Comparison of the interdigitated emitter and matrix emitter microwave power transistors

Several new designs of microwave power transistors have been reported in the past few years. However, the merits of each of the different designs have not been studied experimentally. This paper discusses results of an investigation in which transistors having an interdigitated emitter structure are compared directly with transistors utilizing the matrix emitter structure. In order to minimize the variations introduced in the device processing the matrix transistor and the interdigitated transistor were designed on the same 20 × 30 mils²bar. Both devices have the same base area of 3 × 8 mils²and the same emitter size of 1.25 microns, which is approaching the limit of the present contact photolithography technology. The above design parameters result in a packing density (defined as the ratio of emitter periphery to base area) of 5.0 for the interdigitated geometry and 6.5 for the matrix geometry.