Evaluation of High Power 6H-SiC Microwave Field-Effect Transistors for High Temperature Operation

There is an increasing need in many military systems to have solid state microwave devices with higher power capability, higher reliability, and higher operating temperatures. These devices would be important for airborne radar systems, electronic warfare and countermeasure systems, and airborne and space-based communications systems. While conventional semiconductor materials such as SI and GaAs are already being used near their limits of output power and operating temperature, the potential of SiC is just beginning to be demonstrated. High temperature 6H-Sic MESFETs and JFETs have been demonstrated to 500 C. Physical modeling has shown that an ideal 1 um gate length 6H-SiC MESFET at 25 C would have a power density of 3.2 W/MM at 10 GHz (3-6 times higher than achievable in GaAs). Furthermore, this modeling has shown that if the MESFET were operated at 500, it would still have an output power of 1.6 W/mm at 10 GHz. While the room temperature potential of the SiC MESFET will very likely be achieved, there are some factors that could pervent a MESFET strcuture from meeting its potential at high temperature. The amount of gate leakage known to exist for Schottky contacts at 500-600C could degrade the RF performance of the devices. Therefore, it is proposed that 6H-SiC JFET structures be investigated for high temperature, high frequency operation. The JFET will take advantage of the much lower leakage current inherent in SiC pn junctions at high temperature due to the wide bandgap. This effort will include physical modeling (RT and 500C), design and fabrication of JFET structures. High temperatures RF measurements of both MESFET and JFET devices will also be performed. The most promising of these devices will be further developed in Phase II of this program. be performed. The most promising of these devices will be further developed in Phase II of this program.