VSWR testing of RF-power GaN transistors

A novel procedure for voltage standing wave ratio (VSWR) ruggedness testing of GaN-HEMTs is described. In the test the transistor is exposed to an increasing level of VSWR stress and an extensive set of marker parameters are monitored before, during, and after stress. A gate- and drain-lag pulse response test has been developed that reveals VSWR stress influence on slow surface charges. Recovery is monitored after each stress-point. It has been found that high VSWR stress of GaN-HEMTs at low supply voltages foremost causes a temporary shift in pinch-off voltage. Prolonged stress at even moderate VSWR levels at higher supply voltage can lead to structural changes and irreversible degradation of the electrical performance. The mechanism for this degradation is found to be a combination of thermal and field stress.