas 50. In other words, it may be advantageous to avoid the influence of the temperature increase of the measuring gas 50 or the pressure change caused by the temperature increase of the measuring gas on the MEMS diaphragm. This can be achieved by sealing the emitter element or the sensor element. If the emitter element or the emitter is embodied as a closed structure, a vacuum or an inert protective gas can be arranged between the emitter units, such as heating wires, which enable infrared radiation of the emitter element to the measuring gas, but prevent or at least reduce the heat propagation. If the sensor element is embodied as a closed structure and the emitter element 20 is present in an open form, the measuring gas heats up, but the pressure change does not act on the MEMS diaphragm. In both cases, the photoacoustic signal can be measured without the superposition of the expansion of the measuring gas caused by the temperature increase. It is also possible to seal the emitter element and the sensor element in a sealed manner.

[0043] The combination of emitter elements and sensor elements can be generalized according to the concept of a multi-wafer concept. This enables any combination of closed and open elements, which form open or closed emitter elements or sensor elements, respectively. It is also possible to optionally implement the measuring chamber in a closed volume. The combination of elements can be arbitrary. In addition, the emitter elements and / or the sensor elements themselves can be composed of layers of different substrate elements or wafers. Figure 2a -e to describe.

[0044] Figure 1b A gas sensor 5 is shown, which has a sensor element 10, a measuring chamber 15 and an emitter element 20. The sensor element 10 has a MEMS diaphragm 25 and a reference chamber 30, which has a reference fluid 35 located therein. The MEMS diaphragm 25 is arranged in a first substrate region 40, and the cavity of the reference chamber 30 is arranged in a second substrate region 45. The measuring chamber 15 is designed to accommodate a measuring gas 50. In addition, the first and second substrate regions 40, 45 forming the sensor element 10 are sealed and connected to each other. In addition, according to one embodiment, the sensor element 10 and the emitter element 20 can also have a sealed connection, so that a sealed measuring chamber 15 is formed. This can extend the life of the emitter element 20.

[0045] in addition, Figure 1bAn emitter element 20 is shown, which is designed to emit electromagnetic radiation 55. The electromagnetic radiation 55 passes through a radiation path 60 which, starting from the emitter element 20, has a measuring chamber 15 and a reference chamber 30. In order to separate the measuring gas and the reference fluid from one another spatially, a layer 65 permeable to the electromagnetic radiation 55 is arranged between the reference chamber 30 and the measuring chamber 15. In addition, the emitter element 20 and the sensor element 10 are mechanically connected to one another.

[0046] The reference fluid is, for example, a gas mixture comprising the gas to be detected, such as CO2 (carbon dioxide), CO (carbon monoxide), NO x (nitrogen oxide) and the like, and optionally includes a buffer gas. The buffer gas serves as another reference gas, for example, by expanding the selectivity of the reference cell to a gas mixture or another gas. In this way, one or more other gases can be present in the reference chamber in addition to the gas to be detected, so that the gas sensor reacts sensitively to the measurement gas including the gas present in the reference gas. In addition, moisture can be introduced into the reference chamber to determine the moisture content of the measurement gas. In other words, it serves as an element for modifying or optimizing the transmission section, wherein the transmission section has the following steps. Starting from the temperature or electromagnetic radiation of the emitter element 20, a pressure change is generated in the reference chamber 30, wherein the pressure change depends on the absorption of the electromagnetic radiation by the measurement gas (for example, inversely proportional). The pressure change in the reference chamber can be measured by the deflection of the diaphragm in the sensor 10. In addition, the sensitivity of the gas sensor 5 or the sensor element 10 can be adjusted by the buffer gas, so that the desired sensitivity can be achieved, for example, by reducing or increasing the buffer gas portion in the case of an expected oversteering or understeering of the MEMS diaphragm.

[0047] The embodiment shows a MEMS membrane 25 which is designed to convert the energy of electromagnetic radiation present in a reference chamber 30 into an output signal. The output signal can be generated based on a deflection that depends on the current energy of the electromagnetic radiation. Thus, the MEMS membrane can form, for example, a micromechanical capacitive sensor, such as a microphone. The micromechanical capacitive sensor is designed to measure, for example, capacitively, a deflection of the MEMS membrane relative to a counter electrode (not shown).

[0048] Figure 1c A schematic diagram of a device having an emitter element and a sensor element is shown. Figure 1a Schematic diagrams of different arrangements of gas sensors 5 . Figure 1bThe arrangement of the emitter element 20 and the sensor element 10 along a projection line extending laterally through the emitter element and the sensor element is shown. In this case, the emitter element 20 and the sensor element 10 are connected to one another at a main surface area extending laterally. According to one embodiment, a radiation path 60 of the electromagnetic radiation 55 extends through the measurement gas 50 adjoining the emitter element 20 and the sensor element 10. The bending or deflection of the electromagnetic radiation 55 from the main surface area 75 of the emitter element, where the electromagnetic radiation is emitted, to the main surface area 80 of the sensor element, where the electromagnetic radiation enters the sensor element, is performed, for example, by a reflective element (not shown), such as the inner side of the housing, which has a reflective effect on the electromagnetic radiation 55. Figure 3 An embodiment of this arrangement is shown.

[0049] Figure 2a A schematic diagram of an emitter element 20 and a sensor element 10 for use in a gas sensor according to an embodiment is shown. The sensor element 10 can also have a third substrate region 85 in addition to the first substrate region and the second substrate region 45, which in the embodiment shown here is a closing element of the sensor element 10. Similar to the sensor element, the emitter element can also have a first substrate region 90 and a second substrate region 95, wherein the first substrate region 90 has an emitter unit 100, which is designed to emit electromagnetic radiation 55. The emitter unit 100 is, for example, an infrared emitter (IR emitter), which can be realized by a meandering arrangement of the heating wire. The second substrate region 95 of the emitter element has a cavity 105, which is designed to minimize the thermal mass of the emitter element. According to further embodiments, the second substrate region 95 of the emitter element can have a material that is transparent to the electromagnetic radiation 55 in addition to or instead of the cavity 105. In addition, the emitter element 20 also has a third substrate region 110, which forms a closing element of the emitter element. It should also be noted that with regard to Figure 2b -d The described embodiments can also be applied to Figure 2a .

[0050] According to this arrangement, the emitter element 20 may form a black body emitter (or Planckian emitter).An ideal black body emitter completely absorbs incident electromagnetic radiation of any wavelength and re-emits the absorbed energy as electromagnetic radiation having a characteristic spectrum that depends only on temperature.

[0051] Figure 2bA schematic diagram of an emitter element 20 and a sensor element 10 for use in a gas sensor according to an embodiment is shown. The sensor element 10 can also have a third substrate region 85 in addition to the first substrate region and the second substrate region 45, which in the embodiment shown here is a closing element of the sensor element 10. Similar to the sensor element, the emitter element can also have a first substrate region 90 and a second substrate region 95, wherein the first substrate region 90 has an emitter unit 100, which is designed to emit electromagnetic radiation 55. The emitter unit 100 is, for example, an infrared emitter (IR emitter), which can be realized by a meandering arrangement of the heating wire. The second substrate region 95 of the emitter element has a cavity 105, which is designed to minimize the thermal mass of the emitter element. According to further embodiments, the second substrate region 95 of the emitter element can have a material that is transparent to electromagnetic radiation 55 in addition to or instead of the cavity 105. In addition, the emitter element 20 also has a third substrate region 110, which forms a closing element of the emitter element.

[0052] According to this arrangement, the emitter element 20 may form a black body emitter (or Planckian emitter).An ideal black body emitter completely absorbs incident electromagnetic radiation of any wavelength and re-emits the absorbed energy as electromagnetic radiation having a characteristic spectrum that depends only on temperature.

[0053] According to an embodiment, the second substrate region 95 of the emitter element may also have an electromagnetic radiation-permeable layer 115 similar to the electromagnetic radiation-permeable layer 65 of the second substrate region of the sensor element, wherein Figure 4b , an embodiment in which layers 65 and 115 form a measuring chamber is shown. Layer 115 may also optionally have an opening 120. Opening 120 may enable a reference fluid to enter cavity 105, so that the absorption path of the temperature radiation emitted from the emitter element is extended. In addition, cavities are optionally formed in the first and third substrate regions of the emitter element, which are respectively configured to reduce the thermal mass of the sensor element and to form a cavity 125 for realizing a black body emitter. Optionally, cavity 125 and 105 are filled with a buffer gas, which is configured to minimize degradation of the emitter unit and / or improve the quality of the emitter element. In this embodiment, it is advantageous to configure layer 115 without opening 120 in order to separate the buffer gas from the measurement gas.

[0054] Optionally, a shadow mask 130 is also arranged in the radiation path 60 (not shown here), which is designed to reduce the direct electromagnetic radiation of the radiator element to the MEMS membrane 25. However, the shadow mask allows electromagnetic radiation to enter the reference chamber. For this purpose, the shadow mask, for example, only covers a part of the electromagnetic radiation-transmissive layer of the sensor element, or it is Figure 2e The embodiment described in the figure can be arranged in front of the MEMS membrane in the reference chamber. In other words, the optional shadow mask does not shade the reference chamber 30, but only the membrane 25. For this purpose, the layer 65, which is transparent to electromagnetic radiation, for example a glass sheet, is advantageously coated or blackened in the region of a projection line extending in the thickness direction to the membrane 25. As a result, the electromagnetic radiation 55 can excite the reference fluid in the reference chamber 30 via the region bordering the shadowing membrane 130, but the direct electromagnetic radiation onto the MEMS membrane 25 is significantly reduced. As a result, the MEMS membrane is heated significantly less, thereby reducing wear or fault signals due to heating and reducing the deflection of the same membrane caused by this (comparable to the effect in the case of bimetallic materials).

[0055] The shadow mask 130 also reduces the heating of the pressure balance chamber 135. The pressure balance chamber 135 is connected to the reference chamber 30 via an opening 140 in the MEMS diaphragm 25. A slow gas exchange between the reference chamber and the pressure balance chamber takes place via the opening, so that pressure changes in the reference chamber and the pressure balance chamber are balanced over a longer period of time and thus prestressing of the MEMS diaphragm 25 over changes over a longer period of time is avoided. Rapid pressure changes cannot be balanced via the opening 140, so that the MEMS diaphragm 25 or the sensor element 10 can measure these rapid changes. It should be noted that the shadow mask 130 is optional in all the illustrated embodiments, even if it is drawn in the associated figures.

[0056] The substrate regions of the sensor element and the emitter element can advantageously comprise silicon. Thus, in the manufacturing method, the same substrate region of the sensor element and the emitter element can be realized in a common MEMS manufacturing method. The separately manufactured substrate regions are stacked according to the embodiment and arranged to form a wafer stack or substrate stack (wafer stack or substrate stack). In order to fix the substrate regions, these substrate regions can be connected to each other, for example, by means of anodic bonding or glass frit bonding (English: Glass frit bonding), so that a connection element depending on the method is formed between the substrate regions (e.g. wafers). The second substrate region (top layer) of the sensor element 45 or the emitter element 95, or the first substrate region (bottom layer) of the sensor element 85 or the emitter element 110 can also be constructed as a glass wafer or have a glass part, for example in the form of a window.

[0057] In the illustrated arrangement, the sensor element 10 and the emitter element 20 can be operated laterally side by side in a housing, for example as a pressure sensor (see Figure 3 ) or alternatively separated by sawing marks 145.

[0058] Figure 2c Shown in Figure 2b The embodiment described in Figure 2b A spacer 160 is added. If the sensor element 10 and the emitter element 20 are assembled as shown in FIG. 4 , a measuring chamber can be formed between the spacers. In the exemplary embodiment shown, the emitter element and the MEMS diaphragm are closed and not in contact with the measurement gas. In addition to the arrangement of the spacer on the sensor element shown here, a spacer can also be arranged on the emitter element. In addition, Figure 2c A closed layer 115 is shown, that is to say the layer 115 has no openings 120. The measuring gas therefore does not come into contact with the emitter 110. Furthermore, a protective gas may be introduced into the cavities 105 and / or 125 in order to reduce degradation of the emitter.

[0059] Figure 2d Shown according to Figure 2b Schematic diagram of a sensor element 10 and an emitter element 20 of different embodiments. This embodiment shows a second substrate region 45, 95 of a sensor element and an emitter element, for example, comprising glass or silicon dioxide (SiO2). This can be a structured glass wafer. The glass wafer can also be connected to the substrate region below it at the substrate region 40 or 90 by means of anodic bonding. In addition, the cavity 105 can be at least part of a measurement chamber 15 in this embodiment, into which the measurement gas to be measured can be introduced. The measurement chamber 15 is therefore at least partially located in the emitter element 20.

[0060] Figure 2e A schematic diagram of a sensor element 10 and an emitter element 20 is shown in cross section. This exemplary embodiment shows an unsealed emitter element 20 and a sealed sensor element 10. In order to seal the sensor element 10 in a gas-tight manner, an infrared window 65 can be arranged above the second substrate region 45 of the sensor element. The infrared window can be connected to the first substrate region 40 by means of anodic bonding or other suitable methods as already described. In addition, the sensor element has a perforated counter-electrode 180 located on the top. The counter-electrode 180 can include polysilicon, metal, a layer composed of a dielectric, such as SiN (silicon nitride) and metal, or a combination of the materials. Here, preferably a material that reflects infrared radiation (such as metal) can be used. This can be achieved by a metallized perforated counter-electrode. The counter-electrode 180 forms a functional counterpart to the MEMS diaphragm in order to form a micromechanical capacitive sensor, such as a microphone. In addition, the counter-electrode 180 is implemented as a perforated in the illustrated exemplary embodiment and thus simultaneously performs the task of a shadow mask. The smaller the perforation is implemented, the better the shielding of the MEMS diaphragm 25. The counter electrode can be fastened to a holding structure 175 which comprises an oxide, for example.

[0061] Alternatively, it is also possible to seal only the emitter element or the emitter in a gas-tight manner. The sensor element remains open. In this way, a heating of the measurement gas can be avoided, for example, by surrounding the emitter element, for example a heating wire, so that only the emitted infrared radiation is incident on the measurement gas and generates there a photoacoustic signal that can be measured by the sensor element. Thus, an expansion of the measurement gas due to a heating that is transmitted to the MEMS diaphragm and superimposed on the photoacoustic signal is avoided.

[0062] Figure 3 The schematic diagram shows the emitter element and the sensor element in the housing 150. Figure 2d The housing 150 has an inlet and an outlet 155a, b for the measuring gas 50, through which the measuring gas can enter the housing 50. The housing 150 is, for example, an SMD (Surface Mounted Device, German: Surface Mount Device) housing. In addition, the housing 150 has a main surface area on the side facing the sensor element and the emitter element, which is designed to reflect electromagnetic radiation 55 from the emitter element 20 onto the sensor element 10.

[0063] Figure 4a A schematic diagram of a gas sensor according to an embodiment is shown, in which an emitter element and a sensor element are stacked in a thickness direction. The gas sensor is based on the emitter element and the sensor element. Figure 2a In order to obtain Figure 4a The embodiment shown in Figure 2a The sawing mark 145 shown in the figure separates the sensor element from the emitter element and stacks them at the main surface area of ​​the second substrate area located outside. A spacer 160 can preferably be arranged between the sensor element and the emitter element, which forms a measuring chamber 15 between the sensor element and the emitter element. The spacer 160 can be, for example, a connecting element generated by connecting the adjacent substrate areas. In addition, the spacer can include a semiconductor material (for example silicon) or glass. Through the opening in the spacer 160, the measuring gas can be introduced into the measuring chamber. The further embodiments described with respect to the following figures can also be applied analogously to the embodiments shown here, taking into account the absence of a reference chamber.

[0064] Figure 4b A schematic diagram of a gas sensor according to an embodiment is shown, in which an emitter element and a sensor element are stacked in a thickness direction. The gas sensor is based on the emitter element and the sensor element. Figure 2b In order to obtain Figure 4b The embodiment shown in Figure 2bThe sawing mark 145 shown in the figure separates the sensor element from the emitter element and stacks them at the outer main surface area of ​​the respective second substrate area. A spacer 160 can preferably be arranged between the sensor element and the emitter element, which forms a measuring chamber 15 between the sensor element and the emitter element. The spacer 160 can be, for example, a connecting element generated by connecting the adjacent substrate areas. In addition, the spacer can include a semiconductor material (for example silicon) or glass. Through the opening in the spacer 160, the measuring gas can be introduced into the measuring chamber.

[0065] As already described, the sensor element and the emitter element can be connected together with the spacer, for example by means of anodic bonding or other bonding methods, and the spacer itself can also be implemented by a suitable bonding material, for example a bonding layer, in the case of a bonding method using an intermediate layer as used, for example, in eutectic bonding, frit bonding or adhesive bonding. These arrangements are advantageous because the measuring gas 50 (not shown here) is neither in contact with the emitter element nor with the sensor element in the measuring chamber 15, but is present between the sensor element and the emitter element in a defined area delimited by the spacer 160 and the layers 65 and 115 permeable to electromagnetic radiation. Potential contamination or accelerated degradation of the sensor element and the emitter element caused by the measuring gas is thus avoided. In other words, the sensor element and the emitter element themselves are closed or sealed.

[0066] The exemplary embodiment shows a gas sensor that is sensitive to carbon dioxide (CO2). The carbon dioxide concentration in the measurement gas can have, for example, 1000 ppm (parts per million, German: parts per million). In the reference chamber and the pressure balance chamber 30, 135, a reference fluid can be present, which comprises, for example, 50 to 100% carbon dioxide and optionally a buffer gas portion. Optionally, a buffer gas filling can also be present in the cavity 125. If a buffer gas is present adjacent to the emitter unit, i.e. in the cavity 105 or 125, it can act as an inert protective gas, i.e. slow down the degradation of the emitter. Nitrogen, argon or other heavy gases can act as protective gases, which prevent or at least slow down surface changes that are caused, for example, by a large amount of heating of the emitter.

[0067] Alternatively or in addition, the buffer gas at the emitter can also be used to filter the output radiation in order to (further) limit the bandwidth of the relatively broadband electromagnetic radiation of the emitter unit so that the narrowband electromagnetic radiation impinges on the measurement gas. The relatively broadband electromagnetic radiation at the emitter can have a bandwidth between 1 μm and 10 μm, wherein the filtered narrowband electromagnetic radiation has a bandwidth between 0.2 μm and 0.5 μm, for example. In order to obtain the measurement accuracy of the gas sensor, it is advantageous that the buffer gas does not contain the measurement gas to be determined. The filtering function can also be achieved by a suitable separation between the emitter and the measurement chamber. Thus, for example, the layer 115 that is permeable to electromagnetic radiation is configured as a filter element. This can be achieved by specially treating the glass sheet or using a Fabry-Perot filter.

[0068] If the buffer gas is present adjacent to the MEMS membrane 25 or in the reference chamber, the buffer gas can also fulfill the function of a protective gas for the MEMS membrane. Alternatively or additionally, the buffer gas can also contain the measurement gas to be determined, i.e., for example, the gas to be measured or the gas mixture to be measured, as a reference.

[0069] This exemplary embodiment shows an emitter element 20 and a sensor element 10 arranged in a projection plane which extends in the thickness direction towards the emitter element and the sensor element, wherein the second substrate region of the sensor element is connected to the emitter element in a sealed and closed manner. As already described, a spacer 160 can be introduced between the emitter element and the sensor element. The connection is advantageously carried out by means of anodic bonding or another suitable method for connecting substrate regions. For the electrical contacting of the emitter element and the sensor element, connection terminals of the sensor cell and the MEMS membrane can be implemented between the second and third substrate regions of the sensor element and the emitter element or between the first and second substrate regions, which connection terminals can be contacted, for example, via contact pads.

[0070] Figure 4c Shown based on Figure 2d Schematic diagram of a gas sensor 5 constructed of a sensor element 10 and an emitter element 20 of the embodiment shown in FIG. Figure 4b As described, the sensor element and the emitter element can be separated at the sawing marks so that the second substrate area of ​​the sensor element can be connected to the second substrate area of ​​the emitter element so that a gas sensor stacked in the thickness direction is produced, which comprises six substrate areas in the embodiment shown. The embodiment shown has a sealed microphone 25, while the measuring chamber is integrated into the emitter element and has direct contact with the emitter unit 100. This embodiment enables a minimal implementation of the gas sensor 5 in the x, y and z directions.

[0071] Figure 5a The results are shown based on the Figure 2a and 4a The embodiment shown in FIG. 1 is a schematic diagram of a gas sensor 5 according to an embodiment of the invention. The embodiment of the emitter element 20 differs from the embodiment described in that the first substrate region 90 is rotated 180° about an axis extending through the substrate region on the side. The emitter unit 100 can be arranged on the surface on the substrate region 90 and exposed from the back side by the opposite main surface region, for example by etching. Thus, the emitter element 20 can be operated on the back side. The same principle can also be applied to the MEMS membrane 25 in the first substrate region 40 of the sensor element, but this is not explicitly shown in the figure.

[0072] in addition, Figure 5a The contacting of the gas sensor 5 on a circuit board 165 (PCB) is shown, which is described in more detail according to the following figure. Other embodiments as described with respect to 5b-d can be applied to Figure 5a That way, according to Figure 5b The contacting of TSV 170 ′ described in is also possible.

[0073] Figure 5b Shown according to Figure 2b and Figure 4b The embodiment shown in FIG. 1 is a schematic diagram of a gas sensor 5 according to an embodiment of the invention. The embodiment of the emitter element 20 differs from the embodiment described in that the first substrate region 90 is rotated 180° about an axis extending through the substrate region on the side. The emitter unit 100 can be arranged on the surface on the substrate region 90 and exposed from the back side by the opposite main surface region, for example by etching. Thus, the emitter element 20 can be operated on the back side. The same principle can also be applied to the MEMS membrane 25 in the first substrate region 40 of the sensor element, but this is not explicitly shown in the figure.

[0074] in addition, Figure 5b The contacting of the gas sensor 5 on a circuit board 165 (PCB, Printed Circuit Board) is shown. Figure 5b 1 shows contacting by means of contact elements 170, for example by means of wires, which contact the outwardly embodied contacts of the gas sensor 5 with the printed conductors 165. For this purpose, it is advantageous if the substrate plane 40 of the sensor element has a larger diameter than the substrate region located above it, such as Figure 5bAs shown in . The contact structures of MEMS membrane 25 can thus be exposed at the main surface region of first substrate region 40 . The contacts of emitter unit 100 are likewise implemented at the main surface region and are connected to conductor tracks 165 via contact elements 170 .

[0075] Alternatively, the connection terminals of MEMS diaphragm 25 and emitter unit 100 can be guided to conductor tracks 165 , for example, by means of TSVs 170 ′ within the substrate region and contact-connected there.

[0076] It is also possible—but not shown—for example to route the connecting terminals of the emitter unit 100 onto the substrate plane of the MEMS membrane and to make contact there with the two contact elements 170 .

[0077] Figure 5c Shown Figure 2d and 4c The embodiment of is based on the embodiment of. Figure 5b As described in , emitter unit 100 is operated on the rear side. Furthermore, the etched cavity of substrate region 90 is designed as measuring chamber 15 . Figure 5c As already about Figure 5b As described, the contacting of the printed circuit board 165 by means of the contact element 170 is shown.

[0078] Figure 5d according to Figure 4c The embodiment of shows another contacting scheme. According to this embodiment, the contacts of the emitter element and the sensor element are implemented laterally at the main surface area of ​​the emitter element and the sensor unit. The laterally implemented contacts are directly in contact with the circuit board 165, which is arranged parallel to the thickness direction of the emitter element and the sensor element.

[0079] Although some aspects are described in conjunction with an apparatus, it is understood that these aspects may also represent a description of a corresponding method, so that a block or device of an apparatus may also be understood as a corresponding method step or a feature of a method step. Similarly, aspects described in conjunction with or as a method step may also represent a description of a corresponding block or detail or feature of a corresponding apparatus.

[0080] The above embodiments are merely illustrative of the principles of the present invention. It is readily understood that modifications and variations of the arrangements and details described herein will be apparent to other professionals. It is therefore intended that the present invention be limited only by the claims that follow and should not be limited by the specific details presented herein based on the description and illustration of the embodiments.

Claims

1. A gas sensor (5), comprising: A sensor element (10) comprising a MEMS diaphragm (25) and a reference chamber (30), wherein the MEMS diaphragm (25) is arranged in a first substrate region (40) of the sensor element (10) and the cavity of the reference chamber (30) is arranged in a second substrate region (45) of the sensor element (10); a measuring chamber (15) configured to contain a measuring gas (50); and An emitter element (20) is designed to emit electromagnetic radiation (55), wherein the electromagnetic radiation (55) passes from the emitter element (20) through a radiation path (60) which starts from the emitter element (20) and has a measuring chamber (15) and a reference chamber (30), and wherein the measuring chamber (15) is spatially separated from the reference chamber (30) by a layer (65) which is permeable to electromagnetic radiation (55), wherein the emitter element (20) comprises a first substrate region (90) and a second substrate region (95), wherein the first substrate region (90) of the emitter element (20) has an emitter unit (100) and the second substrate region (95) of the emitter element (20) has a cavity (105) which is designed to minimize the thermal mass of the emitter element (20); The gas sensor (5) comprises a stack composed of multiple layers of different substrates according to a multi-wafer solution, wherein the sensor element (10) is constructed as a substrate stack having multiple layers of different substrates, and the emitter element (20) is constructed as another substrate stack having multiple layers of different substrates; and the substrate stack of the sensor element (10) and the substrate stack of the emitter element (20) are arranged fixedly and laterally side by side with each other, so that the emitter element (20) and the sensor element (10) are arranged in a projection plane extending laterally to the emitter element (20) and the sensor element (10), wherein the emitter element and the sensor element are arranged in a housing (1). 50), the housing (150) is configured to reflect electromagnetic radiation (55) in the emitter element (20) onto the sensor element (10), and the cavity in the housing (150) forms the measuring chamber (15); or the substrate stack of the sensor element (10) and the substrate stack of the emitter element (20) are arranged in a stacked manner in the thickness direction, so that the emitter element (20) and the sensor element (10) are arranged in a projection plane extending in the thickness direction toward the emitter element and the sensor element, wherein the cavity (105) in the emitter element or the cavity between the emitter element (20) and the sensor element (10) forms the measuring chamber (15).

2. The gas sensor (5) according to claim 1, The reference chamber (30) has a reference fluid (35) located therein, wherein a first substrate region (40) and a second substrate region (45) of the sensor element (10) are sealed and connected to one another.

3. The gas sensor (5) according to claim 1 or 2, wherein the MEMS diaphragm (25) is designed to convert energy of the electromagnetic radiation (55) present in the reference chamber (30) into an output signal.

4. The gas sensor (5) according to claim 1 or 2, wherein the MEMS membrane (25) is designed to have a deflection depending on the current energy of the electromagnetic radiation (55). 5 . The gas sensor ( 5 ) according to claim 1 , wherein the emitter element ( 20 ) is designed to emit electromagnetic radiation ( 55 ) in a pulsed manner at a frequency of greater than 0.1 Hz. 6 . The gas sensor ( 5 ) according to claim 5 , wherein the emitter element ( 20 ) is designed to emit electromagnetic radiation ( 55 ) in a pulsed manner at a frequency of greater than 0.5 Hz. 7 . The gas sensor ( 5 ) according to claim 6 , wherein the emitter element ( 20 ) is designed to emit electromagnetic radiation ( 55 ) in a pulsed manner at a frequency of greater than 1 Hz.

8. The gas sensor (5) according to claim 1 or 2, wherein the emitter unit (100) is designed to emit electromagnetic radiation (55).

9. The gas sensor (5) according to claim 1 or 2, wherein the first substrate region (90) and the second substrate region (95) of the emitter element (20) are hermetically closed and connected to one another.

10. The gas sensor (5) according to claim 1 or 2, wherein a shadow mask (130) is arranged in the radiation path (60), wherein the shadow mask (130) is designed to reduce direct electromagnetic radiation of the emitter element (20) onto the MEMS diaphragm (25).

11. The gas sensor (5) according to claim 1 or 2, wherein the MEMS membrane is away from the direct optical path of the electromagnetic radiation so as to reduce direct electromagnetic radiation from the emitter element (20) to the MEMS membrane (25).

12. A gas sensor (5) according to claim 1 or 2, wherein the first substrate region (40) of the sensor element (10) and the first substrate region (90) of the emitter element (20) are implemented on the same substrate, and / or wherein the second substrate region (45) of the sensor element (10) and the second substrate region (95) of the emitter element (20) are implemented on the same substrate.

13. The gas sensor (5) according to claim 1 or 2, wherein the second substrate region (45) of the sensor element (10) is connected to the emitter element (20) in a hermetically sealed manner.

14. A gas sensor (5) according to claim 1 or 2, wherein the contacts of the emitter element and the sensor element are guided to a common substrate plane by means of through-substrate vias (TSVs) in the emitter element and the sensor element and are implemented on a main surface area of ​​the gas sensor accessible from the outside.

15. A gas sensor (5) according to claim 1 or 2, wherein the contact parts of the emitter element and the sensor element are implemented on the side at the surface area of ​​the emitter element and the sensor element, wherein the circuit board (165) is arranged parallel to the thickness direction of the emitter element and the sensor element and contacts the contact parts implemented on the side. 16 . The gas sensor ( 5 ) according to claim 1 , wherein the emitter element has an emitter unit ( 100 ) for emitting electromagnetic radiation ( 55 ), the emitter unit ( 100 ) being an infrared emitter.

17. The gas sensor (5) according to claim 1 or 2, wherein the MEMS membrane (25) forms a micromechanical capacitive sensor.

18. The gas sensor (5) according to claim 1 or 2, wherein the MEMS membrane (25) is designed as a microphone.

19. The gas sensor (5) according to claim 1 or 2, wherein the emitter element is designed as a microelectromechanical emitter.

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