A universal wafer-level capping process for MEMS and microdevices

This Small Business Innovation Research (SBIR) Phase I project provides a universal capping technology for microelectromechanical systems (MEMS) and other microdevices. The technology will allow for thousands of moving MEMS devices to get protected from the environment in an inert gas or vacuum. The cap wafer technology itself has already been developed-the focus of this project is to develop a wide range of solder alloy bonding technologies which will allow for strong bonds, good electrical connectivity to the devices and vacuum/hermetic seals with virtually zero leak rates for a wide range of processes and device functionalities. The bond strengths will depend on the metal deposition conditions, the thermal budget before and after bonding and chemical reactions between each material (gold-indium, nickel-tin, silver-indium, silver-tin, copper-indium, etc.). Electrical characterization will involve optimizing the deposited metal stack in order to achieve low electrical resistances, optimized chemical potentials for ohmic contact and low paracitics. Initially the bond uniformity will be characterized by inspection, but will eventually be characterized with hermetically/vacuum sealed sensors allowing for fine leak rate measurement (<10-15 cubic centimeters/second) and the characterization of outgassing (desorption of atoms from the microcavity surfaces), in order to characterizing the yield of functional hermetic/vacuum packages. The broader impact/commercial potential of this project is to provide a universal packaging technology for microelectromechanical systems (MEMS). Packaging (providing electrical connectivity and environmental protection) is generally the most difficult part of bringing MEMS to market. The MEMS market is expected to grow from $8 billion in 2008 to $15 billion by 2012. An approximately $11 billion portion of this market can benefit from cost efficient wafer-level packaging. A wide range of industrial and academic researchers are developing packaging solutions for emerging MEMS markets including radio frequency (RF) switches, microfluidics, micro-batteries, infrared (IR) sensors and biomedical devices. The technology in this project will provide a universal packaging solution for all of these devices. This will have several effects on the market: 1) It will allow for these emerging MEMS devices to be cost effectively packaged helping them get to market, 2) it will simplify the value chain for production allowing MEMS designers to choose the optimal process/manufacturing house without consideration of their capping technology and 3) it will enhance innovation by allowing researchers to focus on the functionality of the MEMS device itself without having to consider the package design.