Study of radiation effects in /spl gamma/-ray irradiated power VDMOSFET by DCIV technique

Abstract

Direct-current current-voltage (DCIV) measurement was used to monitor interface recombination currents in /sup 137/Cs /spl gamma/-ray irradiated commercial power VDMOSFETs. The data are correlated with the subthreshold I-V data and charge-pumping current data, which are obtained after various biased-annealing steps. The DCIV method is found to be a convenient technique in monitoring the radiation effects in power VDMOSFET devices. Various parameters measured with the DCIV technique are discussed in conjunction with the charge-pumping data and the data from the midgap method. A two-dimensional MOS device simulator, MINIMOS, was used to illustrate the DCIV data. The simulation results illustrate well the dependence of the measurable DCIV parameters on various radiation-induced physical parameters such as interface-trap density, fixed oxide charge density, and surface recombination velocity. A biased annealing experiment in nonirradiated virgin devices showed that the second current peak in the double peak structure of the DCIV data may be associated with the slow-frequency (300-6000 Hz) charge-pumping signal.