Preparation method of wafer-level MEMS sensor for gas detection

Abstract

The invention provides a preparation method of a wafer-level MEMS sensor for gas detection, belongs to the technical field of gas sensors, and aims to solve the technical problem of poor stability of a sensor chip caused by non-uniform thickness of a gas sensitive film in a silicon-based MEMS gas sensor. The preparation method of the MEMS sensor comprises the following steps: (1) dividing a silicon wafer substrate into a plurality of sensing unit areas, and preparing a micro hot plate on each sensing unit area; (2) preparing a gas-sensitive thick film above each micro hot plate by adopting a silk-screen printing technology to form an MEMS gas sensor array; (3) performing high-temperature sintering annealing on the MEMS gas sensor array; and (4) scribing and packaging the annealed MEMS gas sensor array to form a single MEMS gas sensor. According to the invention, the gas-sensitive thick film is prepared on the complete wafer, the film thicknesses of different devices are kept consistent, and the consistency and stability of the MEMS gas sensor are improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of gas sensors, and in particular relates to a method for preparing a wafer-level MEMS sensor for gas detection. Background Art

[0002] With the development of society and the advancement of science and technology, the scale of industrial production has gradually expanded, but accidents caused by this have also continued to occur. For example, the flammable, explosive, toxic and harmful gases produced by the petrochemical and coal mining industries, once these gases exceed the standard or leak, will seriously affect the health of production personnel and surrounding residents. If an explosion occurs, it will cause casualties and property losses. In addition, with the improvement of people's living standards and the change in people's requirements for home environment decoration, the problem of indoor air quality has become increasingly prominent, and malignant cases caused by excessive toxicity after decoration have been reported from time to time. In order to ensure safety and prevent accidents before they happen, people have developed various detection methods and detection instruments, among which gas sensors have been widely used in the production and life fields of various industries.

[0003] Gas sensors are mainly divided into electrochemical, semiconductor, thermal conduction and optical types. Among them, semiconductor sensors are increasingly valued because of their high detection sensitivity, short response recovery time, small component size, long life and low price. MOS gas sensors are the most important type of semiconductor gas sensors. The second type is gas sensors made of semiconductor single crystals as the base material. The sensitivity mechanism of the two is different. According to the difference in the sensitivity mechanism of the two, they are divided into two types: resistance type and non-resistance type gas sensors. Resistance type gas sensors are widely used at present. According to their molding process and structural type, they can be divided into three categories: sintering type, thin film type and thick film type. Thick film gas sensors mainly use screen printing and other technologies to form a thick film with a porous structure. It has a larger specific surface area, more adsorption sites, good sensitivity, and a simple manufacturing process. The equipment can be semi-automated and suitable for mass production.

[0004] MEMS sensor, or micro-electromechanical system, is a multidisciplinary frontier research field developed on the basis of microelectronics technology. 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 intelligent realization. With the rapid development of MEMS technology, gas sensors have also developed in the direction of miniaturization, intelligence, integration and low power consumption. The microstructure gas sensor made by MEMS technology integrates the heating element and the sensitive element into one, achieving a significant reduction in power consumption from hundreds of mW to tens of mW, and can achieve highly consistent preparation at the industrial level. However, in the process of integrating the gas-sensitive thick film into the MEMS micro-hotplate, a single device is still used for independent operation, resulting in uneven thickness, excessive coating area and other process precision problems, which will affect the consistency and stability of the sensor. Summary of the invention

[0005] In response to the technical problem of poor sensor chip stability caused by uneven thickness of gas-sensitive films in silicon-based MEMS gas sensors, the present invention proposes a method for preparing wafer-level MEMS sensors for gas detection, in which a gas-sensitive thick film is prepared on a complete wafer to ensure that the film thickness between different devices remains consistent, thereby improving the consistency and stability of the MEMS gas sensor.

[0006] In order to achieve the above object, the technical solution of the present invention is achieved as follows:

[0007] A method for preparing a wafer-level MEMS sensor for gas detection comprises the following steps:

[0008] (1) A silicon wafer substrate is divided into a plurality of sensing unit regions, and a micro-hotplate is prepared on each sensing unit region;

[0009] (2) Using screen printing technology to prepare a gas-sensitive thick film on each micro-hotplate to form a MEMS gas sensor array;

[0010] (3) performing high temperature sintering annealing on the MEMS gas sensor array;

[0011] (4) Slicing and packaging the annealed MEMS gas sensor array to form a single MEMS gas sensor.

[0012] The material of the micro-hotplate is platinum metal.

[0013] The method of preparing the gas-sensitive thick film by screen printing technology in step (2) is as follows: aligning the heating area of ​​the micro-hotplate with the hollow area of ​​the screen for screen printing, depositing printing ink on the micro-hotplate, and forming a gas-sensitive thick film after the printing ink is cured.

[0014] The alignment error between the heating area and the hollow area of ​​the screen is (0-5) μm.

[0015] The preparation method of the printing ink comprises: uniformly mixing metal oxide powder and solvent, wherein the average particle size of the metal oxide powder is (80-100) nm.

[0016] The mass ratio of the metal oxide powder to the solvent is (2.5-1.5):1.

[0017] The metal oxide is tin oxide, tungsten oxide, zinc oxide, indium oxide or copper oxide; the solvent can be one or more of water, alcohols or ketones; the alcohol is ethanol or ethylene glycol, and the ketone is acetone.

[0018] The screen thickness in the screen printing is 10-50 μm, and the screen material is metal, nylon, or polyester.

[0019] The high temperature sintering is annealing in a sintering furnace, the temperature is 300-800° C., and the duration is 1-5 hours.

[0020] The thickness of the gas-sensitive thick film is 10-50 μm.

[0021] The wafer-level MEMS gas sensor prepared by the above method is used for the detection of gases such as VOC, CO, and NO2.

[0022] Beneficial effects of the present invention:

[0023] (1) The wafer-level MEMS gas sensor preparation method provided by the present invention prepares a MEMS micro-hotplate based on the entire wafer substrate, prepares a gas-sensitive thick film in the heating area of ​​each sensing unit of the MEMS micro-hotplate, and realizes wafer-level preparation of a gas-sensitive thick film with high bonding strength through annealing. In addition, the present invention first prepares a gas-sensitive thick film on a MEMS micro-hotplate wafer, and then slices and packages it after annealing to form a single MEMS gas sensor. Compared with the prior art method of first slicing the MEMS micro-hotplate and then preparing the gas-sensitive thick film and packaging it, the method of the present invention belongs to wafer-level preparation, and the resulting single MEMS gas sensor has better consistency, is simpler to transfer, and has lower cost.

[0024] (2) The present invention uses screen printing technology to achieve patterned uniform deposition of the gas-sensitive thick film, so that the gas-sensitive material only works in the heating area of ​​each sensor unit, avoiding the electrical crosstalk problem between the test electrode and the heating electrode in the traditional thin film transfer method, and also eliminating the influence of the large-area coverage of the gas-sensitive thick film on the subsequent sensor packaging welding, ensuring the consistency of the thick film thickness and resistance value between sensors and the consistency of MEMS gas sensors. At the same time, it is convenient for the standardized preparation of semiconductor MEMS gas sensors, and can significantly improve the production efficiency and yield rate of MEMS gas sensors. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0026] Figure 1 It is a schematic diagram of the structure of a wafer-level MEMS sensor;

[0027] In the figure, 1. base; 2. adhesive I; 3. micro hot plate chip; 4. gas sensitive material; 5. lead; 6. adhesive II; 7. cover plate.

[0028] Figure 2 This is the test circuit diagram of the MEMS sensor.

[0029] Figure 3 This is a stability test diagram of the MEMS sensor prepared for Comparative Example 1.

[0030] Figure 4 This is a stability test diagram of the MEMS sensor prepared in Example 1. DETAILED DESCRIPTION

[0031] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0032] Example 1

[0033] A wafer-level MEMS sensor for gas detection, having a structure such as Figure 1 As shown, it includes a base, a micro-hotplate chip is fixed on the base by adhesive I, and an external passage is formed by leads, a gas-sensitive thick film is provided on the micro-hotplate chip, a cover plate is provided above the gas-sensitive thick film, and the cover plate is fixed on the base by adhesive II.

[0034] A method for preparing a wafer-level MEMS sensor comprises the following steps:

[0035] (1) The silicon wafer is a 6-inch wafer, and the wafer substrate is divided into a number of (1*1) mm sensing unit areas. A micro-hotplate made of platinum metal is prepared on each sensing unit area;

[0036] (2) 25 g of tin oxide powder with an average particle size of 90 nm was mixed with 10 g of ethanol to prepare printing ink; a nylon screen with a thickness of 30 μm was fixed on the top of the wafer substrate, the heating area of ​​the micro-hotplate was aligned with the hollow area of ​​the screen, the printing ink was placed on the screen, and the printing ink was positioned and transferred to the micro-hotplate pattern by a printing machine, and a gas-sensitive thick film with a thickness of 30 μm was prepared on each micro-hotplate to form a MEMS gas sensor array;

[0037] (3) calcining the MEMS gas sensor array at 500°C for 3 hours;

[0038] (4) Slicing and packaging the annealed MEMS gas sensor with a laser hidden cutting device to form a single MEMS gas sensor. Packaging process: The gas-sensitive chip is fixed inside the base by an adhesive, and an Au lead is electrically connected to the base by a wire bonding machine. The stainless steel cover is fixed to the ceramic base by an adhesive and cured.

[0039] Comparative Example 1

[0040] A wafer-level MEMS sensor, having the same structure as that in Example 1, and a preparation method comprising the following steps:

[0041] (1) The silicon wafer is a 6-inch wafer, and the wafer substrate is divided into a number of (1*1) mm sensing unit areas. A micro-hotplate made of platinum metal is prepared on each sensing unit area;

[0042] (2) 25 g of tin oxide powder with an average particle size of 90 nm was mixed with 10 g of ethanol to form a slurry; a gas-sensitive thick film with a thickness of 30 μm was prepared on each micro-hotplate by a dot coating method to form a MEMS gas sensor array;

[0043] (3) calcining the MEMS gas sensor array at 500°C for 3 hours;

[0044] (4) Slicing and packaging the annealed MEMS gas sensor with a laser hidden cutting device to form a single MEMS gas sensor. Packaging process: The gas-sensitive chip is fixed inside the base by an adhesive, and an Au lead is electrically connected to the base by a wire bonding machine. The stainless steel cover is fixed to the ceramic base by an adhesive and cured.

[0045] The MEMS sensors prepared by the methods described in Example 1 and Comparative Example 1 were tested. Figure 2The circuit and conditions shown in the figure are tested - Vh = 2.5V, Vc = 5.0V, RL = 20KΩ, ①-⑧ in the figure represent pins. V0 is the output value of the sensor in clean air, Vs is the output value under 50ppm ethanol gas conditions, and Vs-V0 is the difference between the output value under 50ppm ethanol gas conditions and the output value in clean air.

[0046] from Figure 4 The normal distribution diagram of V0 and Vs-V0 under the process conditions of the present invention shows that the product consistency is significantly better than Figure 3 The consistency of the process conditions of the mid-point coating. The data concentration of the process of the present invention is relatively high, which is more conducive to the control of the production process.

[0047] Example 2

[0048] A method for preparing a wafer-level MEMS sensor comprises the following steps:

[0049] (1) The silicon wafer is a 6-inch wafer, and the wafer substrate is divided into several (1*1) mm sensing unit areas, and a micro-hotplate is prepared on each sensing unit area;

[0050] (2) 20 g of zinc oxide powder with an average particle size of 90 nm was mixed with 10 g of ethanol to prepare printing ink; a nylon screen with a thickness of 30 μm was fixed on the top of the wafer substrate, the heating area of ​​the micro-hotplate was aligned with the hollow area of ​​the screen, the printing ink was placed on the screen, and the printing ink was positioned and transferred to the micro-hotplate pattern by a printing machine, and a gas-sensitive thick film with a thickness of 30 μm was prepared on each micro-hotplate to form a MEMS gas sensor array;

[0051] (3) calcining the MEMS gas sensor array at 500°C for 3 hours;

[0052] (4) Slicing and packaging the annealed MEMS gas sensor with a laser hidden cutting device to form a single MEMS gas sensor. Packaging process: The gas-sensitive chip is fixed inside the base by an adhesive, and an Au lead is electrically connected to the base by a wire bonding machine. The stainless steel cover is fixed to the ceramic base by an adhesive and cured.

[0053] Example 3

[0054] A method for preparing a wafer-level MEMS sensor comprises the following steps:

[0055] (1) The silicon wafer is a 6-inch wafer, and the wafer substrate is divided into several (1*1) mm sensing unit areas, and a micro-hotplate is prepared on each sensing unit area;

[0056] (2) 15 g of indium oxide powder with an average particle size of 90 nm was mixed with 10 g of ethanol to prepare printing ink; a nylon screen with a thickness of 30 μm was fixed on the top of the wafer substrate, the heating area of ​​the micro-hotplate was aligned with the hollow area of ​​the screen, the printing ink was placed on the screen, and the printing ink was positioned and transferred to the micro-hotplate pattern by a printing machine, and a gas-sensitive thick film with a thickness of 30 μm was prepared on each micro-hotplate to form a MEMS gas sensor array;

[0057] (3) calcining the MEMS gas sensor array at 500°C for 1 hour;

[0058] (4) Slicing and packaging the annealed MEMS gas sensor with a laser hidden cutting device to form a single MEMS gas sensor. Packaging process: The gas-sensitive chip is fixed inside the base by an adhesive, and an Au lead is electrically connected to the base by a wire bonding machine. The stainless steel cover is fixed to the ceramic base by an adhesive and cured.

[0059] Example 4

[0060] A method for preparing a wafer-level MEMS sensor comprises the following steps:

[0061] (1) The silicon wafer is a 6-inch wafer, and the wafer substrate is divided into several (1*1) mm sensing unit areas, and a micro-hotplate is prepared on each sensing unit area;

[0062] (2) 25 g of tin oxide powder with an average particle size of 80 nm was mixed with 10 g of ethanol to prepare printing ink; a nylon screen with a thickness of 50 μm was fixed on the top of the wafer substrate, the heating area of ​​the micro-hotplate was aligned with the hollow area of ​​the screen, the printing ink was placed on the screen, and the printing ink was positioned and transferred to the micro-hotplate pattern by a printing machine, and a gas-sensitive thick film with a thickness of 50 μm was prepared on each micro-hotplate to form a MEMS gas sensor array;

[0063] (3) calcining the MEMS gas sensor array at 300°C for 3 hours;

[0064] (4) Slicing and packaging the annealed MEMS gas sensor with a laser hidden cutting device to form a single MEMS gas sensor. Packaging process: The gas-sensitive chip is fixed inside the base by an adhesive, and an Au lead is electrically connected to the base by a wire bonding machine. The stainless steel cover is fixed to the ceramic base by an adhesive and cured.

[0065] Example 5

[0066] A method for preparing a wafer-level MEMS sensor comprises the following steps:

[0067] (1) The silicon wafer is a 6-inch wafer, and the wafer substrate is divided into several (1*1) mm sensing unit areas, and a micro-hotplate is prepared on each sensing unit area;

[0068] (2) 25 g of copper oxide powder with an average particle size of 100 nm was mixed with 10 g of ethanol to prepare printing ink; a nylon screen with a thickness of 30 μm was fixed on the top of the wafer substrate, the heating area of ​​the micro-hotplate was aligned with the hollow area of ​​the screen, the printing ink was placed on the screen, and the printing ink was positioned and transferred to the micro-hotplate pattern by a printing machine, and a gas-sensitive thick film with a thickness of 30 μm was prepared on each micro-hotplate to form a MEMS gas sensor array;

[0069] (3) calcining the MEMS gas sensor array at 800°C for 3 hours;

[0070] (4) Slicing and packaging the annealed MEMS gas sensor with a laser hidden cutting device to form a single MEMS gas sensor. Packaging process: The gas-sensitive chip is fixed inside the base by an adhesive, and an Au lead is electrically connected to the base by a wire bonding machine. The stainless steel cover is fixed to the ceramic base by an adhesive and cured.

[0071] Example 6

[0072] A method for preparing a wafer-level MEMS sensor comprises the following steps:

[0073] (1) The silicon wafer is a 6-inch wafer, and the wafer substrate is divided into several (1*1) mm sensing unit areas, and a micro-hotplate is prepared on each sensing unit area;

[0074] (2) 25 g of tin oxide powder with an average particle size of 80 nm was mixed with 5 g of ethanol and 5 g of water to prepare printing ink; a nylon screen with a thickness of 10 μm was fixed on the top of the wafer substrate, the heating area of ​​the micro-hotplate was aligned with the hollow area of ​​the screen, the printing ink was placed on the screen, and the printing ink was positioned and transferred to the micro-hotplate pattern by a printing machine, and a gas-sensitive thick film with a thickness of 10 μm was prepared on each micro-hotplate to form a MEMS gas sensor array;

[0075] (3) calcining the MEMS gas sensor array at 500°C for 5 hours;

[0076] (4) Slicing and packaging the annealed MEMS gas sensor with a laser hidden cutting device to form a single MEMS gas sensor. Packaging process: The gas-sensitive chip is fixed inside the base by an adhesive, and an Au lead is electrically connected to the base by a wire bonding machine. The stainless steel cover is fixed to the ceramic base by an adhesive and cured.

[0077] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing a wafer-level MEMS sensor for gas detection, characterized in that: The steps include: (1) A silicon wafer substrate is divided into a plurality of sensing unit regions, and a micro-hotplate is prepared on each sensing unit region; (2) Using screen printing technology to prepare a gas-sensitive thick film on each micro-hotplate to form a MEMS gas sensor array; (3) performing high temperature sintering annealing on the MEMS gas sensor array; (4) Slicing and packaging the annealed MEMS gas sensor array to form a single MEMS gas sensor.

2. The method for preparing a wafer-level MEMS sensor for gas detection according to claim 1, characterized in that: The material of the micro-hotplate is platinum metal.

3. The method for preparing a wafer-level MEMS sensor for gas detection according to claim 1, characterized in that: The method of preparing the gas-sensitive thick film by screen printing technology in step (2) is as follows: aligning the heating area of ​​the micro-hotplate with the hollow area of ​​the screen for screen printing, depositing printing ink on the micro-hotplate, and forming a gas-sensitive thick film after the printing ink is cured.

4. The method for preparing a wafer-level MEMS sensor for gas detection according to claim 3, characterized in that: The alignment error between the heating area and the hollow area of ​​the screen is 0-5 μm.

5. The method for preparing a wafer-level MEMS sensor for gas detection according to claim 4, characterized in that: The preparation method of the printing ink is: mixing metal oxide powder and solvent evenly, and the average particle size of the metal oxide powder is 80-100nm.

6. The method for preparing a wafer-level MEMS sensor for gas detection according to claim 5, characterized in that: The mass ratio of the metal oxide powder to the solvent is (2.5-1.5):

1.

7. The method for preparing a wafer-level MEMS sensor for gas detection according to claim 6, characterized in that: The metal oxide is tin oxide, tungsten oxide, zinc oxide, indium oxide or copper oxide; the solvent is one or more of water, alcohols or ketones; the alcohol is ethanol or ethylene glycol, and the ketone is acetone.

8. The method for preparing a wafer-level MEMS sensor for gas detection according to claim 7, characterized in that: The screen thickness in the screen printing is 10-50 μm, and the screen material is metal, nylon, or polyester.

9. The method for preparing a wafer-level MEMS sensor for gas detection according to claim 1, characterized in that: The high temperature sintering temperature is 300-800° C. and the duration is 1-5 hours.

10. The method for preparing a wafer-level MEMS sensor for gas detection according to claim 1, characterized in that: The thickness of the gas-sensitive thick film is 10-50 μm.

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