Design of a multimesa IMPATT diode array optimise for maximum heat dissipation

Abstract

It is shown that an appreciable increase in the dissipation capabilities of an IMPATT diode, can be achieved by making it in the form of a multimesa array structure on a common substrate, which forms the cathode connection. The anode of each mesa diode, is connected through an integrated gold heatsink to a common large external copper heatsink. A complete thermal analysis is performed by numerical technique from which the full temperature map of this composite device is obtained, as function of time in the heating up transient period, and under steady state operation. The analysis takes into consideration, the nonlinearity introduced by the local temperature dependence of the breakdown voltage of each separate mesa diode in the array, which, in turn, controls the current and heat dissipation distribution across the array. From the maximum temperature and the total power dissipation, the thermal resistance is obtained. The dependence of the thermal properties on various array structural parameters, e.g. the number of mesa diodes or the spacing between them, is evaluated. It is shown that by the use of nonuniform spacing, an almost uniform temperature can be achieved across the array device, thus yielding a minimum thermal resistance. It is also shown that even though an increased intermesa spacing in a uniformly arranged array, involves increased parasitic parallel capacitance, there is an optimum spacing that maximises the power-frequency-reactance product (P2f2X) of the device.