GaN electronics for high-temperature applications

Abstract

Gallium nitride is a promising candidate for high-temperature applications. However, despite the excellent performance shown by early high-temperature prototypes, several issues in traditional lateral AlGaN/GaN HEMTs could cause early degradation and failure under high-temperature operation (over 300°C). These include ohmic degradation, gate leakage, buffer leakage, and poor passivation. Besides, enhancement-mode HEMTs are preferred from the application point of view by reducing the circuit complexity and cost. At the same time, the two-dimensional electron gas induced by AlGaN/GaN heterostructures makes HEMTs be naturally depletion-mode devices. This thesis aims to demonstrate devices capable of high-temperature operation without extra cooling systems by combing gate injections transistors (GITs) with ion-implanted refractory metal contacts. The Si ion implantation in AlGaN/GaN heterostructures was comprehensively studied here regarding implantation conditions, activation annealing conditions, metallization schemes. A self-aligned gate-first process, together with etch-stop process, was developed and optimized to improve fabrication efficiency and device uniformity for large-scale integration. Basic logic building blocks, including inverters, NAND gate, NOR gate, SRAM, and ring oscillator, have been demonstrated and characterized at both room temperature and high temperature.