A microelectromechanical system semiconductor hydrogen sensor and its preparation method

Abstract

A microelectromechanical system semiconductor hydrogen sensor and its preparation method. The sensor includes an SnO2 layer, an Au layer, a ZnO layer, a micro-heating plate substrate, and a ceramic substrate arranged from top to bottom. The method: Mount the target on the target position; firmly fix the micro-heating plate substrate on the heating table; evacuate the sputtering chamber to make the vacuum degree of the sputtering chamber reach below 5×10 ‑3 Pa; Introduce argon gas into the chamber until the pressure in the chamber reaches about 1 Pa; form a ZnO thin film with a thickness of 50 - 200 nm on the surface of the micro-heating plate substrate; form an Au thin film with a thickness of 2 - 10 nm on the surface of the ZnO thin film to obtain a ZnO-Au composite material; form an SnO2 thin film with a thickness of 4 - 10 nm on the surface of the Au thin film to obtain a ZnO-Au-SnO2 sandwich sensitive composite film. This sensor has a fast response rate, a short recovery time, and high detection accuracy. This method can prepare a hydrogen sensor with a high response value.

Description

Technical Field

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

[0002] According to the gas-sensing characteristics, gas sensors can be divided into semiconductor gas sensors, electrochemical gas sensors, solid electrolyte gas sensors, catalytic combustion gas sensors, optical gas sensors, etc. Among them, semiconductor gas sensors are currently 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, and have thus received much attention in the past decade or so. 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 is still one of the key points and difficulties in the industry. Early semiconductor oxide gas sensors were based on ceramic tubes and had high power consumption; later, mature planar oxide semiconductor gas sensors were developed, and although the power consumption problem was improved to a certain extent, their power consumption was still relatively high, resulting in a relatively serious problem of device heating, thus requiring a more efficient heat insulation system and a larger-capacity power supply to maintain the stable operation of the device, which would further increase the volume and weight of the device and was not conducive to integration.

[0004] MEMS (Micro-Electro-Mechanical System) sensors refer to sensors with some component sizes below 100 micrometers, which can be realized based on microfabrication technology and are an emerging interdisciplinary research field. Compared with traditional sensors, it has the characteristics of small size, light weight, low cost, low power consumption, high reliability, suitable for mass production, easy integration, and easy implementation of intelligence. 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 this type of metal oxide semiconductor sensor, stability, sensitivity, and the ability to be mass-produced are all problems that need to be solved in the current industry. At present, the hydrogen-sensitive materials for preparing hydrogen sensors have a low response rate, low detection accuracy, and short service life, which severely limits the mass production and wide application of hydrogen sensors. Therefore, there is an urgent need to provide a hydrogen sensor with a fast response rate, short recovery time, good stability, high sensitivity, and 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 microelectromechanical system semiconductor hydrogen sensor and a preparation method thereof. The method has a simple implementation process and low preparation cost, can realize the preparation of a hydrogen sensor sensitive material for a micro-heating plate with good controllability, high repeatability and good consistency. At the same time, it can effectively improve the material adhesion, and ensure that the obtained hydrogen sensitive material has the advantages of high detection accuracy, high reusability and good consistency, and 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 high detection accuracy, which is beneficial to improving the practicability and stability of the hydrogen sensor.

[0007] To achieve the above object, the present invention provides a preparation method of a microelectromechanical system semiconductor hydrogen sensor, comprising the following steps:

[0008] Step 1: Prepare the required ZnO target, Au target and SnO 2 target, and install the zinc oxide, gold and tin dioxide targets on different target positions of the magnetron sputtering instrument respectively, and make them located 45 ° above the ultraviolet lamp and the air inlet obliquely;

[0009] Step 2: Connect the micro-heating plate substrate to a high-temperature resistant ceramic substrate by wire bonding, then fix the ceramic substrate firmly on the rotary heating table, close the vacuum door, and perform an airtightness check to ensure that there is no air leakage.

[0010] Step 3: Connect a cooling water source at the cooling port and an argon supply source at the air inlet; turn on the magnetron sputtering system, evacuate the sputtering chamber to make the vacuum degree of the sputtering chamber reach below 5×10 -3 Pa;

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

[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 radio frequency switch, and start the formal coating process until a ZnO thin film with a thickness of 50-200 nm is formed on the surface of the micro-heating plate substrate.

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

[0014] Step 7: Replace the working target with SnO 2 target, adjust the sputtering angle, set the sputtering power and sputtering time, and then start to officially sputter SnO 2 film on the surface of the Au film until a SnO film with a thickness of 4 - 10 2 nm is formed on the surface of the Au film to obtain a ZnO - Au - SnO 2 sandwich - type sensitive composite film;

[0015] Step 8: Open the sputtering chamber and take out the ZnO - Au - SnO 2 sandwich - type sensitive composite film for fabricating a hydrogen sensor.

[0016] Furthermore, to ensure that the fabricated hydrogen - sensitive material can have a higher response value, in Step 5, the thickness of the ZnO film is 100 nm, in Step 6, the thickness of the Au film is 4 nm, and in Step 7, the thickness of the SnO 2 film is 6 nm.

[0017] Furthermore, to ensure that the fabricated hydrogen - sensitive material can have excellent properties, in Step 2, the purity of the ZnO target, Au target, and SnO 2 target is above 99.99%.

[0018] Furthermore, to ensure that the fabricated hydrogen - sensitive material can have excellent properties, in Step 5, the sputtering operation is carried out under the condition that the radio - frequency power supply power is 50 W. At the same time, the distance between the ZnO target and the micro - heating plate substrate is 10 cm, and the sputtering duration is controlled within 1800 s.

[0019] Furthermore, to ensure that the fabricated hydrogen - sensitive material can have excellent properties, in Step 6, the distance between the Au target and the micro - heating plate substrate is 10 cm. At the same time, the sputtering operation is carried out under the conditions that the radio - frequency power supply power is 30 W and the argon gas flow rate is 30 sccm, and the sputtering duration is controlled within 10 s.

[0020] Furthermore, to ensure that the fabricated hydrogen - sensitive material can have excellent properties, in Step 7, the distance between the SnO 2 target and the micro - heating plate substrate is 10 cm. At the same time, the sputtering operation is carried out under the conditions that the radio - frequency power supply power is 60 W and the argon gas flow rate is 30 sccm, and the sputtering duration is controlled within 20 s.

[0021] The present invention first modifies the ZnO thin film with a metal Au thin film material, and then deposits SnO on the surface layer of Au-ZnO 2 metal oxide particle layer to construct a sandwich heterostructure sensitive material. By adding an Au modification layer on the basis of the ZnO thin film, the response contact surface of ZnO to gas is increased. Since the Au modification also has a catalytic promotion effect on the breaking of hydrogen chemical bonds, hydrogen is more easily adsorbed, effectively improving the response value. Moreover, Au and ZnO can form a Schottky barrier, further improving the response value of ZnO to hydrogen. On this basis, the SnO 2 thin film is sputtered onto the surface layer of the ZnO thin film that has been compounded with noble metals, further increasing the contact surface of oxygen and hydrogen. And because SnO 2 has two valence states of +3 and +4, its autocatalytic effect will accelerate the breaking of the chemical bond of H 2 , prompting the adsorption response to be faster. In addition, according to the properties of semiconductor oxides, semiconductor contacts can be divided into PN junctions, P-P junctions and N-N junctions. SnO 2 and ZnO are both N-type semiconductors, which will form an N-N heterojunction, effectively significantly improving the response speed. In a large number of practices, it is found that the thicknesses of the Au thin film and the SnO 2 thin film are crucial for improving the response value of the hydrogen sensor. When both the Au thin film and the SnO 2 thin film are too thin, the effect of improving the response value is limited, making the increased cost not proportional to the obtained response benefit. And when the Au thin film is too thick, the resistance of the sensitive composite film will be too low, and then the response value will also be lower. When the SnO 2 thin film is too thick, it will completely cover the Au and ZnO composite film, which results in only SnO 2 responding to hydrogen, thus causing the response value to decrease. Through a large number of experimental combinations and continuous optimization and selection, it is innovatively found that for the ZnO-Au-SnO 2 sandwich sensitive composite film, when the thickness of the ZnO thin film is 50-200 nm, the thickness of the Au thin film is 2-10 nm, and the thickness of the SnO 2 thin film is 4-10 nm, such a combined sandwich structure not only has a ZnO-Au Schottky barrier, but also has an N-N junction of ZnO-SnO 2 , and can also avoid the situation of response value reduction caused by unreasonable thickness combination. Therefore, its response value is higher than that of single ZnO-Au or ZnO-SnO 2Higher, 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 a hydrogen-sensitive material. Magnetron sputtering is a batch planar vacuum preparation process, which can batch prepare sensitive materials within a range of 4 inches at one time, and can realize the batch preparation of thousands of MEMS semiconductor hydrogen sensors at one time. Moreover, it can continuously carry out thin film preparation operations. This process not only has a simple preparation process, but also has good continuity and is suitable for mass production. In addition, during the magnetron sputtering process, the sensitive material atoms have a strong interaction with the substrate, and the obtained thin film has good adhesion and stable performance. Usually, direct current magnetron sputtering is generally used to prepare metal films. Although this method has a relatively fast preparation rate, it is difficult to accurately control the thickness of the coating. For the ZnO-Au-SnO 2 For the sandwich sensitive composite film, the thickness of any layer of the film has a crucial impact on the overall combined response value. Therefore, a hydrogen-sensitive material with a high response value cannot be prepared by using the direct current magnetron sputtering method. 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-SnO 2 sandwich sensitive composite film can be accurately controlled within the set range. Furthermore, not only can a hydrogen sensor with a high response value be obtained, but also the hydrogen response performance of the hydrogen sensor can be effectively regulated by accurately adjusting the thickness of each layer. The present invention uses radio frequency magnetron sputtering to prepare the sensitive material of the ZnO-Au-SnO 2 sandwich structure MEMS hydrogen sensor, effectively improving the processing accuracy. At the same time, during the plating process, the impact of the introduced argon gas on the target material strengthens the adhesion of the coating, effectively improving the distribution uniformity and adhesion of the sensitive composite film, and ensuring that the obtained hydrogen-sensitive material has good stability and reliability.

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

[0023] The present invention also provides a microelectromechanical system semiconductor hydrogen sensor, which is prepared by using a preparation method of a microelectromechanical system semiconductor hydrogen sensor. It includes an SnO layer arranged from top to bottom 2 film, Au film, ZnO film layer, micro-heating plate substrate and ceramic substrate. Among them, SnO2 The thickness of the thin film is 4 to 10 nm, the thickness of the ZnO thin film is 50 to 200 nm, and the thickness of the Au thin 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 thin film is 100 nm, the thickness of the Au thin film is 4 nm. In step seven, the thickness of the SnO 2 thin film is 6 nm.

[0025] In the present invention, based on ZnO as the base material, an Au modification layer is added, which increases the response contact surface of ZnO to gases. Moreover, due to the modification of Au, it also has a catalytic promotion effect on the breaking of hydrogen chemical bonds, making hydrogen more easily adsorbed and effectively improving the response value. Furthermore, Au and ZnO can form a Schottky barrier, further enhancing the response value of ZnO to hydrogen. On this basis, the SnO 2 thin film is sputtered onto the surface layer of the ZnO thin film compounded with noble metals, further increasing the contact surface between oxygen and hydrogen. And because SnO 2 has two valence states of +3 and +4, its autocatalytic effect will accelerate the breaking of the chemical bond of H 2 , promoting a faster adsorption response. It is found in a large number of practices that the thicknesses of the Au thin film and the SnO 2 thin film are crucial for improving the response value of the hydrogen sensor. When both the Au thin film and the SnO 2 thin film are too thin, the effect of improving the response value is limited, making the increased cost not proportional to the obtained response benefit. While when the Au thin film is too thick, it will cause the resistance of the sensitive composite film to be too low, and thus the response value is also lower. And when the SnO 2 thin film is too thick, it will completely cover the Au and ZnO composite film, resulting in only SnO 2 responding to hydrogen, thus causing the response value to decrease. Through a large number of experimental combinations and continuous optimization and selection, it is innovatively found that for the ZnO-Au-SnO 2 sandwich sensitive composite film, a sandwich structure with a ZnO thin film thickness of 50 to 200 nm, an Au thin film thickness of 2 to 10 nm, and an SnO 2 thin film thickness of 4 to 10 nm has both a ZnO-Au Schottky barrier and a ZnO-SnO 2The N-N junction can also avoid the reduction of the response value caused by the unreasonable thickness combination. Therefore, its response value is higher than that of a single ZnO-Au or ZnO-SnO 2 and thus 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 a high detection accuracy, which is beneficial to improving the practicability and stability of the hydrogen sensor. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 is a schematic diagram of the preparation process of the ZnO-Au-SnO 2 sandwich sensitive composite film in the present invention;

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

[0028] Figure 3 is the ZnO-Au-SnO in the present invention 2 flow chart of the preparation method of the sandwich sensitive composite film;

[0029] Figure 4 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 is the hydrogen response diagram of three samples in Examples 2-4 of the present invention at the optimal working temperature of 453 °C;

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

[0032] Figure 7 is in Example 3 of the present invention at 10 ppm hydrogen concentration, the real-time change curve of the resistance during five-cycle tests;

[0033] Figure 8 is in Example 3 of the present invention at 40 ppm hydrogen concentration, the real-time change curve of the resistance during five-cycle tests;

[0034] Figure 9 is in Example 3 of the present invention at 100 ppm hydrogen concentration, the real-time change curve of the resistance during five-cycle tests;

[0035] Figure 10 is the SEM image of Example 2 of the present invention;

[0036] Figure 11 is the SEM image of Example 3 of the present invention;

[0037] Figure 12 It is the SEM image of Embodiment 4 of the present invention. Detailed implementation manners

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

[0039] As Figures 1 to 12 shown, the present invention provides a preparation method of a microelectromechanical system semiconductor hydrogen sensor, including the following steps:

[0040] Step 1: Prepare the required ZnO target, Au target and SnO 2 target, and respectively install the zinc oxide, gold and tin dioxide targets on different target positions of the magnetron sputtering instrument, and make it located 45 ° above the ultraviolet lamp and the air inlet obliquely;

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

[0042] Step 3: Connect the cooling water source at the cooling port and connect the argon supply source at the air inlet; turn on the magnetron sputtering system, evacuate the sputtering chamber, and make the vacuum degree of the sputtering chamber reach below 5×10 -3 Pa;

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

[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 radio frequency switch, and start the formal coating process until a ZnO film with a thickness of 50-200 nm is formed on the surface of the micro-heating plate substrate;

[0045] Step 6: Replace the working target with the 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 2-10 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 the SnO 2 target, adjust the sputtering angle, set the sputtering power and sputtering time, and then start sputtering the SnO 2 film on the surface of the Au film until an SnO film with a thickness of 4-10 nm is formed on the surface of the Au film, and SnO 2A thin film to obtain ZnO-Au-SnO 2 A sandwich-type sensitive composite film;

[0047] Step Eight: Open the sputtering chamber and take out the ZnO-Au-SnO 2 sandwich-type sensitive composite film for fabricating a hydrogen sensor.

[0048] To ensure that the fabricated hydrogen-sensitive material can have a higher response value, in Step Five, the thickness of the ZnO thin film is 100 nm, in Step Six, the thickness of the Au thin film is 4 nm, and in Step Seven, the thickness of the SnO 2 thin film is 6 nm.

[0049] To ensure that the fabricated hydrogen-sensitive material can have excellent properties, in Step Two, the purities of the ZnO target, Au target, and SnO 2 target are all above 99.99%.

[0050] To ensure that the fabricated hydrogen-sensitive material can have excellent properties, in Step Five, sputtering operation is carried out under the condition that the radio frequency power supply power is 50 W. Meanwhile, the distance between the ZnO target and the micro-heating plate substrate is 10 cm, and the sputtering duration is controlled within 1800 s.

[0051] To ensure that the fabricated hydrogen-sensitive material can have excellent properties, in Step Six, the distance between the Au target and the micro-heating plate substrate is 10 cm. Meanwhile, sputtering operation is carried out under the conditions that the radio frequency power supply power is 30 W and the argon gas flow rate is 30 sccm, and the sputtering duration is controlled within 10 s.

[0052] To ensure that the fabricated hydrogen-sensitive material can have excellent properties, in Step Seven, the distance between the SnO 2 target and the micro-heating plate substrate is 10 cm. Meanwhile, sputtering operation is carried out under the conditions that the radio frequency power supply power is 60 W and the argon gas flow rate is 30 sccm, and the sputtering duration is controlled within 20 s.

[0053] In the present invention, the ZnO thin film is first modified with the metal Au thin film material, and then SnO is deposited on the surface layer of Au-ZnO 2A metal oxide particle layer is used to construct a sandwich heterocomposite sensitive material. By adding an Au modification layer on the basis of the ZnO thin film, the response contact surface of ZnO to gas is increased. Due to the modification of Au, it also has a catalytic promotion effect on the breaking of the chemical bond of hydrogen, making hydrogen more easily adsorbed and effectively improving the response value. Moreover, Au and ZnO can form a Schottky barrier, further improving the response value of ZnO to hydrogen. On this basis, the SnO 2 thin film is sputtered onto the surface layer of the ZnO thin film that has been compounded with noble metals, further increasing the contact surface of oxygen and hydrogen. And because SnO 2 has two valence states of +3 and +4, its autocatalytic effect will accelerate the breaking of the chemical bond of H 2 , promoting a faster adsorption response. In addition, according to the properties of semiconductor oxides, semiconductor contacts can be divided into PN junctions, P-P junctions, and N-N junctions. SnO 2 and ZnO are both N-type semiconductors, and an N-N heterojunction will be formed, effectively and significantly improving the response speed. In a large number of practices, it is found that the thicknesses of the Au thin film and the SnO 2 thin film are crucial for improving the response value of the hydrogen sensor. When both the Au thin film and the SnO 2 thin film are too thin, the improvement effect on the response value is limited, making the increased cost not proportional to the obtained response benefit. And when the Au thin film is too thick, it will cause the resistance of the sensitive composite film to be too low, and then the response value will also be lower. When the SnO 2 thin film is too thick, it will completely cover the Au and ZnO composite film, which results in only SnO 2 responding to hydrogen, so the response value decreases. Through a large number of experimental combinations and continuous optimization and selection, it is innovatively found that for the ZnO-Au-SnO 2 sandwich sensitive composite film, when the thickness of the ZnO thin film is 50 - 200 nm, the thickness of the Au thin film is 2 - 10 nm, and the thickness of the SnO 2 thin film is 4 - 10 nm in such a combined sandwich structure, it not only has the ZnO-Au Schottky barrier, but also has the N-N junction of ZnO-SnO 2 , and can also avoid the situation where the response value decreases due to unreasonable thickness combination. Therefore, its response value is higher than that of a single ZnO-Au or ZnO-SnO 2Higher, 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 thin films, and then prepares a hydrogen-sensitive material. Magnetron sputtering is a batch planarization vacuum preparation process. It can batch prepare sensitive materials within a range of 4 inches at one time, and can realize the batch preparation of thousands of MEMS semiconductor hydrogen sensors at one time. Moreover, it can continuously carry out thin film preparation operations. This process not only has a simple preparation process, but also has good continuity and is suitable for mass production. In addition, during the magnetron sputtering process, the sensitive material atoms have a strong interaction with the substrate, and the obtained thin film has good adhesion and stable performance. Usually, direct current magnetron sputtering is generally used to prepare metal thin films. Although this method has a relatively fast preparation rate, it is difficult to precisely control the thickness of the coating. For the ZnO-Au-SnO 2 sandwich sensitive composite film, the thickness of any layer of the film has a crucial impact on the overall combined response value. Therefore, it is impossible to prepare a hydrogen-sensitive material with a high response value by using the direct current magnetron sputtering method. The present invention innovatively uses radio frequency magnetron sputtering to precisely control the thickness of the metal layer, so that the thickness of any layer in the ZnO-Au-SnO 2 sandwich sensitive composite film can be precisely controlled within the set range. Furthermore, not only can a hydrogen sensor with a high response value be obtained, but also the hydrogen response performance of the hydrogen sensor can be effectively regulated by precisely adjusting the thickness of each layer. The present invention uses radio frequency magnetron sputtering to prepare the ZnO-Au-SnO 2 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 strengthens the adhesion of the coating, effectively improves the distribution uniformity and adhesion of the sensitive composite film, and can ensure that the obtained hydrogen-sensitive material has good stability and reliability.

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

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

[0056] In order to obtain a hydrogen sensor with a higher response value, the thickness of the ZnO thin film is 100 nm, the thickness of the Au thin film is 4 nm, and the thickness of the SnO 2 thin film is 6 nm.

[0057] In the present invention, on the basis of ZnO as the base material, an Au modification layer is added, so that the response contact surface of ZnO to the gas is increased. Due to the modification of Au, it will also have a catalytic promotion effect on the breaking of the chemical bond of hydrogen, making hydrogen more easily adsorbed and effectively improving the response value. Moreover, Au and ZnO can form a Schottky barrier, further improving the response value of ZnO to hydrogen. On this basis, the SnO 2 thin film is sputtered onto the surface layer of the ZnO thin film that has been compounded with noble metals, further increasing the contact surface of oxygen and hydrogen. And because SnO 2 has two valence states of +3 and +4, its autocatalytic effect will accelerate the breaking of the chemical bond of H 2 , promoting a faster adsorption response. It is found in a large number of practices that the thicknesses of the Au thin film and the SnO 2 thin film are crucial for improving the response value of the hydrogen sensor. When both the Au thin film and the SnO 2 thin film are too thin, the effect of improving the response value is limited, making the increased cost not proportional to the obtained response benefit. And when the Au thin film is too thick, it will cause the resistance of the sensitive composite film to be too low, and then the response value is also lower. When the SnO 2 thin film is too thick, it will completely cover the Au and ZnO composite film, which results in only SnO 2 responding to hydrogen, thus causing the response value to decrease. Through a large number of experimental combinations and continuous optimization and selection, it is innovatively found that for the ZnO-Au-SnO 2 sandwich sensitive composite film, a sandwich structure with a ZnO thin film thickness of 50 to 200 nm, an Au thin film thickness of 2 to 10 nm, and an SnO 2 thin film thickness of 4 to 10 nm is adopted. Such a structure not only has a ZnO-Au Schottky barrier but also has a ZnO-SnO 2The N-N junction can also avoid the situation where the response value decreases due to unreasonable thickness combination. Therefore, its response value is higher than that of a single ZnO-Au or ZnO-SnO 2 Higher. 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 a high detection accuracy, which is beneficial to improving the practicability and stability of the hydrogen sensor.

[0058] In order to further elaborate on the present invention in depth, the present invention will be described below through embodiments: Example 1:

[0059] Check whether all valves of the magnetron sputtering instrument are in the initial setting state to ensure that the vacuum chamber is in a closed state before evacuation. Ensure that the cooling water has been connected before powering on the magnetron sputtering instrument. Start the main power supply of the magnetron sputtering instrument. Connect high-purity argon gas to the gas 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. Open the mechanical pump and the stop valve to start evacuating. When the air pressure in the vacuum chamber drops below 10 Pa, press the working button of the molecular pump. When the molecular pump is stable, adjust the air pressure in the vacuum chamber to below 5×10 -3 Pa. Open the voltage regulating switch and the inlet valve. After about 10 seconds, open the flow meter, set the flow rate to 30 sccm, introduce argon gas and adjust the air pressure in the vacuum chamber to about 1 Pa and stabilize it. Start the RF sputtering power supply, set the power to 50 W, set the sputtering time to 0.5 hours, and a pure zinc oxide thin film can be obtained after sputtering. After depositing the zinc oxide thin film, turn off the RF sputtering power supply, the flow meter, the inlet valve, and the voltage regulating switch. Replace the working target of the magnetron sputtering instrument with the gold target, and readjust the air pressure in the vacuum chamber to below 5×10 -3 Pa again. Open the voltage regulating switch, the inlet valve, and the flow meter again, set the flow rate to 30 sccm, introduce argon gas and adjust the air pressure in the vacuum chamber to about 1 Pa and stabilize it. Start the RF sputtering power supply, set the power to 30 W, set the sputtering time to 10 seconds, and a gold-modified zinc oxide gas-sensitive thin film can be obtained after sputtering.

[0060] Repeat the above steps and adjust the sputtering time of the Au target to 20 seconds and 30 seconds respectively. Finally, a pure zinc oxide thin film and gold-modified zinc oxide gas-sensitive thin films with sputtering times of 10 seconds, 20 seconds, and 30 seconds are obtained respectively.

[0061] Figure 4It shows the hydrogen response diagrams of four samples in this embodiment at the optimal working temperature of 483 °C. Through comparison, it is found that the ZnO-Au(4nm) composite film has the best response effect; Example 2:

[0062] Check whether all valves of the magnetron sputtering instrument are in the initial setting state to ensure that the vacuum chamber is in a closed state before evacuating. Ensure that the cooling water has been connected before powering on the magnetron sputtering instrument. Start the main power supply of the magnetron sputtering instrument. Connect high-purity argon gas to the gas 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 to start evacuating. When the air pressure in the vacuum chamber drops below 10 Pa, turn on the working button of the molecular pump. When the molecular pump is stable, adjust the air pressure in the vacuum chamber to below 5×10 -3 Pa. Turn on the pressure regulating switch and the intake valve. After about 10 seconds, turn on the flow meter, set the flow rate to 30 sccm, introduce argon gas and adjust the air pressure in the vacuum chamber to about 1 Pa and stabilize it. Start the RF sputtering power supply, set the power to 50 W, set the sputtering time to 0.5 hours, and obtain a pure zinc oxide thin film after sputtering. After depositing the zinc oxide thin film, turn off the RF sputtering power supply, the flow meter, the intake valve and the pressure regulating switch. Replace the working target of the magnetron sputtering instrument with the gold target, and readjust the air pressure in the vacuum chamber to below 5×10 -3 Pa again. Turn on the pressure regulating switch, the intake valve and the flow meter again, set the flow rate to 30 sccm, introduce argon gas and adjust the air pressure in the vacuum chamber to about 1 Pa and stabilize it. Start the RF sputtering power supply, set the power to 30 W, set the sputtering time to 10 seconds, and obtain a gold-modified zinc oxide gas-sensitive thin film after sputtering. After depositing the gold thin film, turn off the RF sputtering power supply, the flow meter, the intake valve and the pressure regulating switch. Replace the working target of the magnetron sputtering instrument with the tin dioxide target, and readjust the air pressure in the vacuum chamber to below 5×10 -3 Pa again. Turn on the pressure regulating switch, the intake valve and the flow meter again, set the flow rate to 30 sccm, introduce argon gas and adjust the air pressure in the vacuum chamber to about 1 Pa and stabilize it. Start the RF sputtering power supply, set the power to 60 W, set the sputtering time to 10 seconds, and obtain a ZnO-Au(4nm)-SnO 2 (4nm) composite film. Example 3:

[0063] The difference between this example and Example 2 is that the sputtering time of the tin dioxide thin film is adjusted to 20 seconds, and after sputtering, a ZnO-Au(4nm)-SnO 2 (6nm) composite film is obtained. Example 4:

[0064] The difference between this example and Example 2 is that the sputtering time of the tin dioxide thin film is adjusted to 40 seconds, and after sputtering, a ZnO-Au(4nm)-SnO 2 (10nm) composite film is obtained.

[0065] Compare 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 through comparison that the ZnO-Au(4nm)-SnO 2 (6nm) composite film has the best response effect, significantly superior to the ZnO-Au(4nm)-SnO 2 (4nm) composite film and the ZnO-Au(4nm)-SnO 2 (10nm) composite film; Figure 6 The real-time change curve of the sensor resistance of the ZnO-Au(4nm)-SnO 2 (6nm) composite film at different hydrogen concentrations is shown. It can be seen from the figure that the resistance change of this composite film at different hydrogen concentrations is obvious; Figure 7 The real-time change curve of the sensor resistance of the ZnO-Au(4nm)-SnO 2 (6nm) composite film during five-cycle tests at a hydrogen concentration of 10 ppm is shown. It can be seen from the figure that the resistance change of this composite film during multiple cycle tests is still obvious, indicating its excellent reusability; Figure 8 The real-time change curve of the sensor resistance of the ZnO-Au(4nm)-SnO 2 (6nm) composite film during five-cycle tests at a hydrogen concentration of 40 ppm is shown. It can be seen from the figure that the resistance change of this composite film during multiple cycle tests is still obvious, indicating its excellent reusability; Figure 9 The real-time change curve of the sensor resistance of the ZnO-Au(4nm)-SnO 2 (6nm) composite film during five-cycle tests at a hydrogen concentration of 100 ppm is shown. It can be seen from the figure that the resistance change of this composite film during multiple cycle tests is still obvious, indicating its excellent reusability. Figure 10 The SEM image of the ZnO-Au(4nm)-SnO 2 (4nm) composite film is shown, Figure 11 The SEM image of the ZnO-Au(4nm)-SnO2 (6nm) SEM image of the composite film, Figure 12 showing ZnO-Au(4nm)-SnO 2 (10nm) SEM image of the composite film. By comparison, it is found that ZnO-Au(4nm)-SnO 2 (6nm) composite film has the most ideal microstructure, and its contact surface is more conducive to hydrogen adsorption, which can further help 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 of claim 1, 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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