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

Channel temperature T_ch of GaAs MESFETs, determined by means of electrical measurements (ΔV_gs), 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 T_ch derived from ΔV_gs 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 R_th, 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.