Pressure sensor is a kind of equipment used to detect pressure signals and convert pressure signals into electrical signals according to certain rules, which are widely used in various production, industry and aerospace fields. With the subdivision of application fields, pressure measurement in high-temperature and harsh environments such as high-temperature oil wells and various engine cavities is becoming more and more important, and the data used in general pressure sensors will fail when they exceed a certain temperature, resulting in pressure measurement failure. Therefore, high-temperature pressure sensors have become a very important research direction.
Classification of High Temperature Pressure Sensors:
According to the different materials used, high-temperature pressure sensors can be divided into polycrystalline silicon (Poly-Si) high-temperature pressure sensors, SiC high-temperature pressure sensors, SOI (silicon on insulator) high-temperature pressure sensors, SOS (silicon on sapphire) silicon-sapphire pressure sensors, optical fiber high-temperature pressure sensors and other different types. Judging from the current development status, the research status and prospects of SOI high-temperature pressure sensors are very ambitious. The following is a first introduction to SOI high-temperature pressure sensors.
The development of SOI high-temperature pressure sensor mainly relies on the drum of SOI data. SOI refers to the semiconductor material composed of SiO2 as the insulating layer embedded in the center of the Si lining layer and the Si top equipment layer. The special structure of SOI makes the insulation between the equipment layer and the lining layer complete, eliminating the door latch effect common in bulk silicon, and improving the reliability of the equipment. In addition, due to the high-temperature characteristics of the SOI device layer, it is an aspirational data for the fabrication of high-temperature pressure sensors.
In principle, SOI high-temperature pressure sensors primarily use the piezoresistive effect of monocrystalline silicon. When the force is applied to the silicon crystal, the crystal lattice is deformed, which in turn causes the mobility of the carriers to change, which makes the resistivity of the silicon crystal change. After etching 4 varistors in a specific direction of the top equipment layer of the SOI, the Wheatstone bridge is formed; A pressure back cavity is etched into the lining layer of the SOI to form a pressure-sensitive structure.
Preparation process of SOI high-temperature pressure sensor
The fabrication process of SOI high-temperature pressure sensor involves multiple MEMS processes, including varistor preparation, metal lead preparation, pressure sensitive film preparation and pressure cavity encapsulation.
The key to the preparation of varistors lies in the control of doping concentration and the optimization of the subsequent etching molding process. The metal lead layer is primarily used to connect the Wheatstone bridge; The preparation of pressure-sensitive membranes mainly relies on the deep silicon etching process; The packaging of the pressure chamber usually varies depending on the use of the pressure sensor, and the two possible packaging forms are presented here.
Since the current commercial high-temperature pressure sensors cannot well meet the needs of pressure measurement in particularly harsh environments such as high-temperature oil wells and aero engines, the research on high-temperature pressure sensors in the future has become a must.
Due to its special structure and high temperature characteristics, SOI data has become the aspiration data of high-temperature pressure sensors, and the future research on SOI high-temperature pressure sensors should focus on dealing with the long-term stability of sensors in high-temperature harsh environments, self-heating problems and improving the accuracy of pressure sensors.
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