Zinc oxide pressure sensor is a polycrystalline semiconductor ceramic element made of a plurality of metal oxides, a classic electronic ceramic process, based on zinc oxide. Its microstructure is shown in Figure 1. Zinc oxide ceramics are composed of zinc oxide grains and grain boundaries, in which the sonarized impurities are donated in the zinc oxide crystal particles, which contains a large number of metal oxides in the crystal boundary material to form a large number of boundary states, so that every micro The unit is a backbracentry barrier, and the entire ceramic is a combination with a plurality of backrests of Schottky string string. Figure 2 is an equivalent circuit of a pressure sensitive resistor.
The typical V-I characteristic curve of zinc oxide pressure sensor is shown in Figure 3:
Pre-wear zone: In this area, the voltage applied to the pressure sensor is smaller than its pressure sensitive voltage, which conductive belongs to the thermal excitation electron conductance engine. Therefore, the pressure-sensor is equivalent to an insulating resistor (RB is much greater than RG) above 10MΩ, and only the resistive current of the pressure sensor is only a micro-level, which can be seen as an open circuit. The area is the state where the voltage-sensitive resistor is active when the circuit is operating normally.
Breakfasting area: When the pressure sensor is applied to an overvoltage of the pressure sensitive voltage, the conductive belongs to the tunnel breakdown electron conductance mechanism (Rb and Rg equivalent), and its voltammetical characteristics are excellent in nonlinear conductance properties, ie :
I \\u003d CVα
Where i is a constant related to the current, C and the formulation and process of the pressure sensor, the voltage across the V-pressure resistor, α is a nonlinear coefficient, generally greater than 30
It can be seen from the above formula. In the breakdown area, the slight change of the pressure-sensitive resistor end voltage can cause dramatically changes in the current, the pressure sensitive resistor is using this characteristic to suppress the overvoltage magnitude and absorption or release. Surge energy caused by the voltage.
Upset: When the overvoltage is large, the voltammetry characteristics of the pressure-sensitive resistor are mainly determined by the voltammetry characteristics of the grain resistance when the current is greater than about 100A / cm2 through the current of the pressure sensor. At this time, the voltammetry characteristics of the pressure sensor are linearly conductive, namely:
The current and voltage of the rising zone are almost linear. The pressure-sensitive resistor has deteriorated in the region, and it has lost its characteristics such as the energy of the overvoltage, absorb or release the surge.
According to the conductive mechanism of the pressure sensitive resistor, its response speed to the overvoltage is very fast, such as lead type and dedicated electrode products, the general response time is less than 25 nanoseconds. Therefore, as long as the selection and use, the varistor has excellent inhibition of the transient overvoltage that appears in the line, thereby achieving the purpose of other components in the protection circuit from overvoltage damage.