Compact THz Oscillators with Resonant Tunneling Diodes and Application to High-Capacity Wireless Communications

Our recent results of THz oscillators using GaInAs/AlAs resonant tunneling diodes (RTDs) were reported. For high frequency oscillation, the delay time of electrons was reduced. The delay time is composed of the dwell time in the resonant tunneling region and the transit time in the collector depletion region. The dwell time was reduced by a narrow quantum well, and a fundamental oscillation up to 1.31 THz with the output power of 10 microwatts was obtained at room temperature. The dependence of the oscillation frequency on thickness of collector spacer layer was investigated to obtain the optimum spacer thickness for short transit time and small capacitance, and a fundamental oscillation at 1.37 THz with 10 microwatts was achieved. A higher frequency is further possible with the structure optimization. For high output power, the offset slot antenna and coherent power combining were demonstrated, and 610 microwatts at 620 GHz was obtained with a two-element offset-antenna array. The spectral linewidth less than 10 MHz and a frequency change with bias voltage were also obtained. A preliminary experiment on wireless data transmission was demonstrated with the direct intensity modulation of RTD oscillator with bias voltage, and a transmission rate of 3 Gbps with the bit error rate of 3E-5 was obtained at 540 GHz. The bit rate is limited at present by the external capacitance around RTD.