A high-capacitance ratio implanted MMIC varactor for broadband phase shifters and tuners

A new variable-area ion-implanted varactor has been developed to increase the available capacitance ratio from the conventionally obtained values of 3.5:1 to values in excess of 12:1. the new variable-area varactor uses a channel implant with a depth and doping profile that varies rapidly across the anode width; this yields a Schottky barrier capacitor with an active area that decreases as the depletion depth increases, in contrast to conventional varactors where fringing yields an active area that increases. RF resonance data as a function of DC bias for the new varactor design show low loss (f/sub c/>100 GHz) and a tuning range of 3.3:1 that is consistent with the measured DC capacitance ratio of 11:1. Since the bandwidth of both phase shifters and tuners varies as the square root of the available capacitance ratio, this new varactor has important applications for broadband, agile frequency systems. Presented are a simplified theoretical discussion of the design concept, a description of one approach that has been used to realize this design, and low frequency and RF data.<>