InAlAs/InGaAs varactor diodes with THz cutoff frequencies fabricated by planar integrated technology

Future space-based radiotelescopes and planetary radar projects plan to include THz frequency coverage. Such applications necessitate the use of high-reliability compact local oscillators (LO's) to drive the THz receivers' mixers. While THz molecular lasers can provide high power, they are bulky and not reliable enough for space applications. Presently, solid-state LO's show the greatest potential reliability and compactness. Among the solid-state sources, LO's based on varactor multiplier chains show the most promise in terms of potential output power and efficiency. The highest performance diodes have traditionally relied on whisker anode contacting which is suitable only for discrete devices and has limited reliability. To address these problems, planar diodes have been proposed and demonstrated using GaAs. This paper reports on a planar integrated technology which, unlike previous approaches, utilizes InP-based materials and plated Au airbridges to contact the anode. This airbridge technology reduces parasitics by avoiding the use of a bridge-supporting dielectric. The In/sub x/A/sub 1-x/As/InGaAs heterojunction concept permits high C-V nonlinearity, reduced access resistance (R/sub s/) and high saturation velocity. Furthermore, this developed technology is fully planar and lends itself to integration with passive elements for monolithic applications.<
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