Resonant gas sensor and manufacturing method thereof

Abstract

The invention provides a resonant gas sensor and a manufacturing method thereof. The resonant gas sensor comprises a detection light source used for generating detection light capable of being absorbed by gas to be detected; the detection cavity is arranged on a light path of the detection light; the cavity wall, opposite to one side of the detection light source, of the detection cavity is made of a material which is transparent relative to detection light, the detection cavity is communicated with a detection environment through a through hole so as to obtain to-be-detected target gas in the detection environment, and a piezoelectric resonator capable of changing the resonance state along with the change of environment sound pressure is arranged in the detection cavity. According to the invention, two 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 material for absorbing 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.

Description

Technical Field

[0001] This invention relates to the field of MEMS, and more particularly to a 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 resonant gas sensor and a method for manufacturing the same, which can improve the detection performance of the gas sensor.

[0004] To address the aforementioned problems, this invention provides a 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 disposed in the optical path of the detection light; the cavity wall of the detection cavity on the side opposite to the detection light source 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; and a piezoelectric resonator disposed within the detection cavity, which can change its resonance state with changes in ambient sound pressure.

[0005] Optionally, the detection light is infrared light, the gas to be tested is selected from carbon dioxide, ammonia, methane, carbon monoxide, nitric oxide, ozone, and hydrogen sulfide; the cavity wall material of the detection gas chamber is single-crystal silicon or glass.

[0006] Optionally, a filter is included in the optical path of the detection light and between the piezoelectric resonator and the detection light source. The filter is used to perform bandpass filtering on the detection light. The filter is disposed on the inner wall of the detection cavity.

[0007] 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.

[0008] To address the aforementioned problems, the present invention provides a method for fabricating a resonant gas sensor, comprising: forming a detection light source on the upper surface of a first substrate; forming a recess on the lower surface of the first substrate at a position corresponding to the detection light source, and forming a notch on the sidewall of the recess for subsequent formation of a through hole for communicating with the detection environment, wherein the first substrate is made of a material transparent to the detection light; forming a piezoelectric resonator on the surface of a second substrate; and bonding the first substrate and the second substrate in a manner in which the detection light source, the recess, and the piezoelectric resonator are aligned with each other, wherein the recess and the second substrate form a detection cavity.

[0009] Optionally, a filter is formed on the bottom surface of the recess, the filter being used to bandpass filter the detection light.

[0010] This invention employs two 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 photoacoustic 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

[0011] Appendix Figure 1 The diagram shows the implementation steps of a specific embodiment of the manufacturing method of the resonant gas sensor of the present invention.

[0012] Appendix Figure 2A To be continued Figure 2E The diagram shown is a process flow chart of a specific embodiment of the manufacturing method of the resonant gas sensor described in this invention. Detailed Implementation

[0013] The specific embodiments of the resonant gas sensor and its manufacturing method provided by the present invention will be described in detail below with reference to the accompanying drawings.

[0014] Appendix Figure 1The diagram illustrates the implementation steps of a specific embodiment of the fabrication method of the resonant gas sensor of the present invention, including: Step S11, forming a detection light source on the upper surface of a first substrate; Step S12, forming a recess on the lower surface of the first substrate at a position corresponding to the detection light source, and forming a notch on the sidewall of the recess for subsequent formation of a through hole for communicating with the detection environment, wherein the first substrate is made of a material transparent to the detection light; Step S13, forming a filter on the bottom surface of the recess, wherein the filter is used for bandpass filtering of the detection light; Step S14, forming a piezoelectric resonator on the surface of a second substrate; Step S15, bonding the first substrate and the second substrate in a manner in which the detection light source, the recess, and the piezoelectric resonator are aligned with each other, wherein the recess and the second substrate form a detection cavity.

[0015] Appendix Figure 2A To be continued Figure 2E The diagram shown is a process flow chart of a specific embodiment of the manufacturing method of the resonant gas sensor described in this invention.

[0016] Appendix Figure 2A As shown, referring to step S11, a detection light source 211 is formed on the upper surface of 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 to form 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 is formed on the first substrate 21 using semiconductor manufacturing processes. A reflective layer 215 can be further fabricated on the surface of the first substrate 21 to concentrate the irradiation direction of the detection light. 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 capping layer for subsequent bonding to form a detection cavity. The detection principle of the sensor described in this specific embodiment is based on the absorption of detection light by the gas being detected to reflect the gas concentration. 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.

[0017] Appendix Figure 2BAs shown, referring to step S12, a recess 212 is formed on the lower surface of the first substrate 21 at a position corresponding to the detection light source 211, and a notch 213 is formed on the sidewall of the recess 212 for subsequent formation of a through-hole for communication with the detection environment. The first substrate 21 is made of a material transparent to the detection light. Since the first substrate 21 is used for the light-transmitting portion of the cavity wall for subsequent formation of the detection gas, the first substrate 21 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 first substrate 21 is single-crystal silicon, glass, or sapphire. The formation methods of the recess 212 include, but are not limited to, dry etching and wet etching.

[0018] Appendix Figure 2C As shown, referring to step S13, a filter 214 is formed on the bottom surface of the recess 212. The filter 214 is used to perform bandpass filtering on the detection light. This step is optional. The purpose of forming the filter 214 is to filter the incoming light, allowing only the detection light to pass through and filtering out other wavelengths of light, reducing environmental noise and improving detection accuracy.

[0019] Appendix Figure 2D As shown, referring to step S14, a piezoelectric resonator 221 is formed on the surface of a second substrate 22. 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. The piezoelectric resonator 221 is preferably formed in a recess on the surface of the second substrate 22. In this specific embodiment, the piezoelectric resonator 221 includes a cantilever beam 222, which includes a piezoelectric ceramic layer 223 and counter electrodes 224 and 225 disposed on the upper and lower surfaces of the piezoelectric ceramic layer 223. The cantilever beam 222 and the second substrate 22 are electrically isolated by an insulating layer 227.

[0020] Steps S11 to S14 above form two different structures on two different substrates, and their execution order can be interchanged. Forming two different structures on two 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.

[0021] Appendix Figure 2EAs shown, referring to step S15, the first substrate 21 and the second substrate 22 are bonded together with the detection light source 211, the recess 212, and the piezoelectric resonator 221 aligned with each other. The recess 212 and the second substrate 22 form a detection cavity 241. Bonding can be performed using electrostatic bonding or other methods, and annealing is used to strengthen the bond. Since this figure is a cross-sectional view, the notch 213 on the sidewall of the first recess 212 is closed in the direction perpendicular to the front and back of the plane. The notch 213 is used to ensure that the gas environment inside the detection cavity 241 matches the detection environment, thereby achieving the detection purpose.

[0022] The method described above uses two substrates to fabricate different structures, which are then assembled by bonding. The processes for the key structures are independent of each other and do not affect each other when fabricating different structures, resulting in high process stability.

[0023] 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; an optional filter 214 and a detection cavity 241 sequentially arranged in the optical path of the detection light, wherein the filter 214 performs bandpass filtering on the detection light; the cavity wall of the detection cavity 241 on the side opposite to the detection light source 211 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 concentration of the gas to be measured in the detection environment; and a piezoelectric resonator 221 that can change its resonance state with the change of ambient sound pressure is provided in the detection cavity 241.

[0024] The working principle of the above structure is as follows: The detection chamber 241 is connected to the detection environment through a through-hole, 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 it passes through the detection chamber 241. However, when the gas to be detected is present in the environment, the detection light is partially absorbed when it passes through the detection chamber 241. During detection, a resonant signal is applied to the piezoelectric resonator 221 from the outside to cause it to vibrate. The difference in infrared absorption causes a change in the ambient sound pressure of the detection chamber 241. The change in sound pressure causes a change in the vibration frequency of the piezoelectric cantilever beam 222. By measuring the change in the output voltage signal of the counter electrodes 224 and 225, the change in the concentration of the gas to be detected in the environment is reflected, thus achieving the purpose of gas detection. The above structure uses optical signals, which has high detection sensitivity, fast response speed, and large detection range. Moreover, the detection chamber does not contain any absorbent material for the gas to be detected, so it can respond promptly to changes in concentration without signal lag due to gas residue.

[0025] 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 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 positioned in the optical path of the detection light; The cavity wall of the detection chamber on the side opposite to the detection light source 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 in the detection environment. A piezoelectric resonator that can change its resonance state with the change of ambient sound pressure is installed in the detection chamber.

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

3. The resonant 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 resonant gas sensor according to claim 1, characterized in that, The detection light path includes a filter between the piezoelectric resonator and the detection light source, the filter being used for bandpass filtering of the detection light.

5. The resonant gas sensor according to claim 4, characterized in that, The filter is disposed on the inner wall of the detection cavity.

6. The resonant gas sensor according to claim 1, characterized in that, 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.

7. A method for manufacturing a resonant gas sensor, characterized in that, include: A detection light source is formed on the upper surface of a first substrate; A recess is formed on the lower surface of the first substrate at a position corresponding to the detection light source, and a notch is formed on the sidewall of the recess for subsequent formation of a through hole for communicating with the detection environment. The first substrate is made of a material that is transparent to the detection light. A piezoelectric resonator is formed on the surface of a second substrate; The first substrate and the second substrate are bonded together by aligning the detection light source, the recess, and the piezoelectric resonator, and the recess and the second substrate form a detection cavity.

8. The method according to claim 7, characterized in that, A filter is formed on the bottom surface of the recess, and the filter is used to perform bandpass filtering on the detection light.

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