ZnO varistors for protection against nuclear electromagnetic pulses

The use of ZnO-based metal-oxide-varistor materials in a transient protection device for communications circuits against the effects of nuclear electromagnetic pulses (NEMP) is discussed. The guidelines for such devices call for subnanosecond response time to NEMP and an insertion loss of less than 0.4 dB at 100 MHz. We have measured the response of varistor materials to ∼500-ps rise time pulses of various amplitudes and durations. No varistor ’’turn on’’ time is evident in these data indicating that the initiation of the highly nonlinear conduction process takes place in less than 5×10−10 s. The insertion loss is calculated from the known high-frequency electrical properties and found to agree quite closely with the experimentally determined value of 0.1 dB at 100 MHz for varistor chips of cross section 0.025×0.025 cm and thickness 0.01 cm. A packaging configuration for these chips is also described. We conclude that ZnO varistors have application in an NEMP protective device.