Among various types of sensors, pressure sensors have the advantages of small size, light weight, high sensitivity, stability, reliability, low cost, and easy integration.They can be widely used in pressure, height, acceleration, liquid flow, flow rate, liquid level, and pressure. Measurement and control. In addition, it is also widely used in water conservancy, geology, meteorology, chemical industry, medical and health. Because the technology is a combination of planar technology and three-dimensional processing, and is easy to integrate, it can be used to make sphygmomanometers, anemometers, water speed meters, pressure gauges, electronic scales and automatic alarm devices. Pressure sensors have become the most mature, most stable, and most cost-effective type of sensor among all types of sensors. Therefore, the technical personnel engaged in modern measurement and automatic control must understand and familiarize themselves with the development process and development trend of pressure sensors.
Development history of pressure sensors
This stage was mainly marked by the invention of the bipolar transistor in 1947. Since then, this characteristic of semiconductor materials has been widely used. Smith (C.S. Smith) discovered the piezoresistive effect of silicon and germanium in 1945, that is, when an external force acts on a semiconductor material, its resistance will change significantly. A pressure sensor made based on this principle is a strain resistance sheet adhered to a metal film, that is, a force signal is converted into an electrical signal for measurement. The minimum size at this stage is approximately 1 cm.
2. Development stage (1960-1970)
With the development of silicon diffusion technology, technicians select the appropriate crystal orientation on the (001) or (110) crystal plane of silicon to directly diffuse the strain resistance on the crystal plane, and then process it into a concave shape on the back to form a thinner silicon. An elastic diaphragm is called a silicon cup. This form of silicon cup sensor has the advantages of small size, light weight, high sensitivity, good stability, low cost, and easy integration. It has realized a metal-silicon eutectic, which provides the possibility for commercial development.
3. Commercialization stage (1970-1980)
Based on the silicon cup diffusion theory, silicon anisotropic etching technology is applied. The processing technology of diffusion silicon sensors is mainly based on silicon anisotropic etching technology, which has developed into silicon anisotropic processing that can automatically control the thickness of the silicon film. Technologies include V-groove method, auto-stop method of concentrated boron, auto-stop method of anodizing method, and micro-computer controlled auto-stop method. Because multiple surfaces can be etched simultaneously, thousands of silicon pressure films can be produced simultaneously, which realizes an integrated factory processing mode and further reduces costs.
4. The stage of micromachining (1980-present)
The emergence of nanotechnology at the end of the last century has made micromachining processes possible. Through the micro-machining process, the structure-type pressure sensor can be processed by computer control, and its linearity can be controlled in the micron range. This technology can be used to process and etch micron-sized trenches, strips, and films, making the pressure sensor enter the micron stage.
The development trend of pressure sensors
At present, there is a growing demand for small pressure sensors in the market. Such small sensors can work in extremely harsh environments, and require very little maintenance and maintenance. The data collected in various important organs will not affect the normal life of people.
Pressure sensors have been increasingly integrated with other measurement sensors to form measurement and control systems. Integrated systems increase operating speed and efficiency in process control and factory automation.
Due to the emergence of integration, some microprocessors can be added to the integrated circuit, so that the sensor has functions such as automatic compensation, communication, self-diagnosis, and logical judgment.
Another development trend of pressure sensors is expanding from the mechanical industry to other fields, such as automotive components, medical instruments and energy environment control systems.