Gas Sensors

Abstract

The present disclosure relates to gas sensors. According to one embodiment, a gas sensor includes: a substrate having a cavity, the cavity being used to provide an optical interaction path for interaction of filtered IR (IR=infrared) radiation having a central wavelength λ0 with a target gas in the cavity, wherein the cavity is for an ambient gas containing a target gas component; a thermal emitter arranged to emit broadband IR radiation, wherein the thermal emitter is optically coupled to the cavity; a wavelength selection structure arranged to filter the broadband IR radiation emitted by the thermal emitter and to provide filtered IR radiation having a central wavelength of λ0 in the cavity, wherein the wavelength selection element is optically coupled between the thermal emitter and the cavity, or wherein the wavelength selection element is formed as a bonding structure of the cavity; and an IR detector arranged to provide a detector output signal based on the signal strength of the filtered IR radiation that has passed through the optical interaction path in the cavity and is received by the IR detector.

Description

Technical Field

[0001] Embodiments relate generally to the field of sensor devices and more particularly to the field of gas sensors. In particular, embodiments relate to an integrated gas sensor, such as an integrated free-beam IR gas sensor (IR=infrared). Background Art

[0002] The detection of environmental parameters in the surrounding atmosphere is becoming increasingly important when implementing appropriate sensors, for example, in mobile devices, in home automation applications such as smart homes, and in, for example, the automotive industry. However, with the widespread use of sensors, there is also a particular need to be able to produce such sensors as cheaply as possible, thus being cost-effective. However, the resulting reliability and accuracy of the sensors should still be maintained or even improved.

[0003] In particular, the field of monitoring the air quality in our environment is gaining more and more attention. A typical optical sensor consists of a light source, a filter element for wavelength selection, a detector and a sample area where the light between the light source and the detector interacts with the ambient medium. Typically, such sensors are large and assembled from discrete subcomponents.

[0004] Generally, there is a need in the art for a method of achieving an improved gas sensor having reduced manufacturing requirements and providing sufficient sensitivity for a target gas to be detected by the sensor device.

[0005] This need can be solved by the gas sensor according to the present invention.

[0006] Furthermore, the specific implementation of the gas sensor is defined in the following. Summary of the invention

[0007] According to one embodiment, a gas sensor includes: a substrate having a cavity, the cavity being used to provide a gas having a central wavelength λ 0 The invention relates to a method for filtering the broadband IR radiation emitted by the thermal emitter and for providing a broadband IR radiation having a central wavelength λ in the cavity. 0 a wavelength selective structure for filtered IR radiation, wherein the wavelength selective element is optically coupled between the thermal emitter and the cavity, or wherein the wavelength selective element is formed as an incorporated structure of the cavity; and an IR detector arranged to provide a detector output signal based on the signal strength of the filtered IR radiation that has passed through the optical interaction path in the cavity and is received by the IR detector.

[0008] According to another embodiment, a gas sensor comprises: a substrate having a cavity for providing an optical interaction path for an IR (IR=infrared) radiation component to interact with a target gas in the cavity, wherein the cavity is accessible to an ambient gas including the target gas; a thermal emitter arranged to emit broadband IR radiation having an IR (IR=infrared) radiation component, wherein the thermal emitter is optically coupled to the cavity; an IR detector arranged to provide a detector output signal based on a signal strength of the IR radiation component that has passed through the optical interaction path in the cavity and is received by the IR detector; and a wavelength selective structure arranged to filter the broadband IR radiation emitted by the thermal emitter, wherein the wavelength selective element is optically coupled between the cavity and the IR detector for providing the IR detector with a wavelength having a central wavelength λ 0 The filtered IR radiation of the IR radiation component of . BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Embodiments of the present gas sensor are described herein with reference to the accompanying drawings.

[0010] Figure 1A shows a schematic cross-sectional view of an integrated gas sensor according to one embodiment;

[0011] Figure 1B shows a schematic cross-sectional view of a top wafer and a bottom wafer in a separated state (e.g., before bonding the two wafers);

[0012] Figure 2 shows a schematic cross-sectional view of an integrated gas sensor according to another embodiment;

[0013] Figure 3A shows a schematic cross-sectional view of an integrated gas sensor according to another embodiment;

[0014] Figure 3B shows a schematic cross-sectional view of a top wafer and a bottom wafer in a separated state (e.g., before bonding the two wafers);

[0015] Figure 4 shows a schematic cross-sectional view of an integrated gas sensor according to another embodiment;

[0016] Figure 5 shows a schematic cross-sectional view of an integrated gas sensor according to another embodiment;

[0017] Figure 6A-6F Schematic top views showing different possible implementations of the geometry of the cavity for providing an optical interaction path according to other embodiments;

[0018] Fig. 7A-B shows an enlarged schematic cross-sectional view of a deflection structure of an integrated gas sensor according to other embodiments;

[0019] Fig. 8A shows a schematic cross-sectional view of an integrated gas sensor according to another embodiment;

[0020] Figure 8B shows a schematic 3D view of an integrated gas sensor according to one embodiment and in particular the geometry of the cavity of the integrated gas sensor; and

[0021] Fig. 9A -I shows a schematic 3D view (schematic snapshot) of a method for manufacturing an integrated gas sensor according to one embodiment.

[0022] Before discussing the present embodiment in further detail using the drawings, it should be pointed out that in the drawings and the specification, the same elements and elements having the same functions and / or the same technical or physical effects generally have the same figure marks or are identified as the same names, so that the descriptions of these elements and their functions in different embodiments can be interchangeable or can be applied to each other in different embodiments. DETAILED DESCRIPTION

[0023] In the following description, embodiments will be discussed in detail, however, it should be understood that the embodiments provide many applicable concepts that can be embedded in a variety of semiconductor devices. The specific embodiments discussed are only illustrative of specific ways to manufacture and use the present concepts, and do not limit the scope of the embodiments. In the following description of the embodiments, the same or similar elements having the same functions are associated with the same reference numerals or names, and the description of these elements will not be repeated for each embodiment. Moreover, unless otherwise specifically noted, the features of the different embodiments described below may be combined with each other.

[0024] It should be understood that when an element is referred to as being "connected" or "coupled" to another element, it may be directly connected or coupled to the other element, or there may be intervening elements. Conversely, when an element is referred to as being directly "connected" or "coupled" to another element, there are no intervening elements. Other terms used to describe the relationship between elements should be interpreted in a similar manner (e.g., "between" versus "directly between," "adjacent" versus "directly adjacent," and "on" versus "directly on," etc.).

[0025] For the convenience of describing different embodiments, the drawings include a Cartesian coordinate system x, y, z, wherein the xy plane corresponds to (i.e., is parallel to) the first main surface region of the semiconductor substrate, and wherein the depth direction perpendicular to the first main surface region and into the semiconductor substrate corresponds to the "z" direction, i.e., is parallel to the z direction. In the following description, the term "lateral" refers to a direction parallel to the y direction, wherein the term "vertical" refers to a direction parallel to the z direction.

[0026] Figure 1A 1 shows a schematic cross-sectional view of an integrated gas sensor 100 for sensing the amount or concentration of a target gas component in an ambient gas or ambient gas mixture (eg, air) according to one embodiment. Figure 1A , the drawing plane is parallel to the xz plane.

[0027] The integrated gas sensor 100 includes a substrate 110 having a cavity 120 for providing a gas having a central wavelength λ 0 The interaction of the filtered IR (IR=infrared) radiation "R" of the integrated gas sensor 100 with the target gas in the cavity 120 provides an optical interaction path 120-1, wherein the cavity 120 is accessible to the ambient gas or ambient gas mixture including the target gas component. The integrated gas sensor 100 also includes a device arranged to emit broadband or incoherent IR radiation R 0 A thermal emitter 130 is provided, wherein the thermal emitter 130 is optically coupled to the cavity 120.

[0028] The integrated gas sensor 100 further comprises a filter arranged to filter the broadband IR radiation R emitted by the thermal emitter 130. 0 and is used to provide a central wavelength λ in the cavity 120 0 A wavelength selective structure 140 for filtering the filtered (= narrowband) IR radiation R.

[0029] According to one embodiment, the wavelength selection element 140 may be optically coupled between the thermal emitter 130 and the cavity 120. Thus, the wavelength selection element 140 may include, for example, an optical bandpass filter structure. According to another embodiment, the wavelength selection element 140 may be formed as a bonding structure of the cavity 120. Thus, for example, the wavelength selection element 140 may include a wavelength selection coating of the cavity 120 or a photonic crystal structure laterally surrounding the cavity 120. Furthermore, for example, the wavelength selection element 140 may include a combination of at least two of the following: an optical bandpass filter structure between the thermal emitter 130 and the cavity 120, a wavelength selection coating of the cavity 120, and a photonic crystal structure laterally surrounding the cavity 120.

[0030] The integrated gas sensor 100 further comprises an IR detector 150 arranged to provide a detector output signal S based on the signal strength of filtered IR radiation R that has passed through the optical interaction path 120-1 in the cavity 120 and is received by or incident upon the IR detector 150. OUT The IR detector 150 has a central wavelength λ 0 The device is sensitive to filtered IR (IR=infrared) radiation R.

[0031] The cavity 120 is arranged to provide a length l of the optical interaction path 120-1. 120-1 , length l 120-1 Significantly larger than the central wavelength λ of the filtered IR radiation R 0 (eg, at least 100 times as much). In addition, the portion of the cavity 120 that forms the optical interaction path 120-1 may be configured to guide a light having a central wavelength λ by standard reflection. 0 Filtered IR radiation R. In contrast to total internal reflection, standard reflection is used, which is a mechanism in waveguides. According to one embodiment, the inner sidewall portions 120-A...120-D of the cavity 120 may at least partially include a central wavelength λ 0 The filtered IR radiation R has a highly reflective coating.

[0032] In the interaction region 120-1, the target component absorbs the 0 The IR radiation R, which has a central wavelength λ 0 If the IR radiation R falls within the absorption spectrum of the target gas component, the degree of absorption depends on the concentration of the target gas component in the ambient gas or is a measure of it.

[0033] According to one embodiment, the substrate 110 may include at least one inlet hole or opening 160 leading to the cavity 120 to provide entry and / or exchange of ambient gas having a target gas component into the cavity 120. The at least one inlet hole 160 may include a plurality of inlet holes 160, or a perforation may be formed in the substrate 110.

[0034] like Figure 1A As shown, the optical interaction path 120-1 may extend parallel or substantially parallel to the bottom sidewall (= first major surface area) 120-A and the top sidewall (= second major surface area) 120-B of the cavity 120, so that the filtered IR radiation R is transmitted along or substantially along the lateral plane of the substrate 110 (parallel to Figure 1A The xy plane) is guided.

[0035] According to one embodiment, the bottom sidewall 120 -A and the top sidewall 120 -B of the cavity 120 may extend parallel to each other along the optical interaction path 120 - 1 to provide a substantially constant height h along the optical interaction path 120 . 120 The height h of the cavity 120 is 120 Can be larger than the central wavelength λ 0 , where h 120 >λ 0 , where h 120 The length l of the cavity 120 defining the interaction length in the gas is about 10 to 100 μm. 120 Can be absorbed by gas and used in CO 2 In the case of , it may correspond to an effective length of 1-5 mm (for an absorption band of 4.26 μm). The width w of the cavity 120 is 120 (Parallel to Figure 1A The y direction in the 120 (Or significantly larger and more complex, in the case of two-dimensional optics, including regions with focusing and refocusing structures 170.) Finally, the layers within the filter structure(s) 140 may be, for example, of the order of 0.15-2 μm.

[0036] According to an embodiment, if the medium or gas in the cavity 120 can be considered to have a refractive index of n=1 (or n≈1), then the medium or gas having a central wavelength λ 0 The filtered IR radiation R propagates along the optical interaction path 120-1 in the cavity 120. In the case where the medium or gas in the cavity 120 has a refractive index n≠1, the filtered IR radiation R has a resulting central wavelength λ 0 / n.

[0037] According to one embodiment, for example, in addition to the coupling region (see, for example, Fig. 7A ), the cavity 120 of the gas sensor 100 may at least partially include a vertical (eg, parallel to) optical interaction path 120-1. Figure 1A xz plane and / or yz plane) side walls 120-C, 120-D.

[0038] According to one embodiment, in Figure 1A In the cross-sectional view parallel to the xy plane of the gas sensor 100, the cavity 120 of the gas sensor 100 may include a zigzag shape or a spiral shape to provide a correspondingly shaped optical interaction path 120-1 and provide a lateral dimension l greater than the substrate 110. 101 The resulting length l of the optical interaction path 120-1 is 120-1 The length l of the optical interaction path 120-1 is 120-1 It can be the lateral dimension l of the substrate 110 101at least 2, 5 or 10 times of that.

[0039] like Figure 1A As shown, the substrate 110 may include a first partial substrate (=first wafer) 110-1 and a second partial substrate (=second wafer) 110-2 bonded to each other. At least one of the first partial substrate 110-1 and the second partial substrate 110-2 includes a recess for providing a cavity 120 between the bonded first partial substrate 110-1 and the second partial substrate 110-2. At least one of the first partial substrate 110-1 and the second partial substrate 110-2 includes an additional recess 120 for providing at least one entry hole 160 to the cavity 120. Therefore, the first partial substrate 110-1 can form a cover of the cavity 120 for providing an optically closed cavity 120 along the optical interaction path 120-1 to propagate a light having a central wavelength λ 0 The filtered IR radiation R of

[0040] like Figure 1A As shown, the gas sensor 100 may also include at least one radiation guiding element 170 in the cavity 120, such as a mirror and / or a grating, for guiding or coupling the filtered IR radiation R into the optical interaction path 120-1 and / or focusing the filtered IR radiation R onto the IR detector 150, such as onto a radiation detecting / sensitive surface of the IR detector 150.

[0041] According to one embodiment, the IR emitter 130 may include a conductor (eg, a semiconductor strip and / or a metal strip) having a main radiation emission direction for emitting broadband IR radiation R in a plane perpendicular to (orthogonal to) the main emission surface area. 0 The conductor may include a highly doped semiconductor strip, wherein the metal cover at least partially covers the main emission surface area of ​​the semiconductor strip. Thus, the semiconductor strip may include a highly doped silicon material to form a black body radiator and may be configured to have an operating temperature in the range between 600 and 1000 K under actuation conditions. The IR emitter 130 may be connected to a power source ( Figure 1A ), for providing electrical energy as an activation signal to put the IR emitter 130 in an activated state for radiation emission.

[0042] The main radiation emission direction of the IR emitter 130 is relative to the lateral extension plane of the cavity 120 (eg, Figure 1A In the case where the gas sensor 100 is angularly offset from the xy plane of the cavity 120, the gas sensor 100 may include a radiation directing element(s) 170 in the form of a deflection structure in the cavity 120 for deflecting or directing the filtered IR radiation R into the optical interaction path 120-1 of the cavity 120. Figure 1AAs shown, the main radiation emission direction of the IR emitter 130 may be perpendicular to a lateral extension plane of the cavity 120 , and thus (substantially) perpendicular to the optical interaction path 120 - 1 of the filtered IR radiation R in the cavity 120 .

[0043] According to one embodiment, the wavelength selection structure 140 may be formed as an optical bandpass filter structure having a narrow transmission band for providing a wavelength having a central wavelength λ 0 According to one embodiment, the wavelength selection structure 140 may include at least one of the following: a filter structure between the IR emitter 130 and the cavity 120, a photonic crystal structure in the lateral sidewall regions 120-C, 120-D of the cavity 120, and / or a photonic crystal structure for providing a wavelength having a central wavelength λ in the cavity 120. 0 The wavelength selective coating of the inner wall regions 120-A...120-D of the cavity 120 that filters the (narrowband) IR radiation R is provided.

[0044] like Figure 1A As shown, a region 162 of the substrate 110 in which the radiation R is transmitted to enter the cavity 120 and on which the emitter is located, and a region 164 of the substrate 110 in which the radiation R is transmitted to leave the cavity 120 and on which the detector 150 is located can be formed as an opening. If the substrate material of the regions 162, 164 on which the emitter 130 and the detector 150 are located is sufficiently optically transparent, it is not necessary to provide the openings 162, 164 to the cavity 120 at the emitter 130 and the detector 150 through the substrate material.

[0045] According to another embodiment, an additional wavelength selective structure 142 may be optionally arranged to further filter the IR radiation R propagating through the optical interaction path 120-1 and directed to the IR detector 150. The additional wavelength selective element 142 may be optically coupled between the cavity 120 and the IR detector 150 for providing the IR detector with a central wavelength λ 0 The further filtered narrowband IR radiation R. The further wavelength selective element 142 may, for example, comprise an optical bandpass filter structure.

[0046] According to one embodiment, the IR detector 150 may include a resistive temperature sensor, a pyroelectric temperature sensor, a piezoelectric temperature sensor, or a pn junction temperature sensor configured to provide a detector output signal S based on a signal strength of filtered IR radiation R propagating through the optical interaction path 120-1 of the cavity 120 and incident on and thus sensed by the IR detector 150. OUT. Thus, the IR detector 150 may be configured to sense the intensity of the incident filtered IR radiation R. Due to the interaction of the filtered IR radiation R with the target gas components in the cavity 120, the intensity of the incident filtered IR radiation R is a measure of the concentration of the target gas in the cavity 120. Therefore, the output signal S of the IR detector 150 may be OUT The concentration of the target gas in the surrounding environment of the gas sensor is obtained.

[0047] 1 b shows a schematic cross-sectional view of a first partial substrate (top wafer) 110-1 and a second partial substrate (bottom wafer) 110-2 in a separated state, for example, before bonding the two partial substrates to realize a bonded substrate 110. At least one of the first partial substrate 110-1 and the second partial substrate 110-2 may include a recess for providing a cavity 120 between the bonded first partial substrate 110-1 and the second partial substrate 110-2. At least one of the first partial substrate and the second partial substrate 110-1, 110-2 includes a further recess 120 for providing at least one access hole 160 to the cavity 120. Thus, the first partial substrate 110-1 may form a cover of the cavity 120 to provide an optically closed cavity 120 along the optical interaction path 120-1 for propagating a light having a central wavelength λ 0 The filtered IR radiation R of

[0048] Therefore, the cavity 120 can be realized via wafer bonding technology. In this case, the second part substrate (bottom wafer) 110-2 may include a cavity, a source or emitter structure 130, and a detector structure 150 that can be generated, for example, by means of a Bosch etching process. The first part substrate (top wafer) 110-1 is arranged vertically on the second part substrate (bottom wafer) 110-2. The first part substrate (top wafer) 110-1 may include a grating structure 170 for light deflection, for example, implemented as a 50nm (or between 30 and 70nm) polysilicon high line with a spacing of 2μm (or 1 to 3μm). According to one embodiment, the first part substrate (top wafer) 110-1 may also include a glass wafer so as to be anodic bonded with the second part substrate (bottom wafer) 110-2. In this case, temperature exposure during the bonding process must be considered to avoid damaging the metallized area. The region or (multiple) inner walls of the cavity 120 can be metallized, for example, using gold to ensure reflectivity.

[0049] In the present description of the embodiments, the same or similar elements having the same structure and / or function are provided with the same reference numerals or names, wherein a detailed description of these elements will not be repeated for each embodiment. Figure 1A-1BThe above description of is also applicable to other embodiments described below. In the following description, the following is discussed in detail. Figure 1A -The essential differences (e.g., other elements) of the embodiment shown in FIG. B and the technical effects resulting therefrom.

[0050] Figure 2 A schematic cross-sectional view of an integrated gas sensor 100 ′ according to another embodiment is shown.

[0051] like Figure 2 As shown, the integrated gas sensor 100' comprises a substrate 110 having a cavity 120 for providing an optical interaction path 120-1 for an IR (IR=infrared) radiation component to interact with a target gas in the cavity 120, wherein the cavity 120 is accessible to an ambient gas or an ambient gas mixture containing a target gas component.

[0052] The integrated gas sensor 100 further comprises a device arranged to emit incoherent IR radiation R having an IR radiation component R 0 or a broadband thermal emitter 130 , wherein the thermal emitter 130 is optically coupled to the cavity 120 .

[0053] The integrated gas sensor 100 further comprises an IR detector 150 arranged to detect, based on the optical interaction path 120-1 (eg, as broadband IR radiation R) that has passed through the cavity 120. 0 The signal strength of the IR radiation component R incident on the IR detector 150 is used to provide a detector output signal S OUT The IR detector 150 has a central wavelength λ 0 The IR (IR=infrared) radiation component R is sensitive.

[0054] The integrated gas sensor 100 further comprises a wavelength selective structure 142 arranged to filter the broadband IR radiation R emitted by the thermal emitter 130. 0 , wherein the wavelength selection element 142 is optically coupled between the cavity 120 and the IR detector 150 to provide the IR detector 150 with a wavelength having a central wavelength λ 0 The wavelength selective element 142 may comprise an optical bandpass filter structure, for example.

[0055] According to one embodiment, the integrated gas sensor 100 may further include an additional IR detector 152, which is arranged to detect the IR radiation R having passed through the optical interaction path 120-1 in the cavity 120 (eg, as a broadband IR radiation R 0The detector output signal S' is provided by the signal strength of the additional IR radiation component R' received by the IR detector or incident on the IR detector OUT The additional IR detectors 152 have additional central wavelengths λ 1 The additional IR radiation component R' is sensitive.

[0056] According to one embodiment, the further wavelength selective structure 144 is arranged for filtering the broadband IR radiation R emitted by the thermal emitter 130. 0 , wherein the further wavelength selective element 144 is optically coupled between the cavity 120 and the further IR detector 152 to provide the further IR detector 152 with a further wavelength having a central wavelength λ 1 The further wavelength selective element 142 may comprise, for example, an optical bandpass filter structure.

[0057] The above description regarding the structure and function of the IR detector 150 and the wavelength selective structure 140 applies equally to the further IR detector 152 and the further wavelength selective structure 142 .

[0058] When compared to Figure 1A The integrated gas sensor 100 shown and Figure 2 The embodiment of the integrated gas sensor 100' shown is based on Figure 1A The integrated gas sensor 100 uses a wavelength selective structure 140 to filter the broadband IR radiation R emitted by the IR emitter 130 0 , and provide a central wavelength λ 0 The filtered IR radiation R propagates along the optical interaction path 120 - 1 in the cavity 120 .

[0059] like Figure 2 The integrated gas sensor 100 ′ shown can use broadband IR radiation R propagating along the optical interaction path 120 - 1 in the cavity 120 0 Broadband IR radiation R 0 A spectral detector having a central wavelength λ for interacting with a target gas species may be included. 0 IR radiation component R. Broadband IR radiation R 0 A spectral detector having a central wavelength λ for interacting with additional target gas components may also be included. 1 The wavelength selective structure 142 is arranged to filter the broadband IR radiation R upon leaving the cavity 120 and before reaching the IR detector 150. 0 , so that the IR detector 150 receives the IR having the central wavelength λ 0In the optional case of a two-detector arrangement, a further wavelength selective structure 144 is arranged to filter the broadband IR radiation R upon leaving the cavity 120 and before reaching the further IR detector 152. 0 , so that the other IR detector 152 receives the IR having the central wavelength λ 1 The additional IR radiation component R'.

[0060] For example, Figure 2 The integrated gas sensor 100' shown may include sensors for different wavelengths λ 0 , 1 The plurality of detectors 150, 152 are sensitive. Each detector 150, 152 in the plurality of detectors may include a dedicated narrowband filter 140, 142. Providing the plurality of detectors 150, 152 may provide a second wavelength λ 1 The concept also works with more than two detectors.

[0061] Therefore, about Figure 1A The above description of other elements and structures of the integrated gas sensor 100 of -B also applies to Figure 2 The integrated gas sensor 100' is shown in FIG. 1 . Please note that the drawings are not to scale. In practice, the cavity length L 120 With its height h 120 The ratio can be much larger to ensure significant interaction length.

[0062] The characteristics of the integrated gas sensor 100 , 100 ′ can be summarized as follows.

[0063] The integrated gas sensor 100, 100' can be used in consumer electronics, for example, because it can be implemented with less effort using semiconductor technology. The present concept proposes a scheme to combine all parts of the integrated gas sensor 100, 100' in a single integrated design, which can be implemented by semiconductor technology, where a fully functional optical gas sensor can be implemented within a single chip. The integrated (optical) gas sensor 100, 100' provides high selectivity, high accuracy and fast response time. The implementation of the integrated gas sensor 100, 100' in the form of a chip-scale mass-produced sensor system (system on chip) can be the basis for numerous applications in consumer devices. The integrated gas sensor 100, 100' also provides a miniature infrared (IR) absorption gas sensor compatible with CMOS, where optical IR spectroscopy technology has the potential for high selectivity and fast response time to reliably monitor the air quality in the environment. Integration in large sensor networks or dense environmental monitoring can also be a possible application. The improvement in the reliability of optical sensors is an important asset in automotive applications, such as for monitoring CO2 level.

[0064] According to the present concept, an optical gas sensor 100, 100' comprises an IR source 130, filter elements 140, 142, 144, IR detectors 150, 152, and an interaction path 120-1 implemented as a cavity 120 in silicon 110, wherein the sample chamber 120 and the optical path 120-1 are implemented as an integrated cavity 120, wherein light (e.g., IR radiation) is guided in the plane of the wafer 110. For example, the cavity 120 can be generated via a wafer bonding process and can be arbitrarily shaped so as to provide the sample chamber 120 in an integrated small IR absorption gas sensor 100, 100'. In some form, the cavity 120 can have a linear interaction path 120-1, but more generally, a "2D optical bench" can be implemented, including focusing or even dispersive optical elements 170. Based on the design described herein, a reasonable path length of l for light absorption (interaction of IR radiation with the target gas) can be achieved. 120 Likewise, a relatively large cavity cross section (eg compared to a single mode waveguide) will increase yield and facilitate the use of an easily manufactured thermal radiator 130 as a radiation source. All elements of the optical sensor 100, 100' are included and can be manufactured based on silicon-based semiconductor technology.

[0065] A possible implementation of the integrated gas sensor 100, 100' provides a long cavity 120 in which light R passes and gas can enter the long cavity 120 and interact with the radiation R. A thermal IR source 130 together with a filter structure 140, 142, 144 generates radiation R which is detected at the other end of the cavity 120 with a suitable detector 150, 152. For example, the interior of the cavity 120 is reflective. Light is coupled into the cavity 120, which can be achieved by a grating 170.

[0066] To realize a complete integrated gas sensor 100, 100', light R from the light source 130 is effectively in-coupled and, after interacting with the target gas, is directed to the detector 150. A typical implementation may use a thermal radiator 130 with a filter element 140, 142, for example in front of the detector 150 or in front of the emitter 130 or both. For example, the emitter 130 and the filter 140, which are usually based on complex thin layer structures (e.g., filter structures), are manufactured so that they emit light R in a direction perpendicular to the cavity 120. The present specification shows different solutions for bending the light beam, for example, based on grating structures that can be realized by anisotropic etching processes.

[0067] The present concept of the integrated gas sensor 100, 100' is used as an infrared absorption sensor. As a result, it provides high selectivity, accuracy and fast response time. In addition, it is a basically contactless measurement method. In addition, the integrated gas sensor 100, 100' enables integration into a single integrated system, which can be produced by semiconductor technology. Therefore, by using a free beam method, the resulting sensor 100, 100' can be realized to be very small and can be mass-produced. Therefore, the proposed concept uses the full field for interaction with the medium, and in addition, the cross-section of the cavity 120 is much larger than that of a single-mode waveguide (where the cross-section must be on the order of the wavelength). This will achieve higher light flux and higher sensitivity, and achieve a shorter interaction path length. In addition, the damping here will be lower than in a waveguide.

[0068] The integrated gas sensor 100, 100' provides a fully integrated NDIR (NDIR = Non-Dispersive Infrared) micro gas sensor which can be produced based on standard Si semiconductor technology and has a cavity 120 which is larger than the wavelength of light and through which the (target) gas can penetrate. This allows the realization of an integrated NDIR sensor at chip level.

[0069] In the following, many different possible implementations of the integrated gas sensor 100, 100' are exemplarily described. In the present description of the embodiments, identical or similar elements having the same structure and / or function are provided with the same reference numerals or names, wherein a detailed description of such elements will not be repeated for each embodiment.

[0070] Figure 3A A schematic cross-sectional view of an integrated gas sensor 100 according to another embodiment is shown.

[0071] like Figure 3A As shown, the substrate includes a first partial substrate 110-1 and a second partial substrate 110-2 that are mechanically bonded together by means of a structured spacing element 110-3. The structured spacing element 110-3 is arranged between the first partial substrate 110-1 and the second partial substrate 110-2 to provide a cavity 120 between the mechanically bonded first partial substrate 110-1 and the second partial substrate 110-2. The structured spacing element 110-3 can also be arranged between the first partial substrate 110-1 and the second partial substrate 110-2 to provide at least one inlet hole 160 to the cavity 120. Optionally, at least one of the first partial substrate 110-1 and the second partial substrate 110-2 can include at least one inlet hole 160 as a gas passage to the cavity 120.

[0072] Figure 3BA schematic cross-sectional view of a top wafer 110 - 1 and a bottom wafer 110 - 2 in a separated state (eg, before bonding the two wafers (partial substrates) 110 - 1 , 110 - 2 to achieve a bonded substrate 110 ) is shown.

[0073] According to the integrated gas sensor 100, the cavity 120 may be formed by providing (eg, depositing) a structured spacer element 110-3 on the first partial substrate 110-1, wherein the structured spacer element 110-3 forms a surrounding wall of the cavity 120. The thickness h of the structured spacer element 110-3 is 200 Å. 110-3 The thickness h of the structured spacer element 110 - 3 may be greater than 20 μm, or may be between 20 and 100 μm. 110-3 The height h corresponding to the cavity 120 obtained is 120 The second partial substrate 110 - 2 may include a source structure 130 and a detector structure 150 .

[0074] Thus, the cavity 120 can be realized via wafer bonding technology. In this case, the first partial substrate 110-1 may include a recess for the cavity 120, which can be generated by depositing a structured spacing element 110-3 on the first partial substrate 110-1. The second partial substrate 110-2 may include a source or emitter structure 130 and a detector structure 150. The second partial substrate (top wafer) 110-2 is arranged vertically above the first partial substrate (bottom wafer) 110-1. The first partial substrate (top wafer) 110-1 may include a grating structure 170 for light deflection, for example, implemented as a 50nm (or between 30 and 70nm) polysilicon high line with a pitch of 2μm (or 1 to 3μm).

[0075] As Figure 1A An alternative method of integrating the gas sensor 100, Figure 3A The integrated gas sensor 100 may be formed by depositing the structured spacer element 110 - 3 as a surrounding wall of the cavity 120 on the first partial substrate 110 - 1 (rather than by a deep etching process).

[0076] Figure 4 Schematic cross-sectional view of an integrated gas sensor 100, 100' according to another embodiment is shown. Figure 3A The above description of other elements and structures of the integrated gas sensor 100 of FIG. B also applies to Figure 4 An integrated gas sensor 100.

[0077] Figure 4The integrated gas sensor 100 also includes a pair of barrier elements or window elements 180-1, 180-2. The barrier elements 180-1, 180-2 can be arranged to limit and define a sample chamber (or sample volume) 120-1 for the ambient gas. Therefore, the cavity path 120-1 is segmented by barrier elements 180-1, 180-2 (e.g., two thin Si "windows") so as to define a sample chamber filled with gas. The distance between the barrier elements 180-1, 180-2 defines the resulting length l of the optical interaction path 120-1 (=sample chamber) 120-1 .

[0078] The barrier elements 180-1, 180-2 may be transparent to the filtered radiation R or the IR radiation component(s) R, R'. However, the barrier elements (e.g., silicon barriers) 180-1, 180-2 may introduce some reflected light, but, if carefully designed, may also act as optical cavities, which may be used to increase the electric field and, as a result, increase the effective interaction with the analyte.

[0079] Figure 5 A schematic cross-sectional view of an integrated gas sensor 100 , 100 ′ according to another embodiment is shown.

[0080] like Figure 5 As shown, the substrate 110 may include a first partial substrate 110-1 and a second partial substrate 110-2, wherein the first partial substrate 110-1 includes a recess 120, and wherein the second partial substrate 110-2 is formed as a perforated film structure covering the recess 120 in the first partial substrate 110-1. An IR emitter 130 and an optional wavelength selection structure 140 and an IR detector 150 are arranged at the second partial substrate 110-2. The recess 120 in the first partial substrate 110-1 and covered by the second partial substrate 110-2 forms a cavity 120 providing an optical interaction path 120-1. The IR emitter 130 and the optional wavelength selection structure 140 and the IR detector 150 are optically coupled to the optical interaction path 120-1.

[0081] like Figure 5 As shown, the first partial substrate 110-1 and the second partial substrate 110-2 form different parts of the same substrate (single wafer) 110. Therefore, the cavity 120 of the integrated gas sensor 100, 100' can be formed in the single substrate (single wafer) 110 by using sacrificial materials, wherein the process for manufacturing MEMS elements or MEMS microphones can be used.

[0082] exist Figure 5In an embodiment of the present invention, the cavity 120 may be formed by means of a sacrificial layer (carbon or silicon dioxide) covered with a polysilicon layer having an access opening 160 arranged to the sacrificial layer. The cavity 120 is formed by removing the sacrificial layer, wherein the emitter 130 and the detector 150 may be arranged on laterally opposite sides of the cavity 120 at the access opening 162 of the cavity 120. If the substrate material on which the emitter 130 and the detector 150 are located is optically transparent enough, it is not necessary to provide the opening 162 to the cavity 120 through the substrate material at the detector 130 and the emitter 150. However, openings are usually provided.

[0083] Figure 6A-6F Schematic top views (parallel to the xy plane) of different possible realizations of the geometry of the cavity 120 for providing an optical interaction path 120 - 1 of the integrated gas sensor 100 , 100 ′ are shown according to other embodiments.

[0084] According to an embodiment of the present concept, an integrated optical gas sensor 100 , 100 ′ includes a thermal emitter 130 , an interaction path 120 - 1 implemented as a cavity 120 in a substrate 110 (eg, a silicon substrate), an IR detector element 150 and wavelength selective elements 140 , 142 .

[0085] According to an embodiment of the present concept, the cavity 120 for the optical path 120-1 directs light R from the source 130 to the detector(s) 150, 152 substantially in the plane (xy plane) of the wafer 110. The ambient gas may penetrate the cavity 120 and interact with the radiation R. The lateral dimensions of the cavity 120 should be significantly larger than the wavelength λ 0 Therefore, the incoherent radiation R from a simple thermal emitter 130 can be used 0 , thereby reducing the complexity of the system (ie, the integrated gas sensor 100, 100').

[0086] The interior or inner surfaces 120-A ... 120-D of the cavity 120 are highly reflective. This can be achieved, for example, using a reflective coating or metallization of the inner surfaces (e.g., using gold).

[0087] Another possible way to ensure reflectivity may be to use a photonic crystal structure around the cavity 120. Since such a structure does not allow propagation at a specific wavelength corresponding to the optical band gap, this confines the radiation R to the cavity 120 and at the same time provides spectral filtering since all other wavelengths are lost.

[0088] This filtering effect can also be achieved if some or all of the surfaces of the cavity are coated with a selective narrow-band reflective coating.

[0089] The cavity 120 also includes a specific channel 160 for the gas. The cavity 120 may have vertical sidewalls (except for the coupling region, see below) and typically has a diameter greater than the wavelength λ of the light R. 0 The constant height h 120 The light R can be guided by standard reflection (in contrast to total internal reflection used in waveguides). The horizontal dimensions of the cavity 120 can be shaped essentially arbitrarily, which provides a means for optimizing the optical path 120-1 in two dimensions, for example by including focusing mirrors or other optical elements or by implementing a meander structure or helix to increase the effective path length. This will allow the implementation of "2D ray optics", meaning that light can be modeled and controlled in two dimensions and confined in three dimensions by reflection.

[0090] Figure 6A-6F An exemplary top view of a possible structure of a "2D optical platform" is shown.

[0091] As exemplarily shown in Fig. 6a, the cavity 120 forms a linear sample chamber 120-1. One possible way to produce the linear cavity 120 is to provide a groove or a recess in a first partial substrate or wafer 110-1, for example by etching or by deposition, and then wafer-bond the first partial substrate 110-1 with a second partial substrate 110-2 (in which the emitter 130 and the detector 150 are integrated) to produce a closed cavity 120. Other processes and other geometries are also possible. Likewise, other techniques besides wafer bonding can also be used to manufacture the cavity 120, for example, based on techniques used in the manufacture of MEMS microphones.

[0092] like Figure 6B As exemplarily shown in FIG. 1 , the cavity 120 forms a tortuous interaction path 120 - 1 .

[0093] like Figure 6C As shown, the linear cavity 120 is surrounded by a photonic crystal 140 .

[0094] like Fig.6D As exemplarily shown in FIG. 1 , the cavity 120 comprises a radiation guiding element 170 in the form of a deflection structure in the cavity 120 for deflecting or guiding the IR radiation R in the optical interaction path 120-1 of the cavity 120 to provide collimation and / or focusing of the light R onto the detector with a certain horizontal magnification. This enables a smaller source 130.

[0095] As in Fig. 6E As exemplarily shown in FIG. 1 , the cavity 120 comprises the incorporation of a grating 170. The grating 170 may allow separation of spectral components of the IR radiation R.

[0096] like Fig. 6FAs exemplarily shown in FIG. 1 , the cavity 120 comprises an elliptical shape. The elliptical cavity 120 allows substantially collecting the entire light R from a given point and focusing the light on the detector 150 .

[0097] Fig. 7A -B shows an enlarged schematic cross-sectional view of a deflection structure or radiation guiding element 170 in the cavity 120 of the integrated gas sensor 100, 100' according to other embodiments. A radiation guiding element 170 (e.g., a mirror and / or a grating) is arranged in the cavity 120 for guiding or coupling the filtered IR radiation R into the optical interaction path 120-1 and / or for focusing the filtered IR radiation R to the IR detector 150, for example, on a radiation detecting / sensitive surface of the IR detector 150.

[0098] A heat source or emitter may be used as light source 130, which may be implemented, for example, as a conductive area, such as a doped silicon material or metal, etc., which is heated by applying an electric current as an excitation signal. Typically, there is a filter structure 140 in front of the heater 130 in order to filter out the appropriate wavelength λ for interaction with the target gas. 0 Adjustment of the optical bandwidth can also be done in front of the detector 130 or elsewhere in the beam path 120-1. However, filtering directly at the source 130 avoids unnecessary radiation and excessive heating of the rest of the cavity 120. The wavelength selective structure 140 can be implemented to filter the emitted radiation R 0 and providing a guided and spectrally narrow radiation beam R. In some cases, wavelength selective structure 140 is fabricated and arranged in the plane of substrate (wafer) 110 , and thus, radiation R will preferably be emitted in a direction perpendicular to the direction of cavity 120 .

[0099] Thus, the deflection structure 170 is arranged to deflect the light beam (radiation R) into the optical interaction path 120-1. Fig. 7A As shown, the deflection structure 170 can be realized by means of an anisotropic etching process, or as Figure 7B As shown, this can be achieved by using a grating structure. The anisotropic etching process provides a surface region 170 with a tilt angle of, for example, 54.7° (depending on the crystal orientation of the semiconductor substrate 110) and higher efficiency compared to a non-blazed grating. However, the etched deflection structure 170 poses a challenge to the cavity design because it is difficult to ensure the verticality of the cavity sidewalls in all directions.

[0100] Alternatively, the deflection structure 170 may be provided by means of Figure 7B Similar considerations regarding the realization of the further deflection structure 170 apply to the detection part, where the light R can be guided to the detector 150 after passing through the cavity 120 .

[0101] therefore, Figure 7A-7B A possible solution is shown for rotating the emitted light R by approximately 90° so as to propagate the light R along the optical path 120-1. Fig. 7A As shown, a deflection surface 170 is provided at an angle of 54.7° relative to the xy plane, for example, by means of an anisotropic etching process. Figure 7B As shown, the deflection structure 170 is alternatively arranged in the form of a grating to deflect the light beam R in a defined direction.

[0102] According to embodiments of the present concept, in principle, substantially any kind of detector 150 can be used, as long as the detector 150 is sensitive to the IR wavelength λ 0 Sensitive. A cheap implementation of the detector is a resistor, for example in the form of a doped region of a semiconductor, such as a Si material, whose resistance changes when heated. The possibility of "2D ray optics" enables the use of very small sources 130 and / or detectors 150, since it becomes possible to collect and refocus the light (at least in two dimensions), which provides a greatly improved efficiency. The quantum detector 150 can provide a high sensitivity. The same applies to the emission efficiency by means of a quantum emitter 130 (e.g. a quantum cascade laser).

[0103] According to embodiments of the present concepts, relatively high throughput is desired, which enables the use of less sensitive and less complex detection 150 and transmitter 130 schemes.

[0104] Fig. 8A FIG. 1 shows a schematic cross-sectional view of an integrated gas sensor 100 according to another embodiment. Figure 1A-1B The above description also applies to the following Fig. 8A A further embodiment of the invention, in which instead of the radiation guiding element 170 in the form of a grating, Fig. 8A The integrated gas sensor 100 of FIG. 1 uses a deflection surface 170 (see also FIG. 1 ) which is provided, for example, by means of an anisotropic etching process and which is at an angle of 54.7° to the xy plane. Fig. 7A and related descriptions). Fig. 8A As shown, the gas sensor 100 includes a radiation guiding element 170 (e.g., implemented as a reflector) in the cavity 120 for guiding or coupling the filtered IR radiation R into the optical interaction path 120-1 and / or focusing the filtered IR radiation R onto the IR detector 150, for example, onto a radiation detecting / sensitive surface of the IR detector 150.

[0105] according to Fig. 8AIn the implementation of the integrated gas sensor 100, the coupling of the radiation R is achieved by the inclined surface 170, which can be generated, for example, using anisotropic etching in Si (1, 0, 0). The first partial substrate 110-1 includes the inclined surface 170, so that the radiation R emitted by the heater structure 130 is tilted by about 90° after reflection. This can be achieved by means of a first partial substrate 110-1 having a Si (1, 0, 0) material (e.g., a Si (1, 0, 0) wafer).

[0106] However, when considering relatively complex designs of the sample chamber 120 (e.g. corners, bends, etc.), it is also necessary to take into account the resulting effects and deviations from vertical side walls, which can be analyzed on a case-by-case basis, for example. However, it is expected that the incoupling / outcoupling of the radiation R by means of the inclined surface(s) 170 is even more efficient when compared to a grating approach (e.g. see Figure 7B ).

[0107] Figure 8B A schematic 3D view of an integrated gas sensor 100 and in particular the geometry of a folded cavity 120 of the integrated gas sensor 100 according to one embodiment is shown.

[0108] like Figure 8B As shown, a possible solution for beam folding may be realized by anisotropically etched trenches in the semiconductor material of the first partial substrate 110 - 1 and the second partial substrate 110 - 2 .

[0109] Compared to simple linear grooves, the method of anisotropic etching presents challenges for using more complex structures. For example, in the case of a meandering structure for the cavity 120, each turn of the meandering structure can have an inclined surface. This can be used for the following implementation method: the bottom wafer 110-1 and the top wafer 110-2 have only parallel grooves, where the end wall as the deflection structure 170 is tilted 54.7° due to the Si (1, 0, 0) orientation. The wafers 110-1, 110-2 are orthogonally aligned so that a 90° horizontal rotation can be achieved by reflecting the light beam from the grooves in the lower wafer 110-1 to the grooves in the top wafer 110-2, such as in a periscope.

[0110] Figure 9A-9I A schematic 3D top view of a method 200 for producing an integrated gas sensor 100 according to one embodiment is shown as a schematic snapshot (=view I).

[0111] also, Figure 9A-9ISchematic 3D cross-sectional views (=views II, III) through a central region of a respective intermediate device along section line AA and parallel to the xz plane during steps of a method 200 for manufacturing an integrated gas sensor 100 according to one embodiment are shown.

[0112] about Figure 9A-9I The illustrated method 200 points out the fact that this process flow is one example of a variety of ways how the integrated gas sensor 100 may be fabricated, wherein the various process steps may be performed in a different order or combined with additional fabrication steps and / or structuring techniques.

[0113] like Fig. 9A As shown in step 1, a first partial substrate (flat bottom wafer) 110-1 is provided.

[0114] In step 2, a grating structure (deflecting structure) 170 is deposited onto a first major surface region 110-1A of a first partial substrate 110-1.

[0115] In step 3, a structured spacer element 110-3 defining a cavity 120 is grown on the first main surface region 110-1A of the first partial substrate 110-1. As shown in step 3, the grown structure (i.e., the structured spacer element 110-3) also includes an inlet hole 160 for an ambient gas including a target gas. The inlet hole 160 is formed, for example, laterally in the grown structure 110-3.

[0116] In step 4 , metallization 140 is deposited or applied to the exposed surface areas of cavity 120 .

[0117] Step 5 further illustrates providing a second partial substrate 110 - 2 (flat top wafer).

[0118] In step 6, a wavelength selective structure 140, such as a Bragg filter structure, is deposited on the first main surface region 110-2A of the second partial substrate 110-2.

[0119] In step 7 , the thermal emitter (heater) 130 and the IR detector 150 are formed (deposited) on the filter structure 140 on the first major surface region 110 - 2A of the second partial substrate 110 - 2 .

[0120] In step 8, a Bosch etching process is performed for providing a cavity 120 in the partial substrate 110-2, wherein a further metallization of the back side 110-2B (= second main surface area of ​​the second partial substrate 110-2) of the exposed cavity area 120 is performed. Step 8 is only visible in the interior of FIG. 9H of step 8 (views II and III).

[0121] In step 9, a wafer bonding process is performed to bond the first partial substrate 110-1 and the second partial substrate 110-2 to each other, wherein at least one of the first partial substrate 110-1 and the second partial substrate 110-2 includes a recess for providing a cavity 120 between the bonded first partial substrate 110-1 and the second partial substrate 110-1, and providing (multiple) access holes 160 to the cavity 120.

[0122] An implementation example may be based on wafer bonding technology. Other technologies may also be used to produce the cavity 120, for example, based on MEMS microphone technology. In this case, no wafer bonding step is required.

[0123] The basic concept of the integrated gas sensor 100 is to form a cavity 120 in a substrate material 110 (e.g., a semiconductor material such as silicon, germanium) or also in a glass wafer or a substrate made of silicon dioxide material, wherein the side walls have a sufficiently high reflectivity, for example by means of a (vapor deposited) mirror layer. Any metal such as gold, silver, aluminum or a reflective dielectric material can be used as material for the reflective layer that at least partially covers the side walls of the cavity. Except for the embodiment using a sacrificial material, two substrates / wafers are connected to form the cavity 120 for the interaction of IR radiation / target gas.

[0124] According to another embodiment, the side walls can also be formed by means of photonic crystals.

[0125] If the entry holes 160 are provided in the cover layer as perforations (hole field), such as in a backplate (for a microphone), the size of the holes may be chosen such that they effectively act as photonic crystals and include reflectivity for IR radiation R coupled therein.

[0126] In embodiments where a bonding process (anodic bonding) is performed, the substrate or substrate material must be suitable for the bonding process.

[0127] Typically, a filter element 140 is provided at the heat source 130, while a further filter element 142 is optionally provided at the detector 150. The filter elements 140, 142 on both sides increase the selectivity for the IR radiation R. The lateral extension of the cavity 110 120 In the range of millimeters to centimeters, the horizontal extension (height) of the cavity 120 h 120 In the range of 5 to 10 μm or ≤ 200 μm or in the sub-millimeter range.

[0128] Additional embodiments and aspects are described that may be used alone or in combination with the features and functionality described herein.

[0129] According to one embodiment, a gas sensor includes: a substrate having a cavity, wherein the cavity is used to provide a gas sensor having a central wavelength λ0 The invention relates to a method for providing an optical interaction path for the interaction of filtered IR (IR=infrared) radiation emitted by the thermal emitter with a target gas in the cavity, wherein the cavity is accessible to an ambient gas containing components of the target gas; a thermal emitter arranged to emit broadband IR radiation, wherein the thermal emitter is optically coupled to the cavity; and a wavelength selective structure arranged to filter the broadband IR radiation emitted by the thermal emitter and to provide the broadband IR radiation having a central wavelength λ in the cavity. 0 The invention relates to a method for transmitting filtered IR radiation having a wavelength selective element disposed in the cavity, wherein the wavelength selective element is optically coupled between the thermal emitter and the cavity, or wherein the wavelength selective element is formed as a bonding structure of the cavity; and an IR detector arranged to provide a detector output signal based on a signal strength of the filtered IR radiation having passed through the optical interaction path in the cavity and received by the IR detector.

[0130] According to one aspect, the cavity is arranged to provide a length of the optical interaction path of the central wavelength λ of the filtered IR radiation. 0 and the portion of the cavity forming the optical interaction path is configured to guide the light having a central wavelength λ by standard reflection. 0 of filtered IR radiation.

[0131] According to another aspect, the substrate includes at least one access hole to the cavity to provide passage of the ambient gas having the target gas component to the cavity.

[0132] According to another aspect, the optical interaction path extends parallel to the bottom and top sidewalls of the cavity such that the filtered IR radiation is directed along a lateral plane of the substrate.

[0133] According to another aspect, the bottom sidewall and the top sidewall of the cavity extend parallel to each other along the optical interaction path to provide a wavelength greater than the central wavelength λ along the optical interaction path. 0 The constant height h of the cavity.

[0134] According to another aspect, the cavity includes vertical sidewalls along the optical interaction path.

[0135] According to another aspect, the cavity comprises a meandering or spiral shape for providing a correspondingly shaped optical interaction path and for providing a resulting length I of the optical interaction path that is larger than a lateral dimension of the substrate.

[0136] According to another aspect, the substrate comprises a first partial substrate and a second partial substrate bonded to each other, wherein at least one of the first partial substrate and the second partial substrate comprises a recess for providing the cavity between the bonded first and second partial substrates.

[0137] According to another aspect, the gas sensor further comprises a radiation guiding element in the cavity for guiding the filtered IR radiation into the optical interaction path and / or focusing the filtered IR radiation to the IR detector.

[0138] According to another aspect, the substrate comprises a first partial substrate and a second partial substrate mechanically bonded together by means of a structured spacer element, wherein the structured spacer element is arranged between the first partial substrate and the second partial substrate for providing the cavity between the mechanically bonded first partial substrate and the second partial substrate.

[0139] According to another aspect, the first partial substrate comprises a recess and the second partial substrate is formed as a perforated membrane structure covering the recess in the first partial substrate, wherein the IR emitter (and optionally the wavelength selective structure) and the IR detector are arranged at the second partial substrate.

[0140] According to another aspect, the IR emitter comprises a conductor having a main emission surface area for emitting broadband IR radiation in a main radiation emission direction.

[0141] According to another aspect, the conductor comprises a highly doped semiconductor strip, wherein a metal cover layer at least partially covers the main emitting surface area of ​​the semiconductor strip.

[0142] According to another aspect, the main radiation emission direction of the IR emitter is angularly offset from a lateral extension plane of the cavity, the gas sensor further comprising: a deflection structure in the cavity for deflecting the filtered IR radiation into the optical interaction path in the cavity.

[0143] According to another aspect, the wavelength selection structure is formed to have an optical bandpass filter structure for providing a narrow transmission band to provide a user with the central wavelength λ 0 of filtered IR radiation.

[0144] According to another aspect, the wavelength selective structure comprises at least one of the following: a filter structure between the IR emitter and the cavity, a photonic crystal structure in the lateral sidewall region of the cavity, and a wavelength selective coating in the inner wall region of the cavity for providing a wavelength selective coating having a central wavelength λ in the cavity (120). 0of filtered (narrowband) IR radiation.

[0145] According to another aspect, the IR detector comprises a resistive temperature sensor, a pyroelectric temperature sensor, a piezoelectric temperature sensor or a pn junction temperature sensor, which is configured to provide a detector output signal based on the signal intensity of the filtered IR radiation propagating through the optical interaction path of the cavity and incident on the IR detector.

[0146] According to another aspect, the IR detector is configured to sense an intensity of incident filtered IR radiation, the intensity of incident filtered IR radiation being a measure of the concentration of the target gas in the cavity.

[0147] According to one embodiment, a gas sensor comprises: a substrate having a cavity, the cavity being used to provide an optical interaction path for an IR (IR=infrared) radiation component to interact with a target gas in the cavity, wherein the cavity is accessible to an ambient gas containing the target gas; a thermal emitter arranged to emit broadband IR radiation having the IR (IR=infrared) radiation component, wherein the thermal emitter is optically coupled to the cavity; an IR detector arranged to provide a detector output signal based on a signal strength of the IR radiation component that has passed through the optical interaction path in the cavity and is received by the IR detector; and a wavelength selection structure arranged to filter the broadband IR radiation emitted by the thermal emitter, wherein the wavelength selection element is optically coupled between the cavity and the IR detector for providing the IR detector with a wavelength having a central wavelength λ 0 The filtered IR radiation of the IR radiation component of .

[0148] According to one aspect, the gas sensor further comprises: a further IR detector arranged to provide a detector output signal based on a signal strength of the IR radiation that has passed through the optical interaction path in the cavity and is received by the IR detector; and a further wavelength selective structure arranged to filter the broadband IR radiation emitted by the thermal emitter, wherein the wavelength selective element is optically coupled between the cavity and the further IR detector to provide the further IR detector with a further wavelength having a central wavelength λ. 1 The filtered IR radiation of the additional IR radiation component.

[0149] Although some aspects have been described as features in the context of an apparatus, it is clear that such description may also be seen as a description of corresponding features of a method. Although some aspects have been described as features in the context of a method, it is clear that such description may also be seen as a description of corresponding features with respect to the functionality of the apparatus.

[0150] In the preceding “Detailed Description of the Invention”, it can be seen that, for the purpose of simplifying the present disclosure, various features are grouped together in the examples. The method of the present disclosure should not be interpreted as reflecting the intention that the examples claimed for protection require more features than the features explicitly recited in each claim. On the contrary, as reflected in the appended claims, the subject matter may be less than all the features of a single disclosed example. Therefore, the appended claims are thus incorporated into the “Detailed Description of the Invention”, where each claim may exist independently as an independent example. Although each claim may be a separate example alone, it should be noted that although a dependent claim may refer to a specific combination with one or more other claims in a claim, other examples may also include a combination of a dependent claim with the subject matter of each other dependent claim, or a combination of each feature with other dependent or independent claims. Unless it is indicated that a specific combination is not intended, such a combination is proposed herein. In addition, it is intended that the features of a claim are also included in any other independent claim, even if the claim is not directly dependent on the independent claim.

[0151] Although specific embodiments have been shown and described herein, those of ordinary skill in the art will appreciate that various alternative and / or equivalent implementations may be substituted for the specific embodiments shown and described without departing from the scope of the present embodiments. This application is intended to cover any adaptation or variation of the specific embodiments discussed herein. Therefore, it is intended that the embodiments be limited only by the claims and their equivalents.

Claims

1. A gas sensor (100), comprising: A substrate (110) having a cavity (120), the cavity (120) being used to provide an optical interaction path (120-1) for interaction of filtered IR radiation (R) having a central wavelength λ0 with a target gas in the cavity (120), wherein an inner surface of the cavity (120) comprises a reflective coating or metallization layer, and wherein the cavity (120) is accessible to an ambient gas including a component of the target gas, The substrate (110) comprises a first partial substrate (110-1) and a second partial substrate (110-2) bonded to each other, wherein at least one of the first partial substrate (110-1) and the second partial substrate (110-2) comprises a recess for providing the cavity (120) between the bonded first partial substrate (110-1) and the second partial substrate (110-2), a thermal emitter (130) arranged to emit broadband IR radiation (R0), wherein the thermal emitter (130) is formed on the second partial substrate (110-2) and optically coupled to the cavity (120) through an optically transparent area or opening (162) of the second partial substrate (110-2), a wavelength selective element (140) arranged for filtering the broadband IR radiation (R0) emitted by the thermal emitter (130) and for providing the filtered IR radiation (R) having the central wavelength λ0 in the cavity (120), wherein the wavelength selective element (140) is optically coupled between the thermal emitter (130) and the cavity (120), or wherein the wavelength selection element (140) is formed as a combined structure of the cavity (120), an IR detector (150) formed on the second partial substrate (110-2) and arranged to provide a detector output signal (S) based on the signal strength of the filtered IR radiation that has passed through the optical interaction path (120-1) in the cavity (120) and is received by the IR detector (150) through the optically transparent area or opening (162) of the second partial substrate (110-2); OUT ),as well as A radiation guiding element (170) is further located in the cavity (120) relative to the reflective coating or metallization layer, for guiding or coupling the filtered IR radiation (R) into the optical interaction path (120-1) and / or for focusing the filtered IR radiation (R) to the IR detector (150), wherein the radiation guiding element (170) is formed on the first partial substrate (110-1).

2. The gas sensor (100) according to claim 1, wherein the cavity (120) is arranged to provide a length (l) of the optical interaction path (120-1) of 120 ), the length (l of the optical interaction path (120-1) 120 ) is at least 100 times the central wavelength λ0 of the filtered IR radiation (R), and wherein the portion of the cavity (120) forming the optical interaction path (120-1) is configured to guide the filtered IR radiation (R) having the central wavelength λ0 by standard reflection.

3. The gas sensor (100) according to claim 1 or 2, wherein the substrate (110) comprises at least one access hole (160) leading to the cavity (120) for providing a passage for the ambient gas having the target gas component to pass into the cavity (120).

4. A gas sensor (100) according to claim 1 or 2, wherein the optical interaction path (120-1) extends parallel to the bottom sidewall (120-A) and the top sidewall (120-B) of the cavity (120) so that the filtered IR radiation is guided along the lateral plane of the substrate.

5. The gas sensor (100) according to claim 1 or 2, wherein the bottom sidewall (120-A) and the top sidewall (120-B) of the cavity (120) extend parallel to each other along the optical interaction path (120-1) for providing a constant height (h) of the cavity (120) along the optical interaction path. 120 ), the constant height (h 120 ) is greater than the central wavelength λ0.

6. The gas sensor (100) according to claim 1 or 2, wherein the cavity (120) comprises vertical side walls along the optical interaction path.

7. The gas sensor (100) according to claim 1 or 2, wherein the cavity (120) comprises a meandering shape or a spiral shape for providing a correspondingly shaped optical interaction path (120-1) and providing a resulting length (l) of the optical interaction path (120-1). 120 ), the obtained length (l 120 ) is larger than the lateral dimension of the substrate (110).

8. The gas sensor (100) according to claim 1 or 2, wherein: The radiation guiding element (170) is a grating in the cavity (120) for guiding the filtered IR radiation (R) into the optical interaction path (120-1) and / or focusing the filtered IR radiation (R) to the IR detector (150).

9. A gas sensor (100) according to claim 1 or 2, wherein the substrate (110) includes a first partial substrate (110-1) and a second partial substrate (110-2) mechanically bonded together, wherein a structured spacer element (110-3) is arranged between the first partial substrate (110-1) and the second partial substrate (110-2) to provide the cavity (120) between the mechanically bonded first partial substrate (110-1) and the second partial substrate (110-2).

10. A gas sensor (100) according to claim 1 or 2, wherein the first partial substrate (110-1) includes a recess, and wherein the second partial substrate (110-2) is formed as a perforated membrane structure covering the recess in the first partial substrate (110-1), wherein the thermal emitter (130) and the IR detector (150) are arranged at the second partial substrate (110-2).

11. The gas sensor (100) according to claim 1 or 2, wherein the thermal emitter (130) comprises a conductor having a main emission surface area for emitting broadband IR radiation in a main radiation emission direction.

12. The gas sensor (100) according to claim 11, wherein the conductor comprises a highly doped semiconductor strip, wherein a metal cover layer at least partially covers the main emitting surface area of ​​the semiconductor strip.

13. The gas sensor (100) according to claim 11, wherein the main radiation emission direction of the heat emitter (130) is angularly offset from a lateral extension plane of the cavity (120), the gas sensor (100) further comprising: A deflection structure in the cavity (120) is used to deflect the filtered IR radiation (R) into the optical interaction path in the cavity (120).

14. The gas sensor (100) according to claim 1 or 2, wherein the wavelength selective element (140) is formed as an optical bandpass filter structure with a narrow transmission band for providing filtering of the filtered IR radiation having the central wavelength λ0.

15. The gas sensor (100) according to claim 1 or 2, wherein the wavelength selection element (140) comprises at least one of the following: a resonator structure between the thermal emitter and the cavity (120), a photonic crystal structure in the lateral sidewall region of the cavity (120), and A wavelength selective coating on the inner wall region of the cavity (120) is used to provide the filtered IR radiation having the central wavelength λ0 in the cavity (120).

16. The gas sensor (100) according to claim 1 or 2, wherein the IR detector (150) comprises a resistive temperature sensor, a pyroelectric temperature sensor, a piezoelectric temperature sensor or a pn junction temperature sensor, wherein the resistive temperature sensor, the pyroelectric temperature sensor, the piezoelectric temperature sensor or the pn junction temperature sensor is configured to provide a detector output signal (S) based on a signal strength of the filtered IR radiation (R) propagating through the optical interaction path (120-1) of the cavity (120) and incident on the IR detector (150). OUT ).

17. A gas sensor (100) according to claim 1 or 2, wherein the IR detector (150) is configured to sense the intensity of incident filtered IR radiation (R), the intensity of the incident filtered IR radiation (R) being a measure of the concentration of the target gas in the cavity (120).

18. The gas sensor (100) according to claim 1 or 2, wherein the radiation guiding element (170) is arranged for guiding the filtered IR radiation (R) into the optical interaction path (120-1) and for focusing the filtered IR radiation (R) to the IR detector (150).

19. A gas sensor comprising: A substrate having a cavity (120), the cavity (120) being used to provide an optical interaction path (120-1) for interaction of an IR radiation component with a target gas in the cavity (120), wherein an inner surface of the cavity (120) comprises a reflective coating or a metallized layer, and wherein the cavity (120) is accessible to an ambient gas including the target gas, wherein the substrate (110) comprises a first partial substrate (110-1) and a second partial substrate (110-2) bonded to each other, wherein at least one of the first partial substrate (110-1) and the second partial substrate (110-2) comprises a recess for providing the cavity (120) between the bonded first partial substrate (110-1) and the second partial substrate (110-2), a thermal emitter (130) arranged to emit broadband IR radiation (R0) having said IR radiation component, wherein said thermal emitter (130) is formed on said second partial substrate (110-2) and optically coupled to said cavity (120) through an optically transparent area or opening (162) of said second partial substrate (110-2), an IR detector formed on the second partial substrate (110-2) and arranged to provide a detector output signal (S) based on the signal strength of the IR radiation component that has passed through the optical interaction path in the cavity (120) and is received by the IR detector (150) through the optically transparent area or opening (162) of the second partial substrate (110-2); OUT ),as well as a wavelength selective element (140) arranged for filtering the broadband IR radiation (R0) emitted by the thermal emitter (130), wherein the wavelength selective element (140) is optically coupled between the cavity (120) and the IR detector (150) for providing filtered IR radiation (R) comprising the IR radiation component having a central wavelength λ0 to the IR detector (150), and A radiation guiding element (170) is further located in the cavity (120) relative to the reflective coating or metallization layer, for guiding or coupling the filtered IR radiation (R) into the optical interaction path (120-1) and / or for focusing the filtered IR radiation (R) to the IR detector (150), wherein the radiation guiding element (170) is formed on the first partial substrate (110-1).

20. The gas sensor according to claim 19, further comprising: a further IR detector (152) arranged to provide a detector output signal based on the signal strength of the IR radiation that has passed through the optical interaction path (120-1) in the cavity (120) and is received by the further IR detector (152), and A further wavelength selective element (144) is arranged for filtering the broadband IR radiation (R0) emitted by the thermal emitter (130), wherein the further wavelength selective element (144) is optically coupled between the cavity (120) and the further IR detector (152) for providing filtered IR radiation comprising a further IR radiation component having a further central wavelength λ1 to the further IR detector (152).

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