Electrostatically deflectable polysilicon torsional mirrors

Abstract This paper describes the fabrication of electrostatically deflectable structures using surface micromachining with chemical vapour deposition (CVD) polysilicon. Particular attention has been paid to the realization of torsional mirrors. Free-standing structures with a thickness of 1 μm are produced by lateral etching of a 2 μm sacrificial silicon dioxide layer deposited between the substrate and the CVD polysilicon layer. In order to avoid sticking of completely under-etched structures to the substrate, the polysilicon microstructures are fixed by a frozen solvent after etching of the sacrificial layer and rinsing; subsequently a sublimation process under vacuum is applied. The torsional mirrors are deflectable with voltages of about 20 V. The maximum deflection is approximately 2°. Several mirrors with different dimensions have been made. For comparing and optimizing their mechanical properties and behaviour during deformation, mirror designs are modelled using the finite-element program ANSYS.

[1]  G. Flach,et al.  Piezoresistive accelerometer with overload protection and low cross-sensitivity , 1993 .

[2]  Process optimization of free-standing polysilicon microstructures , 1992 .

[3]  V. P. Jaecklin,et al.  Optical microshutters and torsional micromirrors for light modulator arrays , 1993, [1993] Proceedings IEEE Micro Electro Mechanical Systems.

[4]  N. F. de Rooij,et al.  Line-Addressable Torsional Micromirrors for Light Modulator Arrays , 1994 .

[5]  K. Petersen.  Dynamic micromechanics on silicon: Techniques and devices , 1978, IEEE Transactions on Electron Devices.

[6]  N. F. de Rooij,et al.  Investigations on free-standing polysilicon beams in view of their application as transducers , 1990 .

[7]  R. Howe,et al.  Polycrystalline Silicon Micromechanical Beams , 1983 .

[8]  W. von Münch,et al.  Silicon pressure sensor with integrated bias stabilization and temperature compensation , 1992 .

[9]  T. Christenson,et al.  Fabrication of micromechanical devices from polysilicon films with smooth surfaces , 1989 .

[10]  D. W. Burns,et al.  Mechanical properties of fine grained polysilicon-the repeatability issue , 1988, IEEE Technical Digest on Solid-State Sensor and Actuator Workshop.

[11]  Larry J. Hornbeck,et al.  Deformable-Mirror Spatial Light Modulators , 1990, Optics & Photonics.

[12]  Kurt E. Petersen,et al.  Silicon Torsional Scanning Mirror , 1980, IBM J. Res. Dev..

[13]  Khalil Najafi,et al.  An ultrasensitive silicon pressure-based microflow sensor , 1992 .

[14]  L. Hornbeck,et al.  128 × 128 deformable mirror device , 1983, IEEE Transactions on Electron Devices.

[15]  L. J. Hornbeck,et al.  Current status of the digital micromirror device (DMD) for projection television applications , 1993, Proceedings of IEEE International Electron Devices Meeting.