ELECTRICAL CHARACTERIZATION OF ESD DEGRADATION IN GAAS DEVICES

This paper presents a study of electrical waveforms which characterise the behaviour of the gate Schottky diode of a GaAs MESFET (MEtal Scho ttky FET) under electrostatic discharge (ESD) conditions. It is demons trated that the ESD breakdown threshold is highly dependent on the ext ernal circuit elements of the ESD pulsing apparatus and pulse transmis sion medium and therefore dependent on the circuit model used for ESD threshold assessment. It is also established that a GaAs MES device un der forward bias subthreshold/threshold ESD stress will exhibit a regi on of current controlled negative differential resistance (NDR) which is not observed in the DC characteristics. Beyond this NDR region a re gion of positive differential resistance (PDR) exists and it is whilst operating within this region that thermal breakdown can occur. In con trast, the reverse bias threshold is highly voltage dependent and the DC avalanche voltage must be attained during an ESD pulse for impact i onisation to occur. Continued operation in this avalanche condition, w hich is possible with ESD pulses greater than almost-equal-to -100 V, allows localised heating sufficient to initialise thermal runaway.