Millimeter-wave varactor diodes of greatly improved power generation capability have been developed using multi-layer epitaxial GaAs material. These are "stacked" multijunction diodes in a monolithic form, with as many as three active varactor junctions in series. Single diode power output as high as 10 W peak has been obtained at 35 GHz in pulsed service as a frequency doubler. At 44 GHz, in continuous service, 2.5 W has been obtained. In both cases, the efficiencies exceeded 50%.
INTRODUCTIONIn 1958 when the first varactor diodes were being developed by Uhlir (1), he proposed that high-voltage high-power varactors might be made by using multiple p and n layers alternately in a semiconductor diode to give increased breakdown voltage. Practical development of such a diode has been accomplished recently by T.B. Ramachandran and others at M/A-COM. He applied the principle to IMPATT diodes, Gunn diodes, and varactors. Only the varactor has been developed into a practical device at this date. In June, 1987, the present authors gave preliminary data on this device [6]. In this paper, we review some of that data and present more results with the ISIS varactor. We also present new computations showing the extended capabilities under pulsed operation. Only the varactor has been developed into a practical device at this date. The name ISIS has been selected for the generic form.