The gate threshold voltage (Vth) shift under positive gate bias stress is one of the most important reliability concerns in silicon carbide metal–oxide–semiconductor field effect transistors (SiC MOSFETs). Because dynamic recovery is observed as soon as the gate bias stress is removed, it is remarkably difficult to accurately evaluate Vth shifts. Many studies have focused on how to evaluate Vth shifts of SiC MOSFETs under positive gate bias stress. In this study, this issue is investigated by introducing a fast measurement technique. We show that the measured Vth shift is modified to take the Vth recovery term into consideration. Furthermore, we show that the Vth shift is a saturation phenomenon and that the maximum Vth shift can be predicted using an electron capture and emission model.
Using the combination of a curved crystal analyser and a position sensitive detector, we demonstrate how an energy resolution of a few eV in the energy range of 10 keV can be achieved without suffering a prohibitive loss in the observed intensity. In this preliminary report we describe an experimental set-up in which spectra from Raman, Compton and plasmon scattering can be collected in a matter of hours using monochromatic CuKw radiation from a 1.0 kW x-ray generator. After scattering in either a Be or a graphite target, the x-rays were reflected from the (333) planes of a curved Ge crystal and brought to a focus on a position sensitive proportional counter. In the case of Be, data were collected for three different scattering angles in order to illustrate the various scattering processes which can occur in this region of energy and momentum transfer. The measurements on pyrolitic graphite confirm earlier reports of a striking anisotropy in the spectral distribution of the scattered x-rays, depending upon the direction of the experimental scattering vector relative to the basal planes in this layered crystal. The anisotropy arises from the strong directional dependence of the cross section for plasmon excitation in graphite. Some straightforward improvements to the present apparatus would lead to an increase in the observed intensity by a factor of 40 or more.
The existence of an optical non-linearity of the Kerr-like type in a lyotropic liquid crystal is found in a total internal reflection experiment at a liquid crystaliglass interface. It is shown that the non-linearity is most probably of thermal origin.
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