Wide frequency tuning in resonant-tunneling-diode terahertz oscillator using forward-biased varactor diode

We report wide frequency tuning in a resonant-tunneling-diode (RTD) terahertz oscillator with a small change in the forward bias of a varactor diode integrated with the RTD. The obtained frequency change is 600–730 GHz with the voltage change of 0.4–0.8 V. The rate of this frequency change with bias voltage is much higher than that in the previously reported reverse-bias operation (680–600 GHz with −4 to +0.4 V in the present device). The result is well explained by theoretical analysis using equivalent circuits of the varactor diode and air bridge. The possibility of wider frequency tuning is also discussed.