Photoacoustic sensors and associated manufacturing processes

Abstract

Photoacoustic sensor, comprehensive: a layer stack with multiple wafer-bonded layers, wherein the layer stack comprises: a first wafer-bonded layer (2) with an optical MEMS emitter (4) integrated into the first layer (2), wherein the first layer (2) is made of a semiconductor material and wherein the optical MEMS emitter (4) has a movable structure and is integrated into the semiconductor material; a second wafer-bonded layer (6) stacked above the first layer (2) with a MEMS pressure sensor (8) and an optically transparent window (10), wherein the MEMS pressure sensor (8) and the optically transparent window (10) are arranged laterally offset from each other; and a third wafer-bonded layer (12) stacked above the second layer (6) with a cavity (14) for a reference gas (16), wherein the optical MEMS emitter (4) is designed to transmit optical radiation (26) along an optical path, wherein the optical path passes through the optically transparent window (10) and the cavity (14) for the reference gas (16), and wherein the MEMS pressure sensor (8) is located outside the path of the optical path.

Description

Technical field

[0001] The present disclosure relates to photoacoustic sensors and methods for manufacturing photoacoustic sensors. background

[0002] Photoacoustic sensors can be designed, for example, to detect specific gas species in ambient air. In particular, they can detect harmful or hazardous components in the ambient air. The correct functioning of such photoacoustic sensors can therefore be of great importance in many applications, especially when the sensors are intended to guarantee the safety of workers. Manufacturers of photoacoustic sensors are constantly striving to improve their products. In particular, it may be desirable to provide cost-effective photoacoustic sensors with improved designs. Furthermore, it may be desirable to provide improved manufacturing processes for such photoacoustic sensors.

[0003] German patent application DE 10 2018 120 061 A1 concerns a detector module for a photoacoustic gas sensor. German patent application DE 10 2016 205 024 A1 concerns a gas sensor with a MEMS membrane. Brief description

[0004] Several aspects concern a photoacoustic sensor. The photoacoustic sensor comprises a layer stack with multiple wafer-bonded layers. The layer stack includes a first wafer-bonded layer with an optical MEMS emitter integrated into the first layer, wherein the first layer is made of a semiconductor material and the optical MEMS emitter has a movable structure and is integrated into the semiconductor material; a second wafer-bonded layer stacked above the first layer with a MEMS pressure sensor and an optically transparent window, wherein the MEMS pressure sensor and the optically transparent window are arranged laterally offset from each other; and a third wafer-bonded layer stacked above the second layer with a cavity for a reference gas.The optical MEMS emitter is designed to transmit optical radiation along an optical path, wherein the optical path passes through the optically transparent window and the cavity for the reference gas, and wherein the MEMS pressure sensor is located outside the path of the optical path.

[0005] Several aspects relate to a method for fabricating a photoacoustic sensor comprising a layer stack with multiple wafer-bonded layers. The method includes providing a first wafer-bonded layer with an optical MEMS emitter integrated into the first layer, wherein the first layer is made of a semiconductor material and the optical MEMS emitter has a movable structure and is integrated into the semiconductor material; stacking a second wafer-bonded layer with a MEMS pressure sensor and an optically transparent window above the first layer, wherein the MEMS pressure sensor and the optically transparent window are arranged laterally offset from each other; and stacking a third wafer-bonded layer with a cavity for a reference gas above the second layer.The optical MEMS emitter is designed to transmit optical radiation along an optical path, wherein the optical path passes through the optically transparent window and the cavity, and wherein the MEMS pressure sensor is located outside the path of the optical path. Brief description of the drawings

[0006] The devices and methods according to the disclosure are explained in more detail below with reference to the drawings. The elements shown in the drawings are not necessarily drawn to scale relative to one another. Identical reference numerals may denote identical components. Fig. 1 contains the Fig. 1A to 1E, where the Fig. 1A schematically a cross-sectional side view of a photoacoustic sensor 100 according to the disclosure and the Fig. Figures 1B to 1E illustrate top views of parts of the photoacoustic sensor 100. Fig. Figure 2 schematically illustrates a cross-sectional side view of a photoacoustic sensor 200 according to the disclosure. Fig. Figure 3 schematically illustrates a cross-sectional side view of a photoacoustic sensor 300 according to the disclosure. Fig. Figure 4 schematically illustrates a cross-sectional side view of a photoacoustic sensor 400 according to the disclosure. Fig. Figure 5 schematically illustrates a cross-sectional side view of a photoacoustic sensor 500 according to the disclosure. Fig. Figure 6 schematically illustrates a cross-sectional side view of a photoacoustic sensor 600 according to the disclosure. Fig. Figure 7 schematically illustrates a cross-sectional side view of a photoacoustic sensor 700 according to the disclosure. Fig. Figure 8 schematically illustrates a cross-sectional side view of a photoacoustic sensor 800 according to the disclosure. Fig. Figure 9 schematically illustrates a cross-sectional side view of a photoacoustic sensor 900 according to the disclosure. Fig. Figure 10 schematically illustrates a cross-sectional side view of an emitter component 1000 according to the disclosure. Fig. Figure 11 schematically illustrates a cross-sectional side view of a pressure sensor component 1100 according to the disclosure. Fig. Figure 12 schematically illustrates a cross-sectional side view of a photoacoustic sensor 1200 according to the disclosure. Fig. Figure 13 schematically illustrates a perspective view of a photoacoustic sensor 1300 according to the disclosure. Fig. Figure 14 shows a flowchart of a process for manufacturing a photoacoustic sensor according to the disclosure. Detailed description

[0007] The figures described below illustrate devices and methods according to the disclosure. These devices and methods may be presented in a general way to qualitatively describe aspects of the disclosure. They may also have further aspects that, for the sake of simplicity, cannot be shown in the respective figure. However, each example can be expanded to include aspects described in connection with other examples in the disclosure. Thus, explanations relating to one particular figure can apply equally to examples in other figures.

[0008] The photoacoustic sensor (or photoacoustic gas sensor) 100 of the Fig. 1 can have a first layer 2 with an optical MEMS emitter 4. Above the first layer 2, a second layer 6 with a MEMS pressure sensor 8 and an optically transparent window 10 can be stacked. Furthermore, above the second layer 6, a third layer 12 with a cavity 14 for a reference gas 16 can be stacked. In the example of the Fig. 1. The photoacoustic sensor 100 can optionally have a spacer layer 18 arranged between the first layer 2 and the second layer 6. An opening 20 can be formed in the second layer 6 and the spacer layer 18.

[0009] The first layer 2 is made of a semiconductor material, in particular silicon. The thickness of the first layer 2 in the z-direction can, for example, range from approximately 350 micrometers to approximately 450 micrometers. The optical MEMS emitter 4 is integrated into the first layer 2 or its semiconductor material. Thus, the first layer 2 can also be referred to as a semiconductor chip or MEMS semiconductor chip. The optical MEMS emitter 4 has a movable MEMS structure, which can, for example, be in the form of a heating membrane for generating optical radiation 26. Fig. Figure 1E shows a top view of the first layer 2. From the Fig. As can be seen in Figure 1E, the optical MEMS emitter 4, or its movable structure, can have a circular shape as an example. In other examples, this shape can be chosen differently, for example oval, rectangular, square, etc.

[0010] The first layer 2 can be considered a photoacoustic emitter unit of the photoacoustic sensor 100. The optical MEMS emitter 4 can, in particular, be a broadband emitter designed to emit optical radiation 26 over a wide frequency range. In other words, the radiation 26 emitted by the broadband emitter does not have only predetermined frequencies or frequency bands.

[0011] The terms "optical" and "optical radiation" used in this description can generally refer to a sub-region of the electromagnetic spectrum with wavelengths between approximately 100 nm and approximately 100 µm. That is to say, the optical radiation 26 can, in particular, include at least one of the following: ultraviolet (UV) radiation with a wavelength of approximately 100 nm to approximately 380 nm, infrared (IR) radiation with a wavelength of approximately 780 nm to approximately 100 µm, or radiation with a wavelength of approximately 780 nm to approximately 5 µm, i.e., near-infrared radiation and parts of the mid-infrared radiation. The latter range can include, among others, the absorption lines / bands of carbon dioxide at 4.26 µm and other gas species. More specifically, the optical radiation 26 can have a wavelength of approximately 300 nm to approximately 20 µm.

[0012] The optical MEMS emitter 4 can be configured to emit optical pulses with a predetermined repetition frequency and one or more predetermined wavelengths. A predetermined wavelength can encompass an absorption band of a gas to be detected or of the reference gas 16. The repetition frequency of the optical pulses can be within a low-frequency range or within a frequency range of approximately 1 Hz to approximately 10 kHz, particularly from approximately 1 Hz to approximately 1 kHz. More specifically, a typical frequency range can be between approximately 1 Hz and approximately 100 Hz, corresponding to a pulse duration range of approximately 0.01 s to approximately 1 s.

[0013] Layer 2 can optionally include additional electronic components that may be integrated into a semiconductor material of Layer 2. For example, Layer 2 may include a logic circuit (not shown) designed to logically process signals acquired by the MEMS pressure sensor 8 and / or to control the optical MEMS emitter 4. The logic circuit may, for example, be designed for one or more functions, including control, signal processing, digitization, signal amplification, etc. For instance, the logic circuit may be implemented as an ASIC (Application Specific Integrated Circuit).

[0014] The first layer 2 can have one or more electrical connections 22, which can be arranged, for example, on the top side of the first layer 2. In the top view of the Fig. 1E, for example, the first layer 2 can have four electrical connections 22. The electrical connections 22 can be contacted, for example, by one or more electrical connecting elements 24. In the Fig. Figure 1A shows the electrical connection element 24 as an example of a bond wire. The optical MEMS emitter 4, or its movable structure, can be electrically contacted and, for example, controlled by other components (not shown), particularly external ones, via the electrical connection element 24 and the electrical connection 22.

[0015] The second layer 6 can, for example, be made of a semiconductor material, particularly silicon. The thickness of the second layer 6 in the z-direction can range from approximately 350 micrometers to approximately 450 micrometers. The MEMS pressure sensor 8, or one or more movable MEMS structures of the MEMS pressure sensor 8, can be integrated into the second layer 6 or its semiconductor material. Thus, the second layer 6 can be referred to as a semiconductor chip or MEMS semiconductor chip. The MEMS pressure sensors specified in this description can be, for example, microphones or any other type of pressure sensor or pressure-sensitive sensor, which may be based, for example, on piezoelectric and / or capacitive sensor technology. Fig. Figure 1C shows a top view of the second layer 6. From the Fig. Figure 1C shows that the MEMS pressure sensor 8, or its movable structure, can have a circular shape as an example. In other examples, this shape can be chosen differently, for example oval, rectangular, square, etc. The second layer 6 can be considered a photoacoustic detector unit of the photoacoustic sensor 100.

[0016] Similar to the first layer 2, the second layer 6 can have one or more electrical connections 22, which can be located, for example, on the top side of the second layer 6. In the top view of the Fig. In 1C, the second layer 6 can, for example, have four electrical connections 22. The electrical connections 22 can be contacted, for example, by one or more electrical connecting elements 24. In the example of the Fig. Figure 1A shows the electrical connection element 24 as an example of a bond wire. Signals detected by the MEMS pressure sensor 8 or its movable structure can be transmitted via the electrical connection 22 and the electrical connection element 24 to other components, in particular external ones (not shown).

[0017] The MEMS pressure sensor 8 and the optically transparent window 10 can be arranged laterally, i.e., offset from each other in the x-direction and / or in the y-direction. For example, the optically transparent window 10 can be made of the semiconductor material of the second layer 6. The thickness of the optically transparent window 10 in the z-direction can, for example, be in the range of approximately 100 micrometers to approximately 200 micrometers. From the top view of the Fig. As shown in Figure 1C, the optically transparent window 10 can, for example, have a circular shape. In other examples, the shape can be chosen differently, for example oval, rectangular, square, etc. The optically transparent window 10 can be designed to allow at least some of the optical radiation 26 to pass through. In this context, it should be noted that a silicon material can be at least partially IR-transparent, i.e., permeable to IR radiation.

[0018] In one example, the optically transparent window 10 can have a bandpass structure (not shown) designed to allow at least one wavelength of optical radiation from an absorption band and / or absorption line of the reference gas 16 to pass through. In another example, a bandpass structure can be provided by depositing one or more λ / 4 layers on top of each other onto the optically transparent window 10. These λ / 4 layers can be made of silicon nitride and / or polysilicon, for example. In yet another example, the optically transparent window 10 can have an antireflective coating (not shown) designed to suppress reflection of the optical radiation 26 provided by the optical MEMS emitter 4. The antireflective coating can increase the transmission of the optically transparent window 10.

[0019] The section of opening 20 formed in the second layer 6 can provide a gas channel to the environment (or ambient air) of the photoacoustic sensor 100. In particular, the gas channel can provide a connection to a gas present in the environment that is to be detected. In the example of the Fig. 1A the opening 20 can be located below the optically transparent window 10 and can extend, for example, in the y-direction.

[0020] The third layer 12 can be made of at least one semiconductor material (in particular silicon) or a glass material. The second layer 6 and the third layer 12 can be wafer-bonded, i.e., a connection between the two layers can be made at the wafer level. The cavity 14 for the reference gas 16 can be hermetically sealed. Fig. Figure 1B shows a top view of the third layer 12. From the Fig. Figure 1B shows that the cavity 14 can, by way of example, have a substantially rectangular shape. In other examples, the shape can be chosen differently, for example circular, oval, square, etc. The cavity 14 with the reference gas 16 contained therein can be referred to as the reference cell of the photoacoustic sensor 100. The reference gases 16 specified in this description can be, for example, carbon dioxide, nitrogen oxide, methane, ammonia, etc.

[0021] The following describes the operating principle of photoacoustic sensor 100. The other photoacoustic sensors described herein according to the disclosure can be operated in a similar manner.

[0022] The optical MEMS emitter 4 can transmit the optical radiation 26 along an optical path, which can essentially run in a straight line through the aperture 20 in the spacer layer 18 and the second layer 6, through the optically transparent window 10, and through the reference gas 16. The optical pulses 26 emitted by the optical MEMS emitter 4 can thus pass through the space formed by the aperture 20, which may, for example, be filled with ambient air. As they propagate through the aperture 20, the optical pulses 26 can be at least partially absorbed by components of a gas to be detected, if such a gas is present in the aperture 20 (i.e., in the ambient air). The absorption can be specific to the gas to be detected, e.g., characteristic rotational or vibrational modes of atoms or molecules of the gas to be detected.

[0023] The optical pulses 26 can pass through the optically transparent material of the window 10 into the cavity 14 of the third layer 12 and there encounter atoms or molecules of the reference gas 16. The reference gas 16 can correspond to the gas to be detected. The optical pulses 26 can be at least partially absorbed by the reference gas 16 and cause local pressure increases in the reference gas 16. These pressure increases can be detected by the MEMS pressure sensor 8 or a movable structure of the MEMS pressure sensor 8. The signals detected by the MEMS pressure sensor 8 can be logically processed by one or more circuits (not shown), as already mentioned above.

[0024] If no traces of the gas to be detected are present in the opening 20 or in the ambient air, the optical pulses 26 emitted by the optical MEMS emitter 4 are simply absorbed by the reference gas 16, and the MEMS pressure sensor 8 will acquire a periodic measurement signal with the repetition frequency of the optical pulses 26 and a first amplitude. If, on the other hand, traces of the gas to be detected are present in the opening 20, the optical radiation 26 can also be absorbed by these traces. The MEMS pressure sensor 8 will then output a periodic measurement signal with a second amplitude, which may be smaller than the first amplitude. Based on the magnitudes and profiles of the first and second amplitudes, the presence and / or concentration of the gas to be detected in the ambient air can be determined.If the concentration of the gas to be detected exceeds a predetermined threshold, a signal, in particular a warning signal, can be output by the photoacoustic sensor 100 or an associated device.

[0025] In the example of the Fig. 1. The photoacoustic sensor 100 can optionally have a spacer layer 18 arranged between the first layer 2 and the second layer 6. In particular, the spacer layer 18 and the second layer 6 can be wafer-bonded. A cavity 28 located below the movable structure of the MEMS pressure sensor 8 for the reference gas 16 can be hermetically sealed. The spacer layer 18 can be made of at least one semiconductor material (in particular silicon) or a glass material and can form a section of the opening 20. Fig. Figure 1D shows a top view of the spacer layer 18. From the Fig. In Figure 1D, it can be seen that the section of the opening 20, for example, can have a substantially rectangular shape. In particular, the opening sections of the second layer 6 and the spacer layer 18 can be flush with each other.

[0026] The aperture section of the spacer layer 18 can form part of the gas channel to the environment (or ambient air) of the photoacoustic sensor 100. This gas channel provides a connection to a gas present in the environment that is to be detected. By additionally using the spacer layer 18, the dimension of the aperture 20 in the z-direction, i.e., in the direction of the optical path, can be increased. This allows for an increase in the absorption length, meaning that the optical radiation 26 can be absorbed more effectively due to the longer path it travels through a gas present in the aperture 20 that is to be detected.

[0027] The photoacoustic sensor 100 enables the technical effects described below. The same applies to the other photoacoustic sensors described herein according to the disclosure.

[0028] The optical radiation 26 can be transmitted along the optical path described above and directly strike the reference gas 16. Due to the lateral offset of the MEMS pressure sensor 8 and the optically transparent window 10, the MEMS pressure sensor 8 can be positioned outside the path of the optical system, meaning the optical radiation 26 cannot strike the moving structures of the MEMS pressure sensor 8. This avoids or at least reduces unwanted thermoacoustic interference effects that could distort the readings of the MEMS pressure sensor 8. Such thermoacoustic effects can, in particular, generate an additional pressure pulse due to absorption effects (in conjunction with heating) in the walls of the reference cell.

[0029] When the MEMS pressure sensor 8 is positioned between two silicon layers 12 and 18, only minimal IR absorption of the IR radiation occurs in the reference volume, as the silicon used exhibits high transparency to IR radiation. This also helps to avoid or at least reduce the aforementioned undesirable thermo-acoustic interference effects.

[0030] In the fabrication of the photoacoustic sensor 100, layers 2, 6, 12, and (optionally) 18 can be bonded at the wafer level. This means that at least one of layers 2, 6, 12, and 18 can initially exist in wafer form during the fabrication of the photoacoustic sensor 100. For example, layer 12, or the top layer, can initially be part of a glass or silicon wafer, which can contain any number of additional top layers. The wafers can be bonded together using a wafer bonding technique. Subsequently, the bonded wafers can be separated into multiple photoacoustic sensors 100. Fabricating the photoacoustic sensor 100 at the wafer level using a wafer bonding technique can be more cost-effective compared to other manufacturing methods.

[0031] The layers of the isolated photoacoustic sensor 100 can thus be wafer-bonded, meaning the connections between the individual layers can be in the form of so-called wafer bonds. Depending on the material of the bonded layers, different wafer bonding techniques can be used. For example, wafer bonding without an intermediate layer can be performed. This could involve direct bonding or anodic bonding. Alternatively, wafer bonding can be performed using an intermediate layer. This could involve glass-frit bonding, soldering, eutectic bonding, thermocompression bonding, or adhesive bonding. Adhesive bonding can be carried out, for example, using an adhesive and / or a die-attach film (DAF).

[0032] The photoacoustic sensor 200 of the Fig. 2 can add 100 of the photoacoustic sensor Fig. 1. be at least partially similar. In contrast to the Fig. 1. The photoacoustic sensor 200 can additionally have a further layer 30, which can be stacked below the first layer 2. The additional layer 30 can be made of at least one semiconductor material or a glass material. In one example, the layer 30 can have a logic circuit, which, for example, can be designed to logically process signals detected by the MEMS pressure sensor 8 and / or to control the optical MEMS emitter 4. In this context, and in analogy to the other layers of the photoacoustic sensor 200, the additional layer 30 can, for example, be made from an ASIC wafer or correspond to a single part thereof. In another example, the layer 30 does not necessarily have to have an electrical function, but can, for example, be designed to protect the optical MEMS emitter 4. Analogous to layers 2 and 12 of the Fig. 1. Layer 30 can be electrically contacted via one or more electrical connections 22 and electrical connecting elements 24.

[0033] The photoacoustic sensor 300 of the Fig. 3 may be at least partially similar to the photoacoustic sensors described above, for example the photoacoustic sensor 200 of the Fig. 2. In contrast to Fig. 2 can the layer 30 in the Fig. 3 stacked above layer 12. Layers 30 of the Fig. 2 and Fig. Three can exhibit similar functionalities. Analogous to Fig. 2. Layer 30 can be electrically contacted via one or more electrical connections 22 and electrical connecting elements 24.

[0034] The photoacoustic sensor 400 of the Fig. 4 may be at least partially similar to the photoacoustic sensors described above, for example the photoacoustic sensor 100 of the Fig. 1. In contrast to the Fig. 1 The photoacoustic sensor 400 can have one or more connecting elements 32 which may be designed to mechanically and electrically connect the photoacoustic sensor 400 to a printed circuit board (not shown). In the side view of the Fig. Figure 4 shows two connecting elements 32 as an example. In other examples, the number of connecting elements 32 can be chosen differently, in particular greater than two. In the example of the Fig. 4 The connecting elements 32 can be arranged on the top of the third layer 12, wherein the right connecting element 32 can be electrically connected to the optical MEMS emitter 4 via a first electrical connection 34 and the left connecting element 32 can be electrically connected to the MEMS pressure sensor 8 via a second electrical connection 34.

[0035] In one example, one or more of the electrical connections 34 can be manufactured using a plating technology. The electrical connections 34 can be arranged on a side surface of at least one of the layers of the photoacoustic sensor 400 and can be stepped, i.e., designed to overcome steps that may be formed between stacked layers. The plating technology used can, for example, be based on a lithographic process using a sprayable photomask. In this case, the routing and plating over the affected steps can be performed in a single process step. Alternatively or additionally to the aforementioned plating technology, in other examples the electrical connections 34 can also be configured as through-holes that can extend in the z-direction through the corresponding layers of the photoacoustic sensor 400.Depending on the material of the layers, these connections can be, for example, TSVs (Through Silicon Vias) and / or TGVs (Through Glass Vias).

[0036] The photoacoustic sensor 400 of the Fig. 4 can be directly connected to a printed circuit board (not shown) via the connecting elements 32, for example by soldering. The photoacoustic sensor 400 can therefore be a surface-mount device (SMD). Viewed in the z-direction, the layers of the photoacoustic sensor 400 can be essentially congruent. In other words, the photoacoustic sensor 400 can be a chip-scale package (CSP).

[0037] The photoacoustic sensor 500 of the Fig. 5 may be at least partially similar to the photoacoustic sensors described above. For example, the photoacoustic sensor 500 may be similar to the photoacoustic sensor 400 of the Fig. 4 correspond to an inverted state. In contrast to the Fig. 4. The photoacoustic sensor 500 can be mounted on a printed circuit board 36. The printed circuit board 36 may or may not be considered part of the photoacoustic sensor 500. The printed circuit board 36 may have electrically conductive structures 38 on its upper and / or lower surface, which may be electrically connected to each other via vias 40.

[0038] The photoacoustic sensor 600 of the Fig. 6 may be at least partially similar to the photoacoustic sensors described above, for example the photoacoustic sensor 500 of the Fig. 5. In contrast to the Fig. 5. The photoacoustic sensor 600 can have a photosensitive device 42 arranged on the third layer 12, which can, for example, comprise one or more photodiodes. From the Fig. As can be seen in Figure 6, the photosensitive device 42 can be arranged within the optical path of the optical radiation 26. The photosensitive device 42 can be designed to monitor the output intensity or performance of the optical MEMS emitter 4. By measuring and evaluating the intensity of the emitted optical radiation 26 over time, any degradation of the optical MEMS emitter 4 that may occur over its lifetime can be detected. This can counteract any systematic deviation or drift of the system.

[0039] Furthermore, unlike the photoacoustic sensor 600, it can Fig. 5. A further layer 44 is stacked above the first layer 2. The layer 44 can be made of at least one semiconductor material or a glass material and can be designed to protect the optical MEMS emitter 4. An optically reflective structure 46, for example in the form of a metallization, can be arranged on the underside of the layer 44. In the example of the Fig. 6. The optical MEMS emitter 4 can be designed to transmit the optical radiation 26 predominantly in the negative z-direction. The reflective structure 46 can be designed to reflect optical radiation 26 from the optical MEMS emitter 4 transmitted in a direction deviating from this transmission direction. In the example of the Fig. In particular, optical radiation emitted in the positive z-direction by the optical MEMS emitter 4 can be reflected by the reflecting structure 46. The reflecting structure 46 can thus act as a mirror and amplify the intensity of the optical radiation in the negative z-direction.

[0040] The photoacoustic sensor 700 of the Fig. The photoacoustic sensor 700 can be at least partially similar to the photoacoustic sensors described above. The photoacoustic sensor 700 can have a carrier 48. In one example, the chip carrier 48 can be a laminate, in particular a laminate in the form of a printed circuit board-like organic multilayer substrate. In this respect, the chip carrier 48 can, for example, have similar properties to the printed circuit board 36 of the photoacoustic sensor 700. Fig. 5. In another example, the chip carrier 48 can be a ceramic chip carrier. In yet another example, the chip carrier 48 can be a leadframe, which can be made of a metal and / or a metal alloy.

[0041] A sensor device 50 and a logic circuit 52 in the form of a semiconductor chip or a semiconductor package can be arranged on the upper side of the chip carrier 48. In the example of the Fig. 7. The sensor device 50 can be connected to the sensor 100. Fig. 1. Similar. In the example of the Fig. 7. The sensor device 50, the logic circuit 52, and the carrier 48 can be electrically connected to each other via bond wires. Furthermore, a cover 54 with one or more sound openings 56 can be arranged above the top of the chip carrier 48. The carrier 48 and the cover 54 can form a cavity 58, wherein the sensor device 50 and the logic circuit 52 can be arranged on a mounting surface of the carrier 48 within the cavity 58.

[0042] The cover 54 can, for example, be made of a metal or a metal alloy. The sound opening 56 can optionally be at least partially covered by a membrane (not shown). The membrane can, for example, be porous, thus allowing gas flow or gas exchange between the cavity 58 and the environment of the photoacoustic sensor 700. The membrane can prevent the ingress of dirt, contaminants, particles, etc., into the cavity 58. The membrane can, for example, be made of a metallic and / or organic material.

[0043] The photoacoustic sensor 800 of the Fig. 8 can be used with the photoacoustic sensor 700 of the Fig. 7 are at least partially similar and have the same functionalities. In contrast to the Fig. 7. A sensor device 50 can be used in the example of the Fig. 8 be arranged in a different housing type. The housing of Fig. 8 can have a shell 60 made of a molded compound and a lid 54 with one or more sound openings 56. The shell 60 and the lid 54 can form a cavity 58, wherein the sensor device 50 can be arranged on a bottom surface of the shell 60 in the cavity 58. In the Fig. 8 The sensor device 50 can, for example, be used with the photoacoustic sensor 300 of the Fig. 3. A logic circuit can be integrated into layer 30 of the sensor device 50, as described above.

[0044] In the example of the Fig. 8. The shell 60 and / or the lid 54, for example, can be made from a mold compound. Mold compounds mentioned in this description can include at least one epoxy, a filled epoxy, a glass fiber-filled epoxy, an imide, a thermoplastic, a thermosetting polymer, or a polymer blend. The mold compounds can be manufactured using one or more of the following techniques: compression molding, injection molding, powder molding, liquid molding, etc.

[0045] Electrical conductors 62 can run through the shell 60, via which the photoacoustic sensor 800 can be electrically connected to, for example, a circuit board (not shown). In the example of the Fig. 8. The electronic components arranged in the housing can be electrically connected to the electrical terminals 62 via bond wires. Thus, an electrical connection between a printed circuit board and the electronic components arranged in the housing can be provided via the electrical terminals 62 and the bond wires.

[0046] The photoacoustic sensor 900 of the Fig. 9 can use the photoacoustic sensors 700 and 800 of the Fig. 7 and Fig. 8 are at least partially similar and have the same functionalities. In contrast to the Fig. 7 and Fig. 8 can a sensor device 50 in the Fig. 9 be arranged in a different housing type. In the example of the Fig. 9 the sensor device 50 can for example be the photoacoustic sensor 100 of the Fig. 1. be similar.

[0047] The photoacoustic sensor 900 can have a conductor frame 64 with one or more mounting surfaces (e.g., in the form of die pads 66) and one or more connecting conductors (leads or pins) 68. The connecting conductors 68 can, for example, be bent in a gull-wing shape. In the example of the Fig. 9. The sensor device 50 can be mounted on the top of the die pad 66, and a logic circuit 52 on the underside of the die pad 66. The photoacoustic sensor 900 can have an encapsulation material 70, which may, for example, be made of a molded compound. Furthermore, the photoacoustic sensor 900 can have a cover 54 with one or more sound openings 56, wherein the cover 54 may, for example, be made of a molded compound, a metal, and / or a metal alloy. The logic circuit 52 can be embedded in the encapsulation material 70, thereby protecting any photosensitive structures of the logic circuit 52 from light. The conductor frame 64, the encapsulation material 70, and the cover 54 can form a cavity 58, wherein the sensor device 50 can be arranged in the cavity 58.

[0048] The emitter component 1000 of the Fig. 10 can have a layer 2 with an optical MEMS emitter 4. The layer 2 can, for example, be the second layer 2 from the Fig. 1. A cover 72 can be arranged above layer 2, which can be made of at least one glass material or a semiconductor material. In the example of the Fig. 10. The lid 72 may have a recess. On the inside of the lid 72, for example, an optically reflective structure in the form of a metallization may be present, as already mentioned in connection with the Fig. 6 was described. The cover 72 can be designed, among other things, to protect the optical MEMS emitter 4 and, in particular, its movable structures.

[0049] The pressure sensor component 1100 of the Fig. 11 can have a layer 6 with a MEMS pressure sensor 8 and an optically transparent window 10, wherein the MEMS pressure sensor 8 and the optically transparent window 10 can be arranged laterally offset from each other. The layer 6 can, for example, be located next to the second layer 6 in the Fig. 1. A spacer layer 18 can be arranged on the underside of layer 6 (see [reference]). Fig. 1) Furthermore, another layer 12 with a cavity 14 for a reference gas 16 can be mounted on the top of layer 6 (see [reference]). Fig. 1).

[0050] The photoacoustic sensor 1200 of the Fig. 12 may be at least partially similar to the photoacoustic sensors described above. In particular, the housing of the photoacoustic sensor 1200 may be similar to that described in the Fig. The housing type described in section 9 is at least partially similar. The pressure sensor component 1100 can be mounted on the upper mounting surface of the carrier or die pads 66. Fig. 11 are arranged, while on the lower mounting surface of the die pad 66 the emitter component 1000 of the Fig. The two components 1000 and 1100 can thus be separated from each other by the diepad 66. The conductor frame 64 or the diepad 66 can have an opening 74. Together with the recesses of the components 1000 and 1100, the opening 74 can form a cavity 76, which can form a gas channel to an environment or ambient gas of the photoacoustic sensor 1200, as already described in connection with previous examples. The components 1000 and 1100 can be arranged above the diepad 66 such that the optical MEMS emitter 4 can transmit optical radiation along an optical path, wherein the optical path runs through the opening 74, the cavity 76, the optically transparent window 10 and the cavity 14 for the reference gas 16. Analogous to the previous examples, the MEMS pressure sensor 8 can be located outside the path of the optical path.

[0051] The photoacoustic sensor 1300 of the Fig. 13 can, for example, be used with the photoacoustic sensors 900 and 1200 of the Fig. 9 and Fig. 12 will be similar. Unlike the Fig. 9 and Fig. 12 the carrier can in the Fig. 13 in the form of a PCB-like substrate 78, on the top and / or bottom of which, for example, the components in the Fig. 9 and Fig. The 12 components shown can be arranged in the Fig. 13 These components need not necessarily be visible, as they can be concealed by one or more covers or encapsulation materials 70. The encapsulation materials 70 can have one or more openings 56 that provide a gas connection between the environment of the photoacoustic sensor 1300 and its interior.

[0052] The substrate 78 can remain at least partially uncovered by the encapsulation materials 70 and may have one or more electrical connections 80 on its upper and / or lower surface. The emitter and / or pressure sensor components arranged within the encapsulation materials 70 can be electrically contacted from outside the photoacoustic sensor 1300 via these electrical connections 80. The photoacoustic sensor 1300 need not necessarily be a surface-mountable device. Rather, the photoacoustic sensor 1300 can, for example, be inserted into a socket (not shown) with the portion of the substrate 78 uncovered by the encapsulation materials 70. The socket may contain internal electrical contact elements which can be electrically connected to the electrical connections 80 when the sensor is inserted.

[0053] In the process of Fig. Paragraph 14 describes a method for manufacturing a photoacoustic sensor according to the disclosure. Therefore, the method can be read in conjunction with the preceding examples. The method of Fig. 14 is presented in a general way to qualitatively describe aspects of the revelation. The procedure may include further aspects, which are described in the Fig. Figures 14 are not shown or described for the sake of simplicity. For example, the procedure can be extended to include one or more of the aspects described in connection with the preceding figures.

[0054] In 82, a first layer with an optical MEMS emitter can be provided. In 84, a second layer with a MEMS pressure sensor and an optically transparent window can be stacked above the first layer, the MEMS pressure sensor and the optically transparent window being arranged laterally offset from each other. In 86, a third layer with a cavity for a reference gas can be stacked above the second layer. The optical MEMS emitter can be configured to transmit optical radiation along an optical path, the optical path passing through the optically transparent window and the cavity, and the MEMS pressure sensor can be located outside the path of the optical path. It should be noted that the method of Fig.14 may include one or more further optional actions. For example, stacking the third layer over the second layer may include a wafer bonding action in which the cavity for the reference gas is hermetically sealed. Examples

[0055] The following section explains photoacoustic sensors and related manufacturing processes using examples.

[0056] Example 1 is a photoacoustic sensor comprising: a first layer with an optical MEMS emitter; a second layer stacked above the first layer with a MEMS pressure sensor and an optically transparent window, wherein the MEMS pressure sensor and the optically transparent window are arranged laterally offset from each other; and a third layer stacked above the second layer with a cavity for a reference gas, wherein the optical MEMS emitter is configured to transmit optical radiation along an optical path, the optical path passing through the optically transparent window and the cavity for the reference gas, and wherein the MEMS pressure sensor is arranged outside the path of the optical path.

[0057] Example 2 is a photoacoustic sensor according to Example 1, wherein the second layer and the third layer are wafer-bonded and form a hermetically sealed cavity for the reference gas.

[0058] Example 3 is a photoacoustic sensor according to Example 1 or 2, wherein at least one of the first layer or the second layer is made of a semiconductor material.

[0059] Example 4 is a photoacoustic sensor according to one of the preceding examples, wherein the optically transparent window is made of a second-layer semiconductor material.

[0060] Example 5 is a photoacoustic sensor according to one of the preceding examples, wherein the optically transparent window comprises a bandpass structure designed to allow at least optical radiation with a wavelength of an absorption band or absorption line of the reference gas to pass through.

[0061] Example 6 is a photoacoustic sensor according to one of the preceding examples, wherein the third layer is made of at least one semiconductor material or a glass material.

[0062] Example 7 is a photoacoustic sensor according to one of the preceding examples, wherein the second layer includes an opening that forms a gas channel to an environment of the photoacoustic sensor.

[0063] Example 8 is a photoacoustic sensor according to one of the preceding examples, further comprising: a spacer layer arranged between the first layer and the second layer, having an opening, wherein the optical path passes through the opening of the spacer layer.

[0064] Example 9 is a photoacoustic sensor according to Example 8, wherein the opening of the spacer layer forms part of the gas channel to the environment of the photoacoustic sensor.

[0065] Example 10 is a photoacoustic sensor according to one of the preceding examples, wherein the first layer further comprises a logic circuit designed to logically process signals detected by the MEMS pressure sensor and / or to control the optical MEMS emitter.

[0066] Example 11 is a photoacoustic sensor according to any of Examples 1 to 9, further comprising: a further layer stacked above the first layer or above the third layer, the further layer comprising a logic circuit designed to logically process signals detected by the MEMS pressure sensor and / or to control the optical MEMS emitter.

[0067] Example 12 is a photoacoustic sensor according to any of the preceding examples, further comprising: one or more connecting elements designed to mechanically and electrically connect the photoacoustic sensor to a printed circuit board, the connecting elements being arranged on the third layer and being electrically connected to the optical MEMS emitter and the MEMS pressure sensor via electrical connections.

[0068] Example 13 is a photoacoustic sensor according to Example 12, wherein the electrical connections are manufactured based on a plating technology and are arranged on a side surface of at least one of the layers of the photoacoustic sensor.

[0069] Example 14 is a photoacoustic sensor according to one of the preceding examples, wherein the photoacoustic sensor is a surface-mountable device.

[0070] Example 15 is a photoacoustic sensor according to one of the preceding examples, wherein the photoacoustic sensor is a chip-scale package.

[0071] Example 16 is a photoacoustic sensor according to any of the preceding examples, further comprising: a photosensitive device arranged on the third layer, positioned within the optical path and designed to monitor an output intensity of the optical MEMS emitter.

[0072] Example 17 is a photoacoustic sensor according to any of the preceding examples, further comprising: an optically reflective structure arranged above the first layer, wherein the optical MEMS emitter is configured to transmit optical radiation predominantly in a first direction, and wherein the reflective structure is configured to reflect optical radiation from the optical MEMS emitter transmitted in a direction other than the first direction.

[0073] Example 18 is a photoacoustic sensor according to any of the preceding examples, further comprising: a printed circuit board-like substrate; and a lid with a sound opening, wherein the substrate and the lid form a cavity, the layer stack comprising the first layer, the second layer and the third layer being arranged on a mounting surface of the substrate in the cavity.

[0074] Example 19 is a photoacoustic sensor according to any one of Examples 1 to 17, further comprising: a shell made of a molded compound; and a lid with a sound opening, wherein the shell and the lid form a cavity, the layer stack comprising the first layer, the second layer and the third layer being arranged on a bottom surface of the shell in the cavity.

[0075] Example 20 is a photoacoustic sensor according to any one of Examples 1 to 18, further comprising: a conductor frame, wherein the layer stack with the first layer, the second layer and the third layer is mounted on a first mounting surface of the conductor frame and a logic circuit is mounted on an opposite second mounting surface of the conductor frame; an encapsulation material, wherein the logic circuit is embedded in the encapsulation material; and a cover with a sound opening, wherein the conductor frame, the encapsulation material and the cover form a cavity and the layer stack is arranged in the cavity.

[0076] Example 21 is a photoacoustic sensor comprising: an emitter component comprising: a first layer with an optical MEMS emitter, and a lid arranged over the first layer; and a pressure sensor component separate from the emitter component comprising: a second layer with a MEMS pressure sensor and an optically transparent window, wherein the MEMS pressure sensor and the optically transparent window are arranged laterally offset from each other, and a third layer stacked over the second layer with a cavity for a reference gas, wherein the optical MEMS emitter is configured to transmit optical radiation along an optical path, the optical path passing through the optically transparent window and the cavity for the reference gas, and wherein the MEMS pressure sensor is arranged outside the path of the optical path.

[0077] Example 22 is a photoacoustic sensor according to Example 21, further comprising: a carrier wherein the emitter component and the pressure sensor component are mounted on opposite mounting surfaces of the carrier, wherein the carrier includes an opening and the optical path passes through the opening of the carrier.

[0078] Example 23 is a photoacoustic sensor according to Example 21 or 22, further comprising: an encapsulation material wherein the emitter component is embedded in the encapsulation material; and a lid with a sound opening, wherein the chip carrier, the encapsulation material and the lid form a cavity and the pressure sensor component is arranged in the cavity.

[0079] Example 24 is a method for fabricating a photoacoustic sensor, the method comprising: providing a first layer with an optical MEMS emitter; stacking a second layer with a MEMS pressure sensor and an optically transparent window over the first layer, wherein the MEMS pressure sensor and the optically transparent window are arranged laterally offset from each other; and stacking a third layer with a cavity for a reference gas over the second layer, wherein the optical MEMS emitter is configured to transmit optical radiation along an optical path, the optical path passing through the optically transparent window and the cavity, and wherein the MEMS pressure sensor is arranged outside the path of the optical path.

[0080] Example 25 is a method according to Example 24, wherein the stacking of the third layer over the second layer includes a wafer bonding operation in which the cavity for the reference gas is hermetically sealed.

[0081] Although specific embodiments are presented and described herein, it is obvious to the person skilled in the art that a multitude of alternative and / or equivalent implementations can replace the specific embodiments shown and described without departing from the scope of this disclosure. This application is intended to cover all adaptations or variations of the specific embodiments discussed herein. Therefore, it is intended that this disclosure is limited only to the claims and their equivalents.

Claims

[1] Photoacoustic sensor, comprising: a layer stack with multiple wafer-bonded layers, wherein the layer stack comprises: a first wafer-bonded layer (2) with an optical MEMS emitter (4) integrated into the first layer (2), wherein the first layer (2) is made of a semiconductor material and wherein the optical MEMS emitter (4) has a movable structure and is integrated into the semiconductor material; a second wafer-bonded layer (6) stacked above the first layer (2) with a MEMS pressure sensor (8) and an optically transparent window (10), wherein the MEMS pressure sensor (8) and the optically transparent window (10) are arranged laterally offset from each other; and a third wafer-bonded layer (12) stacked above the second layer (6) with a cavity (14) for a reference gas (16), wherein the optical MEMS emitter (4) is designed to transmit optical radiation (26) along an optical path, wherein the optical path passes through the optically transparent window (10) and the cavity (14) for the reference gas (16), and wherein the MEMS pressure sensor (8) is located outside the path of the optical path. [2] Photoacoustic sensor according to claim 1, wherein the second layer (6) and the third layer (12) are wafer-bonded together and form the cavity (14) for the reference gas (16) hermetically sealed. [3] Photoacoustic sensor according to claim 1 or 2, wherein the second layer (6) is made of a semiconductor material. [4] Photoacoustic sensor according to claim 3, wherein the optically transparent window (10) is made of a semiconductor material of the second layer (6). [5] Photoacoustic sensor according to one of the preceding claims, wherein the optically transparent window (10) comprises a bandpass structure designed to allow at least optical radiation with a wavelength of an absorption band or absorption line of the reference gas (16) to pass through. [6] Photoacoustic sensor according to one of the preceding claims, wherein the third layer (12) is made of at least one semiconductor material or glass material. [7] Photoacoustic sensor according to one of the preceding claims, wherein the second layer (6) comprises an opening (20) which forms a gas channel to an environment of the photoacoustic sensor. [8] Photoacoustic sensor according to any one of the preceding claims, further comprising: a spacer layer (18) arranged between the first layer (2) and the second layer (6) with an opening (20), wherein the optical path passes through the opening (20) of the spacer layer (18). [9] Photoacoustic sensor according to claim 8, wherein the opening (20) of the spacer layer (18) forms part of the gas channel to the environment of the photoacoustic sensor. [10] Photoacoustic sensor according to one of the preceding claims, wherein the first layer (2) further comprises a logic circuit designed to logically process signals detected by the MEMS pressure sensor (8) and / or to control the optical MEMS emitter (4). [11] Photoacoustic sensor according to any one of claims 1 to 9, further comprising: a further layer (30) stacked above the first layer (2) or above the third layer (12), wherein the further layer (30) comprises a logic circuit designed to logically process signals detected by the MEMS pressure sensor (8) and / or to control the optical MEMS emitter (4). [12] Photoacoustic sensor according to any one of the preceding claims, further comprising: one or more connecting elements (32) designed to mechanically and electrically connect the photoacoustic sensor to a printed circuit board (36), wherein the connecting elements (32) are arranged on the third layer (12) and are electrically connected to the optical MEMS emitter (4) and the MEMS pressure sensor (8) via electrical connections (34). [13] Photoacoustic sensor according to claim 12, wherein the electrical connections (34) are manufactured based on a plating technology and are arranged on a side surface of at least one of the layers of the photoacoustic sensor. [14] Photoacoustic sensor according to any of the preceding claims, wherein the photoacoustic sensor is a surface-mountable component. [15] Photoacoustic sensor according to any of the preceding claims, wherein the photoacoustic sensor is a chip-scale package. [16] Photoacoustic sensor according to any one of the preceding claims, further comprising: a photosensitive device (42) arranged on the third layer (12), which is located within the course of the optical path and is designed to monitor an output intensity of the optical MEMS emitter (4). [17] Photoacoustic sensor according to any one of the preceding claims, further comprising: an optically reflective structure (46) arranged above the first layer (2), wherein the optical MEMS emitter (4) is designed to transmit optical radiation predominantly in a first direction, and wherein the reflecting structure (46) is designed to reflect optical radiation transmitted from the optical MEMS emitter (4) in a direction different from the first direction. [18] Photoacoustic sensor according to any one of the preceding claims, further comprising: a printed circuit board-like substrate (48); and a lid (54) with a sound opening (56), wherein the substrate (48) and the lid (54) form a cavity (58), wherein the layer stack with the first layer (2), the second layer (6) and the third layer (12) is arranged on a mounting surface of the substrate (48) in the cavity (58). [19] Photoacoustic sensor according to any one of claims 1 to 17, further comprising: a bowl made from a molded compound (60); and a lid (54) with a sound opening (56), wherein the tray (60) and the lid (54) form a cavity (58), wherein the layer stack with the first layer (2), the second layer (6) and the third layer (12) is arranged on a bottom surface of the tray (60) in the cavity (58). [20] Photoacoustic sensor according to any one of claims 1 to 18, further comprising: a conductor frame (64) wherein the layer stack comprising the first layer (2), the second layer (6) and the third layer (12) is mounted on a first mounting surface of the conductor frame (64) and a logic circuit (52) is mounted on an opposite second mounting surface of the conductor frame (64); an encapsulation material (70), wherein the logic circuit (52) is embedded in the encapsulation material (70); and a lid (54) with a sound opening (56), wherein the ladder frame (64), the encapsulation material (70) and the lid (54) form a cavity (58) and the layer stack is arranged in the cavity (58). [21] Method for manufacturing a photoacoustic sensor comprising a layer stack with several wafer-bonded layers, wherein the method comprises: Providing a first wafer-bonded layer (2) with an optical MEMS emitter (4) integrated into the first layer (2), wherein the first layer (2) is made of a semiconductor material and wherein the optical MEMS emitter (4) has a movable structure and is integrated into the semiconductor material; Stacking a second wafer-bonded layer (6) with a MEMS pressure sensor (8) and an optically transparent window (10) above the first layer (2), wherein the MEMS pressure sensor (8) and the optically transparent window (10) are arranged laterally offset from each other; and Stacking a third wafer-bonded layer (12) with a cavity (14) for a reference gas (16) above the second layer (6), wherein the optical MEMS emitter (4) is designed to transmit optical radiation (26) along an optical path, wherein the optical path passes through the optically transparent window (10) and the cavity (14), and wherein the MEMS pressure sensor (8) is located outside the path of the optical path. [22] Method according to claim 21, wherein the stacking of the third layer (12) over the second layer (6) comprises a wafer bonding operation in which the cavity (14) for the reference gas (16) is hermetically sealed.

Images