AbstractsEngineering

The purpose of this research is to test various output parameters of gallium nitride transistors. These include the voltage-current characteristic, drain-source leakage current, dv/dt immunity, and resistance to single events and radiation hardness. The specific gallium nitride transistors tested are enhancement (normally-off) devices from Efficient Power Conversion (EPC) Corporation. These devices are in passivated die form, with land grid array solder bars. For the voltage-current characteristic, the gallium nitride device was mounted on a printed circuit board. The characteristic was compared to that of conventional devices, such as silicon and silicon carbide, at low and high temperatures. The voltage-current characteristic of gallium nitride shows an on-resistance lower then silicon or silicon carbide devices. Gallium nitride devices are also found to saturate at far lower drain-source voltages than the example silicon and silicon carbide devices, and require a lower gate voltage to turn on fully, which means that lower supply voltages are necessary to take full advantage of the device. The gallium nitride characteristic did have a greater sensitivity to temperature than the conventional devices, however.The drain-source leakage current of gallium nitride devices was also compared to conventional devices, from low to high temperatures. The leakage current for gallium nitride devices was many orders of magnitude higher than the conventional devices tested, and even though leakage current increases with increasing temperature for all the devices tested, the magnitude of the leakage currents associated with gallium nitride devices mean that they may make very good temperature sensors. Gallium nitride has superior dv/dt immunity when compared to conventional devices. The device tested withstood a dv/dt magnitude that was double the maximum dv/dt the conventional devices could withstand. The theoretical dv/dt immunity level of gallium nitride devices is nearly ten times the level of conventional devices. Gallium nitride devices have very good resistance to radiation. Tests done by the manufacturer show that gallium nitride devices can withstand larger amount of radiation than conventional power devices, and have no unwanted effects. In the testing presented in this thesis, a bank of gallium nitride devices had a high drain-source voltage and were turned off. After hundreds of hours, no single event occurred and the devices did not turn on or break at any point. As part of this testing, a substantial increase in the parasitic or noise current was observed upon exposure of the unpackaged device to continuous wave blue laser light. Even more interestingly, after removal of the laser light, the elevated current levels remained, revealing latching effect that has not been observed before in these devices. This latching effect deserves further studies to understand and prevent, or even use in potential applications.