A millimeter wave varactor with low parasitics

P-n and metal-semiconductor GaAs varactors with typical zero-bias capacitance of 0.15 pF and cutoff frequency of 700 GHz have been fabricated. The associated parasitic capacitance was 0.025 pF and the series inductance was 0.08 nH. The varactors have been used without degradation from 15°K to 400°K. The fabrication processes and the properties of these devices are described.