Membrane-based fiber optic hydrogen sensor and method of forming

Abstract

The application provides a MEMS optical fiber hydrogen sensor and a forming method, which comprises a palladium film for absorbing hydrogen, a supporting film comprising a first surface and a second surface and a side surface, the palladium film being located on the first surface of the supporting film, a deformation beam connected to the side surface of the supporting film and capable of being deformed under stress, a frame with a first end connected to the deformation beam, a first reflecting film located on the second surface of the supporting film, a supporting structure with a second end of the frame arranged on a surface of the supporting structure, a second reflecting film opposite to and aligned with the first reflecting film, an FP cavity formed between the first reflecting film and the second reflecting film, and a distance between the first reflecting film and the second reflecting film being a cavity length of the FP cavity, and a detection optical fiber for emitting laser to the FP cavity and receiving reflected laser from the FP cavity, when the wavelength of the received laser changes, the change of the cavity length can be obtained through the wavelength change, thereby obtaining the amount of hydrogen absorbed by the palladium film, and the content of hydrogen in the environment is obtained.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of sensors, in particular to a MEMS optical fiber hydrogen sensor and a forming method. BACKGROUND

[0002] Due to the flammability of hydrogen, the performance requirements for hydrogen sensors are becoming higher and higher in the fields of industrial production, home safety, environmental monitoring and medical treatment. At present, the main hydrogen sensors on the market are mainly divided into semiconductor type and electrochemical type. However, in some applications, both types of sensors have a series of shortcomings: the electrochemical hydrogen sensor is easy to corrode the equipment, the gas sensitivity is not ideal, and the electrolyte needs to be replaced frequently; the working temperature of the semiconductor oxide hydrogen sensor is usually 200-400℃, and because it responds to most combustible gases, it has poor selectivity, and in addition, it also has the disadvantages of complex structure, long response time and short service life.

[0003] The MEMS optical fiber hydrogen sensor can be used to detect the concentration of hydrogen in the environment. In addition to explosion-proof, the MEMS optical fiber hydrogen sensor also has the advantages of simple structure, and can still work normally in the presence of electromagnetic interference and power limitation, so the MEMS optical fiber hydrogen sensor has a wider range of applications than traditional hydrogen sensors. The commonly used MEMS optical fiber hydrogen sensor usually detects the hydrogen concentration in the environment by detecting the change of light intensity, but the light intensity detection method has limited precision and is easily affected by light source intensity fluctuations and fiber bending. SUMMARY

[0004] The purpose of the present application is to provide a MEMS optical fiber hydrogen sensor and a forming method, which can detect the hydrogen concentration without using the method of detecting the change of light intensity, so as to be not limited by the precision of light intensity detection method, and thus not affected by light source intensity fluctuations and fiber bending, thereby improving the detection precision.

[0005] In order to achieve the above purpose, the present application provides a MEMS optical fiber hydrogen sensor, comprising:

[0006] A palladium membrane for absorbing hydrogen;

[0007] A support film for supporting the palladium membrane, the support film comprising opposite first and second faces and a side surface connected between the first and second faces, and the palladium membrane is located on the first face of the support film;

[0008] A deformation beam connected to the side surface of the support film, the deformation beam can be deformed under stress;

[0009] A frame for supporting the deformation beam, the first end of the frame is connected to the deformation beam;

[0010] a first reflective film located on the second surface of the support thin film;

[0011] a support structure having a through hole, the second end of the frame being disposed on the surface of the support structure;

[0012] a second reflective film located in the through hole, the second reflective film being opposite to and aligned with the first reflective film, an FP cavity being formed between the first reflective film and the second reflective film, and the distance between the first reflective film and the second reflective film being the cavity length of the FP cavity; and

[0013] a detection optical fiber for emitting laser to the FP cavity and receiving laser reflected from the FP cavity.

[0014] Optionally, in the MEMS optical fiber hydrogen sensor, the deformation beam is in the shape of a cuboid, one end of the deformation beam being connected to the side surface of the support thin film and the other end being connected to the frame.

[0015] Optionally, in the MEMS optical fiber hydrogen sensor, the support thin film has four side surfaces, each of the side surfaces being connected to at least one deformation beam, and the number of the deformation beams connected to each of the side surfaces being the same.

[0016] Optionally, in the MEMS optical fiber hydrogen sensor, the axis of the first reflective film coincides with the axis of the second reflective film.

[0017] Optionally, in the MEMS optical fiber hydrogen sensor, the radial direction of the through hole coincides with the axis of the second reflective film.

[0018] Optionally, in the MEMS optical fiber hydrogen sensor, the detection optical fiber is located in the through hole.

[0019] Optionally, in the MEMS optical fiber hydrogen sensor, the second reflective film is located on the end surface of the detection optical fiber.

[0020] Optionally, in the MEMS optical fiber hydrogen sensor, the first reflective film comprises a composite dielectric film or a metal film; and the second reflective film comprises a composite dielectric film.

[0021] Correspondingly, the application further provides a forming method of the MEMS optical fiber hydrogen sensor, comprising:

[0022] providing an SOI silicon wafer, the SOI silicon wafer comprising a substrate silicon, a buried oxide layer and a top silicon formed from bottom to top;

[0023] etching the top layer of silicon to form a patterned top layer of silicon, the patterned top layer of silicon comprising a first portion, a second portion and a third portion from inside to outside, the first portion and the second portion forming a support membrane and a deformation beam respectively, the support membrane comprising a first face and a second face opposite to each other;

[0024] etching the substrate silicon to form a through hole, the through hole exposing the buried oxide layer, and the remaining substrate silicon forming a support structure;

[0025] removing the buried oxide layer under the support membrane and the deformation beam, the through hole exposing the second face of the support membrane, and the remaining buried oxide layer and the third portion forming a frame together;

[0026] forming a first reflective film on the second face of the support membrane through the through hole;

[0027] forming a palladium film on the first face of the support membrane;

[0028] providing a detection optical fiber, and forming a second reflective film on an end face of the detection optical fiber; and

[0029] mounting the detection optical fiber and the second reflective film in the through hole, so that the second reflective film is opposite to and aligned with the first reflective film, an FP cavity is formed between the first reflective film and the second reflective film, and a distance between the first reflective film and the second reflective film is a cavity length of the FP cavity.

[0030] Optionally, in the method for forming the MEMS fiber hydrogen sensor, the buried oxide layer under the support membrane and the deformation beam is removed by a hydrofluoric acid wet etching or a gas phase etching method.

[0031] Optionally, in the method for forming the MEMS fiber hydrogen sensor, the method for forming the palladium film on the first face of the support membrane comprises:

[0032] depositing a metal palladium film on the first face of the support membrane by a magnetron sputtering method;

[0033] etching the metal palladium film to form the palladium film.

[0034] In the MEMS fiber hydrogen sensor and the forming method provided by the application, the increase of hydrogen absorbed by the palladium film will cause the volume expansion of the palladium film and / or the deformation of the palladium film, thus causing the deformation of the deformation beam and the change of the cavity length of the FP cavity, and the wavelength of the laser reflected by the FP cavity received by the detection fiber changes, so that the hydrogen absorbed by the palladium film can be calculated by detecting the wavelength change of the laser received by the detection fiber, and the concentration of hydrogen in the environment can be calculated. The embodiment of the application detects the concentration of hydrogen in the environment by the wavelength change of the light, and compared with the prior art, the method for detecting the concentration of hydrogen by detecting the change of light intensity is not used, so that the detection precision is not limited by the light intensity detection method, the influence of the light source intensity fluctuation and the fiber bending is avoided, and the detection precision is improved. BRIEF DESCRIPTION OF DRAWINGS

[0035] Figure 1 is a schematic diagram of the MEMS fiber hydrogen sensor of the embodiment of the application;

[0036] Figure 2 is a top view of the MEMS fiber hydrogen sensor of the embodiment of the application;

[0037] Figure 3 is a flowchart of the forming method of the MEMS fiber hydrogen sensor of the embodiment of the application;

[0038] Figure 4 is a structural schematic diagram of the MEMS fiber hydrogen sensor after etching the top layer of silicon of the embodiment of the application;

[0039] Figure 5 is a structural schematic diagram of the MEMS fiber hydrogen sensor after etching the top layer of silicon of the embodiment of the application;

[0040] Figure 6 is a structural schematic diagram of the MEMS fiber hydrogen sensor after removing the buried oxide layer under the support film and the deformation beam of the embodiment of the application;

[0041] Figure 7 is a structural schematic diagram of the MEMS fiber hydrogen sensor after forming the first reflection film of the embodiment of the application;

[0042] Figure 8 is a structural schematic diagram of the MEMS fiber hydrogen sensor after forming the palladium film of the embodiment of the application;

[0043] Figure 9 is a structural schematic diagram of the MEMS fiber hydrogen sensor after forming the detection fiber of the embodiment of the application;

[0044] In the figure: 110 - palladium film, 120 - support film, 130 - deformation beam, 140 - frame, 141 - buried oxide layer, 142 - third part of patterned top layer of silicon, 150 - first reflective film, 160 - support structure, 161 - bottom layer of silicon, 170 - second reflective film, 180 - detection optical fiber. DETAILED DESCRIPTION

[0045] The specific embodiments of the present application will now be described in detail with reference to the drawings. According to the following description, the advantages and features of the present application will be more clearly understood. It should be noted that the drawings are in extremely simplified form and all use non-precise proportions, only for the purpose of facilitating, clarifying the purpose of assisting the description of the embodiments of the present application.

[0046] In the following, the terms "first", "second", and the like are used to distinguish between like elements, and do not necessarily have to be described in a specific order or time sequence. It is to be understood that these terms, as used in this way, can be replaced where appropriate. Similarly, if the method described herein comprises a series of steps, and the order of these steps presented herein is not necessarily the only order in which these steps can be performed, and some of the steps described can be omitted and / or some other steps not described herein can be added to the method.

[0047] Please refer to Figure 1 and Figure 2 The present application provides a MEMS optical fiber hydrogen sensor, comprising:

[0048] a palladium film 110 for absorbing hydrogen;

[0049] a support film 120 for supporting the palladium film 110, the support film 120 comprising opposite first and second faces and a side surface connecting between the first and second faces, the palladium film 110 being located on the first face of the support film 120;

[0050] a deformation beam 130 connected to the side surface of the support film 120, the deformation beam 130 being capable of generating deformation under force;

[0051] a frame 140 for supporting the deformation beam 130, one end of the frame 140 being connected to the deformation beam 130;

[0052] a first reflective film 150 located on the second face of the support film 120;

[0053] a support structure 160 having a through hole, the other end of the frame 140 being arranged on the surface of the support structure 160; and

[0054] The second reflecting film 170 is located in the through hole, the second reflecting film 170 is opposite to and aligned with the first reflecting film 150, the FP cavity is formed between the first reflecting film 150 and the second reflecting film 170, and the distance between the first reflecting film 150 and the second reflecting film 170 is the cavity length of the FP cavity.

[0055] Preferably, the detection optical fiber 180 is further included, the detection optical fiber 180 is located in the through hole, and the second reflecting film 170 is located at the end face of the detection optical fiber 180. When the palladium film 110 deposited on the first face of the support thin film 120 absorbs hydrogen in the environment, volume expansion and deformation will occur, thus causing the deformation of the support thin film 120 and the deformation beam 130, and finally causing the change of the cavity length of the FP cavity. The laser emitted by the detection optical fiber 180 enters the FP cavity, if the cavity length changes, the wavelength of the laser reflected from the FP cavity will change, and the size of the cavity length change can be calculated according to the change of the wavelength, thus the weight change of the palladium film 110 can be calculated, and the amount of hydrogen absorbed by the palladium film 110 can be calculated, and thus the concentration of hydrogen in the environment can be calculated.

[0056] Preferably, the axis of the first reflecting film 150 and the axis of the second reflecting film 170 coincide. The radial direction of the through hole coincides with the axis of the second reflecting film 170, so that the transmission of the laser transmitted into the FP cavity by the detection optical fiber 180 will not deviate.

[0057] Preferably, the deformation beam 130 is in the shape of a cuboid, one end of the deformation beam 130 is connected to the side face of the support thin film 120, and the other end is connected to the frame 140, that is, one face of the cuboid is connected to the side face of the support thin film 120, and the opposite face is connected to the frame 140, and the edge length is the distance from the side face of the support thin film 120 to the frame 140. The sensitivity of the deformation beam 130 can be improved by making the deformation beam 130 in the shape of a cuboid instead of covering the gap between the side face of the support thin film 120 and the frame 140.

[0058] Preferably, the support thin film 120 has four side faces, and at least one deformation beam 130 is connected to each side face, and the number of the deformation beams 130 connected to each side face is the same. In the embodiment of the present application, one deformation beam 130 is connected to each side face.

[0059] Preferably, the first reflecting film 150 includes a composite dielectric film or a metal film, the material of the metal film includes gold or aluminum, and the composite dielectric film includes one of a plurality of layers of silicon oxide and tantalum oxide alternately arranged, a plurality of layers of silicon oxide and titanium oxide alternately arranged, and a plurality of layers of silicon oxide and nitrogen oxide alternately arranged; and the second reflecting film 170 includes a composite dielectric film, and the composite dielectric film includes one of a plurality of layers of silicon oxide and tantalum oxide alternately arranged, a plurality of layers of silicon oxide and titanium oxide alternately arranged, and a plurality of layers of silicon oxide and nitrogen oxide alternately arranged.

[0060] In the embodiment, the detection optical fiber 180 is located in the through hole. The second reflective film 170 is located at the end face of the detection optical fiber 180. The detection optical fiber transmits the laser of multiple wavelengths to the FP cavity through the second reflective film 170, and the laser is reflected between the first reflective film 150 and the second reflective film 170. The wavelength of the laser reflected from the second reflective film 170 is determined according to the cavity length of the FP cavity. The detection optical fiber 180 can infer the cavity length of the FP cavity, that is, the distance between the first reflective film 150 and the second reflective film 170 and the distance change, by the wavelength of the laser obtained from the second reflective film 170, so as to infer the deformation of the support thin film 120, and then infer the deformation or the expanded volume of the palladium film, and then infer the amount of hydrogen absorbed by the palladium film 110, and then infer the concentration of hydrogen in the environment. The specific calculation formula can be calculated according to the actual situation, which is not described here.

[0061] Correspondingly, please refer to Figure 3 The application further provides a forming method of the MEMS optical fiber hydrogen sensor, comprising:

[0062] S11: providing an SOI silicon wafer, the SOI silicon wafer comprising a substrate silicon, a buried oxide layer and a top layer silicon formed from bottom to top;

[0063] S12: etching the top layer silicon to form a patterned top layer silicon, the patterned top layer silicon is sequentially divided into a first part, a second part and a third part from inside to outside, and the first part and the second part form a support thin film and a deformation beam respectively, and the support thin film comprises opposite first and second faces;

[0064] S13: etching the substrate silicon to form a through hole, the buried oxide layer is exposed in the through hole, and the remaining substrate silicon forms a support structure;

[0065] S14: removing the buried oxide layer below the support thin film and the deformation beam, the through hole exposes the second face of the support thin film, and the remaining buried oxide layer and the third part jointly form a frame;

[0066] S15: forming a first reflective film on the second face of the support thin film through the through hole;

[0067] S16: forming a palladium film on the first face of the support thin film;

[0068] S17: providing a detection optical fiber, and forming a second reflective film at the end face of the detection optical fiber; and

[0069] S18: mounting the detection optical fiber and the second reflective film in the through hole, so that the second reflective film is opposite to and aligned with the first reflective film, an FP cavity is formed between the first reflective film and the second reflective film, and the distance between the first reflective film and the second reflective film is the cavity length of the FP cavity.

[0070] Specifically, first, referring to Figure 2 and Figure 4 , an SOI wafer is provided, which includes a substrate silicon 161, a buried oxide layer 141 and a top silicon formed from bottom to top; then, the top silicon is etched by photolithography and dry etching to form a patterned top silicon, which is divided into a first part, a second part and a third part 142 of the patterned top silicon from inside to outside, respectively, the first part and the second part form a support membrane 120 and a deformation beam 130, respectively, the support membrane 120 includes opposite first and second surfaces.

[0071] Then, referring to Figure 5 , the substrate silicon 161 is etched from the lower surface of the substrate silicon 161 towards the buried oxide layer 141 to stop at the lower surface of the buried oxide layer 143, forming a through hole in the substrate silicon 161, the exposed part of the lower surface of the buried oxide layer 141 in the through hole, the radial direction of the through hole can be perpendicular to the lower surface of the buried oxide layer 141, the remaining substrate silicon 161 serves as a support structure 160.

[0072] Then, referring to Figure 6 , the buried oxide layer 141 under the support membrane 120 and the deformation beam 130 is removed by hydrofluoric acid wet etching or gas phase etching, the through hole exposes the second surface of the support membrane 120, the remaining buried oxide layer 141 and the third part 142 of the patterned top silicon together serve as a frame 140, due to isotropy, a small amount of buried oxide layer 141 under the third part 142 of the patterned top silicon is also etched in the drawing. The surface of the top silicon and the substrate silicon 161 of the provided SOI wafer has the characteristics of smoothness and flatness, so the second surface of the support membrane 120 and the upper surface of the support structure 160 are smooth and flat, so that the first reflective film 150 and the second reflective film 170 are located on the flat surface, so that high interference precision can be obtained in the FP cavity, wavelength signal demodulation method can be used for strain signal detection, the resolution and measurement accuracy of the sensor detection are improved, and the problems of low sensitivity, influence of light source power fluctuation and fiber bending in the FP optical interference cavity using intensity modulation demodulation method and phase modulation demodulation method are solved.

[0073] Then, referring to Figure 7 , a reflective film is formed on the second surface of the support membrane 120 through the through hole, the reflectivity of the reflective film is 95% to 96%, the first reflective film 150 is formed by etching the reflective film, and the radial direction of the through hole coincides with the central axis of the first reflective film 150.

[0074] Then, referring to Figure 8A metal palladium film is deposited on the first surface of the supporting film 120 by a magnetron sputtering method; and the metal palladium film is etched to form the palladium film 110.

[0075] Next, referring to Figure 9 A detection optical fiber 180 is provided, and a second reflective film 170 is formed on the end surface of the detection optical fiber; then, the detection optical fiber 180 and the second reflective film 170 are installed in the through hole, specifically, the detection optical fiber 180 is welded on the supporting structure 160 in the through hole by welding, the second reflective film 170 is opposite to and aligned with the first reflective film 150, an FP cavity is formed between the first reflective film and the second reflective film, and the distance between the first reflective film and the second reflective film is the cavity length of the FP cavity. The detection optical fiber can be a collimating and beam expanding optical fiber. The through hole is used to bond or weld the detection optical fiber to form a MEMS optical fiber hydrogen sensor, which realizes the miniaturization packaging of the MEMS optical fiber hydrogen sensor, reduces the initial packaging stress of the MEMS optical fiber hydrogen sensor, and improves the temperature repeatability and long-term zero-point stability of the MEMS optical fiber hydrogen sensor. By using the collimating and beam expanding optical fiber, the light spot is parallelly expanded to a diameter of 50 μm or more for optical coupling, which can reduce the serious deterioration of the signal caused by beam divergence and angle deviation, thereby reducing the difficulty of coupling and packaging. Moreover, the hydrogen-sensitive microstructure (palladium film, supporting film and deformation beam) is directly integrated with the collimating and beam expanding optical fiber for packaging, which has good impact resistance and high reliability, is maintenance-free, and can accurately measure for a long time. It has more significant advantages in application occasions where installation operation is inconvenient and maintenance is difficult. The whole forming method is developed based on MEMS technology and optical fiber detection technology, which combines the advantages of both and has the advantages of miniaturization, batch production, good consistency, explosion-proof, anti-electromagnetic interference, and no need for power supply.

[0076] In summary, in the MEMS optical fiber hydrogen sensor and forming method provided in the embodiments of the present application, the increase of the hydrogen gas absorbed by the palladium film causes the volume expansion of the palladium film and / or the deformation of the palladium film, which causes the deformation of the deformation beam, and thus the change of the cavity length of the FP cavity, and the change of the wavelength of the laser reflected by the FP cavity received by the detection optical fiber. Therefore, the hydrogen gas absorbed by the palladium film can be calculated by detecting the wavelength change of the laser received by the detection optical fiber, and thus the concentration of the hydrogen gas in the environment can be calculated. In the embodiments of the present application, the concentration of the hydrogen gas in the environment is detected by the change of the wavelength of the light, which can not use the method of detecting the concentration of the hydrogen gas by detecting the change of the light intensity, and thus can not be limited by the precision of the light intensity detection method, and thus can not be affected by the intensity fluctuation of the light source and the bending of the optical fiber, and thus the detection precision can be improved.

[0077] The above merely describes the preferred embodiments of the present application and does not limit the present application in any way. Any person skilled in the art can make any form of equivalent replacement or modification to the technical solutions and technical contents disclosed by the present application without departing from the scope of the technical solutions of the present application, and such changes still belong to the protection scope of the present application.

Claims

1. A MEMS fiber optic hydrogen sensor, characterized in that, include: Palladium membrane, used to absorb hydrogen gas; A support film for supporting the palladium film, the support film including opposing first and second surfaces and a side surface connecting the first and second surfaces, the palladium film being located on the first surface of the support film; A deformation beam is connected to the side of the supporting membrane, and the deformation beam can deform under force; A frame for supporting the deformable beam, with a first end of the frame connected to the deformable beam; The first reflective film is located on the second side of the supporting film; A support structure having a through hole, wherein the second end of the frame is disposed on the surface of the support structure; A second reflective film is located inside the through hole. The second reflective film is opposite to and aligned with the first reflective film. An FP cavity is formed between the first reflective film and the second reflective film, and the distance between the first reflective film and the second reflective film is the cavity length of the FP cavity. as well as A detection fiber is used to emit laser light into the FP cavity and to receive laser light reflected from the FP cavity; The deformable beam is in the shape of a cuboid, with one end connected to the side of the supporting membrane and the other end connected to the frame. The supporting membrane has four sides, each side being connected to at least one deformation beam, and the number of deformation beams connected to each side is the same.

2. The MEMS fiber optic hydrogen sensor as described in claim 1, characterized in that, The axis of the first reflective film coincides with the axis of the second reflective film.

3. The MEMS fiber optic hydrogen sensor as described in claim 1, characterized in that, The radial direction of the through hole coincides with the axis of the second reflective film.

4. The MEMS fiber optic hydrogen sensor as described in claim 1, characterized in that, The detection optical fiber is located inside the through hole.

5. The MEMS fiber optic hydrogen sensor as described in claim 1, characterized in that, The second reflective film is located at the end face of the detection optical fiber.

6. The MEMS fiber optic hydrogen sensor as described in claim 1, characterized in that, The first reflective film includes a composite dielectric film or a metal film; the second reflective film includes a composite dielectric film.

7. A method for forming a MEMS fiber optic hydrogen sensor according to any one of claims 1 to 6, characterized in that, include: An SOI silicon wafer is provided, the SOI silicon wafer comprising a substrate silicon, a buried oxide layer and a top silicon layer formed from bottom to top; The top silicon is etched to form a patterned top silicon, which is divided into a first part, a second part and a third part from the inside to the outside. The first part and the second part respectively form a support film and a deformation beam. The support film includes a first surface and a second surface opposite to each other. The substrate silicon is etched to form vias, exposing the buried oxide layer within the vias, and the remaining substrate silicon forms a support structure. Remove the buried oxide layer beneath the supporting film and the deformable beam, exposing the second side of the supporting film through the through hole; the remaining buried oxide layer and the third part together form a frame. A first reflective film is formed on the second surface of the supporting film through the through-hole; A palladium film is formed on the first surface of the supporting film; A detection optical fiber is provided, and a second reflective film is formed on the end face of the detection optical fiber; as well as The detection fiber and the second reflective film are installed in the through hole such that the second reflective film is opposite to and aligned with the first reflective film, an FP cavity is formed between the first reflective film and the second reflective film, and the distance between the first reflective film and the second reflective film is the cavity length of the FP cavity.

8. The method for forming a MEMS fiber optic hydrogen sensor as described in claim 7, characterized in that, The buried oxide layer beneath the supporting film and deformed beam is removed by hydrofluoric acid wet etching or vapor phase etching.

9. The method for forming a MEMS fiber optic hydrogen sensor as described in claim 7, characterized in that, A method for forming a palladium film on the first surface of the supporting film includes: A palladium film is deposited on the first surface of the support film by magnetron sputtering. The palladium film is etched to form a palladium film.

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