Three-stage pulse measurement technique for characterization of charge trapping in FETs

A difficulty concerning characterization of charge trapping in microwave FETs by performing pulse measurements is the possible overlap between the trapping and self-heating rates. Another difficulty is that the potential introduced by charge trapping modulates the drain-source current differently at bias points with different values of drain-source conductance, gm, and drain transconductance, gd. Measurement of true-DC values for gm and gd at all bias points will then be required for estimating the potential introduced by charge trapping. For devices such as GaN HEMTs, true-DC values for gm and gd at each bias point can be obtained only after thousands or tens of thousands of seconds after pulsing the device. A new pulse-measurement technique is proposed that overcomes these difficulties. The results of measurements performed on a GaN HEMT using the proposed pulse-measurement technique is presented, and the observed trapping behavior is characterized.