Optoacoustic sensor and associated manufacturing method

Abstract

Embodiments of the present disclosure relate to a photoacoustic sensor and a manufacturing method pertaining thereto. A photoacoustic sensor comprises a first layer having an optical MEMS emitter, a second layer stacked on the first layer having a MEMS pressure sensor and a light-transmissive window, wherein the MEMS pressure sensor and the light-transmissive window are arranged laterally offset from each other, and a third layer stacked on the second layer having a cavity for a reference gas. The optical MEMS emitter is designed to transmit optical radiation along an optical path, wherein the optical path extends through the light-transmissive window and the cavity for the reference gas, and wherein the MEMS pressure sensor is arranged outside the extended course of the optical path.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to a photoacoustic sensor and a method of manufacturing a photoacoustic sensor. BACKGROUND

[0002] A photoacoustic sensor can for example be designed for detecting certain gas species in ambient air. In particular, harmful or dangerous components in ambient air can be proven. Thus, a proper functioning of such a photoacoustic sensor is of great importance in many applications, in particular when the photoacoustic sensor needs to guarantee the safety of staff. Photoacoustic sensor manufacturers continuously strive to improve their products. In particular, it can be desirable to provide inexpensive photoacoustic sensors with improved structure. Furthermore, it can be desirable to provide improved methods of manufacturing such photoacoustic sensors. SUMMARY

[0003] Various aspects relate to a photoacoustic sensor. The photoacoustic sensor comprises a first layer having an optical MEMS emitter, a second layer stacked on the first layer having a MEMS pressure sensor and a light-transmissive window, wherein the MEMS pressure sensor and the light-transmissive window are arranged laterally offset from each other, and a third layer stacked on the second layer having a cavity for a reference gas. The optical MEMS emitter is designed to transmit optical radiation along an optical path, wherein the optical path extends through the light-transmissive window and the cavity for the reference gas, and wherein the MEMS pressure sensor is arranged outside the extended course of the optical path.

[0004] Various aspects relate to a photoacoustic sensor. The photoacoustic sensor comprises an emitter component comprising a first layer having an optical MEMS emitter and a cover arranged on the first layer. The photoacoustic sensor further comprises a pressure sensor component separate from the emitter component, the pressure sensor component comprising a second layer having a MEMS pressure sensor and a light-transmissive window, wherein the MEMS pressure sensor and the light-transmissive window are arranged laterally offset from each other, and a third layer stacked on the second layer having a cavity for a reference gas, wherein the optical MEMS emitter is designed to transmit optical radiation along an optical path, wherein the optical path extends through the light-transmissive window and the cavity for the reference gas, and wherein the MEMS pressure sensor is arranged outside the extended course of the optical path.

[0005] Various aspects relate to a method of manufacturing a photoacoustic sensor. The method comprises providing a first layer having an optical MEMS emitter, stacking a second layer having a MEMS pressure sensor and a light-transmissive window on the first layer, the MEMS pressure sensor and the light-transmissive window being arranged laterally offset from each other, and stacking a third layer having a cavity for a reference gas on the second layer. The optical MEMS emitter is designed to transmit optical radiation along an optical path, wherein the optical path extends through the light-transmissive window and the cavity, and wherein the MEMS pressure sensor is arranged outside the extended course of the optical path. BRIEF DESCRIPTION OF DRAWINGS

[0006] The apparatus and method according to the present disclosure are explained in more detail below, with reference to the drawings. The elements illustrated in the drawings are not necessarily drawn to scale relative to each other. The same reference symbols can denote the same parts.

[0007] Fig. 1 contains Figures 1A-1E , Figure 1A A cross-sectional side view of a photoacoustic sensor 100 according to the present disclosure is schematically illustrated, while Figures 1B-1E A top view of a portion of the photoacoustic sensor 100 is illustrated.

[0008] Figure 2 A cross-sectional side view of a photoacoustic sensor 200 according to the present disclosure is schematically illustrated.

[0009] Figure 3 A cross-sectional side view of a photoacoustic sensor 300 according to the present disclosure is schematically illustrated.

[0010] Figure 4 A cross-sectional side view of a photoacoustic sensor 400 according to the present disclosure is schematically illustrated.

[0011] Figure 5 A cross-sectional side view of a photoacoustic sensor 500 according to the present disclosure is schematically illustrated.

[0012] Figure 6 A cross-sectional side view of a photoacoustic sensor 600 according to the present disclosure is schematically illustrated.

[0013] Figure 7 A cross-sectional side view of a photoacoustic sensor 700 according to the present disclosure is schematically illustrated.

[0014] Figure 8 A cross-sectional side view of a photoacoustic sensor 800 according to the present disclosure is schematically illustrated.

[0015] Figure 9 A cross-sectional side view of a photoacoustic sensor 900 according to the present disclosure is schematically illustrated.

[0016] Figure 10 A cross-sectional side view of an emitter component 1000 according to the present disclosure is schematically illustrated.

[0017] Figure 11 A cross-sectional side view of a pressure sensor component 1100 according to the present disclosure is schematically illustrated.

[0018] Figure 12 A cross-sectional side view of a photoacoustic sensor 1200 according to the present disclosure is schematically illustrated.

[0019] Figure 13A perspective view of a photoacoustic sensor 1300 according to the present disclosure is schematically shown.

[0020] Figure 14 A flowchart of a method for manufacturing a photoacoustic sensor according to the present disclosure is shown. DETAILED DESCRIPTION

[0021] The figures described below show apparatuses and methods according to the present disclosure. The described apparatuses and methods can be presented in a general way in order to qualitatively describe aspects of the present disclosure. The described apparatuses and methods can have further aspects which can not be shown in the respective figures for the sake of simplicity. However, the respective examples can be extended to include aspects described in connection with other examples according to the present disclosure. Thus, the explanations relating to a particular figure apply equally to the examples of the other figures.

[0022] The photoacoustic sensor (or photoacoustic gas sensor) 100 of Fig. 1 can have a first layer 2 with an optical MEMS emitter 4. A second layer 6 with a MEMS pressure sensor 8 and a light-transmissive window 10 can be stacked on top of the first layer 2. Furthermore, a third layer 12 with a cavity 14 for a reference gas 16 can be stacked on top of the second layer 6. In the example of 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.

[0023] The first layer 2 can be made of a semiconductor material, in particular silicon, for example. In this case, the first layer 2 can have a thickness in the z-direction in the range of, for example, from about 350 micrometers to about 450 micrometers. The optical MEMS emitter 4 can be integrated into the first layer 2 or its semiconductor material. The first layer 2 can thus also be referred to as a semiconductor chip or a MEMS semiconductor chip. In one example, the optical MEMS emitter 4 can have a movable MEMS structure which can be implemented in the form of a heating film for generating the optical radiation 26, for example. Figure 1E A top view of the first layer 2 is shown. From Figure 1E It can be seen that the optical MEMS emitter 4 or its movable structure can have a circular shape, for example. In further examples, this shape can be chosen differently, for example elliptical, rectangular, square, etc.

[0024] The first layer 2 can be considered a photoacoustic emission unit of the photoacoustic sensor 100. The optical MEMS emitter 4 can be a broadband emitter in particular, which can be designed to emit the optical radiation 26 in a wide frequency range. In other words, the radiation 26 emitted by the broadband emitter can not only have a predetermined frequency but also a predetermined frequency band.

[0025] The terms "optical" and "optical radiation" as used in the present specification can generally refer to a sub-range of the electromagnetic spectrum with wavelengths between about 100 nm and about 100 pm. That is, the optical radiation 26 can particularly include at least one of ultraviolet (UV) radiation with wavelengths of about 100 nm to about 380 nm, infrared (IR) radiation with wavelengths of about 780 nm to about 100 pm, or radiation with wavelengths of about 780 nm to about 5 pm, i.e. near infrared radiation and partial mid infrared radiation. Further, the latter range can include the carbon dioxide absorption line / absorption band at 4.26 pm and other gas species. More specifically, the optical radiation 26 can have wavelengths of about 300 nm to about 20 pm.

[0026] The optical MEMS transmitter 4 can be designed to emit light pulses with a predetermined repetition frequency and one or more predetermined wavelengths. The predetermined wavelengths can include absorption bands of a gas to be probed or the reference gas 16. The repetition frequency of the light pulses can be in a low frequency range or in a frequency range from about 1 Hz to about 10 kHz, particularly from about 1 Hz to about 1 kHz. More specifically, a typical frequency range can be between about 1 Hz and about 100 Hz, corresponding to a pulse duration range of about 0.01 s to about 1 s.

[0027] The first layer 2 can optionally have further electronic elements which can be integrated into the semiconductor material of the first layer 2. In one example, the first layer 2 can have a logic circuit (not shown) which can be designed to logically process signals detected by the MEMS pressure sensor 8 and / or to control the optical MEMS transmitter 4. For example, the logic circuit can be designed for one or more of a control function, signal processing, digitization, signal amplification, etc. For example, the logic circuit can be designed in the form of an ASIC (application specific integrated circuit).

[0028] The first layer 2 can have one or more electrical interfaces 22 which can be arranged, for example, at the top side of the first layer 2. Figure 1E In a top view, the first layer 2 can exemplarily have four electrical interfaces 22. The electrical interfaces 22 can be electrically connected, for example, by one or more electrical connection elements 24. In Figure 1A In the example, the electrical connection elements 24 are exemplarily shown by bonding wires. The optical MEMS transmitter 4 or its movable structure can be electrically contacted and, for example, controlled by the electrical connection elements 24 and the electrical interfaces 22 to further, particularly external, components (not shown).

[0029] The second layer 6 can for example be made of a semiconductor material, in particular silicon. The thickness of the second layer 6 in the z-direction can be in the range from about 350 micrometers to about 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. The second layer 6 can thus be referred to as a semiconductor chip or a MEMS semiconductor chip. The MEMS pressure sensor specified in the present description can for example be a microphone or any other type of pressure sensor or pressure-sensitive sensor, which can for example be based on piezoelectric sensor technology and / or capacitive sensor technology. Figure 1C A top view of the second layer 6 is shown. From Figure 1C It can be seen that the MEMS pressure sensor 8 or its movable structure can for example have a circular shape. In further examples, the shape can be chosen differently, for example elliptical, rectangular, square, etc. The second layer 6 can be regarded as a photoacoustic probe unit of the photoacoustic sensor 100.

[0030] Similar to the first layer 2, the second layer 6 can have one or more electrical interfaces 22, which can be arranged for example at the top side of the second layer 6. The electrical interfaces 22 can be electrically connected for example by one or more electrical connection elements 24. Figure 1C In the top view of the second layer 6, the second layer 6 can for example have four electrical interfaces 22. The electrical interfaces 22 can be electrically connected for example by one or more electrical connection elements 24. Figure 1A In the example of the second layer 6, the electrical connection elements 24 are shown by bonding wires. Signals detected by the MEMS pressure sensor 8 or its movable structure can be transmitted through the electrical interfaces 22 and the electrical connection elements 24 to further, in particular external, components (not shown).

[0031] The MEMS pressure sensor 8 and the light-transmissive window 10 can be arranged laterally, i.e. in the x-direction and / or y-direction, offset from each other. In one example, the light-transmissive window 10 can be made of the semiconductor material of the second layer 6. The thickness of the light-transmissive window 10 in the z-direction can for example be in the range from about 100 micrometers to about 200 micrometers. From Figure 1C It can be seen from the top view of the second layer 6 that the light-transmissive window 10 can for example have a circular shape. In further examples, the shape can be chosen differently, for example elliptical, rectangular, square, etc. The light-transmissive window 10 can be designed to allow at least a portion of the optical radiation 26 to pass through. It is noted in this context that the silicon material can be at least partially IR transparent, i.e. IR radiation penetrable.

[0032] In one example, the light-transmissive window 10 can have a bandpass structure (not shown) which can be designed to allow at least light radiation having a wavelength of an absorption band and / or an absorption line of the reference gas 16 to pass through. In one example, the bandpass structure can be provided by vapor deposition of the light-transmissive window 10 with one or more A / 4 layers on top of each other. In this case, the A / 4 layers can be made of, for example, silicon nitride and / or polysilicon. In another example, the light-transmissive window 10 can have an anti-reflection coating (not shown) which can be designed to suppress reflection of the light radiation 26 which can be provided by the optical MEMS emitter 4. The transmissivity of the light-transmissive window 10 can be increased by the anti-reflection coating.

[0033] The section of the opening 20 formed in the second layer 6 can form a gas channel to the surrounding environment (or ambient air) of the photoacoustic sensor 100. The gas channel can in particular provide a connection to a gas in the surrounding environment and to be probed. In Figure 1A In an example, the opening 20 can be arranged below the light-transmissive window 10 and extend, for example, in the y-direction.

[0034] The third layer 12 can be made of at least one of a semiconductor material (in particular silicon) or a glass material. The second layer 6 and the third layer 12 can be wafer bonded, i.e. the connection of the two layers can be made at wafer level. The cavity 14 for the reference gas 16 can be designed to be hermetically sealed. Figure 1B A top view of the third layer 12 is shown. From Figure 1B It can be seen that the cavity 14 can have, for example, a substantially rectangular shape. In further examples, the shape can be chosen differently, for example circular, elliptical, square, etc. The cavity 14 with the reference gas 16 located therein can be referred to as a reference unit of the photoacoustic sensor 100. For example, the reference gas 16 specified in the present description can be carbon dioxide, nitrogen oxide, methane, ammonia, etc.

[0035] The operation mode of the photoacoustic sensor 100 is described in the following. Other photoacoustic sensors according to the present disclosure described herein can be operated in an analogous manner.

[0036] The optical MEMS emitter 4 can transmit the light radiation 26 along an optical path which can substantially extend in a straight line through the spacer layer 18 and the opening 20 in the second layer 6, through the light-transmissive window 10 and the reference gas 16. The light pulse 26 emitted by the optical MEMS emitter 4 can thus pass through an intermediate space formed by the opening 20 which can be filled, for example, with ambient air. When propagating through the opening 20, the light pulse 26 can be at least partially absorbed by a gas to be probed, if such a gas is present in the opening 20 (i.e. in the ambient air). The absorption can be specific to the gas to be probed, for example a characteristic rotational or oscillation mode of atoms or molecules of the gas to be probed.

[0037] The light pulses 26 can enter the cavity 14 of the third layer 12 through the optically transparent material of the window 10 and there encounter atoms or molecules of the reference gas 16. The reference gas 16 can correspond to the gas to be probed. The light 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 the 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 described above.

[0038] If no share of the gas to be probed is present in the opening 20 or in the ambient air, the light pulses 26 emitted by the optical MEMS transmitter 4 are only absorbed by the reference gas 16 and the MEMS pressure sensor 8 is detected by the periodic measurement signal with the repetition frequency and the first amplitude of the light pulses 26. In contrast thereto, if a share of the gas to be probed is present in the opening 20, the light radiation 26 can additionally be absorbed by these shares. The MEMS pressure sensor 8 will then output a periodic measurement signal with a second amplitude, which can be smaller than the first amplitude. Based on the size and the course of the first and second amplitudes, the presence and / or the concentration of the gas to be probed in the ambient air can be determined. If the concentration of the gas to be probed exceeds a predetermined threshold value, the photoacoustic sensor 100 or a device connected therewith can output a signal, in particular a warning signal.

[0039] In the example of 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. In this case, a cavity 28 for the reference gas 16 located below the movable structure of the MEMS pressure sensor 8 can be designed to be hermetically sealed. The spacer layer 18 can be made of at least one of a semiconductor material, in particular silicon, or a glass material and can form one section of the opening 20. Figure 1D A top view of the spacer layer 18 is shown. From Figure 1D It can be seen that this section of the opening 20 can have a substantially rectangular shape, for example. In particular, the opening portions of the second layer 6 and the spacer layer 18 can terminate flush with each other.

[0040] The opening section of the spacer layer 18 can form part of a gas channel leading to the ambient environment of the photoacoustic sensor 100 (or the ambient air). A connection to the gas to be probed and present in the ambient can be provided by a gas duct. By the additional use of the spacer layer 18, the size of the opening 20 in the z-direction, i.e. the direction of the light path, can be enlarged. In this way, an increase in the absorption length can be provided, i.e. the light radiation 26 can be better absorbed due to the lengthened path through the gas to be probed and located in the opening 20.

[0041] The photoacoustic sensor 100 can provide the following technical effects. The same applies to the further photoacoustic sensors described herein according to the present disclosure.

[0042] The optical radiation 26 can be transmitted along the above-mentioned optical path and in the process directly encounters the reference gas 16. Due to the lateral offset of the MEMS pressure sensor 8 and the light-transmissive window 10, the MEMS pressure sensor 8 can be arranged outside the extended course of the optical path, i.e. the optical radiation 26 does not encounter the movable structure of the MEMS pressure sensor 8. In this way, unwanted thermoacoustic interference effects, which can lead to detection errors of the MEMS pressure sensor 8, can be avoided or at least reduced. Due to absorption effects in the walls of the reference cell (associated with heating), such thermoacoustic effects can in particular generate additional pressure pulses.

[0043] If the MEMS pressure sensor 8 is arranged between the two silicon layers 12 and 18, only slight IR absorption of the IR radiation can occur in the reference volume, since the silicon used has a high transparency for the IR radiation. In this way, too, the mentioned unwanted thermoacoustic interference effects can be avoided or at least reduced.

[0044] During production of the photoacoustic sensor 100, the layers 2, 6, 12 and (optionally) 18 can be connected at wafer level. This means that at least one of the layers 2, 6, 12 and 18 can initially be in the form of a wafer during production of the photoacoustic sensor 100. For example, the layer or cover 12 can initially be part of a glass wafer or a silicon wafer, which can comprise any number of further covers. The wafers can be connected to one another using wafer bonding techniques. The bonded wafers can then be divided into a plurality of photoacoustic sensors 100. Manufacturing the photoacoustic sensor 100 at wafer level using wafer bonding techniques can be more cost-effective than other manufacturing methods.

[0045] The layers of the photoacoustic sensor 100 that are separated can thus be wafer bonded, i.e. the connection between the individual layers can be in the form of so-called wafer bonding. Depending on the materials of the layers that are joined to one another, different wafer bonding techniques can be used. In one example, it can be wafer bonding without an intermediate layer. This can in particular be direct bonding or anodic bonding. Another example can be wafer bonding with an intermediate layer. This can in particular be glass frit bonding, soldering, eutectic bonding, thermocompression bonding or adhesive bonding. For example, the bonding can be carried out using an adhesive and / or a die attach film (DAF).

[0046] Figure 2The photoacoustic sensor 200 can at least partially resemble the photoacoustic sensor 100 of Fig. 1. In contrast to 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 of a 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 similar to the further layer of the photoacoustic sensor 200, the additional layer 30 can for example be manufactured from an ASIC wafer or correspond to an isolated portion 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. Similar to the layers 2 and 12 in Fig. 1, this layer 30 can be electrically contacted by one or more electrical interfaces 22 and electrical connection elements 24.

[0047] Figure 3 The photoacoustic sensor 300 can at least partially resemble the photoacoustic sensors described above, for example Figure 2 The photoacoustic sensor 200. In contrast to Figure 2 Figure 3 The layer 30 in Figure 2 and 3 The layer 30 can have similar functions. Similar to Figure 2 The layer 30 can be electrically contacted by one or more electrical interfaces 22 and electrical connection elements 24.

[0048] Figure 4 The photoacoustic sensor 400 can at least partially resemble the photoacoustic sensors described previously, for example the photoacoustic sensor 100 of Fig. 1. In contrast to Fig. 1, the photoacoustic sensor 400 can be designed to be mechanically and electrically connected to a circuit board (not shown). In Figure 4 In a side view, two connection elements 32 are exemplarily shown. In further examples, the number of connection elements 32 can be chosen differently, in particular greater than two. In Figure 4 In the example of Fig. 4, the connection elements 32 can be arranged on the top side of the third layer 12, wherein the right connection element 32 is connected with the optical MEMS emitter 4 via a first electrical connection 34, while the left connection element 32 is electrically connected with the MEMS pressure sensor 8 via a second electrical connection 34.

[0049] ​In one example, one or more electrical connections 34 can be fabricated using electroplating technology. The electrical connections 34 can be disposed on the side surface of at least one layer of the photoacoustic sensor 400 and extend in a stepped manner, i.e., designed to overcome the steps that may form between stacked layers. For example, the electroplating technology used can be based on a photolithography process using a sprayable photomask. Wiring and electroplating over the steps involved can be achieved in a single step. As an alternative or supplement to the above-described electroplating technology, in another example, the electrical connections 34 can also be designed as electrically through-connections that can pass through the corresponding layers of the photoacoustic sensor 400 in the z-direction. Depending on the material of the layers, these through-connections can be, for example, TSVs (Through Silicon Vias) and / or TGVs (Through Glass Vias).

[0050] Figure 4 The photoacoustic sensor 400 can be directly connected to a circuit board (not shown) via connecting element 32, for example, through a soldering process. The photoacoustic sensor 400 can therefore be a surface-mountable component or an SMD (surface mount device). Viewed in the z-direction, the layers of the photoacoustic sensor 400 can be substantially stacked. In other words, the photoacoustic sensor 400 can be a chip-scale package (CSP) or a chip-scale housing.

[0051] Figure 5 The photoacoustic sensor 500 can be at least partially similar to the photoacoustic sensor described above. For example, the photoacoustic sensor 500 can correspond to a sensor in an inverted state. Figure 4 The photoacoustic sensor 400. With Figure 4 Conversely, the photoacoustic sensor 500 may be mounted on a circuit board 36. The circuit board 36 may or may not be considered part of the photoacoustic sensor 500. The circuit board 36 may have conductive structures 38 on its top and / or bottom, which can be electrically connected to each other through through-holes 40.

[0052] Figure 6 The photoacoustic sensor 600 may be at least partially similar to the previously described photoacoustic sensor, for example... Figure 5 The photoacoustic sensor 500. With Figure 5 Unlike other photoacoustic sensors, the photoacoustic sensor 600 may have a photosensitive device 42 arranged on the third layer 12, such as including one or more photodiodes. Figure 6 As can be seen, the photosensitive device 42 can be arranged within the optical path extension of the light 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 light radiation 26 over time, potential degradation of the optical MEMS emitter 4 during its lifespan can be detected. This can thus compensate for system bias or drift.

[0053] and Figure 5Differently, the photoacoustic sensor 600 can also have a further layer 44 stacked on top of the first layer 2. This layer 44 can be made of at least one of a semiconductor material or a glass material and can be configured to protect the optical MEMS transmitter 4. An optical reflective structure 46 can be arranged, for example in a metallized form, on the bottom side of the layer 44. In Figure 6 In an example, the optical MEMS transmitter 4 can be designed to mainly transmit the optical radiation 26 in the negative z-direction. The reflective structure 46 can be designed to reflect the optical radiation 26 of the optical MEMS transmitter 4 which is transmitted in a direction deviating from this transmission direction. In Figure 6 In an example, the optical radiation emitted from the optical MEMS transmitter 4 in the positive z-direction can be reflected by the reflective structure 46. The reflective structure 46 can thus act as a mirror and enhance the intensity of the optical radiation in the negative z-direction.

[0054] Figure 7 The photoacoustic sensor 700 can at least partially resemble the photoacoustic sensor 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 an organic multi-layer substrate similar to a circuit board. In this regard, the chip carrier 48 can for example have properties similar to the circuit board 36 of Figure 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 lead frame, which can be made of a metal and / or a metal alloy.

[0055] The sensor device 50 and the logic circuit 52 in the form of a semiconductor chip or a semiconductor package can be arranged on the top side of the chip carrier 48. In Figure 7 In an example, the sensor device 50 can resemble the sensor 100 in Fig. 1. In Figure 7 In an example, the sensor device 50, the logic circuit 52 and the carrier 48 can be electrically connected to each other by bonding wires. Furthermore, a cover 54 having one or more acoustic apertures 56 can be arranged on top of the top side 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 face of the carrier 48 in the cavity 58.

[0056] The cover 54 can for example be made of a metal or a metal alloy. The acoustic apertures 56 can optionally be at least partially covered by a membrane (not shown). The membrane can for example be porous, such that an air flow or gas exchange can be provided between the cavity 58 and the ambient environment of the photoacoustic sensor 700. The membrane can prevent dirt, contaminants, particles and the like from penetrating into the cavity 58. The membrane can for example be made of a metal and / or an organic material.

[0057] Figure 8 The photoacoustic sensor 800 can at least partially resemble the photoacoustic sensor 700 described above. The photoacoustic sensor 800 can have a carrier 48. In one example, the chip carrier 48 can be a laminate, in particular a laminate in the form of an organic multi-layer substrate similar to a circuit board. In this regard, the chip carrier 48 can for example have properties similar to the circuit board 36 of Figure 7The photoacoustic sensor 700 has the same function. (And...) Figure 7 different, Figure 8 The sensor device 50 in the example can be arranged in other types. Figure 8 The housing may have an outer jacket 60 made of a molding compound and a cover 54 with one or more acoustic holes 56. The outer jacket 60 and the cover 54 may form a cavity 58, in which the sensor device 50 may be arranged on the bottom surface of the outer jacket 60 within the cavity 58. For example, in Figure 8 In the middle, the sensor device 50 can be similar to Figure 3 The photoacoustic sensor 300. As described above, the logic circuitry can be integrated into layer 30 of the sensor device 50.

[0058] exist Figure 8 In the example, the outer casing 60 and / or the cover 54 may be made of, for example, a molding compound. Molding compounds mentioned in this specification may include at least one of epoxy resins, filled epoxy resins, glass fiber filled epoxy resins, imides, thermoplastics, thermosetting polymers, and polymer blends. Molding compounds may be made based on one or more of the following techniques: compression molding, injection molding, powder molding, liquid molding, etc.

[0059] The electrical interface conductor 62 can extend through the jacket 60, and the photoacoustic sensor 800 can be electrically connected to a circuit board (not shown) via the electrical interface conductor. Figure 8 In this example, the electronic components arranged in the housing can be electrically connected to the electrical interface conductor 62 via bonding wires. Therefore, an electrical connection between the circuit board and the electronic components arranged in the housing can be provided via the electrical interface conductor 62 and the bonding wires.

[0060] Figure 9 The photoacoustic sensor 900 can be at least partially similar to Figure 7 and 8 The photoacoustic sensors 700 and 800 have the same functions. Figure 7 and 8 different, Figure 9 The sensor device 50 can be arranged in other ways. For example, in Figure 9 In the example, sensor device 50 can be similar to photoacoustic sensor 100 of Figure 1.

[0061] The photoacoustic sensor 900 may have a lead frame 64 having one or more mounting surfaces (e.g., in the form of a chip pad 66) and one or more interface conductors (leads or pins) 68. The interface conductors 68 may, for example, be bent into a wing shape (“gull-wing”). Figure 9In this example, sensor device 50 may be mounted on the top side of chip pad 66, while logic circuitry 52 may be mounted on the bottom side of chip pad 66. Photoacoustic sensor 900 may have encapsulation material 70, which may be made, for example, of a molding compound. Furthermore, photoacoustic sensor 900 may have a cover 54 with one or more acoustic holes 56, wherein cover 54 may be made, for example, of a molding compound, metal, and / or metal alloy. Logic circuitry 52 may be embedded in encapsulation material 70, thus protecting any photosensitive structures that may be present in logic circuitry 52 from light. Leadframe 64, encapsulation material 70, and cover 54 may form a cavity 58, within which sensor device 50 may be disposed.

[0062] Figure 10 The emitter component 1000 may have a layer 2 with an optical MEMS emitter 4. For example, layer 2 may be similar to the second layer 2 in FIG. 1. A cover 72, which may be made of at least one of glass material or semiconductor material, may be disposed on layer 2. Figure 10 In the example, the cover 72 may have a recess. For example, an optical reflective structure, such as a metallized structure, may be present on the inner side of the cover 72, as already incorporated. Figure 6 As described, the cover 72 can be designed to protect the optical MEMS transmitter 4, especially its movable structure.

[0063] Figure 11 The pressure sensor component 1100 may have a layer 6 with a MEMS pressure sensor 8 and a light-transmitting window 10, wherein the MEMS pressure sensor 8 and the light-transmitting window 10 may be arranged laterally offset from each other. For example, layer 6 may be similar to the second layer 6 in FIG. 1. A spacer layer 18 may be arranged on the bottom side of layer 6 (see FIG. 1 for this). In addition, another layer 12 having a cavity 14 for a reference gas 16 may be mounted on the top side of layer 6 (see FIG. 1 for this).

[0064] Figure 12 The photoacoustic sensor 1200 may be at least partially similar to the photoacoustic sensor described above. Specifically, the housing of the photoacoustic sensor 1200 may be at least partially similar to... Figure 9 The housing type described in the document. Figure 11 The pressure sensor component 1100 can be arranged on the mounting surface of the carrier or chip pad 66, while Figure 10The emitter component 1000 can be arranged on the lower mounting face of the chip pad 66. The two components 1000 and 1100 can thus be separated from each other by the chip pad 66. The lead frame 64 or the chip pad 66 can have an opening 74. The opening 74 together with the cutouts in the components 1000 and 1100 can form a cavity 76 which can form a gas channel to the ambient environment or surrounding gas of the photoacoustic sensor 1200 as already described in connection with the previous examples. The components 1000 and 1100 can be arranged on top of the chip pad 66 such that the optical MEMS emitter 4 can transmit optical radiation along an optical path which extends through the opening 74, the cavity 76, the light-transmissive window 10 and the cavity 14 for the reference gas 16. Similar to the previous examples, the MEMS pressure sensor 8 can be arranged outside the extended course of the optical path.

[0065] For example, Figure 13 The photoacoustic sensor 1300 can be similar to the photoacoustic sensors 900 and 1200 of Figure 9 and 12 Unlike the photoacoustic sensors 900 and 1200 of Figure 9 and 12 , Figure 13 The carrier in the photoacoustic sensor 1300 can be designed in the form of a PCB-like substrate 78 on the top side and / or bottom side of which components such as the emitter component 1000 and the pressure sensor component 1100 shown in Figure 9 and 12 may be arranged. These components do not necessarily have to be visible in Figure 13 as they can be covered by one or more cover or encapsulation materials 70. One or more openings 56 can be formed in the encapsulation material 70 which can provide a gas connection between the surrounding environment of the photoacoustic sensor 1300 and its interior.

[0066] The substrate 78 can remain at least partially uncovered by the encapsulation material 70 and have one or more electrical interfaces 80 on the top side and / or bottom side thereof. The emitter and / or pressure sensor components arranged within the encapsulation material 70 can be electrically contacted from the outside of the photoacoustic sensor 1300 via the electrical interfaces 80. The photoacoustic sensor 1300 does not necessarily have to be a surface-mountable component. Rather, the photoacoustic sensor 1300 can for example be inserted into a socket (not shown) with the part of the substrate 78 not covered by the encapsulation material 70. The socket can have electrical contact elements on the inside thereof which can electrically connect with the electrical interfaces 80 when inserted.

[0067] Figure 14 The method of is a method of manufacturing a photoacoustic sensor of the present disclosure. In this regard, the method can be read in conjunction with the previous examples. Figure 14 The method of is presented in a general way to qualitatively describe aspects of the present disclosure. For the sake of simplicity, the method can have steps which are not necessarily performed in the order as presented in Figure 14Other aspects are not shown and described. For example, the method can be extended by one or more aspects described in connection with the preceding figures.

[0068] At 82, a first layer having an optical MEMS transmitter can be provided. At 84, a second layer having a MEMS pressure sensor and a light-transmissive window can be stacked on top of the first layer, wherein the MEMS pressure sensor and the light-transmissive window are arranged laterally offset from each other. At 86, a third layer having a cavity for a reference gas can be stacked on top of the second layer. The optical MEMS transmitter can be designed to transmit optical radiation along an optical path, wherein the optical path extends through the light-transmissive window and the cavity, and wherein the MEMS pressure sensor can be arranged outside the extended course of the optical path. It should be noted that, Figure 14 The method of can have one or more further optional actions. For example, stacking the third layer on top of the second layer can comprise a wafer bonding operation, wherein the cavity for the reference gas is hermetically sealed.

[0069] Examples

[0070] In the following, photoacoustic sensors and related manufacturing processes will be explained using examples.

[0071] Example 1 is a photoacoustic sensor, comprising: a first layer having an optical MEMS transmitter; a second layer stacked on top of the first layer, having a MEMS pressure sensor and a light-transmissive window, wherein the MEMS pressure sensor and the light-transmissive window are arranged laterally offset from each other; and a third layer stacked on top of the second layer, having a cavity for a reference gas, wherein the optical MEMS transmitter is designed to transmit optical radiation along an optical path, wherein the optical path extends through the light-transmissive window and the cavity for the reference gas, and wherein the MEMS pressure sensor is arranged outside the extended course of the optical path.

[0072] Example 2 is the photoacoustic sensor according to example 1, wherein the second layer and the third layer are wafer bonded and hermetically seal the cavity for the reference gas.

[0073] Example 3 is the 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.

[0074] Example 4 is the photoacoustic sensor according to any of the preceding examples, wherein the light-transmissive window is made of a semiconductor material of the second layer.

[0075] Example 5 is the photoacoustic sensor according to any of the preceding examples, wherein the light-transmissive window comprises a bandpass structure designed to at least allow optical radiation having a wavelength of an absorption band or an absorption line of the reference gas to pass through.

[0076] Example 6 is the photoacoustic sensor of any of the preceding examples, wherein the third layer is made of at least one of a semiconductor material or a glass material.

[0077] Example 7 is the photoacoustic sensor of any of the preceding examples, wherein the second layer includes an opening forming a gas passage to an ambient environment of the photoacoustic sensor.

[0078] Example 8 is the photoacoustic sensor of any of the preceding examples, further comprising: a spacer layer arranged between the first layer and the second layer, the spacer layer having an opening, wherein the optical path extends through the opening of the spacer layer.

[0079] Example 9 is the photoacoustic sensor of Example 8, wherein the opening of the spacer layer forms part of a gas passage to an ambient environment of the photoacoustic sensor.

[0080] Example 10 is the photoacoustic sensor of any 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.

[0081] Example 11 is the photoacoustic sensor of any of Examples 1 to 9, further comprising: a further layer stacked on top of the first layer or on top of the third layer, wherein the further layer comprises a logic circuit designed to logically process signals detected by the MEMS pressure sensor and / or to control the optical MEMS emitter.

[0082] Example 12 is the photoacoustic sensor of any of the preceding examples, further comprising: one or more connection elements designed to mechanically and electrically connect the photoacoustic sensor with a circuit board, wherein the connection elements are arranged on the third layer and electrically connected to the optical MEMS emitter and the MEMS pressure sensor via electrical connections.

[0083] Example 13 is the photoacoustic sensor of Example 12, wherein the electrical connections are made based on a plating technique and are arranged on a side surface of at least one of the layers of the photoacoustic sensor.

[0084] Example 14 is the photoacoustic sensor of any of the preceding examples, wherein the photoacoustic sensor is a surface mountable component.

[0085] Example 15 is the photoacoustic sensor of any of the preceding examples, wherein the photoacoustic sensor is a chip scale package.

[0086] Example 16 is the photoacoustic sensor of any of the preceding examples, further comprising a light sensitive device arranged on the third layer, the light sensitive device arranged within an extended course of the light path and designed to monitor an output intensity of the optical MEMS emitter.

[0087] Example 17 is the photoacoustic sensor of any of the preceding examples, further comprising an optical reflective structure arranged on the first layer, wherein the optical MEMS emitter is designed to transmit the optical radiation primarily in the first direction, and wherein the reflective structure is designed to reflect the optical radiation of the optical MEMS emitter transmitted in a direction deviating from the first direction.

[0088] Example 18 is the photoacoustic sensor of any of the preceding examples, further comprising a substrate similar to a circuit board, and a cover with an acoustic aperture, wherein the substrate and the cover form a cavity, wherein the layer stack with the first layer, the second layer, and the third layer is arranged on a mounting face of the substrate in the cavity.

[0089] Example 19 is the photoacoustic sensor of any of the preceding examples, further comprising a jacket made of a molding compound, and a cover with an acoustic aperture, wherein the jacket and the cover form a cavity, wherein the layer stack with the first layer, the second layer, and the third layer is arranged on a bottom face of the jacket in the cavity.

[0090] Example 20 is the photoacoustic sensor of any of the preceding examples, further comprising a lead frame, wherein the layer stack with the first layer, the second layer, and the third layer is mounted on a first mounting face of the lead frame, and a logic circuit is mounted on an opposite second mounting face of the lead frame, a packaging material, wherein the logic circuit is embedded in the packaging material, and a cover with an acoustic aperture, wherein the lead frame, the packaging material, and the cover form a cavity, and the layer stack is arranged in the cavity.

[0091] Example 21 is a photoacoustic sensor, comprising: an emitter component comprising a first layer with an optical MEMS emitter and a cover arranged on the first layer, and a pressure sensor component separate from the emitter component comprising a second layer with a MEMS pressure sensor and a light transparent window, wherein the MEMS pressure sensor and the light transparent window are arranged laterally offset from each other, and a third layer stacked on the second layer with a cavity for a reference gas, wherein the optical MEMS emitter is designed to transmit optical radiation along a light path, wherein the light path extends through the light transparent window and the cavity for the reference gas, and wherein the MEMS pressure sensor is arranged outside an extended course of the light path.

[0092] Example 22 is the photoacoustic sensor of example 21, further comprising a carrier, wherein the emitter component and the pressure sensor component are mounted on opposite mounting faces of the carrier, wherein the carrier comprises an opening and the light path extends through the opening of the carrier.

[0093] Example 23 is the 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 cover with an acoustic aperture, wherein the chip carrier, the encapsulation material and the cover form a cavity, and the pressure sensor component is arranged in the cavity.

[0094] Example 24 is a method for manufacturing 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 a light-transmissive window on top of the first layer, the MEMS pressure sensor and the light-transmissive window being arranged laterally offset from each other; and stacking a third layer with a cavity for a reference gas on top of the second layer, wherein the optical MEMS emitter is designed to transmit optical radiation along an optical path, wherein the optical path extends through the light-transmissive window and the cavity, and wherein the MEMS pressure sensor is arranged outside the extended course of the optical path.

[0095] Example 25 is the method according to example 24, wherein stacking the third layer on top of the second layer comprises a wafer bonding operation, wherein the cavity for the reference gas is hermetically sealed.

[0096] Although specific embodiments are shown and described herein, it will be understood by those skilled in the art that various changes in form and details can be made therein without departing from the scope of the disclosure. This application is intended to cover any and all such variations. Thus, the present disclosure is intended to be limited only by the claims and their equivalents.

Claims

1. A photoacoustic sensor, comprising: a first layer (2) having an optical MEMS emitter (4); a second layer (6) stacked on the first layer (2) having a MEMS pressure sensor (8) and a light-transmissive window (10), wherein the MEMS pressure sensor (8) and the light-transmissive window (10) are arranged laterally offset from each other; a third layer (12) stacked on the second layer (6) having a cavity (14) for a reference gas (16); and a spacer layer (18) arranged between the first layer (2) and the second layer (6), the spacer layer having an opening, wherein the optical MEMS emitter (4) is designed to transmit optical radiation (26) along an optical path, wherein the optical path extends through the opening of the spacer layer (18), the light-transmissive window (10) and the cavity (14) for the reference gas (16), and wherein the MEMS pressure sensor (8) is arranged outside the extension of the optical path.

2. The photoacoustic sensor according to claim 1, wherein the second layer (6) and the third layer (12) are wafer bonded and the second layer (6) and the third layer (12) form the cavity (14) for the reference gas (16) in a gas-tight manner.

3. The photoacoustic sensor according to claim 1 or 2, wherein at least one of the first layer (2) or the second layer (6) is made of a semiconductor material.

4. The photoacoustic sensor according to claim 1 or 2, wherein the light-transmissive window (10) is made of a semiconductor material of the second layer (6).

5. The photoacoustic sensor according to claim 1 or 2, wherein the light-transmissive window (10) comprises a bandpass structure designed to at least allow optical radiation having a wavelength of an absorption band or an absorption line of the reference gas (16) to pass through.

6. The photoacoustic sensor according to claim 1 or 2, wherein the third layer (12) is made of at least one of a semiconductor material or a glass material.

7. The photoacoustic sensor according to claim 1 or 2, wherein the second layer (6) comprises an opening forming a gas passage to an ambient environment of the photoacoustic sensor.

8. The photoacoustic sensor according to claim 7, wherein the opening of the spacer layer (18) forms a part of the gas passage to the ambient environment of the photoacoustic sensor.

9. The photoacoustic sensor according to claim 1 or 2, wherein the first layer (2) further comprises a logic circuit designed to logically process a signal detected by the MEMS pressure sensor (8) and / or to control the optical MEMS emitter (4).

10. The photoacoustic sensor according to claim 1 or 2, further comprising: - a further layer (30) stacked on top of the first layer (2) or on top of 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).

11. The photoacoustic sensor of claim 1 or 2, further comprising: one or more connecting elements (32) designed to mechanically and electrically connect the photoacoustic sensor with a circuit board (36), wherein the connecting elements (32) are arranged on the third layer (12) and are electrically connected with the optical MEMS emitter (4) and the MEMS pressure sensor (8) by means of electrical connections (34).

12. The photoacoustic sensor of claim 11, wherein the electrical connections (34) are made on the basis of a galvanic technique and are arranged on a lateral surface of at least one of the layers of the photoacoustic sensor.

13. The photoacoustic sensor of claim 1 or 2, wherein the photoacoustic sensor is a surface-mountable component.

14. The photoacoustic sensor of claim 1 or 2, wherein the photoacoustic sensor is a chip-scale package.

15. The photoacoustic sensor of claim 1 or 2, further comprising: a light-sensitive device (42) arranged on the third layer (12), the light-sensitive device being arranged within the extended course of the light path and being designed to monitor the output intensity of the optical MEMS emitter (4).

16. The photoacoustic sensor of claim 1 or 2, further comprising: an optical reflection structure (46) arranged on the first layer (2), wherein the optical MEMS emitter (4) is designed to transmit optical radiation mainly in a first direction, and wherein the reflection structure (46) is designed to reflect optical radiation of the optical MEMS emitter (4) transmitted in a direction deviating from the first direction.

17. The photoacoustic sensor of claim 1 or 2, further comprising: a substrate similar to a circuit board; and a cover (54) with an acoustic aperture (56), wherein the substrate and the cover (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 in the cavity (58).

18. The photoacoustic sensor of claim 1 or 2, further comprising: an outer jacket (60) made of a molding compound; and a cover (54) with an acoustic aperture (56), wherein the outer jacket (60) and the cover (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 outer jacket (60) in the cavity (58).

19. The photoacoustic sensor of claim 18, further comprising: ​ ​ a leadframe, wherein the layer stack with the first layer (2), the second layer (6) and the third layer (12) is mounted on a first mounting face of the leadframe and a logic circuit (52) is mounted on an opposite second mounting face of the leadframe; a packaging material (70), wherein the logic circuit (52) is embedded in the packaging material (70); and a cover (54) with an acoustic hole (56), wherein the leadframe, the packaging material (70) and the cover (54) form a cavity (58) and the layer stack is arranged in the cavity (58).

20. An optoacoustic sensor, comprising: a transmitter component (1000) comprising: a first layer (2) with an optical MEMS transmitter (4), and a cover (72) arranged above the first layer (2); and a pressure sensor component (1100) separate from the transmitter component (1000), comprising: a second layer (6) with a MEMS pressure sensor (8) and a light-transmissive window (10), wherein the MEMS pressure sensor (8) and the light-transmissive window (10) are arranged laterally offset from each other, a third layer (12) stacked above the second layer (6) with a cavity (14) for a reference gas (16), and a spacer layer (18) arranged between the first layer (2) and the second layer (6), the spacer layer having an opening, wherein the optical MEMS transmitter (4) is designed to transmit optical radiation (26) along an optical path, wherein the optical path extends through the opening of the spacer layer (18), the light-transmissive window (10) and the cavity (14) for the reference gas (16), and wherein the MEMS pressure sensor (8) is arranged outside the extension of the optical path.

21. The optoacoustic sensor of claim 20, further comprising: a carrier, wherein the transmitter component (1000) and the pressure sensor component (1100) are mounted on opposite mounting faces of the carrier, wherein the carrier comprises an opening (74) and the optical path extends through the opening (74) of the carrier.

22. The optoacoustic sensor of claim 21, further comprising: a packaging material (70), wherein the transmitter component (1000) is embedded in the packaging material (70); and a cover (54) with an acoustic hole (56), wherein the carrier, the packaging material (70) and the cover (54) form a cavity (58) and the pressure sensor component (1100) is arranged in the cavity (58).

23. A method for manufacturing an optoacoustic sensor, the method comprising: providing a first layer (2) with an optical MEMS transmitter (4); arranging a spacer layer (18) with an opening above the first layer (2); stacking a second layer (6) with a MEMS pressure sensor (8) and a light-transmissive window (10) above the spacer layer (18), the MEMS pressure sensor (8) and the light-transmissive window (10) being arranged laterally offset from each other; and stacking a third layer (12) having a cavity (14) for a reference gas (16) on top of the second layer (6), wherein the optical MEMS transmitter (4) is designed to transmit optical radiation (26) along an optical path, wherein the optical path extends through the opening of the spacer layer (18), the light-transmissive window (10) and the cavity (14), and wherein the MEMS pressure sensor (8) is arranged outside the extension of the optical path.

24. The method according to claim 23, wherein stacking the third layer (12) on top of the second layer (6) comprises a wafer bonding operation, wherein the cavity (14) for a reference gas (16) is hermetically sealed.

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