A novel electrostatic actuator for micro deformable mirrors: fabrication and test

High performance adaptive optics systems for both astronomy and ophthalmology require deformable mirrors with a continuous membrane, a high actuator density and a stroke of several microns CEA/LETI and LAOG are collaborating to develop such devices, using a new kind of electrostatic actuator based on the so-called zipping effect. These new actuators can reach a large vertical force (more than 100 /spl mu/N for an active area of 800/spl times/800 /spl mu/m/sup 2/), and a large vertical stroke (more than 6 /spl mu/m). An innovative process based on SOI wafer bonding is used for the actuator array. The quasi-static response matches the FEM simulations, showing a good linearity. The dynamic response presents a clean non-resonant behaviour, with 1dB gain and 20/spl deg/ phase error at 2 kHz. A modulated control voltage is used to minimize the charging effects in the dielectric layer. A continuous membrane is manufactured separately, and a first assembly test was made on a single actuator. This promising test shows that an inter-actuator stroke of 2 /spl mu/m is possible with a continuous membrane and a voltage of 150 V. The peak to peak deflexion of the whole mirror should be larger than 6 /spl mu/m.