A Resilient Large-Piston Electrothermal Micromirror and Its Application in Handheld Fourier-Transform Near-Infrared Microspectrometers

Abstract Handheld Fourier-transform near-infrared (FTNIR) microspectrometers demand MEMS micromirrors capable of generating large piston displacement (LPD) for high spectral resolution, alongside the strict mechanical robustness required for field deployment. However, conventional electrothermal actuators rely on rigid and brittle inorganic dielectrics (e.g., Al-SiO2), which severely suffer from impact-induced fracture and inherently restrict the maximum actuation stroke. Here, we demonstrate a highly robust LPD electrothermal micromirror driven by an aluminum-photosensitive polyimide (Al-PSPI) bimorph actuator. The device features a 1 mm × 1 mm square mirror within a compact 1.85 mm × 1.85 mm footprint. Leveraging the superior mechanical compliance and resilience of PSPI, the actuators can survive drop heights up to 1.9 m, a 25-fold improvement over conventional Al-SiO2 bimorph counterparts. The micromirror achieves a maximum piston displacement exceeding 450 μm at an ultra-low driving voltage of 7.5 V, exhibiting a fundamental resonance frequency of ~588 Hz and a rapid response time of ~30 ms. To validate its practical utility, the micromirror was integrated into a compact, 350-gram handheld FTNIR prototype. The compact FTNIR achieves a spectral resolution of 26.2 cm-1 and covers a wide spectral range from 800 nm to 2500 nm, and it maintains stable operation under rigorous logarithmic sweep vibration testing (1 g, 20–2000 Hz, 12 min). This work establishes a versatile actuator design paradigm that fundamentally resolves the structural fragility of large-stroke MEMS mirrors, paving the way for next-generation portable hyperspectral imaging and highly reliable interferometric systems operating in extreme environments.