An optically flat micromirror using a stretched membrane with crystallization-induced stress

Minoru Sasaki, Takashi Sasaki, Kazuhiro Hane, Hideo Miura

Research output: Contribution to journalArticlepeer-review

22 Citations (Scopus)


A flat and lightweight micromirror with a drum design is realized using a tense polycrystalline (poly-) Si membrane across a rigid crystalline (c-) Si ring. The tensile stress of ∼600 MPa is obtained using the crystallization of amorphous (a-) Si film. The tension keeps the membrane flat. Compared to the previous research, the initial film has a purer amorphous phase, and a larger stress is obtained. In addition to the design dependence, the membrane flatness is found to depend on the process sequence relating to the timing of the crystallization. A peak-to-valley surface deformation of ∼20 nm is realized in a 500 μm diameter mirror satisfying the optical flatness of <λ/10 for visible light. Since the crystallization-induced stress is temperature independent, the mirror flatness is stable against temperature even with a metal coating for higher reflectivity.

Original languageEnglish
Article number044004
JournalJournal of Optics A: Pure and Applied Optics
Issue number4
Publication statusPublished - 2008 Apr 1


  • Amorphous
  • Crystallization
  • Micromirror
  • Optical flatness
  • Tensilestress

ASJC Scopus subject areas

  • Atomic and Molecular Physics, and Optics


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