650-GHz Resonant-Tunneling-Diode VCO With Wide Tuning Range Using Varactor Diode

We fabricated a wide-range varactor-tuned terahertz oscillator using a resonant tunneling diode (RTD). An AlAs/InGaAs double-barrier RTD and a varactor-diode mesa were integrated into a 20-μm-long slot antenna. A wide tuning range of ~11% (70 GHz) of the center frequency of 655 GHz was achieved by changing the depletion-layer capacitance of the varactor diode with a dc sweep from -4 to 0.5 V. The dependence of the output power on the varactor-diode bias was also measured. These experimental results agreed well with theory.