**4. Conclusions**

To conclude, this paper presents the design, simulation, and experimental validation of a room-temperature monolithic resonant triple-band THz thermal detector, which was fully implemented in a CMOS process, allowing reduced fabrication complexity and lower production cost. The detector was composed of a compact triple-band octagonal ring antenna loaded with a polysilicon resistor and a sensitive PTAT sensor. The responsivity, noise equivalent power, and thermal time constant of the detector were experimentally assessed at 0.91 THz, 2.58 THz, and 4.2 THz, showing relatively better measurement results. The detector also has natural scalability to focal plane arrays, demonstrating significant advances

in developing compact, room-temperature, low-cost, and mass-production multiband THz detection systems.

**Author Contributions:** Conceptualization, X.W., T.-P.L., S.-X.Y. and J.W.; methodology, X.W. and S.-X.Y.; software, X.W. and S.-X.Y.; validation, X.W., T.-P.L., S.-X.Y. and J.W.; formal analysis, J.W.; investigation, X.W., T.-P.L., S.-X.Y. and J.W.; resources, T.-P.L. and J.W.; data curation, X.W. and S.-X.Y.; writing—original draft preparation, X.W. and S.-X.Y.; writing—review and editing, S.-X.Y. and J.W.; visualization, X.W. and S.-X.Y.; supervision, S.-X.Y. and J.W.; project administration, S.-X.Y. and J.W.; funding acquisition, T.-P.L. and J.W. All authors have read and agreed to the published version of the manuscript.

**Funding:** This work was supported by the State Key Laboratory of Complex Electromagnetic Environment Effects on Electronics and Information System (No. CEMEE2022G0201) and the China Postdoctoral Science Foundation (Grant No. 2020M680883).

**Data Availability Statement:** Not applicable.

**Conflicts of Interest:** The authors declare no conflict of interest.
