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Thermal influence on S22 kink behavior has been carried out on a 0.15 μm gate length AlGaN/GaN/SiC high electron mobility transistor over a wide range of temperature. The size and the shape of the S22 kink effect (KE) in terms of biasing and temperature have been evaluated. The main finding is that S22 of the studied device is affected by two kinks: the first one appears at approximately 19 GHz and then the second one appears at about 43 GHz. The impact of the intrinsic circuit parameters on the S22 kink phenomena is inspected to assess their contribution. In addition, a new procedure is proposed to quantify this type of phenomenon by defining the kink area as the area between the two curves corresponding to S22 with and without the KE. The relevance of this study emerges from the fact that an exhaustive characterization of these anomalous phenomena can empower RF engineers to effectively take them into account for both modeling and design purposes. [ABSTRACT FROM AUTHOR]

The main aim of this article is to present an experimental analysis of the thermal influence on the positive derivatives of the real parts of impedance parameters against frequency (PDRZ) for microwave GaN and GaAs based HEMTs. The PDRZ effect is investigated with respect to temperature by both heating and cooling the studied devices. The main findings are that both devices are affected by the PDRZ effect, although with different severity and onset frequency. Due to the extrinsic resistances response with temperature, the real parts of impedance parameters shift towards higher values, especially for the GaAs HEMT. By de-embedding appropriate values of the extrinsic capacitances, the PDRZ effect can be neutralized in both devices. As the extrinsic capacitances are thermally unresponsive, roughly the same values of the extrinsic capacitances are achieved for all the studied temperatures. [ABSTRACT FROM AUTHOR]

Shifts in the threshold voltage VT subject to temperature in AlGaN/GaN-based high-electron-mobility transistors (HEMTs) grown on silicon carbide substrate are reported. Variation of VT with drain–source voltage and temperature is investigated, including experimental characterization, modelling and analysis. Possible parameters that affect VT are Schottky barrier height of the device, along with trap-assisted phenomena, aluminium concentration and polarization fields depending on the dielectric, were studied. The threshold voltage and Schottky barrier height shift positively with temperature, and a zero temperature coefficient point in the transfer curve was found before the threshold voltage. An analytical model for threshold voltage VT based on lattice-mismatched AlxGa1−xN/GaN HEMTs is presented based on aluminium mole concentration, and it is found that VT shifts towards more negative values with increasing aluminium concentration. The model correctly predicts device performance and is found to be consistent with the measured results. These results are valuable for understanding the underlying physics of GaN/SiC HEMTs and their optimization with temperature. [ABSTRACT FROM AUTHOR]

This paper investigated the temperature effects on the performance of the AlGaN/GaN high electron mobility transistor (HEMT) with a 150 nm and 250 nm gate length on a SiC substrate over a temperature range of −40 to 150 °C including experimental characterization, modelling and analysis by on-wafer measurements up to 50 GHz. All the DC and small signal parameter variations with ambient temperature on the same set of devices have been reported for the first time. The temperature coefficient of all the DC and small signal parameters as well as ft and fmax were reported. Some of the extracted equivalent circuit parameters with the theoretical data of the evolution of electrical parameters and the relevant physical equations involved have been compared using the same biasing condition for further accuracy. The theoretical results are shown to be consistent with the extracted data. Some results are also experimentally verified with previous works cited in the paper. The results provide some valuable insights for the underlying physics of the device parameters affected by temperature. [ABSTRACT FROM AUTHOR]