A new actuation structure for the deformation of continuous mirrors for adaptive optics

摘要

This work demonstrates a novel technique for the realization and the actuation of continuous-membrane for adaptive optic applications. This original device exhibits, for the first time, both positive and negative membrane deflection with individual pixel displacement of +/- 10 μm, which is one order of magnitude larger than usual approaches., without diffractive interference. The principle of the device relies on an array of actuators which allow a pixel based motion of the continuous mirror. These actuators are torsional electrostatic plates suspended 90 μm above the substrate which can achieve large angle deflection, up to 15°when underneath electrodes are biased. The fabrication is based on a self-assembling polysilicon process : the 3D structures are lifted up by the buckling of the supporting beams induced by scratch-drive actuation (SDA). The 3D structures are locked to mechanical anchors, and then an Au/SiO_2/Si_3N_4 membrane is fixed above these actuators thanks to spacer made out of thinned silicon wafer. The spacer thickness is determined to ensure a good mechanical contact between the membrane and the actuators. Once the voltage is applied to the buried actuation electrodes, lifted polysilicon plates rotate by electrostatic actuation, and thus, the mechanical coupling makes the membrane deflect above its zero-plane. This concept was experimentally validated using a reflecting Au/SiO_2/Si_3N_4 membrane, and a 5 μm-thick translucent plastic film reported an a 25 mm~2 KOH-etched silicon stand. Using visible-light optical tools, deformation of the membrane was demonstrated, with positive deflection up to 10 μm for an actuation voltage of 200V.