Evaluation oftheeffect ofthethermal cycling temperature ontheconduction current in alumina substrates.

Charging anddischarging currents havebeen measured inanalumina substrate before andafter thermal treatment consisting inapplying thermal stepof negative andpositive values(-20°C-50°C). Both transient andsteady-state current havebeenanalysed. Theaverage applied voltage ranged from0 to5kV. Transient currents suggested aphenomenon generating spacecharges inthebulkofthematerial athighfields. Belowthehighfield regime, ohmicandsub-ohmic regime arebeenidentified. Anyway, itwasobvious that thethermal treatment increased hugely theconduction current withafactor ofalmost twodecades. Nousually Schottky-type injection ortunnel-type wasfoundfrom ourmeasurements.