Abstract:We proposed and fabricated resonant-tunneling-diode (RTD) terahertz (THz) oscillators with a structure for high-frequency direct modulation, which is useful for high-capacity THz wireless communications. The oscillator is composed of RTD and slot antenna. To obtain high cut-off frequency of direct modulation, the capacitance of the metal-insulator-metal (MIM) layer forming the slot antenna was reduced without decrease in THz output power which was a problem in the previous structure. A cut-off frequency of 30 GHz was obtained in direct intensity modulation of the device oscillating at 350 GHz with the reduced MIM capacitance of 0.7 pF.

In this paper, we proposed and fabricated resonant-tunneling-diode (RTD) terahertz oscillators integrated with slot-fed patch antennas to extract output power without using typical Si lenses. A square patch antenna with a 170 m-long side was fabricated on a 7 m-thick benzocyclobutene (BCB) layer stacked on an RTD with a slot resonator. The RTD oscillated at 510 GHz, and an output power of 40 W radiated in the upward direction without the Si lens. An equivalent circuit model was proposed to estimate the output power, and the circuit parameters were derived from the calculated admittance by electromagnetic simulation. The dependence of the output power on the side length of the patch antenna agreed with the theoretical calculation. Higher output power was expected with the optimization of BCB thickness and RTD with a high current density. The radiation pattern was measured, and a directivity of 7 dBi was obtained.

Short-Abstract-We proposed and fabricated resonanttunneling-diode (RTD) terahertz oscillators integrated with slotcoupled patch antennas for extraction of output power without the use of Si lenses. By eliminating a usually used bulky Si lens, we obtained a compact room-temperature terahertz oscillator. A 170-m square patch antenna was fabricated on a 7-m-thick BCB layer stacked on an RTD with a slot resonator. The RTD oscillated at 500 GHz, and the output power of ~40 W was radiated in the upward direction at the resonance of patch antenna coupled to the RTD and slot resonator. The measured radiation pattern reasonably agreed with theoretical analysis.

Although the direct-modulation frequency in a resonant-tunneling-diode oscillator increases by reducing the metal-insulator-metal capacitance, the output power degrades simultaneously. We figured out this mechanism using an equivalent circuit model. Based on this result, a novel structure was proposed and fabricated, and terahertz oscillation without degradation in output power was obtained.

In all spectroscopic methods, there exists an integral equation relating the observed spectrum and the intensity distribution observed by the spectroscopic instrument. An improved spectrum can be reconstructed by solving this integral equation. A process of eigenvalue analysis based on the theory of Hilbert and Schmidt was developed and applied to solve the equation. Formulation of this method and some computer simulations are presented on the results from a Fabry-Perot interferometer, a diffraction grating, and a two-beam interferometer. We also apply this method to spectroscopic techniques and considerations of resolution.