Packaging-compatible wafer level capping of MEMS devices

A cost-effective, wafer-level package process for microelectromechanical devices (MEMS) is presented. The movable part of MEMS device is encapsulated and protected while in wafer form so that commodity, lead-frame packaging can be used. A polymer epoxycyclohexyl polyhedral oligomericsilsesquioxanes has been used as a mask material to pattern the sacrificial polymer as well as overcoat the air-cavity. The resulting air-cavities are clean, debris-free, and robust. The cavities have substantial strength to withstand molding pressures during lead-frame packaging of the MEMS devices. A wide range of cavities from 20 mu m x 400 mu m to 300 mu m x 400 mu m have been fabricated and shown to be mechanically stable. These could potentially house MEMS devices over a wide range of sizes. The strength of the cavities has been investigated using nano-indentation and modeled using analytical and finite element techniques. Capacitive resonators packaged using this protocol have shown clean sensing electrodes and good functionality. (C) 2012 Elsevier B.V. All rights reserved.