Micro-clamps for precise positioning of 120° silicon double mirrors in a MOEMS gyroscope

Micro silicon double mirrors have been developed specifically for the design of a novel micro-optical gyroscope. By using wafers with a well-defined angular offset to the (100) plane, an etching angle of 60° can be achieved by wet-chemical etching with KOH. Two likewise structured wafers are connected by means of silicon direct bonding and consequently form 120°double mirrors. A big advantage of these double mirrors is that inaccuracies during assembly onto a micro optical table, such as shifts in the x- and y-direction and twists around the vertical axis are compensated by the mirror and a fixed angle of reflection is maintained. Assembly tolerances for the other two rotational degrees of freedom cannot be compensated in this way yet and a precise rotational alignment of the mirror elements in an optical resonator is still required. Therefore a micro clamping device was developed that can be used in the assembly of a micro-optical gyroscope. The key elements are micro spring structures integrated in the micro-optical table which can be pushed back to allow the insertion of the mirror elements and press the mirrors against two lithographically defined mechanical stops. Various designs of clamping devices were fabricated and their suitability in an optical gyroscope was evaluated.