The pressure sensor is the most widely used sensor. Traditional pressure sensors are mainly mechanical structural devices, and use the deformation of elastic elements to indicate pressure, but this kind of structure is large in size and light in weight, and cannot provide electrical output. With the development of semiconductor technology, semiconductor pressure sensors have also emerged. Its characteristics are small size, light weight, high accuracy and good temperature characteristics. Especially with the development of MEMS technology, semiconductor sensors are developing towards miniaturization, with low power consumption and high reliability.
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 chambers, high temperature oil level and detection, oil well pressure measurement and other fields. At present, the most researched high temperature pressure sensors mainly include SOS, SOI, SiO2, Poly2Si and other semiconductor sensors, as well as sputtered alloy 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 higher sensitivity, better temperature stability, lower power consumption, and are only sensitive to pressure, but not sensitive to stress. Therefore, capacitive pressure sensors are widely used in many fields.
1 The basic composition and manufacturing process of the device
The sensitive element of the silicon capacitive pressure sensor is a semiconductor thin film, which can be made of monocrystalline silicon, polycrystalline silicon, etc. using semiconductor technology. A typical capacitive sensor consists of upper and lower electrodes, an insulator and a substrate. When the membrane is under pressure, the membrane will deform to a certain extent. Therefore, the distance between the upper and lower electrodes will change to a certain extent, which will change 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 measuring circuit with a compensation function should be used to perform non-linear compensation for the output capacitance. Because the high-temperature pressure sensor works in a high-temperature environment, the compensation circuit will be affected by the ambient temperature, resulting in larger errors. The high-temperature pressure sensor based on model recognition 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 recognition. The temperature in the high temperature working area can reach 350℃. The sensor is composed of platinum resistance and capacitive pressure sensor.
The high temperature pressure sensor is composed of a silicon diaphragm, a substrate, a lower electrode and an insulating layer. The bottom electrode is located on the thickly supported substrate. An insulating layer is evaporated on the electrode. The silicon diaphragm is formed by etching from the front and back sides 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 by bonding technology to form a silicon diaphragm capacitive pressure sensor with certain stability [2]. Since platinum resistance is high temperature resistant and sensitive to temperature, platinum resistance can be used as an ordinary resistance, but also can be used as a temperature sensor to detect the temperature of the measured environment.