Breakdown Voltage Analysis of High Electron Mobility Transistor

Abstract

Since the invention of the metal-oxide-semiconductor field-effect-transistor (MOSFET), the
semiconductor industry for electronics has been dominated by silicon (Si). The reason being the cost and ease of creating a native oxide on Si which enables the well established complementary metal-oxide-semiconductor (CMOS) process which has revolutionised the digital world we live in. Si, however,is a low band gap material (1.1 eV) and although used in power semiconductor sector over the years, new materials with superior properties are being investigated as potential replacements especially in power sector.Since past three decades, power management efficiency and cost have shown steady improvement as innovations in power MOSFET structures, technology, and circuit topologies have paced the
growing need for electrical power in our daily lives. In the last few years, however, the rate of improvement has slowed as the silicon power MOSFET has approached its theoretical bounds. Due to the limitations reached by silicon devices, new materials are emerging to cater the needs of today’s scenario. The prominent being the Gallium Nitride based High Electron Mobility Transistors.

GaN based devices have superior performance in field of power electronics as well as in many high frequency applications. This is due to its characteristic property of large bandgap,leading to high breakdown field and high mobility,allowing it to be used in high frequency applications. In the field of power converters two key power-switch requirements are there: (1) high blocking voltage with as small as possible resistance of the drift region that supports the blocking voltage and (2) high switching speed. Silicon based MOSFET have limitations of low breakdown voltage, high on resistance and low switching frequency. On contrary GaN based HEMT have high breakdown voltage capacity along with high switching speed which makes it far beyond its competitor, silicon based devices.

In this paper, breakdown voltage analysis is done and various aspects of improving the breakdown voltage are studied. On a specific note, detailed study on effect of passivation layer on breakdown voltage is done,considering structure miniaturisation, reduced on -resistance, high blocking voltage and high switching frequency. Moreover, passivation layer addition has multipurpose role in GaN based HEMT viz. removal of current collapse,protection to device, increment of breakdown voltage etc. Results from this study show electric field modification as the dielectric constant is increased. This modification is in terms of electric field distribution beneath gate-drain region especially at the drain edge of the gate. This lowering of electric field, as a result of distribution,helps in significant increment of breakdown voltage along with removal of current collapse. It is also observed that when pas sivation thickness is increased, breakdown voltage also increases.