Improving Terahertz-Detection Sensitivity of $8 \times 8$ FET Arrays Through Liquid-Nitrogen Cooling in a Compact Low-Noise Cryostat

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Abstract
We show that the sensitivity of antennacoupled field-effect transistors (FETs) to terahertz (THz) radiation improves continuously with decreasing temperature. The noise-equivalent power (NEP) of 540 GHz patch-antenna-coupled FETs decreases as temperature reduces to 20 K. We project NEP values approaching $1\rm{--}2\rm{ pW}/\sqrt{\rm{Hz}}$ under efficient power coupling conditions (e.g., using a superstrate Si-lens), which is comparable to superconducting niobium transitionedge sensors (TESs) at 4 K. Building on these findings, a compact, low-noise, liquid-nitrogen-cooled (77 K) FETbased direct (incoherent) THz-power sensing system for spectroscopy applications was realized. Here, an $8 \times 8$ pixel-binned detector array fabricated in a commercial 65-nm Si-CMOS process, was optimized for operation in the 2.85-3.4 THz band. Characterization was performed in the focal plane of a 2.85-THz quantumcascade laser delivering $\sim 2\rm{ mW}$ of THz power. A linear dynamic range exceeding 67 dB was achieved without saturation (for 1 Hz-detection bandwidth). The system provides a -3 dB readout bandwidth of 5 MHz, exceeding that of conventional thermal detectors (typically 1 kHz). Combined with its broad temperature operability (20-300 K) and compact design, the system is particularly well suited for space- and payload-constrained platforms such as balloon- and satellite-based missions, where deep cryogenic cooling is impractical.
Funding Information
  • Lithuanian Science Foundation (S-MIP-22-83)
  • European Commission (101053716)
  • European Regional Development Fund (KPOD.01.18-IW.03-0019/23)
  • Deutsche Forschungsgemeinschaft (RO 770 49-1)
  • INTEREST collaborative research program program (SPP 2314)
  • UK Research and Innovation (MR/Y011775/1)
  • UK Research and Innovation (MR/S016929/1)
  • Engineering and Physical Sciences Research Council (EP/W028921/1)

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