High-power IMPATT diodes on diamond heat sinks

This paper presents calculated and experimental results which demonstrate that the performance of IMPATT diodes is significantly improved by the use of diamond heat sinks. Oscillator test results on germanium IMPATT diodes at 6.2 GHz indicate about 50 to 100 percent increase in power output for diamond versus copper heat-sinked units without compromising other oscillator characteristics. An increase in thermal conductance of about 40 percent is realized for diodes mounted on selected high-conductivity diamonds compared to units mounted on copper. Considerations of IMPATT wafer design for optimum power performance on high thermal conductance heat sinks are discussed. Thermal conductivity of naturally occurring diamonds ranges from 1.0 to 5.0 times that of copper which necessitates selection of stones to realize maximum thermal conductance. This paper presents the results of a study of diamond thermal conductivity, its measurement, and its relationship to diamond optical properties. The dependence of diode thermal conductance on die area for diamond heat-sinked devices has been obtained by computer solution of the heat flow equations for the relevant geometries. These calculations have been corroborated by measurement of the thermal conductance of diodes with various die diameters.