Active-matrix addressed micromirror array for wavefront correction in adaptive optics

For an enhanced wavefront correction in Adaptive Optics especially in the case of high-order aberrations we developed a new monolithic integrated micromirror device providing a dense array of 240 x 200 piston-type mirror elements on top of an active CMOS address matrix for a closer wavefront approximation. After an analytical and numerical modeling the micromirrors were designed and fabricated by means of aluminum surface-micromachining. Using a basic pixel size of 40 x 40 mum(2) a mechanical stroke of at least 450 nm could be achieved at address voltages below 30V, which is suitable for both active matrix addressing and a phase correction modulo 2pi in the visible. This also includes the option of an incremental increase of the actual mirror size in units of the address grid in order to allow for an extended analog deflection range. Furthermore, we designed and fabricated an active address matrix using a special high voltage CMOS process providing a full analog capability for address voltages up to 35V. Thereby, also a special light shielding as well as chemical mechanical polishing (CMP) for a high surface planarization. have been incorporated. The completed devices were experimentally characterized by surface profile measurements using white light interferometry. After determining the deflection characteristic we successfully demonstrated the analog operation capability by programming different height patterns into the matrix at an 8 bit resolution provided by the external driving board.