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We report the dependence of oscillation frequency on the well and barrier thicknesses in a resonant tunneling diode (RTD) terahertz oscillator integrated with a planar slot antenna. The oscillation frequency increased with decreasing well and barrier thicknesses because of the reduction in dwell time in the resonance region. Room-temperature fundamental oscillation of up to 1.31 THz with an output power of about 10 µW was achieved in the RTD with a 3.9-nm-thick well and 1.0-nm-thick barriers.

We report resonant tunneling diode (RTD) oscillators with a high output power of around 400 µW at frequencies of 530–590 GHz. RTDs with a graded emitter and thin barriers were employed to obtain large negative differential conductance at high frequencies for high output power. An optimized structure of offset slot antennas was also used to maximize the radiation conductance. The highest output power obtained in this study was 420 µW at 548 GHz for an RTD with a peak current density of 24 mA/µm2; the RTD was placed 58 µm apart from the center of a 130-µm-long slot antenna.

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SiOx films deposited by evaporation under oxygen atmosphere were investigated to form low defect density insulating layers in Josephson integrated circuits. The defect density is high in SiOx films deposited under an oxygen pressure of less than 1.33×10−3 Pa, but it decreases greatly in films deposited under higher oxygen pressure. This can be explained by the presence or absence of elemental Si in the films. Elemental Si is present in films deposited under low oxygen pressure, but not in films deposited under higher oxygen pressure. The insulating characteristics of a SiOx film deposited under an oxygen pressure of 1.33×10−2 Pa are excellent.