Ultrasound enhanced electrostatic batch assembly for MEMS

This paper describes ultrasound enhanced electrostatic batch assembly (U2EBA) as a low-cost, batch microassembly method to assemble 3D microsystems. U2EBA involves placing the die in an external DC electric field perpendicular to the substrate and actuating the die with an off-chip, bulk-piezoelectric ceramic. The foremost advantages of this method are the simplicity of the assembly setup, applicability to a broad range of surface micromachining processes, lack of any additional fabrication steps or unusual materials, and fully off-chip nature that requires no electrical or mechanical contact to the assembled microstructures. After an investigation of the forces involved in U2EBA, experiments aiming to quantify the anti-stiction effect of ultrasonic actuation are described. Yield rates reaching up to 100% are reported from 8 × 8 arrays of hinged mirror/paddle structures with dimensions of 97 μm × 180 μm. Reasons of failure for the unassembled structures and the maximum limit for the electrostatic assembly forces are discussed. Experiments on different hinged microstructures allowed comparison of design parameters and revealed a 22% improvement in the assembly yield due to the addition of dimples over the paddle region of the microstructures.

Graphical abstractFigure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Simple, low-cost, batch microassembly method is demonstrated. ► Forces involved in the microassembly process are described. ► We showed assembly yields reaching up to 100% on hinged 8x8 micromirror arrays. ► The method is non-contact and it does not require any wirebonding. ► Ultrasonic actuation and dimples improve the assembly yield.