Experimental Characterization and Modeling of RF Performance of GaN-on-Si Power e-HEMTs Including Temperature Effects

In the last few years, much effort was devoted to the realization of high-performance, rugged and reasonably low-cost transistors, suitable for the increasing number of applications in the Power Electronics field. GaN High-Electron-Mobility transistors (HEMTs) provided a viable solution to these challenges, becoming a promising option for high-frequency, high-power and high-temperature applications, thanks to the unique properties of GaN material. GaN HEMTs have become essential devices in modern communication systems, including 5G networks, radar and satellite communications. If epitaxially grown on lower-cost wafers made of Si or SiC, such devices provide high-breakdown voltages, good thermal properties and very fast operation at reasonably low cost. Since in many circuit configurations adopted for power applications it is required to have normally-off (enhancement) devices, the standard (depletion) structure of HEMTs for microwave power applications had to be modified. Usually, a p-gate structure is adopted. Being this a relatively new technology, not all electrical performance aspects have been so far reported in the literature, particularly the RF response ones. In this paper, an experimental investigation of RF performances carried out on a power Si-eHEMT produced by the GaN4AP partner STMicroelectronics is reported. Specifically, the dependence on operating conditions – bias and temperature – of the SGT120R65AL power Si-eHEMT was characterized, in terms of both DC and RF response. A set of SPICE-compatible circuit models (bias depending) was also developed. To this purpose it was necessary to design and build a custom Transistor Test Fixture (TTF) with provision for temperature control (via a Peltier module) and sensing (via four Platinum Resistance Temperature Detectors - RTDs).