Flat free-standing silicon diaphragms using silicon-on-insulator wafers

Flat, free-standing silicon diaphragms for use as tunable micromirrors were demonstrated. Silicon-on-insulator (SOI) wafers were employed to realize s ingle-crystal mirrors, which are nearly free from residual strain. Using a wet chemical etch and a release process, free-standing structures were fabr icated. A surface bowing approximately 10 nm was measured, indicating the l ack of residual strain in the diaphragm. This value is much less than typic ally observed in polysilicon structures with diaphragms formed by chemical vapor deposition. Electrostatic actuation of the free-standing diaphragm wa s demonstrated and observed as a shift in the optical transmission spectrum of the Fabry-Perot cavity formed by the membrane and the substrate surface . A displacement of the membrane of approximately 200 nm was inferred from the wavelength shift of the transmission peak at an applied DC bias of 25 V . (C) 2000 Elsevier Science S.A. All rights reserved.