The commonly used semiconductor pressure sensor uses N-type silicon wafer as the substrate. Firstly, the silicon wafer is made into an elastic stress-bearing part with a certain geometry. At the stress-bearing part of the silicon wafer, four P-type diffusion resistors are made along different crystal directions, and then a four-arm Wheatstone bridge is formed with these four resistors. Under the action of external force, the changes of resistance values become electrical signals. This wheatstone bridge with pressure effect is the heart of the pressure sensor, which is usually called piezoresistive bridge (as shown in Figure 1). The characteristics of piezoresistive bridge are as follows: ① the resistance values of the four arms of the bridge are equal (all r0); ② The piezoresistive effect of adjacent arms of the bridge is equal in value and opposite in sign; ③ The resistance temperature coefficient of the four arms of the bridge is the same, and they are always at the same temperature. In fig. 1, R0 is the resistance value without stress at room temperature; RT is the change caused by the temperature coefficient of resistance (α) when the temperature changes; Υ Rδ is the change of resistance caused by strain (ε); The output voltage of the bridge is u=I0 Δ Rδ=I0RGδ (constant current source bridge).

Where I0 is constant current source current and e is constant voltage source voltage. The output voltage of the piezoresistive bridge is directly proportional to the strain (ε) and has nothing to do with RT caused by the temperature coefficient of resistance, which greatly reduces the temperature drift of the sensor. The most widely used semiconductor pressure sensor is a sensor for detecting fluid pressure. Its main structure is a capsule made of monocrystalline silicon (as shown in Figure 2). The diaphragm is made into a cup, and the bottom of the cup is the part that bears the external force, and the pressure bridge is made on the bottom of the cup. The ring pedestal is made of the same silicon single crystal material, and then the diaphragm is bonded to the pedestal. This kind of pressure sensor has the advantages of high sensitivity, small volume and solidity, and has been widely used in aviation, space navigation, automation instruments and medical instruments.