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

2026-02-27

AI Summary

This work proposes a compact self-mixing radar system based on a single terahertz resonant tunneling diode (RTD) to address the demand for high-precision sensing of micrometer-scale displacements and thin-film thicknesses. For the first time, a single RTD is employed simultaneously as a 280 GHz tunable oscillator and a self-mixing detector, eliminating the need for an external heterodyne receiver chain. By sweeping the oscillation frequency to induce self-mixing interferometry, low-frequency signals are extracted to demodulate displacement and thickness information. Experimental results demonstrate a minimum detectable displacement of approximately 5 μm and successful discrimination of polymer films with thicknesses of 12.5, 25, and 50 μm, confirming the effectiveness and innovation of this approach for miniaturized, high-precision sensing applications.

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Abstract

Resonant tunneling diodes (RTDs) provide room-temperature terahertz oscillation and strong nonlinear mixing, enabling compact monostatic sensors in which a single device acts as both a bias-tunable oscillator and a self-oscillating mixer. This paper presents a 280 GHz-band radar concept enabled by a single RTD, which exploits self-mixing to generate a low-frequency radar interferometric signal while sweeping the RTD oscillation frequency. We show that the RTD self-mixing waveform can be interpreted from a radar perspective and processed to extract micrometer-scale displacement and thin-film thickness changes from repeated sweeps. Using the proposed technique, we experimentally demonstrate a minimum detectable displacement of ~5 um and quantitatively resolve polymer film thicknesses of 12.5, 25, and 50 um.

Problem

• micrometer-scale displacement
• thickness sensing
• terahertz
• resonant-tunneling diode
• radar interferometry

Innovation

• resonant tunneling diode
• terahertz radar
• self-mixing interferometry
• micrometer displacement sensing
• thin-film thickness measurement