Si Superstrate Lenses on Patch-Antenna-Coupled TeraFETs: NEP Optimization and Frequency Fine-Tuning

This paper presents a study on performance optimization and resonant frequency modification of terahertz detectors by the use of hyper-hemispherical silicon superstrate lenses. The detectors are patch-TeraFETs, i.e., field-effect transistors with monolithically integrated patch antennas fabricated with a commercial 65-nm CMOS foundry process and designed for an operation frequency of 580 GHz. We demonstrate a strong improvement of the optical noise-equivalent power optical NEP, referenced against the total radiation power) reaching a value of 16 pW/Hz^(1/2). We show, furthermore, that the resonance frequency can be efficiently fine-tuned by the choice of the material and the thickness of a dielectric layer placed between the transistor and the superstrate lens. The resonance frequency can be shifted by more than 15 % of the center frequency (up to 100 GHz for the 580 GHz devices). The design of the on-chip optics can be employed for post-fabrication tailoring of the detector's resonance frequency to target specific spectral positions.