Analog and digital cell library in high voltage GaN-on-Si Schottky power semiconductor technology

Abstract

Self-heating and application related rapid rise in die temperature of GaN High Electron Mobility Transistors (HEMTs) poses serious reliability risk to the device during operation. To mitigate this risk, there is a need for on-chip device protection before the device reaches overheat condition. A cell library of analog and digital building blocks was designed using only depletion mode HEMTs, Schottky Barrier Diodes (SBDs) and passives in high voltage GaN-on-Si power semiconductor technology. Stand-alone small geometry HEMTs and SBDs, voltage references, comparators, a level shifter, a logic circuit and a proportional to absolute temperature (PTAT) circuit are designed to form the core of a novel monolithically integrated thermal shutdown circuit as a self-protection feature of a 600V power HEMT. Since complementary devices are not yet available in this technology, direct coupled diode transistor logic was used and voltage level shifting was done using diodes. SBDs are exploited to design a PTAT voltage source due to a lack of p-n junction diodes. Functionality of the thermal shutdown circuit was verified through simulation and by fabrication. Here we report the results of the first phase in which the functional building blocks are designed as individual cells. Measurement results demonstrate that each circuit works in agreement with simulation.