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9 February 2007 CMOS integrable micromirrors with highly improved drift-stability
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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 &mgr;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.
© (2007) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Jan U. Schmidt, Jens Knobbe, Andreas Gehner, and Hubert Lakner "CMOS integrable micromirrors with highly improved drift-stability", Proc. SPIE 6467, MEMS Adaptive Optics, 64670R (9 February 2007);

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