Gradual Degradation of GaAs FETs Under Normal Operation

The gradual degradation of low-noise and power GaAs FETs under normal operating conditions has been investigated. The degradation of the drain current under both low and normal biasing was monitored for low-noise devices, but only the degradation of the drain resistance was monitored for power GaAs FETs. Using elevated temperatures to stabilize devices and assuming a single monotonically decreasing failure mode, it is relatively simple to determine the device´s long-term reliability within several days of operating at normal temperatures of 100°C or lower. This is accomplished by observing a sufficiently low degradation rate, which, when extrapolated to the desired end-of-life, yields an acceptable low longterm degradation estimation. To minimize the risk associated with the possible existence of compensating gradual degradation modes, the gradual degradation of devices is examined against a second gradual degradation failure criterion, which is based on the device having a sufficient low-degradation second derivative. Fulfilling the second-order failure criterion is more difficult to demonstrate and is the main focus of this investigation.