Fabrication and characterization of an all optically addressed micromirror array

We describe the fabrication process for an optically addressed adaptive optics array. The device consists of a micromirror array cascaded directly on wafer fused gallium arsenide (GaAs)-gallium phosphide (GaP) photodiodes. Optically addressing a photodiode generates a photocurrent which in turn causes a voltage drop across the cascaded mirror via an integrated thin film resistor. This architecture allows parallel optical addressing of individual elements without the need for wire bonding each pixel, which can enable higher density segmented type arrays. We first describe a fabrication process for releasing a free-standing array of low stress SixN micromirrors on an indium phosphide (InP) support substrate. We then present a process for transferring GaAs p-i-n photodiodes on a transparent GaP support substrate using a specially designed wafer fusion fixture. The two samples when stacked together and electrically connected via a specially formulated and patterned semiconductive SU-8 resist form the final device. We report mirror displacements of up to 500 nm using this technique while requiring an optical signal as low as 150 μW.