CN203606386U - MEMS piezoresistive accelerometer - Google Patents

Abstract

The utility model discloses a MEMS piezoresistive accelerometer, include: the piezoelectric actuator comprises a substrate, a frame, an elastic beam, a main mass block, a branch mass block, an upper sealing cap and a plurality of groups of piezoresistors, wherein the main mass block, the branch mass block, the upper sealing cap and the piezoresistors are suspended in the center of the frame through the elastic beam; the frame is fixed at the upper end of the substrate; the supporting mass block is arranged on the elastic beam and forms a special-shaped elastic beam structure with the elastic beam; a plurality of groups of piezoresistors are arranged in the middle of the elastic beam and at the joint of the elastic beam and the frame; the thicknesses of the main mass block and the elastic beam are equal; the upper sealing cap is fixed on the upper end face of the frame, a groove structure is formed in the upper sealing cap, the main mass block is suspended in the groove, and the main mass block can move freely when sensing inertial force in each direction. The utility model discloses a structure of many elastic beams list main mass piece, the change of the different position stress of dysmorphism elastic beam when experiencing not equidirectional inertial force through a main mass piece has effectively reduced the device volume, has advantages such as sensitivity height, natural frequency height, anti high overload capacity are strong simultaneously.

Description

A MEMS piezoresistive accelerometer

technical field

The utility model relates to the field of MEMS sensors, in particular to a MEMS piezoresistive accelerometer integrated with special-shaped beams and three axes.

Background technique

MEMS accelerometers processed with micro-mechanical electronic technology (MEMS) with silicon as the substrate and packaged with silicon-glass bonding technology can be widely used in vibration and shock measurements in the fields of aviation, electronics, automobiles and machinery. With the rise of the micro-mechanical and electronic technology industry, accelerometers are gradually becoming miniaturized and integrated. Because micro-accelerometers using MEMS processing technology have the advantages of small size, light weight, low cost, low power consumption, and easy mass production, they have certain market value and military and civilian prospects.

Common micro-accelerometer products are single-axis, but micro-inertial systems and other applications often require two-axis or three-axis accelerometers to detect acceleration vectors. If only three single-axis accelerometers are used in combination, there will be accompanying The disadvantages of low vector measurement accuracy and large volume. There have been literature reports on the development of multi-axis micro-accelerometer devices, and the use of piezoelectric principles to study the design of three-axis accelerometers, but the device has the disadvantages of low precision and poor stability; The inertial mass detects the three-axis accelerometer, which has a large volume and does not coincide with the center of mass. Silicon piezoresistive accelerometers have been paid attention to and developed due to their advantages such as good linearity, simple peripheral circuits and strong resistance to high overload, and are widely used in acceleration measurement in shock environments.

At present, there are mainly three ways to realize the piezoresistive three-axis accelerometer. The first one is to assemble three single-axis accelerometers to realize the three-axis measurement function, but the accelerometer realized by this method has a large volume and low vector measurement accuracy. low; the second is to process the three-axis accelerometers on the same chip, and each accelerometer has an independent mass block and cantilever beam structure, but the accelerometers processed in this way are complicated in technology and high in processing costs; the third One is to use the same mass to sense acceleration signals in three directions. When the mass senses acceleration in different directions, the resistance values of resistors at different positions will change, so that the Wheatstone bridge composed of resistors The output voltage of the sensor changes, and then the magnitude and direction of the acceleration are detected. The piezoresistive accelerometers realized by these three methods have their own advantages and disadvantages. For the third realization method, the existing single-mass eight-cantilever beam structure has high sensitivity in the vertical axis and low sensitivity in the two horizontal axes. The degree of lateral coupling is high. the

Contents of the invention

The purpose of the utility model is to provide a MEMS piezoresistive accelerometer in order to solve the technical problems of the existing piezoresistive three-axis accelerometer with large volume, complex structure, high coupling degree between axes and large sensitivity difference between different axes. type accelerometer.

In order to achieve the above object, the technical solution adopted by the utility model is: a MEMS piezoresistive accelerometer is provided, including: a substrate, a frame 3, an elastic beam 2 and a main body suspended at the center of the frame 3 by elastic beams 2 Quality block 1, support mass, upper sealing cap 5, multiple groups of piezoresistors; the frame 3 is fixed on the upper end of the substrate, and the frame 3 is used to fix the elastic beam 2 and the main mass 1; the support mass 4 is arranged on the elastic beam 2, and forms a special-shaped elastic beam structure with the elastic beam 2. This structure realizes that when subjected to the inertial force of the x-axis or y-axis, the bending deformation of the elastic beam 2 is larger, thereby improving the x-axis and y-axis The sensitivity of the y-axis; the middle part of the elastic beam 2 and the connection between the elastic beam 2 and the frame 3 are provided with multiple sets of piezoresistors for sensing three vertical axial inertial forces, and the piezoresistors on each axis are connected Constitute a Wheatstone bridge; the thickness of the main mass block 1 is equal to that of the elastic beam 2, so that the center of mass of the main mass block 1 moves up, and the distance from the middle surface of the elastic beam 2 is reduced, so when feeling the inertial forces in different directions, the main The displacement of the mass block 1 is small, and the MEMS piezoresistive accelerometer of the utility model can bear the inertial force of a higher gravitational acceleration g value, so it has good anti-high overload capability; the upper sealing cap 5 is fixed on the upper end surface of the frame 3 , there is a groove structure inside, and the main mass 2 is suspended inside the groove, and moves freely when sensing inertial forces in various directions.

Wherein: the main mass 1 has a centrally symmetrical shape, and a non-centrosymmetrically shaped main mass will cause unnecessary troubles in the connection with the elastic beam, the arrangement of the piezoresistor and the processing technology.

Wherein: for the convenience of preparation, the main mass 1 adopts a square shape which is convenient for processing, and elastic beams 2 perpendicular to each other are respectively arranged on two sets of opposite sides of the square.

Wherein: two elastic beams 2 are arranged on each side of the square main mass 1; the two elastic beams 2 are connected together by the support mass.

Wherein: the main mass block 1 is located on the xy plane, and two groups of opposite elastic beams 2 are perpendicular to each other along the x-axis and the y-axis respectively; the elastic beams 2 along the x-axis are provided with supporting masses that feel the inertial force of the y-axis Block 4, and the piezoresistor that senses the inertial force of the y-axis, the piezoresistor on the x-axis is connected to form a Wheatstone bridge; the elastic beam 2 along the y-axis is provided with a sensor that feels the inertial force of the x-axis The supporting mass 4, and the piezoresistor for sensing the inertial force in the x direction, the piezoresistors on the y-axis are connected to form a Wheatstone bridge.

Wherein: the elastic beam 2 is provided with a through hole 6 for obtaining critical damping.

Wherein: the substrate and the upper sealing cap 5 are made of glass material, and the main mass 1 , elastic beam 2 , frame 3 and support mass 4 are made of silicon material.

The beneficial effects of the utility model are: the utility model adopts the structure of a plurality of elastic beams with a single main mass block, and a support mass block is added on the elastic beam to form a special-shaped elastic beam. The bending deformation of the beam is larger, so the sensitivity of the x-axis and y-axis is improved; when the inertial force in different directions is felt by a main mass, the stress changes at different positions of the special-shaped elastic beam, and the sensors arranged on the elastic beam are different. Multiple groups of piezoresistors with directional inertial force are connected to form a Wheatstone bridge to detect accelerations in different directions, thus effectively reducing the size of the device. By determining the relative position of the elastic beam and the main mass block and the The determination of the shape, thickness and width of the utility model has the advantages of high sensitivity, high natural frequency and strong resistance to high overload.

Description of drawings

Fig. 1 is a structural schematic diagram (a) of the realization mode of a MEMS piezoresistive accelerometer of the utility model.

Fig. 2 is a structural schematic diagram (b) of the realization mode of a MEMS piezoresistive accelerometer of the utility model.

Fig. 3 is a structural schematic diagram (c) of a realization mode of a MEMS piezoresistive accelerometer of the present invention.

Fig. 4 is a structural schematic diagram of an upper sealing cap of a MEMS piezoresistive accelerometer of the present invention.

Fig. 5 is a structural schematic diagram of Embodiment 1 of the present utility model.

Fig. 6 is a schematic diagram of the connection of the piezoresistor according to Embodiment 1 of the present invention.

FIG. 7 is a circuit diagram of a Wheatstone bridge formed by connecting piezoresistors for sensing y-axis inertial force arranged on an elastic beam along the x-axis in Embodiment 1 of the present utility model.

8 is a circuit diagram of a Wheatstone bridge formed by connecting piezoresistors for sensing x-axis inertial force arranged on elastic beams along the y-axis in Embodiment 1 of the present utility model.

FIG. 9 is a circuit diagram of a Wheatstone bridge formed by connecting piezoresistors for sensing z-axis inertial force in Embodiment 1 of the present invention.

Drawings: 1 - main mass block, 2 - elastic beam, 3 - frame, 4 - mass block, 5 - upper sealing cap, 6 - through hole.

Detailed ways

The utility model is described in detail below in conjunction with accompanying drawing and embodiment.

A MEMS piezoresistive accelerometer of the utility model includes: including: a substrate, a frame 3, an elastic beam 2, and a main mass 1 suspended at the center of the frame 3 by elastic beams 2, a supporting mass 4, and an upper sealing cap 5. Multiple groups of piezoresistors; the frame 3 is fixed on the upper end of the substrate, the frame 3 is used to fix the elastic beam 2 and the main mass 1; the support mass 4 is arranged on the elastic beam 2, and is connected with the elastic The beam 2 forms a special-shaped elastic beam structure, and this structure realizes that when subjected to the inertial force of the x-axis or the y-axis, the bending deformation of the elastic beam 2 is larger, thereby improving the sensitivity of the x-axis and the y-axis; the elastic beam 2 The middle part and the connection between the elastic beam 2 and the frame 3 are provided with multiple sets of piezoresistors for sensing three vertical axial inertial forces, and the piezoresistors in each axial direction are connected to form a Wheatstone bridge; the main mass 1 is equal to the thickness of the elastic beam 2, so that the center of mass of the main mass 1 moves up, and the distance from the middle surface of the elastic beam 2 is reduced, so the displacement of the main mass 1 is small when feeling inertial forces in different directions. The MEMS piezoresistive accelerometer can withstand the inertial force of a higher gravitational acceleration g value, so it has a good anti-high overload capability; the upper sealing cap 5 is fixed on the upper end surface of the frame 3, and there is a groove structure inside it. The mass block 2 is suspended inside the groove, and moves freely when sensing inertial forces in various directions.

The main mass 1 has a symmetrical shape to the center. Referring to Figures 1-3, there are three different implementations in which the main mass 1 is circular, square and hexagonal respectively, and the sides of the main mass 1 are provided with mutually perpendicular elastic beams 2 connecting frames 3 . Two elastic beams 2 are used as a group to connect the main mass 1 and the frame 3 in four directions on the side of the main mass 1 .

The main mass block 1 is located on the xy plane, and two sets of opposite elastic beams 2 are perpendicular to each other along the x-axis and the y-axis respectively; the elastic beams 2 along the x-axis are provided with a support mass 4 that feels the inertial force of the y-axis , and the piezoresistor for sensing the inertial force of the y-axis, the piezoresistors on the x-axis are connected to form a Wheatstone bridge; the elastic beam 2 along the y-axis is provided with a supporting mass that feels the inertial force of the x-axis Block 4, and piezoresistors for sensing inertial forces in the x-direction, the piezoresistors on the y-axis are connected to form a Wheatstone bridge. When the main mass 1 is subjected to the inertial force of the x-axis or y-axis, because the force of the x-axis or y-axis will make the main mass 1 basically maintain the original position, so the main mass 1 is equivalent to the special-shaped elastic The other fixed end point of the beam.

Elastic beams 2 are respectively arranged in four directions on the side of the main mass block. If an elastic beam 2 is respectively arranged in each direction, the problem of drift of the zero point position is prone to occur. In order to avoid the drift of the zero point position, the elastic The beam 2 is made very wide, which will inevitably increase the mass of the elastic beam 2, and a large mass will lead to a decrease in sensitivity. In order to solve the above-mentioned technical problems, we set two elastic beams 2 in each direction inside the frame 3, thereby avoiding the problem of drifting of the zero point position and ensuring the sensitivity at the same time. If more than three elastic beams 3 are arranged in each direction, although the problem of zero position drift can also be avoided, the large mass will lead to a decrease in sensitivity. Therefore, preferably, two elastic beams 2 are used in each direction.

Example 1

Referring to Figures 4-5, in this embodiment, the main mass 1 adopts a square shape that is easy to process, and two elastic beams 2 are respectively arranged in four directions on the sides of the square, and two elastic beams 2 on each side 2 is provided with a support mass 4 to connect the two elastic beams 2; the middle part of the elastic beam 2 and the connection between the elastic beam 2 and the frame 3 are provided with piezoresistors R1~ for sensing inertial forces in different directions R24, the elastic beam 2 is provided with a through hole 6; the material of the substrate and the upper cap 5 is glass, and the main mass 1, the elastic beam 2, the frame 3 and the supporting mass 4 are made of silicon; the lining The main mass 1 connected to the elastic beam 2 and the frame 3 are sealed between the bottom and the upper cap 5 through electrostatic bonding, forming a glass-silicon-glass sandwich structure. The overall size is 5000μm × 5000μm × 1400μm; the size of each elastic beam is 1000μm × 200μm × 200μm; the size of the main mass 1 is 600μm × 600μm × 200μm, the main mass 1, multiple elastic beams 2, frame 3 N(100) is selected for the silicon of the supporting mass 4, and Pyrex 7740 is selected for the glass of the substrate and the upper sealing cap 5.

Referring to FIG. 6 , the main mass 1 is located on the xy plane, and the elastic beams 2 on two sets of opposite sides are perpendicular to each other along the x-axis and y-axis respectively. Referring to Fig. 7, the elastic beam 2 along the x-axis is provided with a support mass 4 for sensing the inertial force of the y-axis, including R7, R9, R10, R12, R19, R21, R22 and R24, and connected to form a Wheatstone electric Bridge; with reference to Fig. 8, on the elastic beam 2 along x-axis, be provided with the piezoresistor that senses the inertial force of y-axis, comprise resistance R1, R3, R4, R6, R13, R15, R16 and R18, and connect to form Wheatstone bridge; with reference to Figure 9, piezoresistors for sensing the inertial force of the z-axis are respectively arranged on each elastic beam, including resistors R2, R5, R8, R11, R14, R17, R20 and R23, and connected form a Wheatstone bridge.

The working process of the utility model is: when subjected to the inertial force of the x-axis, the support mass 4 arranged on the elastic beam 2 along the y-axis will produce a large deformation, thereby causing a pressure-sensitive sensor to sense the inertial force of the x-axis The resistance value of the resistance changes, thereby measuring the acceleration of the x-axis; when subjected to the inertial force of the y-axis, the support mass 4 arranged on the elastic beam 2 along the x-axis will produce a large deformation, thereby causing the sensing of the y-axis The resistance value of the piezoresistor of the inertial force changes, thereby measuring the acceleration of the y-axis; when the main mass 1 senses the inertial force of the z-axis perpendicular to its surface, the main mass 1 will move along the z-axis, so that It will cause the resistance value of the piezoresistor sensing the inertial force of the z-axis at the joint between the elastic beam 2 and the frame 3 to change, thereby measuring the acceleration of the z-axis.

The preparation method of a kind of MEMS piezoresistive accelerometer of the utility model comprises the following steps:

Step 1: Process a P-type varistor on a silicon substrate by ion implantation;

Step 2: form the main mass 1, the elastic beam 2, the through hole 6 on the elastic beam 2, the support mass 4 and the frame 3 by using potassium hydroxide KOH wet etching process and ICP deep etching process respectively on the silicon substrate;

Step 3: Metal connection of the Wheatstone bridge formed by the varistor by sputtering process;

Step 4: The upper sealing cap 5 is corroded to form grooves, and the frame 3 is electrostatically bonded to the upper sealing cap 5 using a silicon-glass electrostatic bonding process, and then the lower bottom surface of the frame 3 is electrostatically bonded to the substrate. Complete the overall structural processing of the MEMS piezoresistive accelerometer of the utility model.

The electrostatic bonding between the lower end surface of the frame 3 and the substrate forms the protective base of the entire utility model, which protects the MEMS piezoresistive accelerometer of the utility model.

The above content is a further detailed description of the utility model in combination with the preferred technical solutions, and it cannot be determined that the specific implementation of the utility model is limited to these descriptions. For a person of ordinary skill in the technical field to which the utility model belongs, on the premise of not departing from the concept of the utility model, simple deduction and replacement can also be made, which should be regarded as the protection scope of the utility model. the

Claims (7)

1. a MEMS piezoresistive accelerometer, comprising: substrate, frame (3), elastic beam (2) and be suspended from the parenchyma gauge block (1) of frame (3) center by elastic beam (2); Described frame (3) is fixed on substrate upper end; It is characterized in that: described a kind of MEMS piezoresistive accelerometer also comprises: prop up mass (4), upper sealing cap (5), organize voltage dependent resistor (VDR) more; It is upper that described mass (4) is arranged at elastic beam (2), and form special-shaped elastic beam structure with elastic beam (2); The middle part of described elastic beam (2) and elastic beam (2) and framework (3) junction are provided with many groups voltage dependent resistor (VDR) of three vertical axial inertial force of sensing, and each voltage dependent resistor (VDR) on axially connects and composes Wheatstone bridge; Described parenchyma gauge block (1) equates with the thickness of elastic beam (2); Described upper sealing cap (5) is fixed on framework (3) upper surface, its inner fluted structure, and described parenchyma gauge block (2) is unsettled in inside grooves, and free movement in the time of the inertial force of sensing all directions.

2. a kind of MEMS piezoresistive accelerometer according to claim 1, is characterized in that: the shape of symmetry centered by described parenchyma gauge block (1).

3. a kind of MEMS piezoresistive accelerometer according to claim 1 and 2, is characterized in that: described parenchyma gauge block (1) adopts square, is respectively equipped with mutually perpendicular elastic beam (2) on square two groups relative sides.

4. a kind of MEMS piezoresistive accelerometer according to claim 3, is characterized in that: on each side of described square parenchyma gauge block (1), two elastic beams (2) are set respectively; Described mass (4) links together two elastic beams (2).

5. a kind of MEMS piezoresistive accelerometer according to claim 1, is characterized in that: described parenchyma gauge block (1) is positioned at xy plane, two groups of relative elastic beams (2) are orthogonal along x axle and y axle respectively; On the described elastic beam along x axle (2), be provided with a mass (4) of the inertial force of experiencing y axle, and the voltage dependent resistor (VDR) of the inertial force of sensing y axle, the voltage dependent resistor (VDR) on described x axle connects and composes Wheatstone bridge; On the elastic beam along y axle (2), be provided with a mass (4) of the inertial force of experiencing x axle, and the voltage dependent resistor (VDR) of the inertial force of sensing x direction, the voltage dependent resistor (VDR) on described y axle connects and composes Wheatstone bridge.

6. a kind of MEMS piezoresistive accelerometer according to claim 2, is characterized in that: described elastic beam (2) is provided with through hole (6).

7. a kind of MEMS piezoresistive accelerometer according to claim 1, is characterized in that: described substrate and upper sealing cap (5) are glass material, and described parenchyma gauge block (1), elastic beam (2), framework (3) and a mass (4) are silicon materials.

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