Tunable cylindrical micro lenses based on aluminum nitride membranes

We introduce sputtered aluminum nitride thin films for tunable micro-optics. During lens fabrication, AlN is deposited on a silicon substrate. Silicon is structured by using DRIE, which allows fabrication of circular, rectangular and irregular membrane shapes. In this contribution, we present the design, fabrication and characterization of AlN membranes for tunable cylindrical lenses. An optimized "dogbone" membrane is presented, which deflects cylindrically and has a small footprint. Compared to conventional rectangular membranes the optically useful area is doubled. The load deflection characteristic is investigated and basic relations between the refractive power and applied pressure are found. The relation can be used for tailoring the membrane properties, i.e. their residual stress, for a specific application. According to this calculation, a refractive power of 25 dpt with a lens aperture of 3x3 mm(2) is achieved for 12 kPa of applied pressure. The cylindrical deflection of the "dogbone" membrane is measured. The maximum shape difference in measured to be 270 nm