We present the principle of a terahertz-wave radar and its proof-of-concept experimental verification. The radar is based on a 522 GHz resonant-tunneling-diode oscillator, whose terahertz output power can be easily modulated by superimposing the modulation signal on its bias voltage. By using one modulation frequency and measuring the time delay of the returning signal, a relative measurement of the propagation distance is possible; adding a second modulation frequency removes the ambiguity stemming from the periodicity of the modulation sine wave and allows an absolute distance measurement. We verified this measurement method experimentally and obtained a submillimeter precision, as predicted by theory.

We present the principle and the experimental verification of a distance measurement method based on the propagation of terahertz waves. The method relies on modulating the amplitude of a resonant-tunneling-diode (RTD) oscillator used as terahertz-wave source and on measuring the phase of the detected wave by applying a quadrature mixing technique. The distance measurement is found to have a residual error as small as 0.063 mm (standard deviation), which is a record for an RTD-based terahertz-wave radar system. This is almost five times better than our previous record of 0.29 mm, when an oscilloscope was used for phase measurements; additionally, the quadrature mixing brings about numerous practical benefits, such as greatly reduced cost, size, weight, complexity, and power consumption.

We introduce a new principle for distance measurement in the terahertz-wave range using a resonant-tunneling-diode (RTD) oscillator as a source at 511 GHz and relying on the frequency-modulated continuous-wave (FMCW) radar technique. Unlike the usual FMCW radar, where the sawtooth frequency modulation is applied to the carrier, we propose applying it to a subcarrier obtained by amplitude modulation; this is advantageous when the source cannot be controlled precisely in oscillation frequency, but can easily be modulated in amplitude, as is the case of the RTD oscillator. The detailed principle and a series of proof-of-concept experimental results are presented.

In order to avoid oxygen contamination on the diamond surface as far as possible during the device process, the diamond metal-insulator-semiconductor field-effect transistor (MISFET) was prepared by a reduced-oxygen process including an ultrahigh vacuum (UHV) process for the first time, and its electrical properties were investigated in detail. According to the results, it was found that the electrical properties of the MISFET were improved to a great extent in comparison with those of conventional diamond MISFETs. The observed effective mobility (µeff) was 400 cm2/V·s at room temperature, which is the highest value obtained until now in the diamond FET at room temperature. Besides, the measured transconductance (g m) and surface state density (N SS) of the device operation region was 5 mS/mm and ∼1010/cm2·eV, respectively, which is also comparable with conventional Si metal-oxide-semiconductor field-effect-transistors (MOSFETs) with the same gate length (L g = 30 µm).

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