As society advances towards greater intelligence, functionality, and miniaturization, civilian-grade room-temperature high-precision miniature infrared detectors are increasingly gaining attention. These detectors are expected to feature in electronic devices such as smartphones, smart bracelets, and smart glasses, enabling significant applications in human health monitoring and environmental detection of toxic and harmful gases. Micro-electro-mechanical system (MEMS) infrared thermal detectors are favored for small size, low power consumption, broadband response, and ability to operate at room temperature without requiring cryogenic cooling. However, current room-temperature infrared detectors typically achieve a detectivity of around 10¹⁰ Jones, with noise equivalent temperature difference (NETD) values rarely below 20 mK. Improving the photo-thermal coupling efficiency is essential for enhancing detector sensitivity. Leveraging optical metasurfaces and metamaterials, researchers have developed localized optical-mechanical field control technologies that regulate the spectral, phase, and polarization characteristics of electromagnetic waves. These approaches effectively enhance the photo-thermal coupling efficiency. However, further research is needed to refine the underlying mechanisms of photo-thermal-mechanical conversion and improve performance.

In this paper, we investigate the mechanism of weakly coupled optical-mechanical regulation and mode localization for room-temperature high-sensitivity infrared thermal detection. By combining optical and mechanical localized field regulation, a novel optical-thermal-mechanical-electrical conversion is proposed. Enhanced optical absorption due to localized field effects is amplified through mechanical nodal localization, enabling high-sensitivity infrared spectral detection. This approach addresses the low sensitivity of conventional thermal detectors and achieves high-sensitivity, low-noise infrared detection under room-temperature conditions. Efficient coupling between electromagnetic and mechanical resonances is achieved, and weak coupling of localized resonant modes enables the conversion of optical perturbation signals into highly sensitive responses through modal amplitude shifts.

The proposed detector demonstrates three district electromagnetic resonance absorption peaks within the wavelength range of 5 to 16 μm, with absorption rates of 82.4% (6.0 μm), 97.3% (9.3 μm), and 86.5% (11.7 μm), respectively (Fig. 2). The results also indicate that for both TE and TM electromagnetic waves, high absorption rates are maintained across varying incident angles, demonstrating excellent angular insensitivity (Fig. 4). When external thermal stress disturbances increase, the resonator’s stiffness decreases, leading to changes in modal amplitude. For the first resonator, the first-order modal amplitude decreases while the second-order amplitude increases, signaling a shift in vibrational energy indicative of modal localization. In the second resonator, modal amplitudes remain largely unchanged but gradually diminish as external disturbances increase, confining vibrational energy to specific modes. This modal distribution, characteristic of localization (Fig. 5), effectively transforms optical perturbation signals into highly sensitive responses through modal amplitude shifts. The sensing sensitivity exceeds -4.4736 mW^-1 (Fig. 6), representing a nearly three-order-of-magnitude improvement over the traditional frequency shift method (-0.0073 mW^-1) under similar conditions. This innovative detector design is expected to drive the development of ultra-sensitive uncooled infrared detectors for applications in wearable devices such as smartphones, smart bracelets, and smart glasses.

In this paper, we propose a highly sensitive MEMS infrared thermal detector based on the mode localization optical-mechanical weak coupling mechanism. The detector utilizes a metasurface infrared absorber composed of a patterned metal-dielectric-metal nanostructured titanium array, amorphous silicon dielectric, and titanium metal layers, achieving enhanced localized field absorption over a broad wavelength range (5 to 16 μm). A two-degree-of-freedom weakly coupled micro-mechanical cantilever resonator is designed, leveraging the modal localization mechanism to include significant modal amplitude shifts in response to infrared radiation. Theoretical analysis reveals that the modal localization effect confines mechanical energy within specific resonant modes, and stiffness disturbances caused by infrared radiation trigger substantial amplitude shifts, thus achieving ultra-high detection sensitivity. At the second-order resonant mode, the detection sensitivity reaches approximately -4.4736 mW^-1, a 613-fold improvement over the traditional frequency shift method (-0.0073 mW^-1). The method provides a new approach for enhancing MEMS infrared thermal detector sensitivity. Our approach is expected to facilitate highly sensitive infrared spectral detection at room temperature, with broad applications in wearable electronics and smart sensor systems.