Fluidic self-assembly of micromirrors onto microactuators using capillary forces

The authors discuss the application of self-assembly techniques for positioning microscopic components onto a substrate in a desired configuration. The basis is a fluidic self-assembly technique in which capillary forces assemble microparts with submicrometer alignment precision. A heat-curable acrylate-based adhesive is used to provide the capillary forces for assembly and is then polymerized in a bath of water at 80°C for 16 h with continuous nitrogen bubbling. The application we describe is self-assembly of flat silicon micromirrors; onto surface-micromachined actuators for use in an adaptive-optics mirror array. Photolithography defines shapes of hydrophobic self-assembled monolayers for self-assembly. Mirrors with fill factors up to 95% were assembled. Mirrors 464 μm in diameter and assembled onto actuators remain flat to within 6 nm rms. This mirror quality would be difficult to attain without the process decoupling afforded by microassembly. The general self-assembly approach described here can be applied to parts ranging in size from the nanometer to the millimeter scale and to a variety of part and substrate materials