Seiichirou Kitagawa

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.

Frequency-tunable resonant-tunneling-diode terahertz oscillators applied to absorbance measurement

We show that frequency-tunable terahertz oscillators with resonant-tunneling diodes (RTDs) can be applied to absorbance measurement, using allopurinol as a specimen, which has a characteristic absorption spectra at around 700 GHz. The RTD oscillators used in this experiment are seven elements covering from 420 to 970 GHz. The result was in good agreement with that of time-domain spectroscopy usually used in the terahertz frequency region.

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.