CN110361445B - Multi-parameter high-selectivity CMUTs gas sensor and use and preparation method thereof - Google Patents

Abstract

The invention discloses a multi-parameter high-selectivity CMUTs gas sensor and its use and preparation method. The invention adopts SnO ₂ , ZnO, Fe ₂ O ₃ , WO ₃ and other semiconductor metal oxides, which are simultaneously used as the upper electrode of CMUTs As well as the sensitive identification material, the high selectivity and sensitivity of gas molecules with similar physical and chemical properties or similar gas molecules are realized by using the characteristics of the film quality and the resistance change of the upper electrode caused by the adsorption of gas at the same time. The change of the film quality will cause the change of the resonant frequency of the CMUT; the change of the resistance of the upper electrode will cause the change of the amplitude of the AC voltage between the upper and lower electrodes of the CMUT, and then the change of the vibration amplitude of the CMUT film. The variation of the two output parameters enables highly selective detection of gas molecules. In addition, due to the reusability of the semiconductor oxide sensitive material under temperature regulation, the CMUT gas sensor of the present invention has good repeatability in addition to high selectivity.

Description

A kind of multi-parameter high-selectivity CMUTs gas sensor and its use and preparation method

technical field

The invention relates to MEMS capacitive micro-machined ultrasonic sensor technology and semiconductor oxide sensitive materials, in particular to a multi-parameter high-selectivity CMUTs gas sensor and its use and preparation method.

Background technique

The resonant MEMS gas sensor realizes the gas detection by using the sensitive material layer coated on the surface of the resonant element to absorb the gas to be measured, which causes the mass of the resonant element and thus the change of the resonant frequency. The resonant MEMS gas sensor has the advantages of small size, high sensitivity, low quality detection limit, low power consumption, compatibility with MEMS process, and mass manufacturing. Capacitive Micromachined Ultrasonic Transducers (CMUTs) were originally developed for ultrasonic medical imaging and treatment. Due to their small film quality and high resonance frequency, the vibrating film is damped by air on one side (the other side is vacuum), and its quality Due to its high factor, it can achieve high sensitivity and low detection limit measurement of gases when used in resonators. In addition, compared with the gas sensor based on (Quartz Crystal Microbalance, QCM), the CMUT has a wide operating temperature range (up to 500 °C) and is less affected by the ambient temperature; Rugged for gas detection in harsh environments. Therefore, CMUTs have outstanding performance advantages when used in resonators to achieve high sensitivity and low detection limit gas detection. At present, Professor ^BTKhuri -Yakub of Stanford University and others used CMUTs as biochemical sensors to detect Dimethyl methylphosphonate (DMMP). . D.Barauskas et al. of Kaunas University of Technology used spin coating to functionalize CMUT for _CO measurement, with detection sensitivities of 3.8ppm/Hz and 0.25ppm/Hz, respectively. These studies have demonstrated the feasibility and performance advantages of CMUTs for gas detection.

However, the sensitive material layer and the upper electrode layer of the existing CMUTs gas sensors are designed independently. The sensitive material is only used to selectively adsorb the gas to be measured, while the upper electrode is used to load the electrostatic excitation to make the membrane vibrate. The adsorption of the sensitive film only causes the change of the film quality, which in turn causes the change of the single parameter of the resonant frequency. When there are gas molecules with similar or similar physical or chemical properties, the sensor cannot effectively distinguish them, resulting in false alarms. Therefore, it is difficult for CMUTs gas sensors based on the current structure and working principle to achieve highly selective detection of similar or similar gas molecules to be detected.

SUMMARY OF THE INVENTION

In order to solve the above technical problems, the present invention proposes a multi-parameter high-selectivity CMUTs gas sensor and its use and preparation method.

The technical scheme adopted in the present invention is as follows:

The overall structure of the multi-parameter high-selectivity CMUTs gas sensor of the present invention includes a sensitive film, an electrical insulating film, a cavity, a diffraction grating and a transparent substrate in sequence from top to bottom; wherein the sensitive film not only has gas sensitivity, but also has The sensitive film is used as the upper electrode at the same time; the diffraction grating is made of conductive material and is used as the lower electrode at the same time; the transparent substrate has the characteristics of light transmission; the sensitive film and the electrically insulating film together form the vibration film.

The sensitive thin film is a semiconductor metal oxide thin film with gas sensitivity, and the sensitive thin film can simultaneously change the quality and resistance of the sensitive thin film after being acted on by the gas to be measured.

The sensitive thin film adopts SnO ₂ thin film, ZnO thin film, Fe ₂ O ₃ thin film or WO ₃ thin film, which are gas-sensitive semiconductor metal oxide thin films. The sensitive thin film has gas sensitivity. In addition to the change, it also causes the resistance to change.

The upper electrode and the sensitive thin film are the same thin film, and the sensitive thin film only covers the corresponding area directly above the cavity, or covers the entire CMUTs array area. It is also important to consider designing the sensitive film as a patterned electrode structure that reduces thermal stress.

The electrical insulating film is an insulating material such as a SiO ₂ film, a SiC film or a Si ₃ N ₄ film, and the electrical insulating film is used to achieve electrical insulation between the upper electrode and the lower electrode.

The cavity is a vacuum cavity, and the cross-sectional shape of the cavity is a circle, a square or a regular hexagon. The height of the cavity is designed according to the working voltage requirements and process conditions; the cavity is surrounded by pillars, and the thickness of the pillar is related to the cavity. of the same height.

The diffraction grating is located inside the cavity, and electrical connections are provided between gratings of the diffraction grating and between the diffraction grating and surrounding structures, and the diffraction grating is used to diffract the light reflected by the vibrating film to realize the optical interference displacement detection of the vibrating film, The material of the diffraction grating is a low-resistance material and serves as a lower electrode at the same time.

The surrounding structure of the diffraction grating is electrically connected to the lower electrode of the same material and thickness as the diffraction grating. The shape and width of the electrical connection of the lower electrode are the same as the cross-sectional shape and width of the pillar, respectively. The electrical connection of the lower electrode is used for An electrical connection is made with an external power source. The transparent substrate is a transparent substrate made of transparent materials such as BF 33 or Pyrex 7740, and the transparent substrate is used for realizing thin film displacement optical interferometry.

The thermal expansion coefficients of any two selected materials in the electrical insulating film, the pillars around the cavity, the diffraction grating and the transparent substrate should differ by no more than 20%, and the closer the thermal expansion coefficients are, the better, so as to reduce the process of environmental temperature changes. Effects of moderate thermal stress on sensor performance.

The method of using multi-parameter high-selectivity CMUTs gas sensor, the process includes:

When the measured gas interacts with the sensitive film, the quality and resistance of the sensitive film change simultaneously; the measured gas can be detected by detecting the two output parameters, the resonance frequency and the vibration displacement of the vibrating film.

The sensitive film is a semiconductor metal oxide film with gas sensitivity. After the sensitive film interacts with the gas to be measured, the quality of the wave film and the resistance of the film can be changed at the same time; by adjusting the temperature of the multi-parameter high-selectivity CMUTs gas sensor, the The multi-parameter high-selectivity CMUTs gas sensor repeatedly detects the measured gas for many times. Since semiconductor oxides are used for gas sensitivity, they can achieve good repeatability through temperature adjustment. Therefore, the CMUTs gas sensor can achieve multiple repeatability detection of the measured gas by adjusting the operating temperature of the CMUTs gas sensor, thereby improving the repeatability.

A preparation method of a multi-parameter high-selectivity CMUTs gas sensor mainly includes the following steps:

(1) take an SOI sheet as the first SOI sheet, and take another transparent glass wafer (such as BF33 glass), and carry out standard cleaning and standby to the first SOI sheet and the transparent glass wafer;

(2) adopting anodic bonding method to carry out anodic bonding of the top silicon of the first SOI sheet and the transparent glass wafer under low temperature conditions;

(3) 80% of the thickness of the base silicon of the first SOI sheet is removed by chemical mechanical polishing, then the remaining 20% of the base silicon is removed with a buffer etching solution, and the etching stops on the surface of the buried silicon dioxide of the first SOI sheet;

(4) Photolithography, patterning the shape of the cavity, wet etching the buried silicon dioxide layer of the first SOI sheet, removing the silicon dioxide in the pattern window, etching stops on the silicon surface of the top layer of the first SOI sheet, forming a void The cavity structure and the pillar structure around the cavity; another SOI sheet is taken as the second SOI sheet for cleaning and standby;

(5) Photolithography, patterning the shape of the diffraction grating, wet etching the top silicon of the first SOI wafer, and the etching stops on the upper surface of the transparent glass wafer to form a diffraction grating; at the same time, the top silicon of the second SOI wafer is oxidized, and the top silicon of the second SOI wafer is oxidized at the same time. A silicon dioxide layer is formed on the top silicon surface of the wafer;

(6) Using low temperature fusion bonding method, the remaining buried silicon dioxide on the first SOI sheet (the remaining buried silicon dioxide is used as the pillar of the CMUTs gas sensor) and the silicon dioxide layer on the upper surface of the top silicon of the second SOI sheet are bonded. Vacuum bonding, the cavity is vacuum sealed at this time;

(7) Use chemical mechanical polishing to remove 80% of the thickness of the base silicon of the second SOI sheet, and then use an etching solution to remove the remaining 20% of the base silicon to expose the buried silicon dioxide of the second SOI sheet; dry or wet The method of etching to remove the buried silicon dioxide layer of the second SOI sheet, exposing the remaining top layer silicon after the oxidation of the second SOI sheet;

(8) Use a buffer etching solution to etch the remaining top layer silicon of the second SOI sheet after oxidation, stop the etching at the silicon dioxide layer generated after the oxidation of the top silicon surface of the second SOI sheet, and release the silicon dioxide located on the top layer of the second SOI sheet Silica film on the surface;

(9) sputtering ZnO or _SnO sensitive material layers with semiconductor properties on the surface of the silicon dioxide film by the method of magnetron sputtering to form a sensitive film, and the sensitive film is simultaneously used as the upper electrode of the CMUTs gas sensor;

(10) photolithography, using wet etching to etch the sensitive film, the electrical insulating film and the pillar in turn, the etching stops on the upper surface of the lower electrode electrical connection, exposing the lower electrode pad position;

(11) Spin-coat photoresist and photolithography on the surface of the sensitive material layer, and sputter a metal layer (such as metal aluminum, gold, which are commonly used electrode materials), form electrode pads by a lift-off method, and anneal to reduce the sensitive film (namely, the upper electrode) and the lower electrode are electrically connected to the contact resistances between the upper and lower electrode pads, respectively, to obtain a multi-parameter high-selectivity CMUTs gas sensor.

In order to further improve the selectivity of the sensitive material layer to the measured gas, the process steps after the above-mentioned process step (9) are changed to:

(10) Synthesize a solution for chemical modification, immerse the sensitive film in the solution for surface modification, and improve the sensitivity between the sensitive film and the gas to be measured;

(11) photolithography, using wet etching to etch the sensitive film, the electrical insulating film and the pillar in turn, the etching stops on the upper surface of the lower electrode electrical connection, exposing the lower electrode pad position;

(12) Spin-coat photoresist and photolithography on the upper surface of the sensitive film and the exposed lower electrode electrically connected, and sputter a metal layer (such as metal aluminum, gold, these common electrode materials), and use the peeling method to form electrode pads , and annealed to reduce the contact resistance between the sensitive material layer (ie, the upper electrode) and the electrical connection between the lower electrode and the upper and lower electrode pads, respectively, to obtain a multi-parameter high-selectivity CMUTs gas sensor.

Compared with the prior art, the present invention has the following beneficial effects:

In the existing CMUT structure, the sensitive material layer and the upper electrode layer are designed independently. The sensitive material layer is only used to selectively adsorb the gas to be measured, and the upper electrode is used to load electrostatic excitation; the interaction between the sensitive material layer and the measured gas only causes the film quality It is difficult to identify gas molecules with similar physical or chemical properties, and it is easy to cause false alarms of the sensor. The sensitive film used in the present invention is used as both the sensitive and electrode material, and the interaction between the measured gas molecules and the sensitive film can not only cause the change of the quality of the vibrating film but also the resistance of the upper electrode; the change of the quality of the vibrating film can cause the resonant frequency. The change of the resistance of the upper electrode can cause the electrostatic force loaded on the vibrating film to change, thus causing the amplitude of the vibrating film to change. The physical and chemical properties can be realized through the two parameters of the resonance frequency of the CMUTs and the vibration displacement of the vibrating film. The identification of similar or similar measured gas molecules can effectively improve the selectivity of the sensor. Compared with the conventional CMUTs gas sensor in which the upper electrode and the sensitive material layer are independently designed, the upper electrode and the sensitive material layer (ie, the sensitive film) of the CMUTs gas sensor of the present invention are the same film layer, and the integrated design is adopted, in addition to the above advantages. , also helps to reduce the film quality, and the CMUTs have good unit consistency and low frequency noise, which help to improve the detection sensitivity and detection limit.

Furthermore, the existing CMUTs gas sensors have poor repeatability or recoverability. After the sensitive material layer interacts with the measured gas, it is difficult for the gas molecules to completely separate from the sensitive material, which affects the accuracy of the re-measurement results. The sensitive film (also the upper electrode) of the CMUTs gas sensor of the present invention adopts a semiconductor metal oxide film with gas sensitivity. After the sensitive film interacts with the measured gas, the quality of the wave film and the resistance of the film can be changed at the same time. The good repeatability of the thin film under temperature control can effectively improve the repeatability of CMUTs gas sensors;

When the multi-parameter high-selectivity CMUTs gas sensor of the present invention is in use, when the measured gas interacts with the sensitive film, the quality and resistance of the sensitive film change at the same time; the detection of the two output parameters of resonance frequency and film vibration displacement can realize For the detection of the gas to be measured, the use process is simple, the detection results are accurate, and the effect is good. Further, the sensitive thin film is a semiconductor metal oxide thin film with gas sensitivity, and the sensitive thin film and the measured gas can cause changes in the quality of the wave thin film and the thin film resistance at the same time; by adjusting the multi-parameter high selectivity CMUTs gas sensor The working temperature can realize the repeated detection of the measured gas by the multi-parameter high-selectivity CMUTs gas sensor, and improve the repeatability.

The preparation method of the multi-parameter high-selectivity CMUTs gas sensor of the invention is simple and easy to realize, and the prepared CMUTs gas sensor has excellent performance.

Description of drawings

1 is a schematic structural diagram of a multi-parameter high-selectivity CMUTs gas sensor of the present invention, wherein FIG. 1(a) is a longitudinal cross-sectional view of the multi-parameter high-selectivity CMUTs gas sensor, and FIG. 1(b) is FIG. 1(a) ) in the top view of the part below the section A-A;

2 is a schematic view of a variation structure of a multi-parameter high-selectivity CMUTs gas sensor diffraction grating of the present invention;

FIG. 3 is a schematic structural diagram of a variation of the sensitive material layer (at the same time the upper electrode) of a multi-parameter high-selectivity CMUTs gas sensor according to the present invention;

Figure 4 is a schematic diagram of the working principle of a multi-parameter high-selectivity CMUTs gas sensor of the present invention, wherein Figure 4(a) is a schematic diagram of the interaction between the loading and the sensitive film and the gas when the multi-parameter high-selectivity CMUTs gas sensor is working; Figure 4 ( b) Schematic diagram of the time-dependent change of the vibration displacement of the sensitive film after adsorption and desorption of the measured gas when the multi-parameter high-selectivity CMUTs gas sensor works; Figure 4(c) is the adsorption and desorption of the sensitive film when the multi-parameter high-selectivity CMUTs gas sensor works. Schematic diagram of the change of resonance frequency with time after adsorbing the measured gas;

Fig. 5 is a typical preparation process flow diagram of a multi-parameter high-selectivity CMUTs gas sensor of the present invention;

6 is a process flow diagram of a variation of the preparation process of a multi-parameter high-selectivity CMUTs gas sensor according to the present invention;

In the figure, 1-sensitive film, 2-electric insulating film, 3-pillar, 4-cavity, 5-electrical connection of lower electrode, 6-diffraction grating, 7-electrical connection, 8-transparent substrate, 9-electrode pad .

Detailed ways

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings and embodiments.

Referring to Figure 1(a), Figure 1(b) and Figure 2, the overall structure of the multi-parameter high-selectivity CMUTs gas sensor of the present invention sequentially includes a sensitive film 1, an electrical insulating film 2, a cavity 4, a diffraction film from top to bottom grating 6 and transparent substrate 8 . Among them, the sensitive film 1 is also used as the upper electrode of the CMUT, the cavity 4 is surrounded by pillars 3, the diffraction grating 6 is also used as the lower electrode of the CMUTs, the structure around the diffraction grating 6 is the electrical connection 5 between the lower electrodes, and the gratings of the diffraction grating 6 An electrical connection 7 is provided therebetween. The interaction between the measured gas molecules and the sensitive film simultaneously causes the resonant frequency and the vibration displacement of the CMUTs gas sensor to change at the same time. The high selectivity of the measured gas molecules is achieved through the change of the resonant frequency and the vibration displacement of the vibration film at a fixed frequency. detection.

The sensitive film 1 is made of a semiconductor oxide material with both gas sensitivity and adjustable electrical conductivity. After interacting with the gas to be measured, it can not only change the quality of its own film, but also cause the resistance to change. The sensitive film 1 is made of SnO _2. Semiconductor metal oxide films such as ZnO, Fe ₂ O ₃ or WO ₃ ; the sensitive film 1 is used as a sensitive material layer and an upper electrode at the same time; the thickness and shape design of the sensitive film 1 should be able to increase the specific surface area and ensure conductivity. and the requirement to reduce thermal stress with the electrically insulating film 2 .

In addition to being a part of the CMUT vibrating film, the electrical insulating film 2 is also used to achieve electrical insulation between the upper electrode (sensitive film 1 in the present invention) and the lower electrode (diffraction grating 6). The electrical insulating film 2 is made of SiO ₂ . Thin films of insulating materials such as , Si ₃ N ₄ or SiC, the thickness of the electrical insulating film 2 and the size design of the radius are determined by the operating frequency of the CMUTs gas sensor. The electrical insulating film 2 and the sensitive film 1 together constitute the vibrating film of the CMUTs gas sensor of the present invention, and the total thickness and radius of the vibrating film ultimately determine the operating frequency of the CMUTs.

The cavity 4 is a vacuum cavity, the height of the cavity 4 determines the working voltage of the CMUTs gas sensor, and the shape of the cavity 4 can be a circle, a square, a regular hexagon, or the like.

The pillar 3 is located around the cavity 4, and the height of the pillar 3 is equal to the height of the cavity 4. The material of the pillar 3 can be SiO ₂ , SiC or Si ₃ N ₄ .

On the one hand, the diffraction grating 6 makes the light reflected from the vibrating film form diffracted light, and on the other hand, it is used as the lower electrode of the CMUTs gas sensor; the diffraction grating 6 adopts conductive materials, such as low-resistance silicon and low-resistance polysilicon; the diffraction grating 6 An electrical connection 7 is provided between each grating of the diffraction grating 6; the design of the grating spacing and the number of gratings of the diffraction grating 6 is determined according to the wavelength of the incident light and the radius of the cavity 4, and at the same time it is necessary to ensure sufficient conductivity between the lower electrodes; the thickness of the electrical connection 7 Similar to the diffraction grating 6, the width of the electrical connection 7 should ensure that the conductive connection and resistance between the gratings are as small as possible; the shape of the diffraction grating 6 can be designed as a circular ring as shown in Figure 2 shows a comb-like shape.

The lower electrode electrical connection 5 is used to realize the electrical connection between all the lower electrodes (ie the diffraction grating) of the CMUTs gas sensor and between the lower electrode and the external power supply. The material and thickness of the lower electrode electrical connection 5 and the material of the diffraction grating 6 The thickness and thickness dimensions are respectively the same, and the shape of the lower electrode electrical connection 5 is the same as the cross-sectional shape of the pillar 3 .

The transparent substrate 8 adopts a transparent material, such as BF 33 glass or Pyrex 7740 glass, which is used to realize the detection of incident laser light and diffracted light.

The materials used for the electrical insulating film 2, the pillars 3 around the cavity 4, the lower electrode electrical connection 5 and the transparent substrate 8 should have similar thermal expansion coefficients to reduce thermal stress caused by mismatching thermal expansion coefficients during temperature changes, and further Reduce the impact on the detectability of CMUTs gas sensors. This is because the CMUTs gas sensor of the present invention mainly utilizes the properties of semiconductor oxides to adsorb gas at high temperature and desorb when the temperature decreases to improve the repeatability of the CMUTs gas sensor. Therefore, the structure of the CMUTs gas sensor itself needs to have a good temperature. stability.

In general, the thermal expansion coefficients of any two selected materials in the electrically insulating film, the pillars around the cavity, the diffraction grating and the transparent substrate should differ by no more than 20%, and the closer the thermal expansion coefficients are, the better.

In order to further reduce the thermal stress caused by the mismatch of thermal expansion coefficients between the sensitive film 1 and the insulating film 2 during the temperature change process, the sensitive film 1 can be designed with a pattern, that is, only the electrical insulating film 2 directly above the cavity 4 is covered. , and the shape of the sensitive film 1 is shown in FIG. 3 .

The working principle of the multi-parameter high-selectivity CMUTs gas sensor of the present invention: when the measured gas interacts with the sensitive material layer (ie, the sensitive film 1), the quality and resistance of the sensitive film 1 change simultaneously; Causes the change of the resonant frequency of the vibrating film, and under the condition that the applied DC voltage and the amplitude of the AC voltage remain unchanged, the change of the resistance of the sensitive film 1 will cause the effective voltage across the electrodes of the loaded CMUTs gas sensor to change, which in turn causes static electricity. The change of electric power and vibration amplitude; the detection of two output parameters of resonance frequency and vibration displacement can realize the high selectivity and high sensitivity detection of the measured gas.

In addition, when the sensitive film is a gas-sensitive semiconductor metal oxide film (such as SnO ₂ film, ZnO film, Fe ₂ O ₃ film or WO ₃ film with gas-sensitive semiconductor metal oxide film), due to When the semiconductor oxide is used for gas sensing, good repeatability can be obtained through temperature adjustment, so the CMUTs gas sensor of the present invention has the repeatable detection performance when it is used for gas detection.

The specific user of the multi-parameter and high-selectivity CMUTs gas sensor of the present invention is described in detail with reference to FIG. 4 and the working principle of the multi-parameter and high-selectivity CMUTs gas sensor of the present invention. Referring to Figure 4 (a), when the CMUTs gas sensor of the present invention works, it is necessary to load DC and AC voltage excitation between the sensitive film 1 and the lower electrode at the same time, so that the vibration film composed of the sensitive film 1 and the electrical insulating film 2 vibrates. , to heat the CMUTs gas sensor until the optimal temperature of the sensitive film 1 reacting with the measured gas. At this time, the sensitive film 1 adsorbs the measured gas, and the interaction between the sensitive film 1 and the measured gas causes two parameters to change, that is, the quality and resistance of the sensitive film 1 change. The resistance change of the sensitive film 1 will cause the effective voltage V _C loaded between the upper and lower electrodes of the CMUTs gas sensor to change. Under the condition that the resonant frequency remains unchanged, the vibration amplitude of the vibrating film will be changed. The displacement detection technology of interference can realize the detection of the displacement change of the vibrating film; when the temperature decreases, after the sensitive film 1 desorbs the measured gas, the vibration amplitude returns to the original value. The schematic diagram of the principle is shown in Figure 4(b). In addition, the change in the quality of the sensitive film 1 will change the resonant frequency of the CMUTs gas sensor. The resonant frequency can be detected by sweeping frequency or resonant circuit, and the measured gas concentration can be reflected through the resonant frequency shift. When the temperature decreases, the measured gas and the sensitive film 1 After separation, the quality of the film returns to its original value. At this time, the resonant frequency returns to the resonant frequency value before the interaction with the gas. The schematic diagram of the principle is shown in 4(c). Micro laser emitters and laser detectors can be integrated with CMUTs gas sensors to realize the optical detection of the displacement of the vibrating film; resonant circuits can be integrated with CMUTs gas sensors to realize the detection of resonant frequency; MEMS heaters can be integrated with CMUTs as sensors and the measured gas The interaction provides temperature conditions.

The main process steps of a typical preparation process flow of a multi-parameter high-selectivity CMUTs gas sensor of the present invention are:

(1) take the first SOI sheet 10, and take another transparent BF 33 glass wafer 8, carry out standard cleaning and standby on the surface of the first SOI sheet 10 and the BF 33 glass wafer 8;

(2) The top layer silicon 11 of the SOI sheet 10 and the BF 33 glass wafer 8 are anodic bonded under low temperature conditions by anodic bonding, and the BF 33 glass wafer 8 forms a transparent substrate;

(3) 80% of the thickness of the base silicon of the SOI sheet 10 is removed by chemical mechanical polishing, then the remaining 20% of the base silicon is removed with a buffer etching solution, and the etching stops on the surface of the buried silicon dioxide of the SOI sheet 10;

(4) Photolithography, patterning the shape of the cavity, wet etching the buried silicon dioxide layer of the first SOI sheet 10, removing the silicon dioxide in the cavity pattern window, and etching stops at the first SOI sheet 10 The top silicon surface forms a cavity structure and pillars 3; at the same time, a second SOI sheet 12 is taken for cleaning, for use;

(5) photolithography, patterning the shape of the diffraction grating, wet etching the top layer silicon of the first SOI sheet 10, the etching stops on the upper surface of the BF33 glass wafer 8, and forming a diffraction grating; at the same time, the oxidation method is used on the second SOI sheet 12 The silicon dioxide layer 13 is formed on the top silicon surface of the

(6) The silicon dioxide pillar 3 on the first SOI sheet 10 is vacuum bonded to the silicon dioxide layer 13 on the top silicon of the second SOI sheet 12 by using a low-temperature fusion bonding method. At this time, the cavity is vacuum sealed to form a hollow space. cavity 4;

(7) 80% of the thickness of the base silicon of the second SOI sheet 12 is removed by chemical mechanical polishing, and then an etching solution is used to remove the remaining 20% to expose the buried silicon dioxide of the second SOI sheet 12; and then a dry method is used or wet etching to remove the buried silicon dioxide layer of the second SOI sheet 12 to expose the remaining top layer silicon of the second SOI sheet 12 after oxidation;

(8) using a buffer etching solution to etch the remaining top layer silicon of the second SOI sheet 12 after oxidation, the etching stops at the silicon dioxide layer 13, and an electrical insulating film 2 is formed at this time;

(9) adopting the method of magnetron sputtering to sputter the ZnO sensitive material layer on the upper surface of the electrical insulating film 2 to form the sensitive film 1;

(10) photolithography, patterning, using wet etching to etch the sensitive film 1, the electrical insulating film 2 and the pillar 3 in turn, and the etching stops on the upper surface of the lower electrode electrical connection 5, exposing the lower electrode pad position;

(11) Spin-coating photoresist and photolithography on the upper surface of the sensitive film 1 and the exposed lower electrode electrical connection 5, and sputtering metal aluminum, using the peeling method to form the electrode pad 9 (referring to the upper electrode pad and the lower electrode pad). electrode pad), and annealed to reduce the contact resistance between the sensitive film 1 and the electrical connection 5 of the lower electrode and the electrode pad 9 .

In order to further improve the selectivity of the sensitive material layer 1 to the measured gas, the process steps after the above process step (8) can be changed to:

(9) adopt the method of magnetron sputtering to sputter the ZnO sensitive film 14 on the upper surface of the electrical insulating film 2;

(10) synthesizing a solution for surface modification, immersing the ZnO sensitive film 14 in the solution for surface modification, thereby improving the sensitivity between the ZnO sensitive film 14 and the gas to be measured, and forming the final sensitive material layer 1;

(11) photolithography, using wet etching to etch the sensitive film 1, the electrical insulating film 2 and the pillar 3 in turn, the etching stops at the upper surface of the lower electrode electrical connection 5, exposing the lower electrode pad position;

(12) Spin-coating photoresist and photolithography on the upper surface of the sensitive film 1, and sputtering metal aluminum, using the peeling technique to form the electrode pad 9, and annealing to reduce the sensitive film 1 and the lower electrode electrical connection 5 and the electrode welding Contact resistance between disks 9.

The above is only an embodiment of the present invention, not all or the only embodiment. Any equivalent transformation to the technical solution of the present invention by those of ordinary skill in the art by reading the description of the present invention is the right of the present invention requirements covered.

Claims (8)

1. A multi-parameter high-selectivity CMUTs gas sensor is characterized by sequentially comprising a sensitive film (1), an electric insulating film (2), a cavity (4), a diffraction grating (6) and a transparent substrate (8) from top to bottom; the sensitive film (1) is used as an upper electrode and has the properties of gas sensitivity and capability of changing quality and resistance after the action of gas; the diffraction grating (6) serves as a lower electrode; the sensitive film (1) and the electric insulation film (2) jointly form a vibration film;

the diffraction grating (6) is positioned in the cavity (4), electric connections (7) are arranged among the gratings of the diffraction grating (6) and between the diffraction grating (6) and the surrounding structure, and the diffraction grating (6) is used for diffracting the light reflected by the vibration film;

the difference of the thermal expansion coefficients of any two selected materials in the electric insulation film (2), the support post (3) around the cavity (4), the diffraction grating (6) and the transparent substrate (8) is not more than 20%.

2. The multiparameter high-selectivity CMUTs gas sensor according to claim 1, wherein the sensitive film (1) is a semiconductor metal oxide film with gas sensitivity, and the quality and the resistance of the sensitive film (1) can be simultaneously changed after the sensitive film (1) reacts with the measured gas.

3. A multiparameter highly selective CMUTs gas sensor according to claim 2, wherein the sensitive membrane (1) is SnO₂Film, ZnO film, Fe₂O₃Films or WO₃A film.

4. A multiparameter, highly selective CMUTs gas sensor according to claim 1, wherein the sensitive membrane (1) is covered on the electrically insulating membrane (2) and covers only the corresponding area directly above the cavity (4).

5. Use of the multiparameter highly selective cmut gas sensor of any of claims 1 to 4, wherein the process comprises:

when the measured gas interacts with the sensitive film (1), the quality and the resistance of the sensitive film (1) are changed simultaneously; the detection of the gas to be detected can be realized by detecting two output parameters of the resonance frequency and the vibration displacement of the vibration film.

6. The use method according to claim 5, characterized in that the sensitive film (1) is a semiconductor metal oxide film with gas sensitivity, and the sensitive film (1) can simultaneously cause the quality and the resistance of the wave sensitive film (1) to change after the sensitive film (1) acts on the gas to be detected;

and the temperature of the multi-parameter high-selectivity CMUTs gas sensor is adjusted, so that the multi-time repeated detection of the measured gas by the multi-parameter high-selectivity CMUTs gas sensor is realized.

7. A method for preparing a multiparameter highly selective CMUTs gas sensor according to any one of claims 1-4, comprising the steps of:

s1, taking the first SOI sheet and the transparent glass wafer for cleaning and standby;

s2, carrying out anodic bonding on the top silicon of the first SOI sheet and the transparent glass wafer by adopting an anodic bonding method under a low-temperature condition;

s3, removing 80% of the thickness of the first SOI wafer substrate silicon by adopting a chemical mechanical polishing method, removing the rest 20% of the substrate silicon by using buffer etching liquid, and stopping etching on the first SOI wafer buried layer silicon dioxide;

s4, photoetching and patterning the cavity shape, wet etching the first SOI piece buried layer silicon dioxide layer, removing the silicon dioxide in the pattern window, stopping etching on the top silicon surface of the first SOI piece, and forming a cavity (4) and a support (3) around the cavity (4); taking another SOI sheet as a second SOI sheet, and cleaning the second SOI sheet for later use;

s5, photoetching, patterning the shape of the diffraction grating, wet etching the top silicon layer of the first SOI wafer, and stopping etching on the upper surface of the transparent glass wafer to form the diffraction grating (6); oxidizing the top silicon of the second SOI piece, and generating a silicon dioxide layer on the surface of the top silicon of the second SOI piece;

s6, carrying out vacuum bonding on the buried layer silicon dioxide reserved on the first SOI sheet and the silicon dioxide layer on the upper surface of the top silicon of the second SOI sheet by adopting a low-temperature fusion bonding method, and then carrying out vacuum sealing on the cavity (4);

s7, removing 80% of second SOI piece substrate silicon by adopting a chemical mechanical polishing method, and removing the rest 20% of substrate silicon by adopting buffer etching liquid to expose second SOI piece buried layer silicon dioxide; removing the second SOI buried layer silicon dioxide layer by adopting a dry etching method or a wet etching method to expose the residual top layer silicon of the second SOI after oxidation;

s8, etching the top silicon left after the second SOI sheet is oxidized by adopting buffer etching liquid, stopping etching the silicon dioxide layer generated by oxidizing the top silicon surface of the second SOI sheet, and releasing the silicon dioxide film positioned on the top silicon surface of the second SOI sheet to form an electric insulation film (2);

s9, sputtering the sensitive film (1) on the surface of the electric insulation film (2) by adopting a magnetron sputtering method, wherein the sensitive film (1) is used as an upper electrode;

s10, photoetching, sequentially etching the sensitive film (1), the electric insulation film (2) and the support (3) by wet etching, stopping etching on the upper surface of the lower electrode electric connection (5), and exposing the position of the lower electrode pad;

s11, spin-coating photoresist, photoetching and sputtering a metal layer on the upper surfaces of the sensitive film (1) and the exposed lower electrode electric connection (5), forming an electrode pad (9) by adopting a stripping method, and annealing to reduce the contact resistance between the sensitive film (1) and the electrode pad, thereby obtaining the multi-parameter high-selectivity CMUTs gas sensor.

8. A method for preparing a multiparameter highly selective CMUTs gas sensor according to any one of claims 1-4, comprising the steps of:

s1, taking the first SOI sheet and the transparent glass wafer for cleaning and standby;

s2, carrying out anodic bonding on the top silicon of the first SOI sheet and the transparent glass wafer by adopting an anodic bonding method under a low-temperature condition;

s3, removing 80% of the thickness of the first SOI wafer substrate silicon by adopting a chemical mechanical polishing method, removing the rest 20% of the substrate silicon by using buffer etching liquid, and stopping etching on the first SOI wafer buried layer silicon dioxide;

s4, photoetching and patterning the cavity shape, wet etching the first SOI piece buried layer silicon dioxide layer, removing the silicon dioxide in the pattern window, and stopping etching on the top silicon surface of the first SOI piece to form a cavity (4) and a support (3); taking another SOI sheet as a second SOI sheet, and cleaning the second SOI sheet for later use;

s5, photoetching, patterning the shape of the diffraction grating, wet etching the top silicon layer of the first SOI wafer, and stopping etching on the upper surface of the transparent glass wafer to form the diffraction grating (6); oxidizing the top silicon of the second SOI piece, and generating a silicon dioxide layer on the surface of the top silicon of the second SOI piece;

s6, carrying out vacuum bonding on the buried layer silicon dioxide reserved on the first SOI sheet and the silicon dioxide layer on the upper surface of the top silicon of the second SOI sheet by adopting a low-temperature fusion bonding method, and then carrying out vacuum sealing on the cavity (4);

s7, removing 80% of second SOI piece substrate silicon by adopting a chemical mechanical polishing method, and removing the rest 20% of substrate silicon by adopting buffer etching liquid to expose second SOI piece buried layer silicon dioxide; removing the second SOI buried layer silicon dioxide layer by adopting a dry etching method or a wet etching method to expose the residual top layer silicon of the second SOI after oxidation;

s8, etching the top silicon left after the second SOI sheet is oxidized by adopting buffer etching liquid, stopping etching the silicon dioxide layer generated by oxidizing the top silicon surface of the second SOI sheet, and releasing the silicon dioxide film positioned on the top silicon surface of the second SOI sheet to form an electric insulation film (2);

s9, sputtering the sensitive film (1) on the surface of the electric insulation film (2) by adopting a magnetron sputtering method, wherein the sensitive film (1) is used as an upper electrode;

s10, synthesizing a solution for chemical modification, immersing the sensitive film (1) in the solution for surface modification, and improving the sensitivity between the sensitive film (1) and the gas to be detected;

s11, photoetching, sequentially etching the sensitive film (1), the electric insulation film (2) and the support (3) by wet etching, stopping etching on the upper surface of the lower electrode electric connection (5), and exposing the position of the lower electrode pad;

s12, spin-coating photoresist, photoetching and sputtering a metal layer on the upper surfaces of the sensitive film (1) and the exposed lower electrode electric connection (5), forming an electrode pad (9) by adopting a stripping method, and annealing to reduce the contact resistance between the sensitive film (1) and the electrode pad, thereby obtaining the multi-parameter high-selectivity CMUTs gas sensor.

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