CN100437117C - Composite beam piezoresistive accelerometer - Google Patents

Abstract

This invention relates to a composite beam pressure drag accelerometer; belong to micro machine electronic technology. This invention solves existing problem of that structure of high g accelerometer can not satisfy characteristic request of first order's high inherent rate, wide frequency response scope and worse shock resistance. this accelerometer includes silica-based support carriage shell, spring beam, quality piece that through spring beam overhung in middle of carriage shell, varistor diffused on tip of spring beam. Silica-based support carriage shell undersurface by electrostatic link glass bottom cap. Quality piece is composed by frame body and quality core that through bridge hooked to frame body.

Description

Composite Beam Piezoresistive Accelerometer

technical field

The invention relates to micro-mechanical electronic technology, in particular to a composite beam piezoresistive accelerometer.

Background technique

Accelerometers are widely used in vibration and shock measurement in aerospace, electronics, automotive and mechanical fields. With the rise of the MEMS industry, accelerometers are gradually developing in the direction of miniaturization and integration. Because the micro accelerometer has the advantages of small size, light weight, low cost, low power consumption, and easy mass production, it has a wide range of military and civilian prospects. Among them, the piezoresistive accelerometer is widely used in the acceleration measurement of the shock environment because of its good linearity, simple peripheral circuit, and strong anti-overload ability. Based on the measurement requirements of different shock environments, high-g accelerometers among piezoresistive accelerometers have received extensive attention.

The structures of existing high-g-value accelerometers include cantilever beam structure, fixed-support beam structure and double-island five-beam structure. The advantage of the cantilever beam structure is its high sensitivity, but its first-order natural frequency is low and its frequency response range is narrow. Large lateral sensitivity; fixed beam structure, the mass block moves up and down like a piston, its first-order natural frequency is much higher than that of the cantilever beam structure, which is beneficial to expand the frequency response range of the accelerometer, and can better eliminate the asymmetric structure The influence of the lateral acceleration in the direction of the beam length, but in the case of the same number of strain resistances in the bridge, its sensitivity is lower than that of the cantilever beam structure; the double-island five-beam structure spreads four piezoresistors for detection in the center On the beam, two parallel to the beam and two perpendicular to the beam are connected to form a Wheatstone bridge. This structure has the same characteristics as the fixed beam structure, but the lateral sensitivity is low, and the frequency response characteristics are between the cantilever beam structure and the fixed beam structure. between structures. In short, the structure of the existing high-g-value accelerometer cannot meet the characteristics of high first-order natural frequency and wide frequency response range; in addition, the impact resistance is poor, and the phenomenon of beam fracture will occur under many harsh conditions, so that the accelerometer invalidated.

Contents of the invention

In order to solve the problem that the structure of the existing high-g accelerometer cannot meet the characteristic requirements of high first-order natural frequency and wide frequency response range, and at the same time, the impact resistance is poor, a composite beam piezoresistive accelerometer is proposed.

The present invention is realized by adopting the following technical solutions: a composite beam piezoresistive accelerometer, comprising a silicon-based support frame, an elastic beam, a mass block suspended in the middle of the silicon-based support frame by the elastic beam, and the end of the elastic beam (stress The largest and linearly changing area) is diffused with piezoresistors, the bottom surface of the silicon-based support frame is bonded with a glass bottom cover through electrostatic bonding technology, and the mass block is composed of the frame body and the mass core block fixed in the frame by connecting beam .

When the mass block is subjected to acceleration in the Z direction, the force on the mass block causes the elastic beam to bend and deform, and the piezoresistor on the elastic beam produces strain, which changes the resistance of the piezoresistor, and the Wheatstone bridge composed of piezoresistor connections Output signal, the acceleration value of Z direction can be detected through signal processing, this process is consistent with the principle of existing piezoresistive accelerometer, and at the same time, between the frame body of the mass block and the mass core block of the present invention also Displacement occurs, and the connecting beam deforms. Therefore, when the mass block is impacted by a high-g inertial force, the frame of the mass block can act as a buffer, so that the overall displacement of the mass block is small, and the inertial force it can withstand is large, so that the anti-overload ability is improved, and it is avoided in harsh conditions. The phenomenon of beam fracture occurs under the structure; at the same time, the first-order natural frequency of the structure is high, and the frequency response range is wide.

Analysis by finite element ANSYS software:

Through data comparison, the frequency of the accelerometer of the present invention is higher in terms of frequency, the frequency response is better, and the frequency response range is wide; and the same force is loaded, the maximum equivalent displacement of the accelerometer of the present invention is smaller, namely Under the same conditions, it can withstand a higher g value and realize the function of resisting high overload.

Compared with the prior art, the present invention adopts a mass block structure with a frame. Under the same inertial force, the frame of the mass block acts as a buffer, so that the overall displacement of the mass block of this structure is smaller, so that It can withstand a higher g value, and has the advantages of high first-order natural frequency and wide frequency response range. The invention adopts a silicon-based substrate, carries out anisotropic etching on the (100) crystal plane by wet etching KOH etchant, controls the etching depth through etching time, and adopts the salient angle compensation technology at the same time to obtain A mass block composed of mass core blocks in the frame; and a beam structure obtained by ICP etching. The processing technologies adopted are all existing known technologies, and those skilled in the art can realize the structure of the accelerometer of the present invention through the existing known processing technologies.

The invention has a reasonable structure, can meet the characteristic requirements of high first-order natural frequency and wide frequency response range, and has high anti-overload capability.

Description of drawings

Fig. 1 is a structural representation of the present invention;

Fig. 2 is the A-A sectional view of Fig. 1;

Fig. 3 is a concrete Wheatstone bridge principle diagram that varistor connection of the present invention forms;

In the figure: 1-silicon-based supporting frame; 2-elastic beam; 3-varistor; 4-glass bottom cover; 5-frame; 6-connecting beam; 7-mass pellet.

Detailed ways

The composite beam piezoresistive accelerometer includes a silicon-based support frame 1, an elastic beam 2, and a mass block suspended in the middle of the silicon-based support frame 1 through 2 elastic beams, and a piezoresistor 3 is diffused at the end of the elastic beam 2, The bottom surface of the silicon-based supporting frame 1 is bonded with a glass bottom cover 4 by electrostatic bonding technology, and the mass block is composed of a frame body 5 and a mass core block 7 fixed in the frame body 5 through a connecting beam 6 .

During specific implementation, it is considered that: 1. The power supply of the Wheatstone bridge circuit is powered by a constant voltage source. If the resistance value is large, the power consumption is small and the temperature is not easy to rise; 2. The resistance value is large, the change is large, and the output The piezoresistor 3 is arranged at the end of the elastic beam 2 , that is, at the intersection of the elastic beam 2 , the proof mass, and the silicon-based support frame 1 . The piezoresistors 3 are connected to form a Wheatstone bridge, and the acceleration in the Z direction is finally obtained according to the output signal of the bridge.

Claims (1)

1. A composite beam piezoresistive accelerometer, comprising a silicon-based support frame (1), an elastic beam (2), and a mass block suspended in the middle of the silicon-based support frame (1) through the elastic beam (2), elastic A piezoresistor (3) is diffused at the end of the beam (2), and a glass bottom cover (4) is bonded to the lower surface of the silicon-based support frame (1) through electrostatic bonding technology, and the feature is that the mass block is formed by the outer frame body (5) and the mass core block (7) fixed in the outer frame body (5) through the connecting beam (6).

Images