Instantaneous temperature profiles inside semiconductor power devices: Part I

Under electrical load the crystal temperature inside a semiconductor power device changes substantially both in space and in time. Its measurement with good resolution in temperature, in time as well as in space, was attempted by detecting the thermal radiation emitted from an operational semiconductor device that was thick enough to be opaque to thermal infrared. A cooled InSb detector is followed by an amplifier allowing for a tradeoff between time resolution (the overall time constant varied from 0.5 to 86 µs) and temperature resolution, such that their product remained constant. For temperature fields periodic in time, sampling methods and signal averaging are applied which further improve temperature resolution with time and space resolution remaining unchanged. A large improvement in speed of response with respect to conventional methods results. For a fixed surface point the time dependence of temperature is obtained. Fixing the observation window in time leads to profiles of instantaneous temperature across a selected line of the exposed semiconductor which are in good agreement with those predicted by a recent theoretical model. In Part I the case of thick slices is treated. The extension to thin slices which are transparent to thermal infrared are treated in Part II.