A high-fill-factor electrothermally-actuated analog micromirror array with hidden actuators and optimized interconnects for light projection

Electrothermally-actuated analog micromirror arrays (ET-AMAs) offer large displacement, low driving voltage, and ease of scaling to large optical apertures, making them promising for analog light projection with a wide and variable field of view (FOV). However, achieving high optical efficiency and high‑contrast projection requires arrays with high fill factor and flat mirror surfaces, which conventional ET-AMA designs struggle to provide. To address these limitations, we present a 4 × 4 ET-AMA with a hidden‑actuator configuration and a dual‑conductive‑layer stacked interconnect scheme, enabling fill factors as high as 84%. To improve the mirror surface quality, the fabrication process employs a tailored deep‑silicon‑etch sidewall profile to form easily removable silicon sacrificial layers, together with highly selective isotropic etching gases. This technique significantly enhances the microstructure release efficiency and minimizes damage to the mirror-supporting silicon frames. The fabricated ET-AMAs exhibit an average radius of curvature of the mirror surfaces as large as 94.5 cm. The micromirrors achieve an optical scanning range of ±9° under a low DC voltage of 2.72 V, meeting the FOV requirements for applications such as automotive head-up displays. Demonstrations of block‑wise multimodal actuation and 16‑pixel pattern generation further highlight the ET-AMA’s strong beam‑modulation capability and its flexible, efficient variable‑FOV light projection potential.