Test Setup for Measuring the Impact of Gate Stress on a GaN-HEMT's Output Characteristic

Precisely estimating conduction losses requires knowledge of the device's output characteristic in the ohmic region. For GaN-HEMTs, it dynamically depends on time, temperature, and applied biases. To study the impact of gate bias over time, a transient measurement approach is applied, that can acquire the start of the output characteristic with a single pulse. This ensures neglectable impact of temperature changes and trapping state on the single measurement. In addition, the short acquisition time allows studying the impact of the bias in the milliseconds range. Therefore, the measurement pulses are altered with stress intervals. While reference measurements for a traditional Si-MOSFET under constant gate bias show almost no change in the output characteristic over time, test results for a commercial GaN-HEMT reveal changes for low gate voltages. This demonstrates that the user should at least be aware of such trapping problems effecting measurements, which may lead to differences in characterization and application.