What is the principle of piezoresistive pressure sensors?
Piezoresistive sensors refer to sensors made of the piezoresistive effect of monocrystalline silicon materials and integrated circuit technology. After the single crystal silicon material is subjected to the action of force, the resistivity changes, and the electrical signal output proportional to the change of force can be obtained according to the measurement circuit. Piezoresistive sensors are used to measure and control pressure, tensile force, differential pressure, and other physical quantities that can be converted into changes in force (e.g., level, acceleration, component, strain, flow rate, vacuum).
When the force acts on the silicon crystal, the crystal lattice of the crystal is deformed, causing the carriers to scatter from one energy valley to another, and the mobility of the carriers is changed, which disturbs the longitudinal and transverse uniformity of the carriers, and then changes the resistivity of the silicon.
These changes vary depending on the orientation of the crystal, so the piezoresistive effect of silicon is related to the orientation of the crystal. The piezoresistive effect of silicon is different from that of metal strain gauges, the change of the former resistance with pressure is mainly the change of resistivity, and the change of the latter resistance is mainly the change of a few scales, and the sensitivity of the former one is 50-100 times greater than that of the latter one.
What should piezoresistive pressure sensors have?
Piezoresistive sensors are ideal for this purpose. For example, it is used to measure the airflow pressure dispersion of the wing of a helicopter, to test the dynamic distortion of the engine air intake, the pulsating pressure of the blade grille and the jitter of the wing. In the measurement of the central pressure of the aircraft jet engine, a specially designed silicon pressure sensor is used, and its operating temperature is more than 500°C. In the air data measurement system of Boeing passenger aircraft, a matching silicon pressure sensor with an accuracy of up to 0.05% is used. In scaled-down wind tunnel model tests, piezoresistive sensors can be installed in dense wind tunnel inlets and engine intake duct models.
What are the components of a piezoresistive pressure sensor?
This type of sensor uses an integrated process to integrate resistance strips on a single crystal silicon diaphragm to make a silicon piezoresistive chip, and the perimeter of the chip is fixed and encapsulated in the housing to find the electrode leads. Piezoresistive pressure sensors, also known as solid-state pressure sensors, are different from adhesive strain gauges, which indirectly sense external forces based on elastic sensitive components, but directly sense the measured pressure based on silicon diaphragms. On one side of the silicon diaphragm is a high-pressure cavity that communicates with the measured pressure, and on the other side is a low-pressure cavity that communicates with the atmosphere. The silicon diaphragm is generally designed as a circular shape with a fixed support around it, and the diameter to thickness ratio is about 20-60. Four P impurity resistance strips are localized and connected to form a full bridge in the circular silicon diaphragm, two of which are located in the compressive stress region and the other two are in the tensile stress region, which are symmetrical relative to the center of the diaphragm.
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