Correlation between thermal resistance, channel temperature, infrared thermal maps and failure mechanisms in low power MESFET devices

Channel temperature Tch of GaAs MESFETs, determined by means of electrical measurements (ΔVgs), has been compared and correlated with thermal maps obtained by high resolution infrared microscopy. Results show that in low power devices with a small number of gates, the value of Tch derived from ΔVgs measurements is close to the maximum values of temperature measured on the hottest junctions on the chip. Local thermal inhomogeneities, in particular those observed in devices characterized by high values of Rth, can explain and confirm results of failure analyses of MESFETs submitted to accelerated life tests in operating conditions where degradation phenomena occur in localized areas of the device.