Principle And Structure of Shock Acceleration Sensor

Principle And Structure of Shock Acceleration Sensor

With the rapid development of silicon micro-mechanical technology (MEMS), a variety of devices based on MEMS technology have emerged. At present, pressure sensors, impact acceleration sensors, optical switches and so on are widely used. With the characteristics of small size, light weight, low cost, low power consumption, high reliability, and its processing process has a certain compatibility with the traditional integrated circuit process, easy to realize the digitalization, intelligence and mass production, it has attracted widespread attention since its emergence, and has been rapidly applied in the fields of automotive, medicine, navigation and control, biochemical analysis, and industrial testing. Among them, shock acceleration sensor is one of the widely used examples. The principles of shock acceleration sensors vary depending on the application, including piezoresistive, capacitive, piezoelectric, resonant, and so on.

By introducing the principle, manufacturing process and application of different shock acceleration sensors, they will have a more comprehensive understanding of shock acceleration sensors.

The sensing element of a MEMS piezoresistive shock acceleration sensor consists of an elastic beam, a mass block and a fixed frame. The piezoresistive shock acceleration sensor is essentially a force sensor. It measures the acceleration a by measuring the force generated by the fixed mass under the action of acceleration F. At the current scale of research, it can be assumed that the basic principle still follows Newton's second law. In other words, the inertial mass of the sensor will generate an inertial force: F=ma when the acceleration a is applied to the sensor.When the inertial force F is applied to the elastic beam of the sensor, it generates a strain proportional to F. When the inertial force F is applied to the elastic beam of the sensor, it generates a strain proportional to F. At this time, the varistor on the elastic beam will also produce changes △ R, the Wheatstone bridge composed of varistors output voltage signals proportional to the voltage.

Piezoresistive accelerometer principle: The signal detection circuit of the system adopts piezoresistive full bridge as the signal detection circuit.

The bridge is powered by a constant voltage source and the bridge voltage is. If it is a positive strain resistor and a negative strain resistor, the output expression of the bridge is:

We ensure the consistency of the piezoresistors in the resistor layout design and manufacturing process.Therefore, it can be assumed that certain variations of the piezoresistor and the variations of the piezoresistor are equivalent.

The expression of the bridge output then becomes:

Sensitivity principle: The piezoresistive signal detection principle is used, the core of which is the piezoresistive effect of semiconductor materials. Piezoresistive effect is a material property that changes the volume resistivity of a material when it is subjected to external mechanical stress. The deformation of the crystal structure destroys the energy band structure, changes the electron mobility and carrier density, and alters the resistivity or conductivity of the material. When a metal resistance wire is unstrained, the original resistance value is: resistivity of the wire; length of the wire; cross-sectional area of the wire.

When a resistance wire is stretched, it elongates, the cross-sectional area decreases accordingly, and the resistivity changes due to lattice deformation and other factors, so the resistance value changes. For the total differential expressed as a relative change, there are piezoresistive coefficients Commonly used semiconductor resistance materials are silicon and germanium. Doping impurities can form p-type or n-type semiconductors. The piezoresistive effect is a change in the lattice arrangement of atoms in response to an external force, which causes changes in carrier mobility and concentration.

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