Temperature nonuniformity and bias-dependent thermal resistance in multi-finger MOS transistors

In this paper, we study self-heating in a multi-finger MOSFET transistor. Different source-drain voltages are applied so that the transistor is in triode and saturation regimes. Thermoreflectance imaging technique was used to obtain high resolution thermal images of the transistor. This allowed us to obtain profiles with high spatial and temperature resolution. We verified that the actual size and shape of the heating source are modified as the biasing condition changes. Detailed comparison between the measurement results and analytical calculations proves that the thermal resistance of transistor is dependent on the biasing condition. It can change by a factor bigger than 5 for different drain-source voltages. Even in the saturation regime, the thermal resistance of the transistor can change by 50% as a function of bias.