Multi-range pressure sensor for high temperature

Abstract

The utility model discloses a multi-range pressure sensor for high temperature, comprising an upper diaphragm, the upper end face of which is used for measuring pressure, the lower end face of which is provided with a groove, and the top of the groove extends downwards to be provided with a silicon island; the lower-layer diaphragm is connected with the lower end face of the upper-layer diaphragm in a bonding mode, the silicon island is in contact with the upper end face of the lower-layer diaphragm, four piezoresistors are arranged on the lower end face of the lower-layer diaphragm, and the four piezoresistors form a Wheatstone bridge; a cavity is formed in the middle of the glass substrate, and the four piezoresistors are all located in the cavity; according to the utility model, the advantages of silicon carbide and monocrystalline silicon are combined, and the pressure sensor not only can work stably in a high-temperature environment, but also has the advantages of high precision, workability and corrosion resistance.

Description

Technical Field

[0001] The utility model relates to the technical field of pressure sensors, in particular to a high-temperature multi-range pressure sensor. Background Art

[0002] With the development of science and technology, pressure sensors are playing an increasingly important role in many fields, such as consumer electronics, automotive industry, and aerospace. Among them, silicon piezoresistive pressure sensors have become the first mass-produced MEMS (micro-electromechanical system) products due to their advantages such as simple manufacturing and high sensitivity, and have been widely used.

[0003] However, traditional silicon piezoresistive pressure sensors have obvious problems under high temperature conditions. Due to the inherent characteristics of silicon materials, the leakage current of the pn junction will increase under high temperature conditions, and the piezoresistance coefficient is also easily affected by temperature, which leads to reduced working stability and accuracy of the sensor. Therefore, the operating temperature of common silicon piezoresistive devices is usually limited to less than 150°C, which seriously limits its application in high temperature environments.

[0004] In order to solve this problem, researchers began to explore new materials, among which silicon carbide has attracted much attention due to its excellent high-temperature stability and corrosion resistance. The band gap width, thermal conductivity and other properties of silicon carbide are several times that of single-crystal silicon, making silicon carbide devices more suitable for high-temperature conditions. However, the high hardness and stable chemical properties of silicon carbide materials also bring difficulties in processing, and both physical and chemical processing methods face great challenges. In addition, the piezoresistance coefficient of silicon carbide is relatively small, resulting in a low output signal when measuring low pressure, which also limits its scope of application.

[0005] Therefore, how to combine the advantages of silicon carbide and single crystal silicon to design a pressure sensor that can work stably in high temperature environments and has high precision, easy processing and corrosion resistance has become an urgent problem to be solved in the current technical field. Summary of the invention

[0006] The purpose of the utility model is to provide a high-temperature multi-range pressure sensor to solve the problems existing in the prior art. Combining the advantages of silicon carbide and single crystal silicon, the pressure sensor can not only work stably in a high temperature environment, but also has high precision, easy processing and corrosion resistance.

[0007] In order to achieve the above purpose, the technical solution adopted by the utility model is:

[0008] A high-temperature multi-range pressure sensor comprises: an upper diaphragm, whose upper end surface is used for pressure measurement, and whose lower end surface is provided with a groove, and whose top extends downward to provide a silicon island; a lower diaphragm, which is connected to the lower end surface of the upper diaphragm by bonding, and the silicon island contacts the upper end surface of the lower diaphragm, and the lower end surface of the lower diaphragm is provided with four varistors, and the four varistors form a Wheatstone bridge; and a glass substrate, wherein a cavity is provided in the middle, and the four varistors are all located in the cavity.

[0009] Furthermore, the upper end of the silicon island is located at the center of the top of the groove, and the lower end of the silicon island corresponds to the geometric midpoint of the four varistors.

[0010] Furthermore, the groove is a truncated pyramid structure, and the silicon island is an inverted truncated pyramid structure.

[0011] Furthermore, the upper diaphragm and the lower diaphragm are both single crystal silicon wafers; the varistor is a silicon carbide piezoresistor doped with nitrogen, and the silicon carbide piezoresistor is formed by etching a silicon carbide layer.

[0012] Furthermore, the area of ​​the upper membrane is larger than that of the lower membrane, and the thickness ratio of the upper membrane to the lower membrane is 22:1 to 18:1.

[0013] Furthermore, the groove and the silicon island are formed on the lower end surface of the upper membrane by using a mask in combination with an anisotropic wet etching process.

[0014] Compared with the prior art, the beneficial effects of the utility model are:

[0015] 1. Since the upper diaphragm does not have any circuit structure, it can directly contact with humid, corrosive or conductive gases without causing circuit damage due to these environmental factors, which greatly broadens the application scenarios of the sensor; the circuit of the lower diaphragm is protected by the upper diaphragm, so there is no need for additional protective layers, such as insulating layers or passivation layers, which not only simplifies the production process, but also significantly reduces the production cost;

[0016] 2. Combining the advantages of silicon carbide and single crystal silicon, the pressure sensor can not only work stably in high temperature environment, but also has high precision, easy processing and corrosion resistance. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 A cross-sectional view of a pressure sensor in one embodiment of the present application;

[0018] Figure 2 A cross-sectional view of an upper membrane in one embodiment of the present application;

[0019] Figure 3A cross-sectional view of a lower membrane in one embodiment of the present application;

[0020] In the figure: 1. upper diaphragm; 2. groove; 3. silicon island; 4. lower diaphragm; 5. varistor; 6. glass substrate; 7. silicon carbide layer. DETAILED DESCRIPTION

[0021] The following will be combined with the drawings in the utility model to clearly and completely describe the technical solution of the utility model. Obviously, the described embodiments are only part of the embodiments of the utility model, not all of the embodiments. Based on the embodiments in the utility model, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the utility model.

[0022] In the description of the present utility model, it should be noted that the terms "center", "upper", "lower", "vertical", "horizontal", "inner", "outer", etc. indicate the orientation or position relationship based on the orientation or position relationship shown in the drawings, or the orientation or position relationship in which the utility model product is usually placed when in use, which is only for the convenience of describing the utility model and simplifying the description, and does not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present utility model. In addition, the terms "first", "second", "third", etc. are only used to distinguish the description, and cannot be understood as indicating or implying relative importance.

[0023] In addition, the terms "horizontal", "vertical" and the like do not mean that the components are required to be absolutely horizontal or suspended, but can be slightly tilted. For example, "horizontal" only means that its direction is more horizontal than "vertical", and does not mean that the structure must be completely horizontal, but can be slightly tilted.

[0024] In the description of the present invention, it is also necessary to explain that, unless otherwise clearly specified and limited, the terms "set", "install", "connect", and "connect" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a direct connection, or an indirect connection through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0025] Silicon piezoresistive pressure sensors are the first mass-produced MEMS products and are widely used in consumer electronics, automotive industry, aerospace and many other fields. The advantages of silicon piezoresistive devices are simple manufacturing and high sensitivity, but silicon piezoresistors have inherent problems such as increased pn junction leakage current under high temperature conditions and piezoresistance coefficient is easily affected by temperature. The operating temperature of common silicon piezoresistive devices is usually limited to less than 150°C.

[0026] Silicon carbide is a new material for high-temperature sensor applications. Its bandgap width, thermal conductivity and other properties are several times that of single-crystal silicon, and silicon carbide devices are more suitable for high-temperature conditions. However, silicon carbide has high hardness and stable chemical properties, which makes it difficult to process by physical or chemical methods.

[0027] Single crystal silicon structures are easy to process, but single crystal silicon piezoresistors cannot withstand high temperatures. Silicon carbide piezoresistors can withstand high temperatures, but processing large silicon carbide structures is difficult and costly, and the piezoresistance coefficient of silicon carbide is small, so the output is low when measuring low pressure.

[0028] In view of the above problems, the present application provides a high temperature multi-range pressure sensor, such as Figures 1 to 3 As shown, it includes: an upper diaphragm 1, whose upper end surface is used for pressure measurement, and a groove 2 is provided on the lower end surface, and a silicon island 3 is provided on the top of the groove 2 extending downward; a lower diaphragm 4 is connected to the lower end surface of the upper diaphragm 1 by bonding, the silicon island 3 is in contact with the upper end surface of the lower diaphragm 4, and four varistors 5 are provided on the lower end surface of the lower diaphragm 4, and the four varistors 5 form a Wheatstone bridge; a glass substrate 6, a cavity is provided in the middle, and the four varistors 5 are all located in the cavity.

[0029] In this embodiment, since the upper diaphragm 1 does not have any circuit structure, it can directly contact humid, corrosive or conductive gases without causing circuit damage due to these environmental factors, which greatly broadens the application scenarios of the sensor; since the circuit of the lower diaphragm 4 is protected by the upper diaphragm 1, no additional protective layer, such as an insulating layer or a passivation layer, is required, which not only simplifies the production process, but also significantly reduces the production cost.

[0030] When the upper diaphragm 1 is subjected to pressure, it will effectively transfer the stress to the lower diaphragm 4 through the middle silicon island 3. This design ensures the uniform and effective transfer of stress. The varistor 5 arranged on the lower diaphragm 4 will change its resistance value as the stress changes. This resistance change directly reflects the magnitude of the pressure acting on the sensor.

[0031] In some embodiments, the upper end of the silicon island 3 is located at the center of the top of the groove 2, and the lower end of the silicon island 3 corresponds to the geometric midpoint of the four varistors 5. The design of the silicon island 3 being located at the center of the top of the groove 2 allows the pressure of the upper diaphragm 1 to be concentratedly transmitted to the silicon island, and the silicon island can distribute the pressure as evenly as possible on the four varistors, thereby improving the accuracy and sensitivity of the measurement.

[0032] In some embodiments, the groove 2 is a truncated pyramid structure, and the silicon island 3 is an inverted truncated pyramid structure. The truncated pyramid structure groove 2 helps to collect pressure over a larger area and guide it to the top of the silicon island. The inverted truncated pyramid design of the silicon island allows the pressure transmitted from the groove to be concentrated in a smaller area, and then more effectively transmitted to the piezoresistor, thereby improving the sensitivity of the sensor.

[0033] In some embodiments, the upper diaphragm 1 and the lower diaphragm 4 are both single crystal silicon wafers; the varistor 5 is a silicon carbide piezoresistor doped with nitrogen, and the silicon carbide piezoresistor is formed by etching a silicon carbide layer 7 .

[0034] Single crystal silicon has excellent mechanical properties and easy processing. However, the performance of single crystal silicon piezoresistors is unstable in high temperature environments. In order to solve this problem, this embodiment uses silicon carbide doped with nitrogen as the material of the varistor 5. Silicon carbide has excellent high temperature stability and corrosion resistance. By doping with nitrogen, the piezoresistive properties of silicon carbide can be further improved, and its sensitivity to pressure changes can be increased; that is, this embodiment combines the advantages of silicon carbide and single crystal silicon. The pressure sensor can not only work stably in high temperature environments, but also has high precision, easy processing and corrosion resistance.

[0035] In some embodiments, the area of ​​the upper membrane 1 is larger than that of the lower membrane 4, and the thickness ratio of the upper membrane 1 to the lower membrane 4 is 22:1 to 18:1; preferably, the thickness of the upper membrane 1 is 400 μm, and the thickness of the lower membrane 4 is 20 μm.

[0036] In this embodiment, by adjusting the size and thickness ratio of the upper diaphragm 1 and the lower diaphragm 4, the range of the sensor can be flexibly modified to meet the needs of different application scenarios. When the area of ​​the upper diaphragm 1 is larger than that of the lower diaphragm 4, it actually plays a stress amplification role, which means that even if the piezoresistance coefficient of the varistor 5 is relatively low, a larger output signal can be obtained through structural design, thereby effectively improving the problem of small output signal caused by the low coefficient of the varistor 5.

[0037] In some embodiments, the groove 2 and the silicon island 3 are formed on the lower end surface of the upper film 1 by using a mask and an anisotropic wet etching process. A mask is used on the lower end surface of the upper film 1.

[0038] In this embodiment, the role of the mask is to protect the area that is not to be corroded and expose the part that needs to be corroded. By accurately designing the pattern of the mask, the shape and size of the groove and silicon island formed after corrosion can be controlled. The upper film coated with the mask is placed in the etching solution. Since the single crystal silicon has anisotropic corrosion characteristics in the etching solution, the etching solution will selectively corrode the silicon material according to the pattern of the mask, and finally form the groove 2 and the silicon island 3.

[0039] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A high temperature multi-range pressure sensor, characterized in that: include: An upper diaphragm (1) has an upper end surface for measuring pressure and a lower end surface provided with a groove (2), and a silicon island (3) extending downward from the top of the groove (2); The lower diaphragm (4) is connected to the lower end surface of the upper diaphragm (1) by bonding, the silicon island (3) is in contact with the upper end surface of the lower diaphragm (4), and the lower end surface of the lower diaphragm (4) is provided with four varistors (5), and the four varistors (5) form a Wheatstone bridge; The glass substrate (6) has a cavity in the middle thereof, and the four varistors (5) are all located in the cavity.

2. A high temperature multi-range pressure sensor according to claim 1, characterized in that: The upper end of the silicon island (3) is located at the center of the top of the groove (2), and the lower end of the silicon island (3) corresponds to the geometric midpoint of the four varistors (5).

3. A high temperature multi-range pressure sensor according to claim 1, characterized in that: The groove (2) is a prism-shaped pyramid structure, and the silicon island (3) is an inverted prism-shaped pyramid structure.

4. A high temperature multi-range pressure sensor according to claim 1, characterized in that: The upper diaphragm (1) and the lower diaphragm (4) are both single crystal silicon wafers; the varistor (5) is a silicon carbide piezoresistor doped with nitrogen, and the silicon carbide piezoresistor is obtained by etching a silicon carbide layer (7).

5. The high temperature multi-range pressure sensor according to claim 1, characterized in that: The area of ​​the upper membrane (1) is larger than that of the lower membrane (4), and the thickness ratio of the upper membrane (1) to the lower membrane (4) is 22:1 to 18:

1.

6. A high temperature multi-range pressure sensor according to claim 1, characterized in that: The groove (2) and the silicon island (3) are formed on the lower end surface of the upper membrane (1) by using a mask in combination with an anisotropic wet etching process.

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