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CMOS integrable micromirrors with highly improved drift-stability

 
: Schmidt, Jan U.; Knobbe, Jens; Gehner, Andreas; Lakner, Hubert

:

Olivier, S.S. ; Society of Photo-Optical Instrumentation Engineers -SPIE-, Bellingham/Wash.:
MEMS adaptive optics : 24 - 25 January 2007, San Jose, California, USA
Bellingham, WA: SPIE, 2007 (SPIE Proceedings Series 6467)
ISBN: 978-0-8194-6580-1
Paper 64670R
Conference "MEMS Adaptive Optics" <2007, San Jose, Calif.>
English
Conference Paper
Fraunhofer IPMS ()
MEMS micro mirror; adaptive optic; amorphous metal film; sputtering; TiAl; stress relaxation

Abstract
The large-scale integration of analog operable MEMS micro-mirrors onto active CMOS address circuitry requires high quality planar reflective optical surfaces but also a stable deflection vs. voltage characteristic. However, for implementing a CMOS compatible surface micromachining process, certain obstacles like a restricted thermal budget and a limited selection of suitable materials must be overcome. In this paper, amorphous TiAl is presented as a new actuator material for monolithical MEMS integration onto CMOS circuitry at room temperature. Sputter deposited TiAl has an x-ray amorphous structure and a low stress gradient. The missing long range order and the high melting point help to virtually eliminate stress relaxation effects, i.e. TiAl hinges behave almost perfectly elastic. In a first study, 40 ?m wide piston mirrors have been implemented onto substrates with fixed wired address electrode arrays. The actuators had a 300 nm TiAl core sandwiched between two layers of 25 nm Al. The devices reach a maximum deflection of about 500 nm at a dc voltage of about 23V. The drift-stability of the deflection has been tested at "worst case" conditions close to the deflection limit. During 30 min of continuous deflection near 500 nm a mechanical drift below 25nm has been observed. TiAl offers the perspective for actuators capable of a stable analog operation, which is essential to many applications, such as adaptive optics.

: http://publica.fraunhofer.de/documents/N-63685.html