Preparation method of gas sensitive layer of MEMS (Micro Electro Mechanical System) gas sensor and dispensing device

Abstract

The invention discloses a preparation method of a gas sensitive layer of an MEMS (Micro Electro Mechanical System) gas sensor. The preparation method comprises the following steps: (1) crushing and grinding a gas sensitive material into uniform powder particles; (2) fully mixing and dispersing a gas sensitive material and a dispersion medium to form gas sensitive slurry; (3) dispensing and coating the gas sensitive slurry on the heating area of the MEMS chip through a piezoelectric valve of a dispensing machine; (4) curing the gas sensitive slurry; (5) packaging the MEMS chip; the invention further discloses a dispensing device, the dispensing device comprises the piezoelectric valve, an air source, a controller, a workbench, a visual detection module and a driving module, the piezoelectric valve comprises a valve body, the valve body is provided with a first connector and a liquid storage cavity, the glue pipe is connected between the first connector and the air source, the valve body is provided with a first flow channel, and the first flow channel is connected between the liquid storage cavity and the first connector. The forming effect of the gas sensitive layer of the MEMS gas sensor can be improved, and the production efficiency can be improved.

Description

Technical Field

[0001] The invention relates to the field of MEMS gas sensors, and in particular to a preparation method and a glue dispensing device for a gas-sensitive layer of a MEMS gas sensor. Background Art

[0002] Gas sensors are key devices for detecting and monitoring the concentration of various gases and are widely used in the fields of industry, security, and environmental monitoring. Among them, MEMS gas sensors based on semiconductor materials have received extensive attention and research in recent years due to their advantages such as miniaturization, low power consumption, and high sensitivity. However, in the mass production process, how to ensure the uniform coating and stable adhesion of gas-sensitive materials on MEMS chips still faces many challenges.

[0003] Piezoelectric dispensing valve (also called piezoelectric valve) is a common device used for dispensing and coating of gas-sensitive materials. It is a precision dispensing device that can use the piezoelectric effect to control the flow of fluid. It has the characteristics of high precision, high stability, high efficiency, and non-contact dispensing.

[0004] The working principle of the piezoelectric dispensing valve is to continuously inject the glue in the liquid storage cavity into the nozzle through the reciprocating striker, and eject the glue from the nozzle to achieve the dispensing coating function. Among them, the liquid storage cavity is connected to the hose for storing gas-sensitive slurry, and the hose is connected to the air source. The air source can apply a certain pressure to drive the gas-sensitive slurry to continuously replenish the liquid storage cavity.

[0005] Affected by the preparation process, gas-sensitive materials are prone to blockage and obstruction in narrow liquid storage cavities and nozzles, affecting the dispensing and spraying effect. Specifically, irregular and uneven glue droplets will be formed on the work surface to be coated with glue, affecting the molding effect of the final gas-sensitive layer, resulting in unstable performance of gas sensors during mass production, and it is difficult to ensure sensitivity and selectivity. In order to avoid this situation, it is necessary to regularly clear the narrow internal spaces such as the liquid storage cavity and nozzle of the piezoelectric valve. For example, when the gas-sensitive slurry in the hose is exhausted, the gas source and the liquid storage cavity and nozzle of the piezoelectric valve are directly connected to clear the blockage through airflow. However, this clearing operation is relatively cumbersome and requires manual participation, which has a certain impact on production efficiency. Summary of the invention

[0006] In order to overcome the above-mentioned defects of the prior art, the present invention provides a method for preparing a gas-sensitive layer of a MEMS gas sensor, comprising the following steps: (1) Grinding the solid gas-sensitive material into uniform powder particles; (2) Fully mix and disperse the gas sensitive material and the dispersion medium to form a uniform and stable gas sensitive slurry; (3) Add the prepared gas-sensitive slurry into the rubber tube of the dispensing machine, pressurize the inside of the rubber tube through the gas source of the dispensing machine to keep the inside of the rubber tube at a constant pressure value, and dispense the gas-sensitive slurry onto the heating area of ​​the MEMS chip through the piezoelectric valve of the dispensing machine; (4) Curing the gas sensitive slurry; (5) Packaging the MEMS chip; In the above step (3), the glue dispensing machine also includes: Self-test process: The state of the glue droplets sprayed on the MEMS chip is detected by the visual inspection module of the glue dispenser, and the pressure condition inside the glue tube is detected by the air pressure sensor; When gas-sensitive materials become clogged or blocked in the narrow liquid storage cavity and nozzle, the glue droplets formed by the injection will become uneven in shape and size, and the internal pressure of the hose will also increase. By testing these two indicators, the equipment can be self-checked.

[0007] The visual inspection module is a module already available on the existing glue dispensing machine, which is used to align with the MEMS chip to determine the position of the glue dispensing coating. In the present invention, the visual inspection module can also be used to detect the state of the glue droplets sprayed on the MEMS chip.

[0008] Cleaning process: When the visual inspection module detects that the glue droplet is in a bad state or the air pressure sensor detects that the internal pressure of the hose exceeds a preset value, the driving module controls the piezoelectric valve to move to the clean area of ​​the workbench, controls the first channel between the hose and the liquid storage cavity to be closed, and controls the second channel between the air source and the liquid storage cavity to be connected, and uses the airflow to deliver the residual gas-sensitive slurry in the liquid storage cavity and the nozzle. After completion, the first channel is controlled to be opened and the second channel is controlled to be closed. The airflow is generated by the air source. In addition to providing pressure to the inside of the hose, the air source can also be used to pass into the second channel to clean the inside of the piezoelectric valve, saving costs and reducing the structural complexity of the equipment.

[0009] Testing process: After the cleaning process is completed, the piezoelectric valve is controlled to move to the test area of ​​the workbench to perform a glue dispensing test on the test chip model. When the visual inspection module detects that the glue drop is in good condition and the air pressure sensor detects that the internal pressure of the hose does not exceed the preset value, the piezoelectric valve is controlled to move to the working area of ​​the workbench to perform glue dispensing and coating on the MEMS chip, otherwise the cleaning process is repeated.

[0010] In step (3), the glue dispensing machine also includes: controlling the piezoelectric valve to move to the clean area of ​​the workbench to discharge glue, exhausting excess air inside the piezoelectric valve, and then controlling the piezoelectric valve to move to the test area of ​​the workbench to calibrate the nozzle in conjunction with the chip model, setting the mark position and calibration value, selecting the alignment angle match according to the shape of the chip model, setting the position tolerance, and detecting the glue dispensing effect through the visual inspection module to realize the debugging function before the glue dispensing work.

[0011] Furthermore, the visual inspection module determines whether the glue droplet is in good condition according to the shape and size of the glue droplet.

[0012] Furthermore, the visual inspection module detects the state of glue droplets formed by glue dispensing in the time interval between each glue dispensing action and the next glue dispensing action, so as to avoid the glue droplets from changing their shape under the action of gravity and improve the recognition effect of the glue droplet state.

[0013] Furthermore, the opening and closing switching of the first channel and the second channel is controlled by a solenoid valve arranged on the piezoelectric valve.

[0014] Furthermore, during the cleaning process, increasing the power of the gas source can improve the cleaning effect.

[0015] In addition, the present invention also provides a dispensing device, including a piezoelectric valve, an air source, a controller, a workbench, a visual inspection module for aligning with a chip, and a driving module for driving the piezoelectric valve to switch positions during the dispensing coating operation. The visual inspection module and the driving module are both connected to the controller. The piezoelectric valve includes a valve body, the valve body is provided with a first joint and a liquid storage cavity, the hose is connected between the first joint and the air source, the valve body is provided with a first flow channel, the first flow channel is connected between the liquid storage cavity and the first joint, the workbench includes an operating area for displaying MEMS chips to be processed, the visual inspection module is also used to identify the state of glue droplets formed by dispensing, the valve body is also provided with a second flow channel, the valve body is provided with a second joint, the second joint and the air source are connected by a pipeline, the second flow channel is connected between the second joint and the first flow channel, and a switching valve that can switch the control hose and the liquid storage cavity or the air source and the liquid storage cavity is provided at the connection between the first flow channel and the second flow channel, and the switching valve is connected to the controller. The visual inspection module detects the state of the glue droplets formed by dispensing and transmits the data to the controller. The controller analyzes the data and identifies whether the glue droplets are in a bad state. The controller controls the operation of the switching valve according to the glue droplet state, so that the air source and the liquid storage cavity are directly connected, and the airflow generated by the air source is used to clean the gas-sensitive slurry that is agglomerated and blocked in the liquid storage cavity and nozzle of the piezoelectric valve. During the cleaning process, the controller can also control the air source to increase the power, thereby improving the cleaning effect.

[0016] Furthermore, an air pressure sensor is arranged between the hose and the air source, and the air pressure sensor is connected to the controller. The air pressure sensor can be arranged at the hose or at the air source. When the gas-sensitive material is blocked or blocked in the narrow liquid storage cavity and the nozzle, the pressure inside the hose will increase. The air pressure sensor feeds back the air pressure value inside the hose to the controller, and cooperates with the controller to realize the self-cleaning control of the piezoelectric valve.

[0017] Further, the switching valve is an electromagnetic valve, which includes an electromagnetic drive mechanism and a valve core. The connection between the first flow channel and the second flow channel includes a sliding cavity. The valve core is arranged in the sliding cavity and is driven by the electromagnetic drive mechanism to move along the sliding cavity. The valve core is distributed with a first passage and a second passage along its movement direction, wherein the two ends of the first passage are respectively arranged at one end and a side of the valve core along its movement direction, and the two ends of the second passage are respectively arranged on the side of the valve core, so that the switchable control hose and the liquid storage cavity or the air source and the liquid storage cavity can be connected.

[0018] Furthermore, the workbench also includes a cleaning area and a test area, and the driving module is also used to drive the piezoelectric valve to move between the working area, the cleaning area and the test area of ​​the workbench. The cleaning area and the test area on the workbench are independent of the working area and can be used to implement cleaning and testing work respectively, reducing interference with the working area, ensuring the cleanliness of the working area, and improving the working effect.

[0019] The beneficial effects of the present invention are as follows: the preparation method and dispensing device of the gas-sensitive layer of the MEMS gas sensor of the present invention can perform self-cleaning in time when blockage or obstruction occurs inside the piezoelectric valve, can improve the molding effect of the gas-sensitive layer of the final MEMS gas sensor product, can reduce the cleaning frequency of the piezoelectric valve, and there is no need to shut down or disassemble the equipment during cleaning, which can improve production efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 A simplified flow chart of a method for preparing a gas-sensitive layer of a MEMS gas sensor according to an embodiment of the present invention; Figure 2 A schematic diagram of various working areas of a workbench of a dispensing device according to an embodiment of the present invention; Figure 3 A schematic diagram of the internal structure of a piezoelectric valve of a dispensing device according to an embodiment of the present invention; Figure 4 for Figure 3 A local enlarged view of the first state; Figure 5 for Figure 3 A partial enlarged view of the second state; Figure 6This is a schematic diagram of module connection of a dispensing device according to an embodiment of the present invention. DETAILED DESCRIPTION

[0021] The method for preparing the gas sensitive layer of the MEMS gas sensor of the present invention is as follows: Figure 1 As shown: the following steps are included: (1) The gas sensitive material made of tungsten oxide as raw material is placed in a planetary ball mill for grinding to ensure that the material particles are uniformly refined to a particle size range of 50-100 nm. The process parameters during ball milling are: ball-to-material ratio 10:1, rotation speed 400 rpm, grinding time 3 hours, intermittent ball milling: every 60 minutes of operation, stop for 15 minutes, and sieve through a 500-mesh screen to remove the particulate impurities in it, and obtain tungsten oxide gas sensitive materials with uniform particle size. The ball-milled gas sensitive material is placed in a vacuum drying oven and heated at 50 °C for 24 hours to ensure that the residual moisture in the material is completely removed, to avoid particle agglomeration during the subsequent preparation of gas sensitive slurry, and to improve the uniformity of the slurry.

[0022] (2) Use 60 g of pineol, 30 g of butyl carbitol acetate, and 10 g of dibutyl phthalate as the dispersion medium, add 4 g of Span 85 as a dispersant, 2 g of ethyl cellulose as a thickener, and 0.5 g of hydrogenated castor oil as a stabilizer, and stir in a water bath at 90 °C until completely dissolved.

[0023] 50g of gas sensitive material was added to the above dispersion medium, and the mass ratio of gas sensitive material to dispersion medium was between 1:2 and 1:5. A magnetic stirrer was first used to stir at room temperature for 30 minutes to ensure that the dispersant and gas sensitive material were fully dissolved. Subsequently, a planetary ball mill stirrer was used to fully mix the slurry. The ball milling parameters were set as follows: ball-to-material ratio 10:1, speed 250 rpm, ball milling time 6 hours, and intermittent ball milling method: every 60 minutes of operation, stop for 15 minutes; The mixed slurry was subjected to ultrasonic treatment at an ultrasonic frequency of 40 kHz, an ultrasonic power of 150 W, and a treatment time of 15 minutes. Intermittent ultrasonic treatment was used: ultrasonic treatment was performed for 5 minutes and then paused for 3 minutes to remove bubbles in the slurry and further improve the uniformity of the slurry. (3) Add the prepared gas-sensitive slurry into the rubber tube of the dispensing machine, pressurize the inside of the rubber tube through the gas source of the dispensing machine to keep the inside of the rubber tube at a constant pressure value, and dispense the gas-sensitive slurry onto the heating area of ​​the MEMS chip through the piezoelectric valve of the dispensing machine; (4) Place the MEMS chip after dispensing in an oven at 300 °C for 2 hours to solidify the gas sensitive slurry and ensure that it is firmly attached to the chip surface.

[0024] (5) Package the cured MEMS chip and select packaging materials that are moisture-proof, dust-proof, and anti-static to ensure the stability of the gas sensitive layer in the external environment. For long-term storage or transportation needs, use anti-static packaging materials and seal them before packaging to ensure that the chip surface and coating are not affected by the external environment.

[0025] In the above step (3), before dispensing and coating, it is also necessary to: Pre-treat the MEMS chip, including: using deionized water or anhydrous ethanol to clean the chip surface to remove surface dirt and impurities, and then drying the chip in an oven at 80°C for 30 minutes to ensure that the chip surface is dry and dust-free.

[0026] The nozzle size of the piezoelectric valve of the dispensing machine is 0.4 mm, and the specific dispensing parameters are set as follows: the feed pressure is 0.1Mpa, the distance between the needle and the substrate is 3 mm, the number of injection points is 1, the valve opening time is 1 ms, the needle drop time is 0.2 ms, and the needle stroke is 70%. During the dispensing process, the operating acceleration of the x-axis, y-axis, and z-axis of the drive module is set to 1000 mm / s², the maximum speed is 100 mm / s, and the time interval between each dispensing is set to 30 ms.

[0027] Control the piezoelectric valve to move to the clean area of ​​the workbench to perform glue removal for 30 seconds to exhaust excess air inside the piezoelectric valve and ensure that the nozzle is not blocked. Subsequently, the nozzle is precisely calibrated and corner matching marks are set at the two diagonal corners of the MEMS chip model with an x-axis position tolerance of 50px and a y-axis position tolerance of 50px. Before formal glue dispensing, a glue dispensing effect test is performed and the glue dispensing effect is inspected by the visual inspection module. After confirmation that it is normal, formal glue dispensing operations are performed.

[0028] In the above step (3), during the dispensing coating, the process also includes: Self-test process: The state of the glue droplets sprayed on the MEMS chip is detected by the visual inspection module of the glue dispensing machine, and the state of the glue droplets refers to the shape and size of the glue droplets formed by the glue dispensing, and the pressure condition inside the glue tube is detected by the air pressure sensor; When gas-sensitive materials become clogged or blocked in the narrow liquid storage cavity and nozzle, the glue droplets formed by the injection will become uneven in shape and size, and the internal pressure of the hose will also increase. By testing these two indicators, the equipment can be self-checked.

[0029] The visual inspection module is a module already available on the existing glue dispensing machine, which is used to align with the MEMS chip to determine the position of the glue dispensing coating. In the present invention, the visual inspection module can also be used to detect the state of the glue droplets sprayed on the MEMS chip.

[0030] Cleaning process: When the visual inspection module detects that the glue droplet is in a bad state or the air pressure sensor detects that the internal pressure of the hose exceeds a preset value, the driving module controls the piezoelectric valve to move to the cleaning area of ​​the workbench, and the solenoid valve on the piezoelectric valve switches to control the first channel between the hose and the liquid storage cavity to be closed, and simultaneously controls the second channel between the air source and the liquid storage cavity to be connected, and the airflow is used to deliver the residual gas-sensitive slurry in the liquid storage cavity and the nozzle. During the cleaning process, increasing the power of the air source can further improve the cleaning effect. After the cleaning is completed, the first channel is controlled to be opened and the second channel is closed. The airflow is generated by the air source. In addition to providing pressure to the inside of the hose, the air source can also be used to pass into the second channel to achieve cleaning inside the piezoelectric valve, saving costs and reducing the structural complexity of the equipment.

[0031] Testing process: After the cleaning process is completed, the piezoelectric valve is controlled to move to the test area of ​​the workbench to perform a glue dispensing test on the test chip model. When the visual inspection module detects that the glue drop is in good condition and the air pressure sensor detects that the internal pressure of the hose does not exceed the preset value, the piezoelectric valve is controlled to move to the working area of ​​the workbench to perform glue dispensing and coating on the MEMS chip, otherwise the cleaning process is repeated.

[0032] The visual inspection module detects the state of glue droplets formed by glue dispensing in the time interval between each glue dispensing action and the next glue dispensing action, so as to avoid the shape change of the glue droplets under the action of gravity and improve the recognition effect of the glue droplet state.

[0033] The embodiment of the dispensing device of the present invention is as follows Figure 2-6As shown, it includes a piezoelectric valve, an air source, a controller, a workbench 2, a visual inspection module for aligning with the chip, and a driving module for driving the piezoelectric valve to switch positions during the dispensing and coating operation. The driving module can drive the piezoelectric valve to move along the x-axis, y-axis, and z-axis directions of the workbench 2. The visual inspection module and the driving module are both connected to the controller. The piezoelectric valve includes a valve body 1, and the valve body 1 is provided with a first connector 7 and a liquid storage cavity. A hose 3 (for storing gas-sensitive slurry) is connected between the first connector 7 and the air source. The upper end of the hose 3 is provided with a connector for connecting to a pipeline. The valve body 1 is provided with a first flow channel 11. The first flow channel 1 1 is connected between the liquid storage cavity and the first joint 7, the workbench 2 includes an operating area 21 for displaying the MEMS chip 41 to be processed, the visual inspection module is also used to identify the state of the glue drop formed by dispensing, the valve body 1 is also provided with a second flow channel 12, the valve body 1 is provided with a second joint 5, the second joint 5 and the air source are connected through a pipeline, the second flow channel 12 is connected between the second joint 5 and the first flow channel 11, and a switching valve 6 that can switch between the control hose and the liquid storage cavity or between the air source and the liquid storage cavity is provided at the connection between the first flow channel 11 and the second flow channel 12, and the switching valve 6 is connected to the controller. The visual inspection module detects the state of the glue droplets formed by dispensing and transmits the data to the controller. The controller analyzes the data and identifies whether the glue droplets are in a bad state according to the size and shape of the glue droplets. For example, glue droplets with irregular shapes and obviously too small sizes can be considered to be in a bad state. The controller controls the operation of the switching valve according to the state of the glue droplets, so that the air source and the liquid storage cavity are directly connected, and the airflow generated by the air source is used to clean the gas-sensitive slurry that is agglomerated and blocked in the liquid storage cavity and nozzle of the piezoelectric valve. The air source can be an air pump. During the cleaning process, the controller can also control the air source to increase the power, thereby improving the cleaning effect.

[0034] An air pressure sensor is arranged between the hose 3 and the air source, and the air pressure sensor is connected to the controller. The air pressure sensor can be arranged at the hose 3 or at the air source. When the gas-sensitive material is blocked or blocked in the narrow liquid storage cavity and the nozzle, the pressure inside the hose will increase. The air pressure sensor feeds back the air pressure value inside the hose 3 to the controller, and cooperates with the controller to realize the self-cleaning control of the piezoelectric valve.

[0035] The switching valve 6 is an electromagnetic valve, which includes an electromagnetic drive mechanism 61 and a valve core 62. The connection between the first flow channel 11 and the second flow channel 12 includes a sliding cavity 13. The valve core 62 is arranged in the sliding cavity 13 and is driven by the electromagnetic drive mechanism 61 to move along the sliding cavity 13. The valve core 62 is provided with a first passage 621 and a second passage 622 along its movement direction. The first passage 621 is an L-shaped structure, and its two ends are respectively arranged at one end and the side of the valve core 62 along its movement direction. The second passage 622 is a straight-line structure, and its two ends are respectively arranged at the side of the valve core 62. When one end of the first passage 621 located at the side of the valve core 62 is aligned with the first flow channel 11, the air source and the liquid storage cavity can be connected. At the same time, due to the obstruction of the valve core 62, the rubber hose 3 and the liquid storage cavity are disconnected (such as Figure 4 As shown in the state), when the two ends of the second passage 622 are aligned with the first flow channel 11, the hose 3 and the liquid storage cavity can be connected, and the air source and the liquid storage cavity are disconnected by the inner wall of the sliding cavity 13 (as shown in the state shown in the state). Figure 5 status shown).

[0036] like Figure 2 As shown, the workbench 2 includes an operating area 21, a cleaning area 22, and a testing area 23, and the driving module is also used to drive the piezoelectric valve to move between the operating area 21, the cleaning area 22, and the testing area 23 of the workbench. The cleaning area 22 and the testing area 23 on the workbench are independent of the operating area 21, and can be used to realize the self-cleaning and testing of the piezoelectric valve, respectively, to reduce interference with the operating area 21, to ensure the cleanliness of the operating area 21, and to improve the operating effect.

[0037] The connection relationship between the modules in the embodiment of the present invention is as follows: Figure 6 As shown, the visual detection module and air pressure sensor are used to sense the working status of the equipment and can transmit sensing signals to the controller, while the drive module, solenoid valve, and air source can execute the instructions sent by the controller.

[0038] Among the above modules, the visual inspection module, the drive module and the air source are the existing hardware on the existing dispensing machine equipment.

[0039] The above embodiment is only one of the preferred specific embodiments of the present invention. Common changes and substitutions made by those skilled in the art within the scope of the technical solution of the present invention are all included in the protection scope of the present invention.

Claims

1. A method for preparing a gas-sensitive layer of a MEMS gas sensor, characterized in that: The following steps are involved: Grind the gas sensitive material into uniform powder; Fully mixing and dispersing the gas sensitive material and the dispersion medium to form a gas sensitive slurry; Add the prepared gas-sensitive slurry into the rubber tube of the dispensing machine, pressurize the inside of the rubber tube through the gas source of the dispensing machine to keep the inside of the rubber tube at a constant pressure value, and dispense the gas-sensitive slurry on the heating area of ​​the MEMS chip through the piezoelectric valve of the dispensing machine; Curing the gas sensitive slurry; Package the MEMS chip; In the above step (3), the glue dispensing machine also includes: Self-test process: The state of the glue droplets sprayed on the MEMS chip is detected by the visual inspection module of the glue dispenser, and the pressure condition inside the glue tube is detected by the air pressure sensor; Cleaning process: When the visual inspection module detects that the glue droplet is in a bad state or the air pressure sensor detects that the internal pressure of the rubber tube exceeds a preset value, the piezoelectric valve is controlled to move to the clean area of ​​the workbench, the first channel between the rubber tube and the liquid storage cavity is controlled to be closed, and the second channel between the air source and the liquid storage cavity is controlled to be connected, and the residual gas-sensitive slurry in the liquid storage cavity and the nozzle is sent out by air flow. After the completion, the first channel is controlled to be opened and the second channel is closed; Testing process: After the cleaning process is completed, the piezoelectric valve is controlled to move to the test area of ​​the workbench to perform a glue dispensing test on the test chip model. When the visual inspection module detects that the glue drop is in good condition and the air pressure sensor detects that the internal pressure of the hose does not exceed the preset value, the piezoelectric valve is controlled to move to the working area of ​​the workbench to perform glue dispensing and coating on the MEMS chip, otherwise the cleaning process is repeated.

2. The method for preparing a gas-sensitive layer of a MEMS gas sensor according to claim 1, characterized in that: In the above step (3), before the glue coating, the glue dispensing machine also includes: controlling the piezoelectric valve to move to the clean area of ​​the workbench to discharge glue, exhausting excess air inside the piezoelectric valve, and then controlling the piezoelectric valve to move to the test area of ​​the workbench to calibrate the nozzle in conjunction with the chip model, setting the mark position and calibration value, selecting the alignment angle match according to the shape of the chip model, setting the position tolerance, and detecting the glue dispensing effect through the visual inspection module.

3. The method for preparing a gas-sensitive layer of a MEMS gas sensor according to claim 1, characterized in that: The visual inspection module determines whether the glue drop is in good condition according to the shape and size of the glue drop.

4. The method for preparing a gas-sensitive layer of a MEMS gas sensor according to claim 1, characterized in that: The visual inspection module detects the state of glue droplets formed by glue dispensing in the time interval after each glue dispensing action is completed and before the next glue dispensing action.

5. The method for preparing a gas-sensitive layer of a MEMS gas sensor according to claim 1, characterized in that: The opening and closing switching of the first channel and the second channel is controlled by the electromagnetic valve arranged on the piezoelectric valve.

6. The method for preparing a gas-sensitive layer of a MEMS gas sensor according to claim 1, characterized in that: During the cleaning process, increase the power of the air source.

7. A dispensing device, comprising a piezoelectric valve, an air source, a controller, a workbench, a visual inspection module for aligning with a chip, and a driving module for driving the piezoelectric valve to switch positions during dispensing and coating operations, wherein the visual inspection module and the driving module are both connected to the controller, the piezoelectric valve comprises a valve body, the valve body is provided with a first joint and a liquid storage cavity, the rubber hose is connected between the first joint and the air source, the valve body is provided with a first flow channel, the first flow channel is connected between the liquid storage cavity and the first joint, the workbench comprises an operating area for displaying MEMS chips, and is characterized in that: The visual inspection module is also used to identify the state of glue droplets formed by dispensing. The valve body is also provided with a second flow channel, and the valve body is provided with a second joint. The second joint and the air source are connected by a pipeline, and the second flow channel is connected between the second joint and the first flow channel. A switching valve that can switch the control hose and the liquid storage cavity or the air source and the liquid storage cavity is provided at the connection between the first flow channel and the second flow channel, and the switching valve is connected to the controller.

8. The dispensing device according to claim 7, characterized in that: An air pressure sensor is arranged between the rubber hose and the air source, and the air pressure sensor is connected to the controller.

9. The dispensing device according to claim 7, characterized in that: The switching valve is an electromagnetic valve, which includes an electromagnetic drive mechanism and a valve core. The connection between the first flow channel and the second flow channel includes a sliding cavity. The valve core is arranged in the sliding cavity and is driven by the electromagnetic drive mechanism to move along the sliding cavity. The valve core is provided with a first passage and a second passage along its movement direction, wherein two ends of the first passage are respectively arranged at one end and a side of the valve core along its movement direction, and two ends of the second passage are respectively arranged on the side of the valve core.

10. The dispensing device according to claim 7, characterized in that: The workbench further comprises a cleaning area and a testing area, and the driving module is further used to drive the piezoelectric valve to move between the working area, the cleaning area and the testing area of ​​the workbench.

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