Piezoresistive sensor
After the solid is subjected to a force, the resistivity will change. This effect is called the piezoresistive effect. This effect of semiconductor materials is particularly strong. There are two types of piezoresistive sensors made of semiconductor materials: one is a sticky strain gauge made of the bulk resistance of a semiconductor material; the other is a diffusion resistor made of an integrated circuit process on a semiconductor material substrate , Said diffusion type piezoresistive sensor. The piezoresistive sensor has a large sensitivity coefficient and high resolution. High frequency response and small size. It is mainly used to measure pressure, acceleration and load parameters.
Because semiconductor materials are very sensitive to temperature, the temperature error of piezoresistive sensors is relatively large, and temperature compensation is necessary.
Composition of piezoresistive pressure sensor
Piezoresistive pressure sensors are also called solid-state pressure sensors. They are different from sticky strain gauges that need to sense external force indirectly through elastic sensitive elements, but directly sense the pressure to be measured through a silicon diaphragm. One side of the silicon diaphragm is a high-pressure chamber connected with the pressure to be measured, and the other side is a low-pressure chamber connected with the atmosphere.
The silicon diaphragm is generally designed into a circular shape with a fixed periphery, with a diameter to thickness ratio of about 20-60. Four P dye resistance strips are diffused in the N-type localized circular silicon diaphragm and connected to form a full bridge. Two of them are located in the compressive stress zone and the other two are located in the tensile stress zone, symmetrical with respect to the center of the diaphragm. The silicon cylindrical sensitive element is also diffused in a certain direction of a certain crystal plane of the silicon cylindrical surface to make resistance strips. Two resistance strips under tensile stress and the other two resistance strips under compressive stress form a full bridge.
There are many types of pressure sensors, such as resistance strain gauge pressure sensors, semiconductor strain gauge pressure sensors, piezoresistive pressure sensors, inductive pressure sensors, capacitive pressure sensors, resonant pressure sensors and capacitive acceleration sensors. But the most widely used is the piezoresistive pressure sensor, which has a very low price, high accuracy and good linearity. This sensor adopts an integrated process to integrate the resistance bar on the monocrystalline silicon diaphragm to form a silicon piezoresistive chip, and the periphery of the chip is fixed and packaged in the shell, and the electrode leads are drawn out.
The piezoresistive pressure sensor is mainly composed of a silicon cup diaphragm and a shell fixed on the silicon cup. There are low-pressure chambers and high-pressure chambers above and below the silicon diaphragm, the high-pressure chamber is connected to the pressure to be measured, and the low-pressure chamber is communicated with the atmosphere, and the pressure of the gauge is measured. It is also possible to pass in high and low pressure respectively to detect the differential pressure. Under the action of the measured pressure or differential pressure, the silicon diaphragm produces strain, and the resistance value of the diffusion resistor changes with the strain. The shape and structure of the sensor are different due to the nature of the measured mass and the pressure measurement environment. A pressure sensor composed of a silicon cup diaphragm is also called a diffused silicon pressure sensor.
The integrated piezoresistive pressure sensor (also known as solid-state pressure sensor) that has appeared uses large-scale integrated circuit technology to integrate diffusion resistance, detection and amplification circuits, temperature compensation circuits, and even power conversion circuits and microprocessors in the same chip. The silicon diaphragm has both signal detection, processing (amplification, calculation, compensation), and memory functions, which greatly improves the stability and measurement accuracy of the sensor.