Micrometer-scale displacement and thickness sensing using a single terahertz resonant-tunneling diode

TL;DR

This paper introduces a compact 280 GHz radar system using a single resonant tunneling diode that can detect micrometer-scale displacements and thin-film thicknesses with high precision.

Contribution

It presents a novel integrated THz radar system exploiting self-mixing in a single RTD for precise displacement and thickness sensing at room temperature.

Findings

Minimum detectable displacement of ~5 micrometers

Resolution of polymer film thicknesses at 12.5, 25, and 50 micrometers

Successful demonstration of a monostatic THz sensor for practical applications

Abstract

Resonant tunneling diodes (RTDs) support room-temperature terahertz (THz) oscillation and simultaneous THz-band detection, enabling compact monostatic THz sensors for practical and cost-effective sensing applications. In this paper, we present a highly integrated 280 GHz-band radar system based on a single RTD that exploits the self-mixing effect to generate a low-frequency interferometric signal. The resulting self-mixing signal is further analyzed from a radar perspective and processed to extract micrometer-scale displacement and thin-film thickness variations. Experimentally, the proposed system demonstrates a minimum detectable displacement of approximately 5 um and quantitatively resolves polymer film thicknesses of 12.5, 25, and 50 um.