Experimental and Theoretical Study of Transient Behavior of Varistors
Final rept. 11 Jan 1988-10 Jan 1989
NORTH CAROLINA UNIV AT CHAPEL HILL DEPT OF PHYSICS AND ASTRONOMY
Pagination or Media Count:
Transient currents below and above the breakdown voltage have been studied for metal oxide zinc oxide varistors. Above the breakdown voltage the voltage overshoot phenomenon effectively lengthens the turn-on time making the turn-off time smaller than the effective turn-on time. Below the breakdown voltage, slow decaying currents following the capacitance-charging peak discharging peak are found to show a power law temporal behavior, 1t to the nth power where n is very close to unity, over a time ranging from one microsecond to thousands of seconds after the beginningend of the applied voltage pulse. Activation energies of these transient currents were found to be approx. 10 meV and approx. 160 meV. We have provided a theoretical explanation of this time dependence tunneling from deep donors into the conduction band as the Fermi level is shifted down across the donor levels by the applied bias. A preliminary effort has been made to relate the cause of the voltage overshoot to the time needed for the depletion layer narrowing and hole creation.
- Electrical and Electronic Equipment