The pressure sensor is the most widely used sensor. The traditional pressure sensor is mainly based on a mechanical structure type device, and the deformation of the elastic element is used to indicate the pressure, but this structure has a large size and light weight, and cannot provide an electrical output. With the development of semiconductor technology, semiconductor pressure sensors also came into being. It is characterized by small size, light weight, high accuracy and good temperature characteristics. In particular, with the development of MEMS technology, semiconductor sensors are developing toward miniaturization, and their power consumption is small and their reliability is high. The sensitive element of a silicon capacitive pressure sensor is a semiconductor thin film, which can be made of single crystal silicon, polycrystalline silicon, etc. Made. A typical capacitive sensor consists of upper and lower electrodes, an insulator, and a substrate. When the membrane is subjected to pressure, the membrane will deform to a certain extent. Therefore, the distance between the upper and lower electrodes changes to a certain extent, thereby changing the capacitance. However, the relationship between the capacitance of the capacitive pressure sensor and the distance between the upper and lower electrodes is a non-linear relationship. Therefore, a measurement circuit with a compensation function should be used to compensate the output capacitance nonlinearly. Since the high-temperature pressure sensor works in a high-temperature environment, the compensation circuit will be affected by the ambient temperature, thereby generating a large error. The high-temperature pressure sensor based on model identification is designed to avoid large errors caused by the compensation circuit working in a high-temperature environment. The design scheme is to separate the sensor device from the amplifier circuit and obtain the pressure of the measured environment through model identification. The temperature in the high-temperature working area can reach 350 ℃. The sensor device is composed of platinum resistance and capacitive pressure sensor. The MEMS process is as follows:
The high-temperature pressure sensor is composed of a silicon diaphragm, a substrate, a lower electrode, and an insulating layer. The lower electrode is located on the thickly supported substrate. An insulating layer is evaporated on the electrode. The silicon membrane is formed by etching the front and back of a silicon wafer using anisotropic etching technology. The gap between the upper and lower electrodes is determined by the etching depth of the silicon wafer. The silicon diaphragm and the substrate are bonded together using bonding technology to form a silicon diaphragm capacitive pressure sensor with certain stability [2]. Because platinum resistance is high-temperature resistant and sensitive to temperature, platinum resistance is used, which can be used as an ordinary resistance or as a temperature sensor to detect the temperature of the measured environment. The parameters of metal platinum resistance and silicon diaphragm are: platinum resistance value is 1000Ω at 0 ℃; resistivity is 1.0526316 × 10-5Ω · cm; density is 21440kg / m3; specific heat is 132.51J / (kg · K), fusing The temperature is 1769 ℃, so the platinum resistance can be processed to a width of 0.02mm; a thickness of 0.2μm; a total length of 3800μm, made in a zigzag shape, and can work normally under a step signal with an amplitude of 10V. The gap between the upper and lower electrodes of the capacitive pressure sensor is 3 μm, the radius of the upper and lower electrodes of the circular plate capacitor is 73 μm, and the capacitance value is 50 pF.
The high temperature pressure sensor is designed to measure the pressure of various gases and liquids in a high temperature environment. It is mainly used to measure the pressure in boilers, pipelines, high-temperature reaction vessels, downhole pressure and pressure in various engine cavities, high-temperature oil level and detection, oil well pressure measurement and other fields. At present, the researched high-temperature pressure sensors are mainly SOS, SOI, SiO2, Poly2Si and other semiconductor sensors, as well as sputtered alloy thin film high-temperature pressure sensors, high-temperature optical fiber pressure sensors and high-temperature capacitive pressure sensors. Compared with piezoresistive pressure sensors, semiconductor capacitive pressure sensors have high sensitivity, good temperature stability, low power consumption, and are only sensitive to pressure and insensitive to stress. Therefore, capacitive pressure sensors are widely used in many fields.