Abstract
Conductive properties of zinc oxide (ZnO) varistor ceramics depend on the boundary barrier structure. By using the photoconductivity switches (PCSS) technology, the boundary breakdown characteristics of ZnO varistors for nanosecond electric pulse response was measured under bias voltage 700 - 1600 V and the relationship between conductance and material structure was analyzed. Charging time of grain boundary capacitor was ∼ 100 ns and shortened with the increase of the bias electric field. The barrier height of ZnO grain boundary was influenced by bias electric field and the grain boundary capacitance was changed accordingly. The calculating numerical results are in agreement with the measured values.
Highlights
INTRODUCTIONA kind of semiconductor ceramic material, is widely used in high- and ultra-high voltage power network, electronic information circuit and control system for the voltage stability and transient overvoltage protection. The conductivity of zinc oxide (ZnO) varistor ceramics is determined by phase composition and distribution, grain size, grain boundary structure, lattice defect, and interface state. Some previous experimental results showed that, the voltage waveform of ZnO varistors achieves peak value earlier than the current waveform for the response of lightning current. The time of voltage peak value ahead of current peak value depends linearly on the amplitude of the shocking current and decreases with the varistor voltage increasing
The photoconductivity switches (PCSS) and zinc oxide (ZnO) varistors were in series connection
When the power supply output was below 600 V, the current of series circuit was less than 10-6 A, that is, the impedance of ZnO varistors was high in the pre-breakdown region and the PCSS partial voltage is lower
Summary
A kind of semiconductor ceramic material, is widely used in high- and ultra-high voltage power network, electronic information circuit and control system for the voltage stability and transient overvoltage protection. The conductivity of ZnO varistor ceramics is determined by phase composition and distribution, grain size, grain boundary structure, lattice defect, and interface state. Some previous experimental results showed that, the voltage waveform of ZnO varistors achieves peak value earlier than the current waveform for the response of lightning current. The time of voltage peak value ahead of current peak value depends linearly on the amplitude of the shocking current and decreases with the varistor voltage increasing. The conductivity of ZnO varistor ceramics is determined by phase composition and distribution, grain size, grain boundary structure, lattice defect, and interface state.. Some previous experimental results showed that, the voltage waveform of ZnO varistors achieves peak value earlier than the current waveform for the response of lightning current.. The breakdown time of ZnO grain boundary was not well known for the pulsed response. In the viewpoints of the Nordeim-Fowler tunneling effect model and the double Schottky barrier model, electron traps are formed by the structural disturbance and the dangling bonds in the grain boundary, which cause the interface state, grain boundary potential and nonlinear conductance.. Based on the PCSS technology and the ultrafast electronics testing methods, the nanosecond pulse response of the ZnO varistors can be measured.. The boundary breakdown characteristics of ZnO varistors is important for its ultrafast electromagnetic protection applications Based on the PCSS technology and the ultrafast electronics testing methods, the nanosecond pulse response of the ZnO varistors can be measured. The boundary breakdown characteristics of ZnO varistors is important for its ultrafast electromagnetic protection applications
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