According to the European recommendation 2000/78/EG, barrier-free access to electronic media has to be realized for visually impaired persons. While text files are presented by Braille cells or acoustically, the realization of graphic displays still requires huge technological expense and high costs. Further improvement is possible by shape memory alloy (SMA) actuators which provide the highest work output of the so-called smart materials. In particular, thin film SMA actuators are of special interest, since they provide much higher actuation frequencies than bulk actuators due to their high surface to volume ratio. In combination with other metallic films, SMA-composites show the two-way behavior right after deposition and annealing treatment. The work output upon the martensitic transformation is about ten times larger than the bimetallic effect. The corresponding actuators can be fabricated by cost effective parallel batch processing including magnetron sputtering and photolithographic structuring.
At caesar, a new mechanism to switch thin film actuators between two stable states has been developed.. Bistable membrane switches can be realized by snap-dome shaped metallic foils which are coated on opposite surfaces with Ti(Ni,Cu) and (Ti,Hf)Ni respectively whereby the narrow hysteresis of Ti(Ni,Cu) is within the broad one of (Ti,Hf)Ni. If both SMAs are martensitic or both are austenitic, they apply similar forces on the intermediate foil and the shape of the membrane remains constant. However, if one of them is austenitic and the other one martensitic, the austenitic one determines the curvature of the membrane. Switching is possible by two different heat pulses. Therefore, energy is only required to change the state of the membrane.
The new mechanism is described and first successful processing steps are presented. The mechanism allows the fabrication of microswitches and tactile displays. It won the second funding prize 2004 of the foundation ONCE, Spain.

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