Fabrication of Resonant-Tunneling-Diode Terahertz Oscillators Using Rectangular Cavity Resonators and Bow-Tie Antennas for High Output Powers

Terahertz (THz) radiation, between light waves and millimeter waves, has been receiving much attention because of its applications. Resonant tunneling diodes (RTDs) are major candidates for THz wave sources, because of their operation at room temperature and compactness. Although we achieved a high frequency oscillation of 1.98 THz by a slot-antenna structure, the output power of RTD oscillators is relatively small, in the order of $10 \mu \mathrm{W}$ at around 1 THz. To increase the output power, we have proposed THz oscillators using RTDs with cavity resonators and bow-tie antennas. The rectangle cavity is expected to reduce the conduction loss and inductance, and the large-area RTD can be used even at high frequency in this oscillator, but can also emit a high output power. A high-power THz oscillation of ~11 mW at around 1 THz is theoretically expected. However, planar slot antennas have been mainly used in conventional monolithic integrated RTD THz oscillators and the development of a fabrication process of the three-dimensional cavity resonator on a semiconductor substrate is required. In this work, we developed and established the fabrication process of the oscillator with cavity resonator using a tri-layer resist process (ZEP/PMGI/PMMA).