High temperature characteristics of AlGaN/GaN high electron mobility transistors

Direct current （DC） and pulsed measurements are performed to determine the degradation mechanisms of A1GaN/GaN high electron mobility transistors （HEMTs） under high temperature. The degradation of the DC characteristics is mainly attributed to the reduction in the density and the mobility of the two-dimensional electron gas （2DEG）. The pulsed measurements indicate that the trap assisted tunneling is the dominant gate leakage mechanism in the temperature range of interest. The traps in the barrier layer become active as the temperature increases, which is conducive to the electron tunneling between the gate and the channel. The enhancement of the tunneling results in the weakening of the current collapse effects, as the electrons trapped by the barrier traps can escape more easily at the higher temperature.

High temperature characteristics of bilayer epitaxial graphene field-effect transistors on SiC Substrate

In this paper,high temperature direct current（DC） performance of bilayer epitaxial graphene device on SiC substrate is studied in a temperature range from 25℃ to 200℃.At a gate voltage of-8 V（far from Dirac point）,the drainsource current decreases obviously with increasing temperature,but it has little change at a gate bias of ＋8 V（near Dirac point）.The competing interactions between scattering and thermal activation are responsible for the different reduction tendencies.Four different kinds of scatterings are taken into account to qualitatively analyze the carrier mobility under different temperatures.The devices exhibit almost unchanged DC performances after high temperature measurements at 200℃ for 5 hours in air ambience,demonstrating the high thermal stabilities of the bilayer epitaxial graphene devices.

Characteristics of High Temperature Rupture of a Cast Ni-Based Superalloy M963

The rupture behavior of a cast Ni-base superalloy M963 at high temperature has been investi- gated. The microstructure examination shows that there exists a large amount of the carbide and γ-γ' eutectic, which is very harmful to the mechanical properties of M963 superalloy. The tensile strength of M963 superalloy both at room temperature and at high temperatures is higher than that of K17G alloy, but the tensile ductility of the former is much lower than that of the latter. In tensile fracture process with the high strain rate, the open carbides are the initiation site and the carbide/matrix interface is the propagation path of cracks. But in fracture process with the low strain rate, the carbide/matrix interface and cast microvoids are the initiation sites, and the carbide/matrix interface is the propagation path of cracks. The effective ways to improve ductility of M963 superalloy are also suggested.

Martensite Aging Effect and Thermal Cyclic Characteristics in Ti-Pd and Ti-Pd-Ni High Temperature Shape Memory Alloys

The effect of thermal cycling and aging in martensitic state in Ti-Pd-Ni alloys were investigated by DSC and TEM observations. It is shown that the thermal cycling causes the decreases in M8 and Af temperatures in Ti50Pd50-xNix, (x=10, 20, 30) alloys, but no obvious thermal cycling effect was observed in Ti50Pd50Pd40Ni10 alloys and the aging effect shows a curious feature, i.e., the Af temperature does not saturate even after relatively long time aging, which is considered to be due to the occurrence of recovery recrystallization during aging.

High-temperature energy storage dielectric with inhibition of carrier injection/migration based on band structure regulation

Dielectric capacitors have a high power density,and are widely used in military and civilian life.The main problem lies in the serious deterioration of dielectric insulation performance at high temperatures.In this study,a polycarbonate(PC)-based energy storage dielectric was designed with BN/SiO_(2)heterojunctions on its surface.Based on this structural design,a synergistic suppression of the carrier injection and transport was achieved,significantly improving the insulating properties of the polymer film.In particular,the composite film achieves optimal high-temperature energy-storage properties.The composite film can withstand an electric field intensity of 760 MV m^(-1)at 100℃and obtain an energy storage density of 8.32 J cm^(-3),while achieving a breakthrough energy storage performance even at 150℃(610 MV m^(-1),5.22 J cm^(-3)).Through adjustment of the heterojunction structure,free adjustment of the insulation performance of the material can be realized;this is of great significance for the optimization of the material properties.