Electrical characterisation of ESD degradation in GaAs devices

Abstract

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