Research status and development trend of pressure sensor
Sensor technology is one of the important technologies of modern measurement and automation systems, from the development of the universe to the seabed exploration, from the production process control to modern civilized life, almost every technology is inseparable from the sensor, therefore, many countries attach great importance to the development of sensor technology, such as Japan’s sensor technology as six core technologies (computer, communication, laser, semiconductor, super Conductors and sensors). In all kinds of sensors, the pressure sensor has the advantages of small size, light weight, high sensitivity, stable and reliable, low cost, easy integration, and can be widely used in the measurement and control of pressure, height, acceleration, liquid flow rate, liquid level, pressure. 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 process and three-dimensional processing, and easy to integrate, it can be used to make blood pressure meters, anemometers, water velocity meters, pressure gauges, electronic weighing and automatic alarm devices. Pressure sensor has become a kind of sensor with the most mature technology, the most stable performance and the highest cost performance. Therefore, professional technicians engaged in modern measurement and automatic control must understand and be familiar with the research status and development trend of pressure sensors at home and abroad.
1. Development history of pressure sensor
Modern pressure sensors are marked by the invention of semiconductor sensors, the development of which can be divided into four stages [1] :
(1) Invention stage (1945-1960) : This stage is mainly marked by the invention of the bipolar transistor in 1947. Since then, this property of semiconductor materials has been widely used. C.S. Smith (1945) discovered the piezoresistive effect of silicon and germanium [2], that is, when an external force acts on a semiconductor material, its resistance will change significantly. According to this principle, the pressure sensor is made by sticking the strain resistor on the metal film, that is, the force signal is converted into an electrical signal for measurement. The minimum size at this stage is approximately 1cm.
(2) Technical development stage (1960-1970) : With the development of silicon diffusion technology, technicians selected the appropriate crystal direction of the silicon (001) or (110) crystal face to directly diffuse the strain resistance on the crystal face, and then processed into a concave shape on the back side to form a thin silicon elastic film, called the silicon cup [3]. This form of silicon cup sensor has the advantages of small size, light weight, high sensitivity, good stability, low cost and easy integration, and realizes metal-silicon eutectic, which provides the possibility for commercial development.
(3) Commercial integrated processing stage (1970-1980) : The anisotropic corrosion technology of silicon was applied on the basis of the silicon cup diffusion theory. The processing technology of the diffused silicon sensor was mainly based on the anisotropic corrosion technology of silicon, and developed into a silicon anisotropic processing technology that can automatically control the thickness of silicon film [4], mainly including V Form groove method, concentrated boron automatic stop method, anodic oxidation automatic stop method and microcomputer control automatic stop method. Since corrosion can be carried out on multiple surfaces at the same time, thousands of silicon pressure films can be produced at the same time, achieving an integrated factory processing model and further reducing costs.
(4) Micromachining stage (1980-present) : The emergence of nanotechnology at the end of the last century made micromachining processes possible.
The structural pressure sensor can be machined by computer control through micromachining technology, and its linearity can be controlled in the range of microns. This technology can be used to process and etch micron-level grooves, strips and films, making the pressure sensor enter the micron stage.