Performance Enhancement of Silicon-Based Sub-Terahertz Detector by Highly Localized Plasmonic Wave in Nano-Ring FET

A compact monolithic trantenna (transistor-antenna) device is presented for a high-performance sub-THz wave detector using 28-nm CMOS foundry process. Based on a highly localized plasmonic wave in a silicon nano-ring field-effect transistor (FET), we obtained a total 535-fold photoresponse ( $\Delta {u}$ ) enhancement in an on-chip measurement as compared with our previous works using the same asymmetry ratio ( $\eta {a}= 30$ ). The inner contact diameter ( ${d} {\textit {in}}$ ) was scaled down from 8 to $0.13 ~\mu \text{m}$ for the parasitic resistance limit case. By changing the ground source from inside to outside the nano-ring FET, we could generate different $\Delta {u}$ polarities, which in turn reduced the junction leakage with improved $|\Delta {u}|$. From a fabricated nano-ring FET with the outer ring grounded source, we observed $5\times $ of additional $|\Delta {u}|$ enhancement followed by $107\times $ with ${d} {\textit {in}}$ scaling. In addition, based on the highly localized plasmonic wave nano-ring FET without any external gain, a record-high free-space responsivity of 12.4 kV/W and a reduced noise equivalent power of 1 pW/Hz $^{0.5}$ were experimentally demonstrated under 0.12-THz radiation.