| PhD Seminar

Name of the Speaker: Ms. Pallavi Kumari (EE21D014)
Guide: Prof. Nandita DasGupta
Venue: ESB-244 (Seminar Hall)
Date/Time: 22nd March 2024 (Friday), 3:30 PM
Title: Fabrication and characterization of stable normally-off Fin-MISHEMT with optimized AlxOy as gate dielectric.

Abstract

GaN-based High Electron Mobility Transistors (HEMTs) are used extensively for high frequency and high power applications due to to their many advantages such as high bandgap, high density of 2-DEG sheet carrier concentration and high saturation velocity. With the increasing demand for high frequency and high-power devices, research in the area of GaN devices has become very important. For conventional GaN based devices a high concentration of 2DEG is present at AlInN/GaN interface without any biasing. This makes these devices normally on type with high gate leakage current resulting in a limited positive gate voltage swing. Thus, normally-off behavior is desired for safe operation and better control. Several techniques such as recessed etch under the gate, p-GaN HEMT, cascode configuration, charge engineering in the gate dielectric of MISHEMTs, and/or Fin-HEMTs have been proposed in literature to achieve “normally-off” behavior of GaN based devices.

In this presentation, we will discuss the realization of normally off GaN based devices by combining the concept of charge engineering in gate dielectric and Fin-HEMT technology. The RF sputtered aluminum oxide (AlxOy) can be used as gate dielectric to achieve normally-off MISHEMT devices. It is observed that the net negative charges in the gate dielectric deplete the 2DEG under the gate resulting in positive shift in the threshold voltage. Although normally off devices using charge engineering in gate dielectric is possible, the device robustness with higher off-state breakdown voltage remains challenging. In literature, it is reported that the normally-off behavior with higher breakdown voltage can be achieved by Fin-MISHEMT technology. The normally-off behavior in Fin-MISHEMT is possible if the fin width is below 100 nm. However, this increases the on-state resistance of the transistor. High on-state resistance effectively increases power loss in the transistor. Thus, there is a trade-off between breakdown voltage and on-state resistance.

In this work we are proposing Fin-MISHEMT device with RF sputtered AlxOy as a gate dielectric to achieve better trade-off between off-state breakdown voltage and on-state resistance.