Non-resonant gas sensor and manufacturing method thereof

Abstract

The invention provides a gas sensor and a manufacturing method thereof. The sensitivity of the gas sensor can be improved. The gas sensor comprises a detection light source used for generating detection light capable of being absorbed by gas to be detected; the detection cavity and the resonant cavity are sequentially arranged on a light path of the detection light; the cavity wall of the detection cavity is made of a material which is transparent relative to the detection light and is communicated with the detection environment through the through hole so as to obtain to-be-detected target gas in the detection environment; the resonant cavity body is filled with target gas with known concentration capable of absorbing the detection light source, and is provided with a piezoelectric resonator capable of generating resonance along with the change of environmental sound pressure. According to the invention, three substrates are adopted to respectively manufacture different structures and are assembled through bonding. And the processes of the key structures are independent from each other and cannot influence each other when different structures are manufactured, so that the process stability is high. The sensor structure adopts a photoacoustic signal mode, the detection sensitivity is high, the response speed is high, and the detection range is large. And the detection cavity does not contain any absorption material for the detected gas, so that timely response can be performed when the concentration is changed, and the situation of signal lag caused by gas residue is avoided. In addition, the target gas with known concentration is used for gas selection, so that expensive components such as an optical filter, a laser and the like are avoided, and the gas sensor with low cost and high integration can be realized.

Description

Technical Field

[0001] This invention relates to the field of MEMS, and more particularly to a non-resonant gas sensor and its fabrication method. Background Technology

[0002] A gas sensor is a sensor that converts the concentration of a gas in the environment into a corresponding electrical signal through physical or chemical means. Common gas sensors typically use a material with specific absorption properties for a particular gas to detect changes in gas concentration in the environment. However, this approach has drawbacks such as low sensitivity, saturation, and long response times. Therefore, improving the performance of gas sensors is a problem that current technology needs to address. Summary of the Invention

[0003] The technical problem to be solved by the present invention is to provide a non-resonant gas sensor and its manufacturing method, which can improve the sensitivity of the gas sensor.

[0004] To address the aforementioned problems, this invention provides a non-resonant gas sensor, comprising: a detection light source for generating detection light that can be absorbed by the gas to be measured; a detection cavity and a resonant cavity sequentially disposed in the optical path of the detection light; the cavity wall of the detection cavity is made of a material transparent to the detection light and is connected to the detection environment through a through hole to obtain the target gas to be measured in the detection environment; the resonant cavity is filled with a gas capable of absorbing the detection light source and is provided with a piezoelectric resonator capable of resonating with changes in ambient sound pressure.

[0005] Optionally, the detection light is infrared light, and the gas to be detected is selected from one of the following: carbon dioxide, ammonia, methane, carbon monoxide, nitric oxide, ozone, and hydrogen sulfide, which absorb infrared light.

[0006] Optionally, the piezoelectric resonator includes a cantilever beam, which includes a piezoelectric ceramic layer and opposing electrodes disposed on the upper and lower surfaces of the piezoelectric ceramic layer.

[0007] Optionally, the resonant cavity is filled with a gas of known concentration that is the same as the gas to be tested.

[0008] To address the aforementioned problems, the present invention provides a method for fabricating a non-resonant gas sensor, comprising: forming a detection light source within a first substrate; forming a first recess and a second recess aligned with each other on opposite surfaces of a second substrate, and forming a notch in the sidewall of the first recess for subsequent formation of a through-hole for communication with the detection environment, wherein the second substrate is made of a material transparent to the detection light; forming a piezoelectric resonator on the surface of a third substrate; and bonding the first substrate, the second substrate, and the third substrate in a manner in which the detection light source, the first recess, the second recess, and the piezoelectric resonator are aligned with each other, wherein the first recess and the first substrate form a detection cavity, and the second recess and the third substrate form a resonant cavity, wherein the resonant cavity is filled with a gas capable of absorbing the detection light source.

[0009] This invention employs three substrates to fabricate different structures, which are then assembled via bonding. The processes for key structures are independent of each other, preventing interference during the fabrication of different structures and ensuring high process stability. The sensor structure utilizes optical signals, resulting in high detection sensitivity, fast response speed, and a wide detection range. Furthermore, the detection chamber does not contain any absorbent material for the detected gas, allowing for timely response to concentration changes without signal lag due to residual gas. Attached Figure Description

[0010] Appendix Figure 1 The diagram shows the implementation steps of a specific embodiment of the non-resonant gas sensor manufacturing method of the present invention.

[0011] Appendix Figure 2A To be continued Figure 2D The diagram shown is a process flow chart of a specific embodiment of the non-resonant gas sensor manufacturing method of the present invention. Detailed Implementation

[0012] The specific embodiments of the non-resonant gas sensor and its manufacturing method provided by the present invention will be described in detail below with reference to the accompanying drawings.

[0013] Appendix Figure 1 The diagram illustrates the implementation steps of a specific embodiment of the non-resonant gas sensor fabrication method of the present invention, including: step S11, forming a detection light source in a first substrate; step S12, forming a first recess and a second recess aligned with each other on opposite surfaces of a second substrate, wherein the second substrate is made of a material transparent to the detection light; step S13, forming a piezoelectric resonator on the surface of a third substrate; and step S14, bonding the first substrate, the second substrate, and the third substrate in a manner in which the detection light source, the first recess, the second recess, and the piezoelectric resonator are aligned with each other.

[0014] Appendix Figure 2A To be continued Figure 2DThe diagram shown is a process flow chart of a specific embodiment of the non-resonant gas sensor manufacturing method of the present invention.

[0015] Appendix Figure 2A As shown, referring to step S11, a detection light source 211 is formed within a first substrate 21. In this specific embodiment, the first substrate 21 is a single-crystal silicon substrate. In other specific embodiments, the material of the first substrate 21 can be selected from any common substrate material used for forming semiconductor devices, such as single-crystal silicon, germanium silicon, silicon on insulator, silicon carbide, gallium nitride, gallium arsenide, and sapphire. The detection light source 211 can be formed by epitaxy or other methods, or an external light source can be assembled into the first substrate 21 by bonding or other methods. The surface of the first substrate 21 can preferably be covered with a reflective layer 212 to concentrate the irradiation direction of the detection light. Furthermore, the first substrate 21 is preferably made of a material that is transparent to the detection light. If the first substrate 21 is not transparent to the detection light, it is necessary to thin the first substrate 21 and then fabricate a cover layer for subsequent bonding to form a detection cavity. The detection principle of the sensor described in this specific embodiment is to reflect the gas concentration by the absorption of detection light by the gas being detected. Therefore, the wavelength of the detection light is preferably a wavelength that can be efficiently absorbed by the gas being detected. For gases such as carbon dioxide, ammonia, methane, carbon monoxide, nitric oxide, ozone, and hydrogen sulfide, infrared light is preferred.

[0016] Appendix Figure 2B As shown, referring to step S12, a first recess 221 and a second recess 222 are formed on opposite surfaces of a second substrate 22, with their positions aligned. A notch 223 is formed on the sidewall of the first recess 221 for subsequent formation of a through-hole for communication with the detection environment. The second substrate 22 is made of a material transparent to the detection light. In this specific embodiment, the second substrate 22 is a single-crystal silicon substrate. In other specific embodiments, the material of the second substrate 22 can be selected from any common substrate material used for forming semiconductor devices, such as single-crystal silicon, germanium silicon, silicon on insulator, silicon carbide, gallium nitride, gallium arsenide, and sapphire. Since the second substrate 22 is used for the light-transmitting portion of the cavity wall for subsequent formation of the detection gas, the second substrate 22 should be made of a material transparent to the detection light. For example, when the detection light is infrared light, the preferred material for the second substrate 22 is single-crystal silicon, glass, or sapphire. The formation methods of the first recess 221 and the second recess 222 include, but are not limited to, dry etching and wet etching.

[0017] Appendix Figure 2CAs shown, referring to step S13, a piezoelectric resonator 231 is formed on the surface of a third substrate 23. The piezoelectric resonator 231 is preferably formed within a recess on the surface of the third substrate 23. In this specific embodiment, the piezoelectric resonator 231 includes a cantilever beam, which includes a piezoelectric ceramic layer 233 and opposing electrodes 234 and 235 disposed on the upper and lower surfaces of the piezoelectric ceramic layer 233. The cantilever beam 232 and the third substrate 23 are electrically isolated by an insulating layer 237. To improve detection efficiency, the third substrate 23 is preferably made of a material that is opaque to detection light and preferably a material with low thermal conductivity to shield the influence of ambient heat on the detection.

[0018] Steps S11 to S13 above form three different structures on three different substrates, and their execution order can be interchanged. Forming three different structures on three different substrates with independent processes avoids cross-contamination between different types of processes. For example, forming a recess may require an alkali metal ion etching process, while forming a cantilever beam requires a metal deposition process. Therefore, the independence of the processes can improve the overall yield.

[0019] Appendix Figure 2D As shown, referring to step S14, the first substrate 21, the second substrate 22, and the third substrate 23 are bonded together with the detection light source 211, the first recess 221, the second recess 222, and the piezoelectric resonator 231 aligned with each other. Bonding can be achieved using electrostatic bonding or similar methods, and annealing is used to strengthen the bond. The first recess 221 and the first substrate 21 form a detection cavity 241. Since this figure is a cross-sectional view, the position of the notch 223 on the sidewall of the first recess 221 is indicated by a dashed line in the direction perpendicular to the front-back plane. The notch 223 is used to ensure that the gas environment inside the detection cavity matches the detection environment, thus achieving the detection purpose. The second recess 222 and the third substrate 23 form a resonant cavity 242. The resonant cavity is filled with a gas capable of absorbing the detection light source. Preferably, the resonant cavity is filled with the same gas as the gas to be measured. To enable the gas sensor to detect multiple gases, any sensitive gas can be selected as the filling gas for the resonant cavity and calibrated subsequently. The filling method can be to leave a filling port when forming the cavity and seal it after filling, or to leave gas release material in the cavity, or to perform bonding directly in an environment containing the gas.

[0020] The method described above uses three substrates to fabricate different structures, which are then assembled by bonding. The fabrication processes for the key structures are independent of each other and do not affect each other during the fabrication of different structures, resulting in high process stability.

[0021] After the above process is completed, the obtained gas sensor includes: a detection light source 211 for generating detection light that can be absorbed by the gas to be measured; a detection cavity 241 and a resonant cavity 242 arranged sequentially in the optical path of the detection light; the cavity wall of the detection cavity 241 is made of a material that is transparent to the detection light and is connected to the detection environment through a through hole to obtain the target gas to be measured in the detection environment; the resonant cavity 242 is filled with a target gas of known concentration that can absorb the detection light source and is equipped with a piezoelectric resonator 231 that can resonate with changes in ambient sound pressure.

[0022] The working principle of the above structure is as follows. The detection chamber 241 is connected to the detection environment through a notch 223, and the gas environment inside the detection chamber is consistent with the detection environment. When there is no gas to be detected in the environment, the detection light is not absorbed when passing through the detection chamber 241 and directly enters the resonant cavity, where it is absorbed by the gas inside the resonant cavity 242. However, when the gas to be detected is present in the environment, the detection light is partially absorbed when passing through the detection chamber 241, reducing the intensity of the detection light entering the resonant cavity. This reduces the intensity of the infrared light absorbed by the gas in the resonant cavity 242. This difference in infrared absorption leads to a change in sound pressure, which causes the piezoelectric cantilever beam 232 to vibrate, outputting a voltage signal through the opposing electrodes 234 and 235. The change in the intensity of the voltage signal directly reflects the change in the concentration of the gas to be detected in the environment, achieving the purpose of gas detection. This structure uses optical signals, resulting in high detection sensitivity, fast response speed, and a large detection range. Furthermore, the detection chamber does not contain any absorbing material for the gas to be detected, so it can respond promptly to changes in concentration without signal lag due to residual gas.

[0023] The above description is only a preferred embodiment of the present invention. It should be noted that those skilled in the art can make several improvements and modifications without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A non-resonant gas sensor, characterized in that, include: A detection light source is used to generate detection light that can be absorbed by the gas to be tested. A detection cavity and a resonant cavity are sequentially arranged in the optical path of the detection light; The cavity wall of the detection chamber is made of a material that is transparent to the detection light and is connected to the detection environment through a through hole to obtain the target gas to be tested in the detection environment; The resonant cavity is filled with a target gas of known concentration that can absorb the detection light source, and is equipped with a piezoelectric resonator that can resonate with changes in ambient sound pressure.

2. The gas sensor according to claim 1, characterized in that, The detection light is infrared light, and the gas to be detected is selected from one of the following: carbon dioxide, ammonia, methane, carbon monoxide, nitric oxide, ozone, and hydrogen sulfide, which absorb infrared light.

3. The gas sensor according to claim 2, characterized in that, The cavity wall material of the gas detection chamber is monocrystalline silicon or glass.

4. The gas sensor according to claim 1, characterized in that, The piezoelectric resonator includes a cantilever beam, which includes a piezoelectric material layer and counter electrodes disposed on the upper and lower surfaces of the piezoelectric material layer.

5. The gas sensor according to claim 1, characterized in that, The resonant cavity is filled with a gas of known concentration that is the same as the gas to be tested.

6. A method for manufacturing a non-resonant gas sensor, characterized in that, include: A detection light source is formed within a first substrate; A first recess and a second recess are formed on opposite surfaces of a second substrate, with their positions aligned with each other. A notch is formed on the sidewall of the first recess for subsequent formation of a via for communicating with the detection environment. The second substrate is made of a material that is transparent to the detection light. A piezoelectric resonator is formed on the surface of a third substrate; A first substrate, a second substrate, and a third substrate are bonded together by aligning the detection light source, the first recess, the second recess, and the piezoelectric resonator with each other. The first recess and the first substrate form a detection cavity, and the second recess and the third substrate form a resonant cavity. The resonant cavity is filled with a gas that can absorb the detection light source.

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