Total ionizing dose effects in power vertical double-diffused metal-oxide-semiconductor field effect transistors

Total ionizing dose effects have been studied in commercial power VDMOSFET devices. New analytical methods have been applied and further developed for characterization of irradiated devices.; Direct-current current-voltage (DCIV) technique was applied to monitor the generation of oxide-trapped charge and interface-trap build-up in the gate oxide region in devices irradiated by Cs-137 γ-ray or X-ray. Various data were measured to analyze accumulated dose and post-irradiation anneal effects. DCIV data are correlated with the subthreshold I-V data and the charge-pumping data. The DCIV method is found to be a convenient in monitoring the radiation effects in the devices.; Two interface-recombination current peaks in the DCIV data of non-irradiated and irradiated devices were investigated. The current peaks show a slightly different rate of increase as a function of the radiation dose. Spectral charge-pumping data showed that the interface-traps have significant increase in the energy below E_i + 0.28 eV in above-midgap and in the energy below E _i − 0.20 eV in below-midgap by the radiation. A device simulator, MINIMOS, was used to examine the DCIV data. The results show that the origins of two current peaks may be two different interface traps.; Effects produced by high electric field stress and by X-ray radiation were compared in an n-channel VDMOSFET. The channel-side interface and the drain-side interface are affected differently by the high field stress, whereas the interfaces are uniformly affected by the radiation. High field stress on the gate oxide did not increase the leakage current, I_bot , in the DCIV data, while the irradiated device showed a significantly increased I_bot. It is suggested that both interfaces should be examined separately for a correct interpretation of the radiation and the high field stress effects.; A detail analysis of capacitance-voltage (CV) characteristics of the device has been made. CV technique measures both interfaces by a single data set, yet distinguishes the two interfaces clearly, while other techniques measure only one of the interfaces. The CV method was suggested as a very simple and effective tool for monitoring degradations of the gate oxide in the devices.