9 February 2007 CMOS integrable micromirrors with highly improved drift-stability
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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 &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.
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Jan U. Schmidt, Jan U. Schmidt, Jens Knobbe, Jens Knobbe, Andreas Gehner, Andreas Gehner, Hubert Lakner, Hubert Lakner, } "CMOS integrable micromirrors with highly improved drift-stability", Proc. SPIE 6467, MEMS Adaptive Optics, 64670R (9 February 2007); doi: 10.1117/12.707630; https://doi.org/10.1117/12.707630
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