Miniature MEMS low-pressure piezoresistive pressure sensor

Abstract

The utility model discloses a micro MEMS low-pressure piezoresistive pressure sensor, comprising a silicon wafer, the front surface of which is provided with a beam membrane structure and the back surface of which is provided with a back cavity; the beam film structure comprises four fan-shaped grooves which are uniformly spaced and circumferentially distributed, a piezoresistor is arranged at the interval of every two adjacent fan-shaped grooves, and the four piezoresistors form a Wheatstone bridge; the glass base is bonded with the lower side of the silicon wafer to form a reference pressure cavity; according to the utility model, the deformation of the silicon wafer is utilized to the greatest extent to generate the change of the resistance value, and the sensitivity of the sensor is improved while the miniaturization is maintained.

Description

Technical Field

[0001] The utility model relates to the technical field of pressure sensors, in particular to a micro MEMS low-pressure piezoresistive pressure sensor. Background Art

[0002] A pressure sensor is a device that can sense pressure signals and convert them into output electrical signals according to a certain mechanism. Pressure sensors can be divided into piezoresistive, capacitive, optical fiber, resonant and piezoelectric types. Among them, piezoresistive pressure sensor is a device that converts pressure signals into electrical signals based on the piezoresistive effect.

[0003] Miniaturization is one of the important parameters in the development of micro pressure sensors, and it has received more and more attention. Miniaturization is one of the important parameters in the development of micro pressure sensors, and it has received more and more attention. Among them, piezoresistive micro pressure sensors have the advantages of low cost, small size and high sensitivity, and are widely used in various fields, such as consumer electronics, industry, automobiles, aerospace, etc.

[0004] Due to the huge demand for the above applications, miniature piezoresistive pressure sensors have attracted extensive research interest. However, in the process of miniaturization of sensors, performance degradation may be encountered. Due to the reduction in size, the stability and accuracy of the sensor may be affected. Therefore, how to ensure the stability and accuracy of its performance while maintaining the miniaturization of the sensor is the focus of current research. Summary of the invention

[0005] The purpose of the utility model is to provide a micro-MEMS low-pressure piezoresistive pressure sensor to address the problems existing in the prior art, which maximizes the use of the deformation of the silicon chip to produce changes in resistance value, thereby improving the sensitivity of the sensor while maintaining miniaturization.

[0006] In order to achieve the above purpose, the technical solution adopted by the utility model is:

[0007] A micro-MEMS low-pressure piezoresistive pressure sensor comprises a silicon wafer, a beam-membrane structure is provided on the front side, and a back cavity is provided on the back side; the beam-membrane structure comprises four equally spaced and circumferentially distributed fan-shaped grooves, a piezoresistor is provided at the interval between each two adjacent fan-shaped grooves, and the four piezoresistors form a Wheatstone bridge; a glass base is bonded to the lower side of the silicon wafer to form a reference pressure cavity.

[0008] Furthermore, the beam membrane structure includes a first straight groove connected to two opposite fan-shaped grooves, and a second straight groove connected to another two opposite fan-shaped grooves, the first straight groove and the second straight groove form a cross, and the first straight groove, the second straight groove and the four fan-shaped grooves form a petal-shaped beam membrane structure.

[0009] Furthermore, the beam-membrane structure is formed on the front side of the silicon wafer by an etching process, and the back side of the silicon wafer is formed on the back side by an anisotropic etching technology.

[0010] Furthermore, the silicon wafer is an SOI silicon wafer, which includes: a top silicon layer, the surface of which is lightly doped to form the varistor, and the beam membrane structure is formed by etching; a substrate silicon layer, which is bonded to the glass base to provide stable mechanical support; and a buried oxide layer, which is located between the top silicon layer and the substrate silicon to ensure electrical isolation between the two.

[0011] Furthermore, bumps are provided on the bonding surfaces of the silicon substrate and the glass base to enhance the bonding force between the two.

[0012] Compared with the prior art, the beneficial effects of the utility model are:

[0013] By precisely arranging the positions of the fan-shaped grooves and the varistor, the design can maximize the use of the deformation of the silicon wafer to produce changes in the resistance value. When external pressure acts on the silicon wafer, the deformation of the beam membrane structure is more concentrated and effective, thereby improving the sensitivity of the sensor.

[0014] The design of the petal-shaped beam membrane structure not only optimizes the stress distribution and reduces the nonlinear deformation caused by stress concentration, but also improves the linearity of the pressure sensor while maintaining its miniaturization.

[0015] The beam-membrane structure is circular as a whole, and the edge of the circular membrane is a continuous curve. The stress distribution is relatively uniform, and it is not easily damaged when subjected to stress. It can increase the reliability and stability of the device, and there is no need to add fillets or chamfers to prevent damage caused by stress concentration. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 This is a front cross-sectional view of a pressure sensor in one embodiment of the present application;

[0017] Figure 2 A top view of a pressure sensor in one embodiment of the present application;

[0018] Figure 3 A three-dimensional diagram of a silicon wafer in one embodiment of the present application;

[0019] Figure 4 This is a front cross-sectional view of a pressure sensor in one embodiment of the present application;

[0020] In the figure: 1, silicon wafer; 101, top silicon; 102, substrate silicon; 103, buried oxide layer; 2, back cavity; 3, fan-shaped groove; 4, varistor; 5, glass base; 6, first straight groove; 7, second straight groove. 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] like Figure 1 to Figure 2 As shown, a micro-MEMS low-pressure piezoresistive pressure sensor includes a silicon wafer 1, a beam-diaphragm structure is provided on the front side, and a back cavity 2 is provided on the back side; the beam-diaphragm structure includes four equally spaced and circumferentially distributed fan-shaped grooves 3, a varistor 4 is provided at the interval between each two adjacent fan-shaped grooves 3, and the four varistors 4 form a Wheatstone bridge; a glass base 5 is bonded to the lower side of the silicon wafer 1 to form a reference pressure cavity.

[0026] In this embodiment, the working principle of the sensor is based on the piezoresistive effect. When external pressure acts on the silicon wafer 1, the beam membrane structure will be deformed, causing the resistance value of the varistor to change, thereby measuring the external pressure. Specifically, when the external pressure increases, the silicon strain diaphragm will bend or stretch. This deformation will cause the varistor to be stressed, causing its resistance value to change. Since the varistor is connected in a Wheatstone bridge, the change in resistance value will cause the bridge to be unbalanced, thereby generating a voltage output. This voltage output is proportional to the external pressure, so the magnitude of the external pressure can be inferred by measuring this voltage.

[0027] By precisely arranging the positions of the fan-shaped grooves 3 and the varistor 4, the design can maximize the use of the deformation of the silicon wafer 1 to produce changes in resistance value. When external pressure acts on the silicon wafer, the deformation of the beam-membrane structure is more concentrated and effective, thereby improving the sensitivity of the sensor.

[0028] The design of four equally spaced and circumferentially distributed fan-shaped grooves makes the entire sensor structure more compact, and efficient pressure detection can be achieved without requiring too large an area, which helps to reduce the size of the sensor and meet the needs of miniaturization and lightweighting.

[0029] The beam-membrane structure is circular as a whole, and the edge of the circular membrane is a continuous curve. The stress distribution is relatively uniform, and it is not easily damaged when subjected to stress. It can increase the reliability and stability of the device, and there is no need to add fillets or chamfers to prevent damage caused by stress concentration.

[0030] In some embodiments, Figure 3 and Figure 4 As shown, the beam membrane structure includes a first straight groove 6 connected to two opposite fan-shaped grooves 3, and a second straight groove 7 connected to another two opposite fan-shaped grooves 3. The first straight groove 6 and the second straight groove 7 form a cross shape. The first straight groove 6, the second straight groove 7 and the four fan-shaped grooves 3 form a petal-shaped beam membrane structure.

[0031] In this embodiment, by adding horizontal and vertical rectangular grooves in the central area, namely the first straight groove 6 and the second straight groove 7, the stress on the four sides of the petal beam is more concentrated; the design of this petal-shaped beam membrane structure not only optimizes the stress distribution, but also reduces the nonlinear deformation caused by stress concentration, so that the pressure sensor can maintain its miniaturization while improving the linearity of the sensor.

[0032] In some embodiments, the front side of the silicon wafer 1 is etched to form a beam-membrane structure, and the back side of the silicon wafer 1 is anisotropically etched to form a back cavity 2.

[0033] In this embodiment, the etching and corrosion process is specifically as follows:

[0034] The shape of the beam membrane structure is defined on the upper surface of the silicon wafer 1 by photolithography and etching techniques.

[0035] Photolithography is a technology that uses photosensitive materials and light of a specific wavelength to create tiny graphics. First, a layer of photoresist is applied to the surface of a silicon wafer 1, and then a special photomask is used to expose the photoresist. After exposure, the photoresist will undergo a chemical reaction, making it easier to remove the positive resist or leave the negative resist in a specific area.

[0036] Next is etching, which can be performed by dry etching or wet etching to remove the portion of the silicon wafer 1 not protected by the photoresist, thereby forming the desired beam membrane structure.

[0037] After the front side etching is completed, the back side of the silicon wafer 1 needs to be processed to form a back cavity structure.

[0038] Etching is performed using anisotropic etching technology, which can precisely control the depth and shape of etching to ensure that the formed back cavity meets the design requirements.

[0039] The formation of the back cavity enables the silicon wafer 1 to produce a greater deformation when subjected to external pressure, thereby improving the sensitivity of the sensor.

[0040] In some embodiments, the silicon wafer 1 is an SOI silicon wafer, which includes: a top silicon 101, whose surface is lightly doped to form a varistor 4, and a beam-membrane structure is formed by etching; a substrate silicon 102, which is bonded to a glass base 5 to provide a stable mechanical support; and a buried oxide layer 103, which is located between the top silicon 101 and the substrate silicon 102 to ensure electrical isolation between the two. The synergistic effect of the top silicon, the buried oxide layer and the substrate silicon ensures the high sensitivity, electrical isolation and mechanical stability of the sensor. The structural characteristics of the SOI silicon wafer make it an ideal choice for manufacturing high-performance, miniaturized pressure sensors.

[0041] In some embodiments, bumps are provided on the bonding surface of the substrate silicon 102 and the glass base 5 to enhance the bonding force between the two. The bumps can provide more contact area during the bonding process, thereby increasing the bonding force. This design helps prevent the separation between the substrate silicon and the glass base during long-term use or when subjected to external forces.

[0042] A micro-MEMS low-pressure piezoresistive pressure sensor forming process, comprising:

[0043] Step 1: Prepare SOI silicon wafer. SOI silicon wafer has a three-layer structure: top silicon, buried oxide layer and substrate silicon.

[0044] Step 2: Lightly doping the top silicon of the SOI wafer, that is, adding a small amount of impurity elements such as boron or phosphorus, changes the conductivity of silicon to form a varistor with a specific resistivity; the resistance value of the lightly doped varistor will change with changes in external pressure.

[0045] Step 3: Use dry etching technology to etch a beam membrane structure on the top silicon of the SOI silicon wafer.

[0046] Step 4: forming a back cavity with a specific shape and depth by anisotropic etching technology.

[0047] Step 5: Precisely align the processed SOI silicon wafer and glass base to ensure that the bonding surfaces of the two are aligned. Under high temperature and a certain pressure, the silicon wafer and glass substrate are tightly attached together so that the chemical bonds between the two will recombine to form a strong bond.

[0048] 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 micro-MEMS low-pressure piezoresistive pressure sensor, characterized in that: include A silicon wafer (1) is provided with a beam-membrane structure on the front side and a back cavity (2) on the back side; the beam-membrane structure comprises four equally spaced and circumferentially distributed fan-shaped grooves (3), a varistor (4) is provided at the interval between each two adjacent fan-shaped grooves (3), and the four varistors (4) form a Wheatstone bridge; A glass base (5) is bonded to the lower side of the silicon wafer (1) to form a reference pressure chamber.

2. A micro MEMS low-pressure piezoresistive pressure sensor according to claim 1, characterized in that: The beam membrane structure comprises a first straight groove (6) connected to two opposite fan-shaped grooves (3), and a second straight groove (7) connected to another two opposite fan-shaped grooves (3), the first straight groove (6) and the second straight groove (7) forming a cross shape, and the first straight groove (6), the second straight groove (7) and the four fan-shaped grooves (3) forming a petal-shaped beam membrane structure.

3. A micro-MEMS low-pressure piezoresistive pressure sensor according to claim 1, characterized in that: The beam membrane structure is formed on the front side of the silicon wafer (1) by an etching process, and the back side of the silicon wafer (1) is formed on the back side of the silicon wafer (1) by an anisotropic etching technology.

4. The micro-MEMS low-pressure piezoresistive pressure sensor according to claim 1, characterized in that: The silicon wafer (1) is an SOI silicon wafer, comprising: A top silicon layer (101), the surface of which is lightly doped to form the varistor (4), and the beam-membrane structure is formed by etching; A silicon substrate (102) is bonded to the glass base (5) to provide a stable mechanical support; The buried oxide layer (103) is located between the top silicon (101) and the substrate silicon (102) to ensure electrical isolation between the two.

5. A micro-MEMS low-pressure piezoresistive pressure sensor according to claim 4, characterized in that: Bumps are arranged on the bonding surfaces of the silicon substrate (102) and the glass base (5) to enhance the bonding force between the two.

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