Balaji Padmanabhan

An industrial process for 650V rated GaN-on-Si power devices using in-situ SiN as a gate dielectric

This paper reports on an industrial DHEMT process for 650V rated GaN-on-Si power devices. The MISHEMT transistors use an in-situ MOCVD grown SiN as surface passivation and gate dielectric. Excellent off-state leakage, on-state conduction and low device capacitance and dynamic Ron is obtained. Initial assessment of the intrinsic reliability data on the in-situ SiN is provided.

Technology and design of GaN power devices

This paper reports on the technology and design aspects of an industrial DHEMT process for 650V rated GaN-on-Si power devices, using an in-situ MOCVD grown SiN as surface passivation and gate dielectric, with low interface state density and excellent TDDB. Optimization of the GaN epi stack results in very low off-state leakage (<;10nA/mm). Due to the reduction of buffer trapping, low dynamic Ron (<;10%) is obtained, both at room temperature and at high temperature.

Unified theory of reverse blocking dynamics in high-voltage cascode devices

This paper investigates the dynamic evolution of the internal voltages in cascode-based high-voltage devices under reverse blocking mode. For the first time, this analysis covers blocking times ranging from fast transitions to steady-state, where leakage current plays a predominant role. A theoretical model is developed with the support of simulation and experimental data for cascode switch and rectifier, constituted by GaN-HEMTs (600V) and Si-FETs (30V). Finally, this knowledge is used to build a GaN cascode switch with enhanced electrical performance and ruggedness.

Negative dynamic Ron in AlGaN/GaN power devices

Through optimization of the GaN buffer structure, 650V rated AlGaN/GaN power devices with negative dynamic Ron are obtained. By judicious tuning of the resistivity of the [C]-doped and unintentionally-doped (UID) layers (i.e. the charge transport properties in these layers), positive rather than the deleterious negative charged trapping can be achieved. Long term reliability testing shows that the positive charge can be retained for days.

Breakthroughs for 650-V GaN Power Devices: Stable high-temperature operations and avalanche capability

Many prior publications have focused on gallium nitride (GaN) dynamic Rdson issues at room temperature, even though GaN power devices have tremendous advantages over silicon (Si) when serving at high temperatures. We show that room-temperature stable dynamic Rdson behavior does not guarantee device reliability, and it is the stable high-temperature dynamic Rdson that determines the ruggedness of the GaN power devices. With our proprietary and innovative designs and optimizations of epitaxial and device structures, we show a completely different dynamic Rdson behavior in contrast to the common trend reported in the literature: a negative dynamic Rdson trend. We demonstrate robust performance and reliability of our new cascode GaN power devices in PFC tests conducted at both room and high temperatures, at high powers, at high-frequency conditions, and in a totem-pole circuit. We speculate on a physical model to explain the observed dynamic Rdson behaviors in terms of trapping, detrapping, and back-gating effects.

First experimental demonstration of solid state circuit breaker (SSCB) using 650V GaN-based monolithic bidirectional switch

Renewable and other distributed energy resources feed electricity to the utility grid and/or local loads through interfacing power electronic converters. These new microgrids are susceptible to short circuit faults, mandating the use of protective circuit breakers. Solid state circuit breakers (SSCB) are needed due to their much faster response than mechanical circuit breakers. This unique application offers a great market opportunity for normally-on WBG switches. This paper, for the first time, experimentally demonstrates the feasibility of using 650V GaN bidirectional devices in SSCB applications.