Nonohmic Contact Planar Varactor Frequency Upconverters for Terahertz Applications

The development of tunerless millimeter and sub-millimeter wavelength frequency upconverters with integrated planar varactor circuits is described in this paper. An upconverter operating at 200 GHz is implemented as a proof-of-principle demonstration, and designs using both ohmic and nonohmic contacts are tested. The nonohmic contact facilitates fabrication. Both the ohmic and nonohmic devices produced similar performance. Using the nonohmic cathode contact technique and an air-bridge process, 1.6-THz integrated upconverter circuits are fabricated, and the conversion loss is measured to be approximately 22 dB with 40 muW of output sideband power with a 10-GHz microwave pump. A phase-shift measurement for the 1.6-THz upconverter using a standing wave method is described and used to corroborate the results