Extreme harsh environment operation of atomic layer deposition enhanced gallium nitride high electron mobility transistors [electronic resource]
Keywords: Mechanical Engineering.

Over the last few decades, electronics and sensing systems have transformed our way of life and have become very reliable and efficient. However, there is a dire need for such electronics to operate dependably for extended periods within extreme harsh environments (e.g. combustion engines, oil exploration, re-entry vehicles, and space missions to Venus). These environments can include combinations of high temperatures up to 3000°C, thermal cycling, fatal doses of ionizing radiation, severe chemical attack, and extreme shock. State-of-the-art electronic systems leverage silicon-on-insulator (SOI) platforms and are limited to operation temperatures below 250°C. This is well below the desired temperature range for harsh applications. Using complex packaging, short usage durations, and active cooling systems, the temperature range can be extended, but this leads to increased cost and complexity in microfabrication processes. Consequently, wide bandgap semiconductor platforms such as gallium nitride (GaN) and silicon carbide (SiC) have emerged for operation within harsh environments. Compelling device demonstrations have been realized at temperatures up to 1000°C, within high-dose ionizing radiation environments, and upon chemical attack. This dissertation presents the comparative results of accelerated lifetime testing performed on commercial-off-the-shelf (COTS) available GaN, SiC, and SOI electronic devices up to 600°C. The COTS GaN and SiC devices failed earlier than predicted lifetimes, extracted with an Arrhenius model, even at temperatures as low as 250°C. This outcome informed the selection of specialized high temperature metal contacts for devices developed in this work. The next part of this dissertation discusses the heterostructured aluminum gallium nitride and gallium nitride (AlGaN/GaN) metal-insulator-semiconductor high electron mobility transistors (MIS‑HEMTs) with an atomic layer deposited (ALD) aluminum oxide (alumina) dielectric (insulator) that were fabricated. The direct-current response of MIS-HEMTs and HEMTs up to 600°C in air, the highest ever reported operation temperature of an AlGaN/GaN MIS-HEMT in an oxidizing environment, is discussed. The HEMTs experienced failure above 350°C, an approximately 400 times increase in leakage current, due to the interfacial reaction and inter-diffusion of the gate metal, nickel/gold (Ni/Au), and AlGaN/GaN. The presence of 50 nm of ALD alumina suppresses the interfacial reaction and functions as a diffusion barrier between Ni/Au and AlGaN/GaN. It was determined that 10 nm of ALD alumina is not sufficient to prevent the degradation due to interfacial reaction and inter-diffusion of the Ni/Au with the AlGaN/GaN. Therefore, there is a critical thickness between 10 nm and 50 nm of ALD alumina to enable long-term operation of AlGaN/GaN electronics in extreme harsh environments. In the final part of this dissertation, radiation hardness of ALD alumina, ALD hafnium oxide (hafnia), and ALD silicon dioxide (silica) dielectric layers is reported. The ALD layers were evaluated up to an approximately 550 krad dose of gamma irradiation. The examination of the capacitance‑voltage characteristics revealed that ALD alumina and hafnia layers had a less than five percent shift in the flatband voltage and negligible shift in the hysteresis voltage. Therefore, ALD alumina and hafnia are promising dielectrics for use in space electronics. Degradation was observed in ALD silica given a 19% shift in flatband voltage and a 35% shift in hysteresis voltage. Thus, ALD silica is a candidate for development of gamma radiation sensors for space applications on a radiation-hard AlGaN/GaN platform.