Current MEMS pressure sensors are silicon piezoresistive pressure sensors and silicon capacitive pressure sensors, both of which are MEMS sensors generated on silicon wafers.
The silicon piezoresistive pressure sensor uses a high-precision semiconductor resistance strain gauge to form a Wheatstone bridge as a power conversion measurement circuit, which has high measurement accuracy, low power consumption, and extremely low cost. The piezoresistive sensor of the Wheatstone bridge, if there is no pressure change, has zero output and consumes almost no electricity. Its electrical principle is shown in Figure 1. The lithographic version of the strain gauge bridge of the silicon piezoresistive pressure sensor is shown in Fig. 2.
Figure 1 Wheatstone bridge electrical principle
Figure 2 Lithographic version of the strain gage bridge
The MEMS silicon piezoresistive pressure sensor adopts the inner wall of a circular stress cup silicon film fixed around the periphery, and uses MEMS technology to directly inscribe four high-precision semiconductor strain gauges at the maximum surface stress, forming a Wheatstone measuring bridge as a force. The electric conversion measuring circuit directly converts the physical quantity of pressure into electric quantity, and the measuring precision can reach 0.01%~0.03%FS. The structure of the silicon piezoresistive pressure sensor is shown in Fig. 3. The upper and lower layers are glass bodies, the middle is silicon wafer, and the middle part of the silicon wafer is made into a stress cup. The upper part of the stress silicon film has a vacuum chamber, which makes it a typical absolute pressure. Pressure Sensor. The surface of the stress silicon film in contact with the vacuum chamber is photolithographically generated to form a resistance strain gauge bridge circuit as shown in FIG. When the external pressure enters the sensor stress cup through the pressure guiding cavity, the stress silicon film will slightly bulge upward due to the external force, and elastic deformation will occur. The four resistance strain gauges will change resistance and destroy the original Wheatstone electric. The bridge circuit is balanced to produce a voltage signal whose bridge output is proportional to the pressure. Figure 4 is a photograph of a physical picture of a silicon piezoresistive pressure sensor such as an IC.
MEMS piezoresistive silicon pressure sensor
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Figure 3 Silicon piezoresistive pressure sensor structure
Figure 4 Silicon piezoresistive pressure sensor
MEMS capacitive pressure sensorThe capacitive pressure sensor uses MEMS technology to create a transverse grid on the silicon wafer. The upper and lower horizontal barriers form a set of capacitive pressure sensors. The upper horizontal barrier is displaced downward by pressure, changing the upper and lower diaphragms. The spacing of the grids also changes the amount of capacitance between the plates, ie, Δ pressure = Δ capacitance. The capacitive pressure sensor is shown in the figure.
Figure 5 Capacitive pressure sensor structure 
Figure 6 capacitive pressure sensor
MEMS pressure sensor applicationMEMS pressure sensors are widely used in automotive electronics: such as TPMS (tire pressure monitoring system), engine oil pressure sensor, automotive brake system air pressure sensor, automotive engine intake manifold pressure sensor (TMAP), diesel common rail pressure sensor; consumer electronics , such as tire pressure gauge, sphygmomanometer, cabinet scale, health scale, washing machine, dishwasher, refrigerator, microwave oven, oven, pressure sensor for vacuum cleaner, washing machine, water dispenser, dishwasher, solar water heater liquid level control pressure Sensors; industrial electronics, such as digital pressure gauges, digital flow meters, industrial batch weighing, etc.
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