A Lightweight Micromirror Made of Atomic-Layer-Deposition Alumina and Silicon with a High Aspect-Ratio Stiffening Structure

A lightweight 2mm diameter scanning micromirror made of atomic layer deposition alumina (ALD-Al
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) was designed and fabricated on a SOI wafer. The key feature of this mirror is an alumina-based high aspect-ratio and 500μm deep stiffening structure on the mirror backside, which is connected to a custom shaped silicon bone. This stiffening structure allows reducing the moment of inertia by a factor of 6.7 compared to that of a solid silicon mirror with the same dimensions. In addition, this enables higher resonance frequencies and reduced power consumption, while at the same time maintaining a predicted low dynamic deformation of less than 80nm at ~35kHz. The proposed mirror was fabricated by combining silicon deep reactive ion etching (Si-DRIE) with ALD-Al
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. Preliminary testing of the fabricated devices shows we achieved an optical scan angle of 10.2 degree at a scan frequency of 32.6 kHz.