250°C voltage compliant SOI MESFET's for high power PWM drive circuits

Silicon Carbide (SiC) junction field effect transistors (JFETs) are ideal for switching high current, high voltage loads in high temperature environments. These devices require external drive circuits to generate pulse width modulated (PWM) signals switching from 0V to approximately 10V. Advanced CMOS microcontrollers are ideal for PWM signals but are limited in output voltage due to their low breakdown. As a result an intermediate buffer stage is required between the CMOS circuitry and the JFET. In this work a discrete silicon-on-insulator (SOI) metal semiconductor field effect transistor (MESFET) was used to drive the gate of a SiC power JFET switching a 120V RMS AC supply into a 30Ω load. The wide operating temperature range and high breakdown voltage of up to 50V make the SOI MESFET ideal for power electronics in extreme environments. Characteristic curves for the MESFET were measured up to 250°C. To drive the JFET, the MESFET was DC biased and then driven by a 1.2V square wave PWM signal to switch the JFET gate from 0 to 10V at frequencies up to 20 kHz. Due to the easy integration of MESFET s into SOI CMOS processes, MESFETs can be fabricated alongside MOSFETs without any changes in the process flow. This work demonstrates the feasibility of integrating a MESFET with CMOS PWM circuitry for a completely integrated SiC driver thus eliminating the need for the intermediate buffer stage.