Abstract
In this work, the theoretical shapes of cavities were investigated as suited for resonant-tunneling diode (RTD) lumped-element oscillators to achieve the highest possible operational frequency. The scope of this work is restricted to cylindrical cavities that are in their dimensions much smaller or similar to the free-space wavelength. The idea is to find a shape that has the highest quality factor possible. The proposed analysis is based on functional variation principles coupled with electric-field integral equation (EFIE) method of moments solver. Simple design parameters were found covering the cavities that are much smaller than the free-space wavelength. The maximum reachable frequency was calculated with these types of new cavities using some theoretical RTD parameters. The theoretical limitation of frequency was also defined for given RTD parameters and fabrication limitations originating from the contact resistance and RTD radius. In order to demonstrate the significance of the findings, a theoretical geometry was compared with a practical resonator shape.
Highlights
D URING the last decades, the terahertz (THz) regime between 1 and 10 THz got in focus due to its broad application area
The highest measured oscillation frequency achieved by an resonant-tunneling diode (RTD) oscillator is 1.98 THz [6], which is a slot antenna-based device with thick electrode to reduce the conduction losses [14]
A problem could be that the normal derivative of H is not continuous on the surface of the cavity. With this assumption in mind, one tries to find the E-field for a given H -field, which could be measured inside the cavity, which still smoothly varies with the change of the resonator geometry
Summary
D URING the last decades, the terahertz (THz) regime between 1 and 10 THz got in focus due to its broad application area. The highest frequency room temperature semiconductor devices in that range are resonant-tunneling diode (RTD)based structures that can operate up to 2 THz [6]. The highest measured oscillation frequency achieved by an RTD oscillator is 1.98 THz [6], which is a slot antenna-based device with thick electrode to reduce the conduction losses [14]. No RTD-based room-temperature lumpedelement oscillator was fabricated in order to successfully reach 3-THz operational frequency, and just theoretical structures were suggested [9], [10]. The exact shape of the cavity is rather important in order to minimize the conduction losses and not to create additional parasitic effects by the closed structure [10]. The parasitics due to the biasing elements and due to the antenna were neglected in the aim to find a theoretical limit
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