Micro electro mechanical system semiconductor hydrogen sensor and preparation method thereof

Abstract

The invention discloses a micro electro mechanical system semiconductor hydrogen sensor and a preparation method thereof. The sensor comprises SnO2, Au and ZnO layers, a micro heating plate substrate and a ceramic substrate which are arranged from top to bottom, the method comprises the following steps: mounting a target material on a target position; stabilizing the micro heating plate substrate on a heating table; vacuumizing the sputtering chamber to enable the vacuum degree of the sputtering chamber to be below 5 * 10 <-3 > Pa; argon is introduced into the cavity until the pressure in the cavity reaches about 1 Pa; a ZnO film with the thickness of 50-200 nm is formed on the surface of the micro heating plate substrate; an Au film with the thickness of 2-10 nm is formed on the surface of the ZnO film, and a ZnO-Au composite material is obtained; and forming a SnO2 thin film with the thickness of 4-10nm on the surface of the Au thin film to obtain the ZnO-Au-SnO2 sandwich sensitive composite film. The sensor is high in response speed, short in recovery time and high in detection precision, and the hydrogen sensor with the high response value can be prepared through the method.

Description

Technical Field

[0001] The present invention belongs to the technical field of MEMS gas sensors, and in particular relates to a micro-electromechanical system semiconductor hydrogen sensor and a preparation method thereof. Background Art

[0002] According to the gas-sensitive characteristics, gas sensors can be divided into semiconductor gas sensors, electrochemical gas sensors, solid electrolyte gas sensors, contact combustion gas sensors, optical gas sensors, etc. Among them, semiconductor gas sensors are the most widely used and most practical type of gas sensors.

[0003] Oxide semiconductor gas sensors have many characteristics such as high sensitivity, fast response / recovery speed, and low cost, so they have attracted much attention in the past decade. The stability and sensitivity of oxide semiconductor gas sensors during long-term use are two key performance indicators. Therefore, the preparation of oxide semiconductor-based gas-sensitive materials with good long-term stability and high sensitivity remains one of the key points and difficulties in the industry. Early semiconductor oxide gas sensors were prepared based on ceramic tubes, which had high power consumption; later, mature planar oxide semiconductor gas sensors were developed. Although the power consumption problem has been improved to a certain extent, its power consumption is still relatively high, resulting in more serious heating problems in the equipment, which requires more efficient insulation systems and larger capacity power supplies to maintain stable operation of the equipment, which will increase the size and weight of the equipment, which is not conducive to integration.

[0004] MEMS (micro-electromechanical system) sensors refer to sensors with some components below 100 microns in size. They can be realized based on micro-machining technology and are an emerging interdisciplinary research field. Compared with traditional sensors, they have the characteristics of small size, light weight, low cost, low power consumption, high reliability, suitable for mass production, easy integration and intelligent realization. With the development of MEMS technology, micro-heating plate substrates have emerged, which can greatly reduce the power consumption of semiconductor gas sensors and are easy to integrate.

[0005] For the commercial application of sensors such as metal oxide semiconductors, stability, sensitivity and whether they can be mass-produced are all issues that need to be solved in the current industry. At present, the hydrogen sensitive materials used to prepare hydrogen sensors have low response rate, low detection accuracy and short service life, which seriously restricts the mass production and large-scale application of hydrogen sensors. Therefore, it is urgent to provide a hydrogen sensor with fast response rate, short recovery time, good stability and high sensitivity, which is conducive to mass production. Summary of the invention

[0006] In view of the problems existing in the above-mentioned prior art, the present invention provides a micro-electromechanical system semiconductor hydrogen sensor and a preparation method thereof. The method has a simple implementation process and low preparation cost, and can realize the preparation of a micro-heating plate hydrogen sensor sensitive material with good controllability, high repeatability and good consistency. At the same time, it can effectively improve the adhesion of the material and ensure that the obtained hydrogen sensitive material has the advantages of high detection accuracy, high reusability and good consistency. It can effectively solve the technical problem of how to quickly, reliably and consistently prepare a batch of hydrogen sensitive materials on a micro-heating plate, and is suitable for large-scale production applications. The hydrogen sensor has a fast response rate, a short recovery time and a high detection accuracy, which is conducive to improving the practicality and stability of the hydrogen sensor.

[0007] In order to achieve the above object, the present invention provides a method for preparing a micro-electromechanical system semiconductor hydrogen sensor, comprising the following steps:

[0008] Step 1: Prepare the required ZnO target, Au target and SnO2 target, and install the zinc oxide, gold and tin dioxide targets on different target positions of the magnetron sputtering instrument, and make them 45° above the UV lamp and the air inlet;

[0009] Step 2: Connect the micro-hotplate substrate to a high-temperature resistant ceramic substrate by gold wire bonding, then secure the ceramic substrate on a rotating heating table, close the vacuum door, and perform an airtightness check to ensure that there is no leakage;

[0010] Step 3: Connect the cooling water source to the cooling port and the argon gas supply source to the air inlet; start the magnetron sputtering system and evacuate the sputtering chamber to a vacuum degree of 5×10 -3 Below Pa;

[0011] Step 4: According to the preset gas flow rate, argon gas is introduced into the cavity until the pressure in the cavity reaches about 1Pa;

[0012] Step 5: Select the ZnO target as the working target, adjust the sputtering angle, set the sputtering power and sputtering time, turn on the RF switch, and start the formal coating process until a ZnO film with a thickness of 50 to 200 nm is formed on the surface of the micro-heating plate substrate;

[0013] Step 6: Replace the working target with an Au target, adjust the sputtering angle, set the sputtering power and sputtering time, and start sputtering the Au film on the surface of the ZnO film until an Au film with a thickness of 2 to 10 nm is formed on the surface of the ZnO film to obtain an Au-ZnO composite material;

[0014] Step 7: Replace the working target with a SnO2 target, adjust the sputtering angle, set the sputtering power and sputtering time, and then start sputtering the SnO2 film on the surface of the Au film until a SnO2 film with a thickness of 4 to 10 nm is formed on the surface of the Au film to obtain a ZnO-Au-SnO2 sandwich sensitive composite film;

[0015] Step 8: Open the sputtering chamber and take out the ZnO-Au-SnO2 sandwich sensitive composite film for preparing a hydrogen sensor.

[0016] Furthermore, in order to ensure that the prepared hydrogen sensitive material can have a higher response value, in step five, the thickness of the ZnO film is 100 nm, in step six, the thickness of the Au film is 4 nm, and in step seven, the thickness of the SnO2 film is 6 nm.

[0017] Furthermore, in order to ensure that the prepared hydrogen sensitive material has excellent performance, in step 2, the purity of the ZnO target, Au target and SnO2 target is all above 99.99%.

[0018] Furthermore, in order to ensure that the prepared hydrogen sensitive material has excellent performance, in step five, sputtering is performed under the condition of a RF power supply of 50 W. At the same time, the distance between the ZnO target and the micro-heating plate substrate is 10 cm, and the sputtering time is controlled at 1800 s.

[0019] Furthermore, in order to ensure that the prepared hydrogen sensitive material has excellent performance, in step six, the distance between the Au target and the micro-heating plate substrate is 10 cm. At the same time, sputtering is carried out under the conditions of an RF power supply of 30 W and an argon gas flow rate of 30 sccm, and the sputtering time is controlled at 10 s.

[0020] Furthermore, in order to ensure that the prepared hydrogen sensitive material has excellent performance, in step seven, the distance between the SnO2 target and the micro-heating plate substrate is 10 cm. At the same time, sputtering is carried out under the conditions of an RF power supply of 60 W and an argon gas flow rate of 30 sccm, and the sputtering time is controlled at 20 s.

[0021] The present invention first modifies the ZnO film with a metal Au film material, and then deposits a SnO2 metal oxide particle layer on the Au-ZnO surface to construct a sandwich heterogeneous composite structure sensitive material. By adding an Au modified layer on the basis of the ZnO film, the response contact surface of ZnO to the gas is increased, and the modification of Au also produces a catalytic promotion effect on the breaking of the hydrogen chemical bond, making hydrogen easier to adsorb, and effectively improving the response value. Furthermore, Au and ZnO can form a Schottky barrier, further improving the response value of ZnO to hydrogen. On this basis, the SnO2 film is sputtered onto the surface of the ZnO film that has been composited with precious metals, further increasing the contact surface of oxygen and hydrogen, and since SnO2 has two valences of +3 and +4, its autocatalytic effect will accelerate the chemical bond breaking of H2, prompting the adsorption response to be faster. In addition, according to the properties of semiconductor oxides, semiconductor contacts can be divided into PN junctions, PP junctions and NN junctions. SnO2 and ZnO are both N-type semiconductors, and NN heterojunctions will be formed, which effectively and significantly improves the response speed. It has been found in a large number of practices that the thickness of Au film and SnO2 film is crucial to improving the response value of hydrogen sensors. When both Au film and SnO2 film are too thin, the effect of improving the response value is limited, making the increased cost not proportional to the response benefit obtained. When the Au film is too thick, the resistance of the sensitive composite film will be too low, and the response value will be lower. When the SnO2 film is too thick, it will completely cover the Au and ZnO composite films, which will result in only SnO2 responding to hydrogen, thus reducing the response value. Through a large number of experimental combination processes, combined with continuous optimization and selection, it is innovatively discovered that for the ZnO-Au-SnO2 sandwich sensitive composite film, a sandwich structure with a ZnO film thickness of 50 to 200 nm, an Au film thickness of 2 to 10 nm, and a SnO2 film thickness of 4 to 10 nm is used. It has both a ZnO-Au Schottky barrier and a ZnO-SnO2 NN junction, and can also avoid the situation where the response value is reduced due to unreasonable thickness combination. Therefore, its response value is higher than that of a single ZnO-Au or ZnO-SnO2, and thus, a hydrogen sensor with a higher response value can be obtained. On this basis, the present invention uses radio frequency magnetron sputtering to prepare metal and oxide films, and then prepares hydrogen sensitive materials. Magnetron sputtering is a batch planarization vacuum preparation process that can batch prepare sensitive materials within a 4-inch range at one time. It can realize the batch preparation of thousands of MEMS semiconductor hydrogen sensors at one time, and it can realize continuous thin film preparation operations. This process is not only simple in preparation process, but also has good continuity and is suitable for mass production. In addition, during the magnetron sputtering process, the atoms of the sensitive material have a strong interaction with the substrate, and the resulting thin film has good adhesion and stable performance.Normally, metal thin films are prepared by DC magnetron sputtering. Although this method has a fast preparation rate, it is difficult to accurately control the thickness of the coating. For the ZnO-Au-SnO2 sandwich sensitive composite film, the thickness of any layer of the film has a crucial influence on the response value of the overall combination. Therefore, it is impossible to prepare hydrogen sensitive materials with high response values ​​by using DC magnetron sputtering. The present invention innovatively uses radio frequency magnetron sputtering to accurately control the thickness of the metal layer, so that the thickness of any layer in the ZnO-Au-SnO2 sandwich sensitive composite film can be accurately controlled within a set range, thereby not only obtaining a hydrogen sensor with a high response value, but also effectively controlling the hydrogen response performance of the hydrogen sensor by accurately adjusting the thickness of each layer. The present invention adopts radio frequency magnetron sputtering to prepare ZnO-Au-SnO2 sandwich structure MEMS hydrogen sensor sensitive material, which effectively improves the processing accuracy. At the same time, during the plating process, the impact of the introduced argon gas on the target material is utilized to enhance the adhesion of the coating, effectively improve the distribution uniformity and adhesion of the sensitive composite film, and at the same time, ensure that the obtained hydrogen sensitive material has good stability and reliability.

[0022] Compared with conventional sensor preparation methods, this method has a simple implementation process and low preparation cost. It can realize the preparation of micro-heating plate hydrogen sensor sensitive materials with good controllability, high repeatability and good consistency. At the same time, it can effectively improve the adhesion of the material and ensure that the obtained hydrogen sensitive material has the advantages of high detection accuracy, high reusability and good consistency. It effectively solves the technical problem of how to quickly, reliably and consistently prepare batches of hydrogen sensitive materials on a micro-heating plate, and is suitable for large-scale production applications.

[0023] The present invention also provides a micro-electromechanical system semiconductor hydrogen sensor, which is prepared by a method for preparing a micro-electromechanical system semiconductor hydrogen sensor, and includes a SnO2 film, an Au film, a ZnO film layer, a micro-heating plate substrate and a ceramic substrate arranged from top to bottom, wherein the thickness of the SnO2 film is 4 to 10 nm, the thickness of the ZnO film is 50 to 200 nm, and the thickness of the Au film is 2 to 10 nm.

[0024] Furthermore, in order to obtain a hydrogen sensor with a higher response value, the thickness of the ZnO film is 100 nm, the thickness of the Au film is 4 nm, and in step seven, the thickness of the SnO2 film is 6 nm.

[0025] The present invention increases the response contact surface of ZnO to gas by adding Au modified layer on the basis of ZnO as base material, and the modification of Au can also produce catalytic promotion effect on the breaking of hydrogen chemical bond, so that hydrogen is easier to adsorb, and the response value is effectively improved. Moreover, Au and ZnO can form Schottky barrier, which further improves the response value of ZnO to hydrogen. On this basis, SnO2 film is sputtered to the surface layer of ZnO film with composite precious metal, which further increases the contact surface of oxygen and hydrogen, and because SnO2 has two valences of +3 and +4, its autocatalytic effect can accelerate the chemical bond breaking of H2, and promote the adsorption response faster. It is found in a large number of practices that the thickness of Au film and SnO2 film is crucial for the response value of hydrogen sensor to improve, and the improvement effect of response value is limited when Au film and SnO2 film are too thin, so that the increased cost is not proportional to the response benefit obtained, and the resistance of sensitive composite film is too low when Au film is too thick, and then the response value is also lower. If the SnO2 film is too thick, it will completely cover the Au and ZnO composite films, which will result in only SnO2 responding to hydrogen, thus reducing the response value. Through a large number of experimental combinations and continuous optimization and selection, it is innovatively found that for the ZnO-Au-SnO2 sandwich sensitive composite film, the sandwich structure with a ZnO film thickness of 50-200nm, an Au film thickness of 2-10nm, and a SnO2 film thickness of 4-10nm has both a ZnO-Au Schottky barrier and a ZnO-SnO2 NN junction, and can also avoid the situation where the response value is reduced due to unreasonable thickness combination. Therefore, its response value is higher than that of a single ZnO-Au or ZnO-SnO2. Therefore, a hydrogen sensor with a higher response value can be obtained, which helps to optimize the overall performance of the MEMS gas sensor. The hydrogen sensor has a fast response rate, a short recovery time, and high detection accuracy, which is conducive to improving the practicality and stability of the hydrogen sensor. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 It is a schematic diagram of the preparation process of the ZnO-Au-SnO2 sandwich sensitive composite film in the present invention;

[0027] Figure 2 It is a reaction principle diagram of magnetron sputtering in the present invention;

[0028] Figure 3 It is a flow chart of the preparation method of the ZnO-Au-SnO2 sandwich sensitive composite film in the present invention;

[0029] Figure 4 It is the hydrogen response diagram of four samples in Example 1 of the present invention at the optimal working temperature of 483°C;

[0030] Figure 5 It is the hydrogen response diagram of the three samples in Examples 2 to 4 of the present invention at the optimal working temperature of 453°C;

[0031] Figure 6 is a graph showing the real-time change of sensor resistance at different hydrogen concentrations in Example 3 of the present invention;

[0032] Figure 7 This is a real-time resistance change curve of Example 3 of the present invention after five cycles of testing at a hydrogen concentration of 10 ppm;

[0033] Figure 8 This is a real-time resistance change curve of Example 3 of the present invention after five cycles of testing at a hydrogen concentration of 40 ppm;

[0034] Fig. 9 This is a real-time resistance change curve of Example 3 of the present invention after five cycles of testing at a hydrogen concentration of 100 ppm;

[0035] Fig.10 is a SEM image of Example 2 of the present invention;

[0036] Fig.11 is a SEM image of Example 3 of the present invention;

[0037] Fig.12 is a SEM image of Example 4 of the present invention. DETAILED DESCRIPTION

[0038] The present invention will be further described below.

[0039] like Figures 1 to 12 As shown, the present invention provides a method for preparing a micro-electromechanical system semiconductor hydrogen sensor, comprising the following steps:

[0040] Step 1: Prepare the required ZnO target, Au target and SnO2 target, and install the zinc oxide, gold and tin dioxide targets on different target positions of the magnetron sputtering instrument, and make them 45° above the UV lamp and the air inlet;

[0041] Step 2: Connect the micro-hotplate substrate to a high-temperature resistant ceramic substrate by gold wire bonding, then secure the ceramic substrate on a rotating heating table, close the vacuum door, and perform an airtightness check to ensure that there is no leakage;

[0042] Step 3: Connect the cooling water source to the cooling port and the argon gas supply source to the air inlet; start the magnetron sputtering system and evacuate the sputtering chamber to a vacuum degree of 5×10 -3 Below Pa;

[0043] Step 4: According to the preset gas flow rate, argon gas is introduced into the cavity until the pressure in the cavity reaches about 1Pa;

[0044] Step 5: Select the ZnO target as the working target, adjust the sputtering angle, set the sputtering power and sputtering time, turn on the RF switch, and start the formal coating process until a ZnO film with a thickness of 50 to 200 nm is formed on the surface of the micro-heating plate substrate;

[0045] Step 6: Replace the working target with an Au target, adjust the sputtering angle, set the sputtering power and sputtering time, and start sputtering the Au film on the surface of the ZnO film until an Au film with a thickness of 2 to 10 nm is formed on the surface of the ZnO film to obtain an Au-ZnO composite material;

[0046] Step 7: Replace the working target with a SnO2 target, adjust the sputtering angle, set the sputtering power and sputtering time, and then start sputtering the SnO2 film on the surface of the Au film until a SnO2 film with a thickness of 4 to 10 nm is formed on the surface of the Au film to obtain a ZnO-Au-SnO2 sandwich sensitive composite film;

[0047] Step 8: Open the sputtering chamber and take out the ZnO-Au-SnO2 sandwich sensitive composite film for preparing a hydrogen sensor.

[0048] In order to ensure that the prepared hydrogen sensitive material has a higher response value, in step five, the thickness of the ZnO film is 100 nm, in step six, the thickness of the Au film is 4 nm, and in step seven, the thickness of the SnO2 film is 6 nm.

[0049] In order to ensure that the prepared hydrogen sensitive material has excellent performance, in step 2, the purity of the ZnO target, Au target and SnO2 target is all above 99.99%.

[0050] In order to ensure that the prepared hydrogen sensitive material has excellent performance, in step five, sputtering operation is carried out under the condition of RF power of 50 W. At the same time, the distance between the ZnO target and the micro-heating plate substrate is 10 cm, and the sputtering time is controlled at 1800 s.

[0051] In order to ensure that the prepared hydrogen sensitive material has excellent performance, in step six, the distance between the Au target and the micro-heating plate substrate is 10 cm. At the same time, sputtering is carried out under the conditions of an RF power supply of 30 W and an argon gas flow rate of 30 sccm, and the sputtering time is controlled at 10 s.

[0052] In order to ensure that the prepared hydrogen sensitive material has excellent performance, in step seven, the distance between the SnO2 target and the micro-heating plate substrate is 10 cm. At the same time, sputtering is carried out under the conditions of an RF power supply of 60 W and an argon gas flow rate of 30 sccm, and the sputtering time is controlled at 20 s.

[0053] The present invention first modifies the ZnO film with a metal Au film material, and then deposits a SnO2 metal oxide particle layer on the Au-ZnO surface to construct a sandwich heterogeneous composite structure sensitive material. By adding an Au modified layer on the basis of the ZnO film, the response contact surface of ZnO to the gas is increased, and the modification of Au also produces a catalytic promotion effect on the breaking of the hydrogen chemical bond, making hydrogen easier to adsorb, and effectively improving the response value. Furthermore, Au and ZnO can form a Schottky barrier, further improving the response value of ZnO to hydrogen. On this basis, the SnO2 film is sputtered onto the surface of the ZnO film that has been composited with precious metals, further increasing the contact surface of oxygen and hydrogen, and since SnO2 has two valences of +3 and +4, its autocatalytic effect will accelerate the chemical bond breaking of H2, prompting the adsorption response to be faster. In addition, according to the properties of semiconductor oxides, semiconductor contacts can be divided into PN junctions, PP junctions and NN junctions. SnO2 and ZnO are both N-type semiconductors, and NN heterojunctions will be formed, which effectively and significantly improves the response speed. It has been found in a large number of practices that the thickness of Au film and SnO2 film is crucial to improving the response value of hydrogen sensors. When both Au film and SnO2 film are too thin, the effect of improving the response value is limited, making the increased cost not proportional to the response benefit obtained. When the Au film is too thick, the resistance of the sensitive composite film will be too low, and the response value will be lower. When the SnO2 film is too thick, it will completely cover the Au and ZnO composite films, which will result in only SnO2 responding to hydrogen, thus reducing the response value. Through a large number of experimental combination processes, combined with continuous optimization and selection, it is innovatively discovered that for the ZnO-Au-SnO2 sandwich sensitive composite film, a sandwich structure with a ZnO film thickness of 50 to 200 nm, an Au film thickness of 2 to 10 nm, and a SnO2 film thickness of 4 to 10 nm is used. It has both a ZnO-Au Schottky barrier and a ZnO-SnO2 NN junction, and can also avoid the situation where the response value is reduced due to unreasonable thickness combination. Therefore, its response value is higher than that of a single ZnO-Au or ZnO-SnO2, and thus, a hydrogen sensor with a higher response value can be obtained. On this basis, the present invention uses radio frequency magnetron sputtering to prepare metal and oxide films, and then prepares hydrogen sensitive materials. Magnetron sputtering is a batch planarization vacuum preparation process that can batch prepare sensitive materials within a 4-inch range at one time. It can realize the batch preparation of thousands of MEMS semiconductor hydrogen sensors at one time, and it can realize continuous thin film preparation operations. This process is not only simple in preparation process, but also has good continuity and is suitable for mass production. In addition, during the magnetron sputtering process, the atoms of the sensitive material have a strong interaction with the substrate, and the resulting thin film has good adhesion and stable performance.Normally, metal thin films are prepared by DC magnetron sputtering. Although this method has a fast preparation rate, it is difficult to accurately control the thickness of the coating. For the ZnO-Au-SnO2 sandwich sensitive composite film, the thickness of any layer of the film has a crucial influence on the response value of the overall combination. Therefore, it is impossible to prepare hydrogen sensitive materials with high response values ​​by using DC magnetron sputtering. The present invention innovatively uses radio frequency magnetron sputtering to accurately control the thickness of the metal layer, so that the thickness of any layer in the ZnO-Au-SnO2 sandwich sensitive composite film can be accurately controlled within a set range, thereby not only obtaining a hydrogen sensor with a high response value, but also effectively controlling the hydrogen response performance of the hydrogen sensor by accurately adjusting the thickness of each layer. The present invention adopts radio frequency magnetron sputtering to prepare ZnO-Au-SnO2 sandwich structure MEMS hydrogen sensor sensitive material, which effectively improves the processing accuracy. At the same time, during the plating process, the impact of the introduced argon gas on the target material is utilized to enhance the adhesion of the coating, effectively improve the distribution uniformity and adhesion of the sensitive composite film, and at the same time, ensure that the obtained hydrogen sensitive material has good stability and reliability.

[0054] Compared with conventional sensor preparation methods, this method has a simple implementation process and low preparation cost. It can realize the preparation of micro-heating plate hydrogen sensor sensitive materials with good controllability, high repeatability and good consistency. At the same time, it can effectively improve the adhesion of the material and ensure that the obtained hydrogen sensitive material has the advantages of high detection accuracy, high reusability and good consistency. It effectively solves the technical problem of how to quickly, reliably and consistently prepare batches of hydrogen sensitive materials on a micro-heating plate, and is suitable for large-scale production applications.

[0055] The present invention also provides a micro-electromechanical system semiconductor hydrogen sensor, which is prepared by a method for preparing a micro-electromechanical system semiconductor hydrogen sensor, and includes a SnO2 film, an Au film, a ZnO film layer, a micro-heating plate substrate and a ceramic substrate arranged from top to bottom, wherein the thickness of the SnO2 film is 4 to 10 nm, the thickness of the ZnO film is 50 to 200 nm, and the thickness of the Au film is 2 to 10 nm.

[0056] In order to obtain a hydrogen sensor with a higher response value, the thickness of the ZnO film is 100 nm, the thickness of the Au film is 4 nm, and the thickness of the SnO2 film is 6 nm.

[0057] The present invention increases the response contact surface of ZnO to gas by adding Au modified layer on the basis of ZnO as base material, and the modification of Au can also produce catalytic promotion effect on the breaking of hydrogen chemical bond, so that hydrogen is easier to adsorb, and the response value is effectively improved. Moreover, Au and ZnO can form Schottky barrier, which further improves the response value of ZnO to hydrogen. On this basis, SnO2 film is sputtered to the surface layer of ZnO film with composite precious metal, which further increases the contact surface of oxygen and hydrogen, and because SnO2 has two valences of +3 and +4, its autocatalytic effect can accelerate the chemical bond breaking of H2, and promote the adsorption response faster. It is found in a large number of practices that the thickness of Au film and SnO2 film is crucial for the response value of hydrogen sensor to improve, and the improvement effect of response value is limited when Au film and SnO2 film are too thin, so that the increased cost is not proportional to the response benefit obtained, and the resistance of sensitive composite film is too low when Au film is too thick, and then the response value is also lower. If the SnO2 film is too thick, it will completely cover the Au and ZnO composite films, which will result in only SnO2 responding to hydrogen, thus reducing the response value. Through a large number of experimental combinations and continuous optimization and selection, it is innovatively found that for the ZnO-Au-SnO2 sandwich sensitive composite film, the sandwich structure with a ZnO film thickness of 50-200nm, an Au film thickness of 2-10nm, and a SnO2 film thickness of 4-10nm has both a ZnO-Au Schottky barrier and a ZnO-SnO2 NN junction, and can also avoid the situation where the response value is reduced due to unreasonable thickness combination. Therefore, its response value is higher than that of a single ZnO-Au or ZnO-SnO2. Therefore, a hydrogen sensor with a higher response value can be obtained, which helps to optimize the overall performance of the MEMS gas sensor. The hydrogen sensor has a fast response rate, a short recovery time, and high detection accuracy, which is conducive to improving the practicality and stability of the hydrogen sensor.

[0058] In order to further elaborate the present invention, the present invention is described below by way of embodiments:

[0059] Embodiment 1:

[0060] Check whether all valves of the magnetron sputtering instrument are in the initial setting state, and ensure that the vacuum chamber is closed before evacuating the vacuum chamber. Ensure that the cooling water is connected before the magnetron sputtering instrument is powered on. Start the main power of the magnetron sputtering instrument. Connect high-purity argon gas to the air inlet of the magnetron sputtering instrument and open the argon gas cylinder. Open the chamber door of the magnetron sputtering instrument, put in the zinc oxide target, gold target and micro-heating plate, and close the chamber door. Turn on the mechanical pump and the stop valve, and start evacuating the vacuum chamber. When the air pressure in the vacuum chamber drops below 10Pa, turn on the molecular pump working button. When the molecular pump is stable, adjust the air pressure in the vacuum chamber to 5×10-3 Pa or less. Turn on the pressure regulating switch, open the air inlet valve, and after about 10 seconds, turn on the flow meter, set the flow rate to 30sccm, introduce argon gas and adjust the air pressure in the vacuum chamber to about 1Pa and stabilize it. Start the RF sputtering power supply, set the power to 50W, set the sputtering time to 0.5 hours, and obtain a pure zinc oxide film after the sputtering. After the zinc oxide film is plated, turn off the RF sputtering power supply, turn off the flow meter, air inlet valve and pressure regulating switch, replace the working target of the magnetron sputtering instrument with a gold target, and readjust the air pressure in the vacuum chamber to 5×10 -3 Pa, open the pressure regulating switch, air inlet valve and flowmeter again, set the flow rate to 30sccm, introduce argon gas and adjust the pressure in the vacuum chamber to about 1Pa and stabilize it. Start the RF sputtering power supply, set the power to 30W, set the sputtering time to 10 seconds, and after the sputtering is completed, a gold-modified zinc oxide gas-sensitive film can be obtained.

[0061] The above steps were repeated, and the sputtering time of the Au target was adjusted to 20 seconds and 30 seconds, respectively. Finally, a pure zinc oxide film and a gold-modified zinc oxide gas-sensitive film with sputtering times of 10 seconds, 20 seconds, and 30 seconds were obtained.

[0062] Figure 4 The hydrogen response diagrams of the four samples in this embodiment at the optimal working temperature of 483°C are shown. By comparison, it is found that the ZnO-Au (4nm) composite film has the best response effect;

[0063] Embodiment 2:

[0064] Check whether all valves of the magnetron sputtering instrument are in the initial setting state, and ensure that the vacuum chamber is closed before evacuating the vacuum chamber. Ensure that the cooling water is connected before the magnetron sputtering instrument is powered on. Start the main power of the magnetron sputtering instrument. Connect high-purity argon gas to the air inlet of the magnetron sputtering instrument and open the argon gas cylinder. Open the chamber door of the magnetron sputtering instrument, put in the zinc oxide target, gold target, tin dioxide target and micro-heating plate, and close the chamber door. Turn on the mechanical pump and the stop valve, and start evacuating the vacuum chamber. When the air pressure in the vacuum chamber drops below 10Pa, turn on the molecular pump working button. When the molecular pump is stable, adjust the air pressure in the vacuum chamber to 5×10 -3 Pa or less. Turn on the pressure regulating switch, open the air inlet valve, and after about 10 seconds, turn on the flow meter, set the flow rate to 30sccm, introduce argon gas and adjust the air pressure in the vacuum chamber to about 1Pa and stabilize it. Start the RF sputtering power supply, set the power to 50W, set the sputtering time to 0.5 hours, and obtain a pure zinc oxide film after the sputtering. After the zinc oxide film is plated, turn off the RF sputtering power supply, turn off the flow meter, air inlet valve and pressure regulating switch, replace the working target of the magnetron sputtering instrument with a gold target, and readjust the air pressure in the vacuum chamber to 5×10 -3Pa, open the pressure regulating switch, air inlet valve and flow meter again, set the flow rate to 30sccm, introduce argon gas and adjust the pressure in the vacuum chamber to about 1Pa and stabilize it. Start the RF sputtering power supply, set the power to 30W, set the sputtering time to 10 seconds, and after the sputtering, a gold-modified zinc oxide gas-sensitive film can be obtained. After the gold film is plated, turn off the RF sputtering power supply, the flow meter, the air inlet valve and the pressure regulating switch, replace the working target of the magnetron sputtering instrument with a tin dioxide target, and readjust the pressure of the vacuum chamber to 5×10 -3 Pa, open the pressure regulating switch, air inlet valve and flowmeter again, set the flow rate to 30sccm, introduce argon gas and adjust the pressure in the vacuum chamber to about 1Pa and stabilize it. Start the RF sputtering power supply, set the power to 60W, set the sputtering time to 10 seconds, and obtain the ZnO-Au(4nm)-SnO2(4nm) composite film after sputtering.

[0065] Embodiment 3:

[0066] The difference between this embodiment and embodiment 2 is that the sputtering time of the tin dioxide film is adjusted to 20 seconds, and a ZnO-Au (4nm)-SnO2 (6nm) composite film is obtained after the sputtering is completed.

[0067] Embodiment 4:

[0068] The difference between this embodiment and embodiment 2 is that the sputtering time of the tin dioxide film is adjusted to 40 seconds, and a ZnO-Au (4 nm)-SnO2 (10 nm) composite film is obtained after the sputtering is completed.

[0069] By comparing the hydrogen response diagrams of the composite films prepared in Example 2, Example 3 and Example 4 at the optimal working temperature of 453°C, it is found that the ZnO-Au (4nm)-SnO2 (6nm) composite film has the best response effect, which is significantly better than the ZnO-Au (4nm)-SnO2 (4nm) composite film and the ZnO-Au (4nm)-SnO2 (10nm) composite film; Figure 6 The real-time change curve of the sensor resistance of the ZnO-Au (4nm)-SnO2 (6nm) composite film under different hydrogen concentrations is shown. It can be seen from the figure that the resistance of the composite film changes significantly under different hydrogen concentrations; Figure 7 The real-time resistance change curve of the ZnO-Au (4nm)-SnO2 (6nm) composite film after five cycles of testing at a hydrogen concentration of 10ppm is shown. It can be seen from the figure that the resistance change of the composite film during multiple cycle tests is still obvious, indicating that it has excellent reusability. Figure 8The real-time resistance change curve of the ZnO-Au (4nm)-SnO2 (6nm) composite film after five cycles of testing at a hydrogen concentration of 40ppm is shown. It can be seen from the figure that the resistance change of the composite film during multiple cycle tests is still obvious, indicating that it has excellent reusability. Fig. 9 The real-time resistance change curve of the ZnO-Au (4nm)-SnO2 (6nm) composite film after five cycles of testing at a hydrogen concentration of 100ppm is shown. It can be seen from the figure that the resistance change of the composite film during multiple cycle tests is still obvious, indicating its excellent reusability. Fig.10 The SEM image of ZnO-Au(4nm)-SnO2(4nm) composite film is shown. Fig.11 The SEM image of ZnO-Au (4nm)-SnO2 (6nm) composite film is shown. Fig.12 The SEM images of ZnO-Au (4nm)-SnO2 (10nm) composite films were displayed. By comparison, it was found that the micromorphology of ZnO-Au (4nm)-SnO2 (6nm) composite film was the most ideal, and its contact surface was easier to adsorb hydrogen, which in turn helped to obtain excellent response values.

Claims

1. A method for preparing a micro-electromechanical system semiconductor hydrogen sensor, characterized in that: The steps include: Step 1: Prepare the required ZnO target, Au target and SnO2 target, and install the zinc oxide, gold and tin dioxide targets on different target positions of the magnetron sputtering instrument, and make them 45° above the UV lamp and the air inlet; Step 2: Connect the micro-hotplate substrate to a high-temperature resistant ceramic substrate by gold wire bonding, then secure the ceramic substrate on a rotating heating table, close the vacuum door, and perform an airtightness check to ensure that there is no leakage; Step 3: Connect the cooling water source to the cooling port and the argon gas supply source to the air inlet; start the magnetron sputtering system and evacuate the sputtering chamber to a vacuum degree of 5×10 -3 Below Pa; Step 4: According to the preset gas flow rate, argon gas is introduced into the cavity until the pressure in the cavity reaches about 1Pa; Step 5: Select the ZnO target as the working target, adjust the sputtering angle, set the sputtering power and sputtering time, turn on the RF switch, and start the formal coating process until a ZnO film with a thickness of 50 to 200 nm is formed on the surface of the micro-heating plate substrate; Step 6: Replace the working target with an Au target, adjust the sputtering angle, set the sputtering power and sputtering time, and start sputtering the Au film on the surface of the ZnO film until an Au film with a thickness of 2 to 10 nm is formed on the surface of the ZnO film to obtain an Au-ZnO composite material; Step 7: Replace the working target with a SnO2 target, adjust the sputtering angle, set the sputtering power and sputtering time, and then start sputtering the SnO2 film on the surface of the Au film until a SnO2 film with a thickness of 4 to 10 nm is formed on the surface of the Au film to obtain a ZnO-Au-SnO2 sandwich sensitive composite film; Step 8: Open the sputtering chamber and take out the ZnO-Au-SnO2 sandwich sensitive composite film for preparing a hydrogen sensor.

2. The method for preparing a micro-electromechanical system semiconductor hydrogen sensor according to claim 1, characterized in that: In step five, the thickness of the ZnO film is 100 nm, in step six, the thickness of the Au film is 4 nm, and in step seven, the thickness of the SnO2 film is 6 nm.

3. The method for preparing a micro-electromechanical system semiconductor hydrogen sensor according to claim 1, characterized in that: In step 2, the purity of the ZnO target, Au target and SnO2 target is all above 99.99%.

4. The method for preparing a micro-electromechanical system semiconductor hydrogen sensor according to claim 1, characterized in that: In step five, sputtering was performed under the condition that the RF power was 50 W. At the same time, the distance between the ZnO target and the micro-heating plate substrate was 10 cm, and the sputtering time was controlled at 1800 s.

5. The method for preparing a micro-electromechanical system semiconductor hydrogen sensor according to claim 1, characterized in that: In step six, the distance between the Au target and the micro-heating plate substrate is set to 10 cm. At the same time, sputtering is performed under the conditions of a RF power of 30 W and an argon gas flow rate of 30 sccm. The sputtering time is controlled to be 10 s.

6. The method for preparing a micro-electromechanical system semiconductor hydrogen sensor according to claim 1, characterized in that: In step seven, the distance between the SnO2 target and the micro-heating plate substrate is set to 10 cm. At the same time, sputtering is performed under the conditions of a RF power of 60 W and an argon gas flow rate of 30 sccm. The sputtering time is controlled to be 20 s.

7. A micro-electromechanical system semiconductor hydrogen sensor, characterized in that: The micro-electromechanical system semiconductor hydrogen sensor is prepared by the preparation method according to any one of claims 1 to 6, which includes a SnO2 film, an Au film, a ZnO film layer, a micro-heating plate substrate and a ceramic substrate arranged from top to bottom, wherein the thickness of the SnO2 film is 4 to 10 nm, the thickness of the ZnO film is 50 to 200 nm, and the thickness of the Au film is 2 to 10 nm.

8. The micro-electromechanical system semiconductor hydrogen sensor according to claim 7, characterized in that: The thickness of the ZnO film is 100 nm, the thickness of the Au film is 4 nm, and the thickness of the SnO2 film is 6 nm.

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