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 x 8 arrays of hinged mirror/paddle structures with dimensions of 97 mu m x 180 mu m. 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. (C) 2013 Elsevier B.V. All rights reserved.