A Metal Interposer for Isolating MEMS Devices from Package Stresses

Abstract

Many classes of MEMS devices, such as those with resonant structures, capacitive readouts, and diaphragm elements, are sensitive to stresses that are exerted by their surrounding package structure. Such stresses can arise as a result of changes in temperature, ambient pressure, or relative humidity. We have demonstrated a dramatic reduction in scale factor bias over temperature for a tuning fork gyroscope by mounting it on an interposer structure within a conventional chip carrier, Fig. 1. Optimization of a MEMS sensor package for high performance subject to various constraints cannot be accomplished by analysis alone Hanson et al. [1]. There are too many unknown parameters, e.g., material properties, process conditions, and components/package interface conditions, to make this feasible. Extensive performance evaluation of packaged sensors is also prohibitively expensive and time consuming. However, recent advances in optoelectronic laser interferometric microscope (OELIM) methodology Furlong and Pryputniewicz [2] offer a considerable promise for effective optimization of the design of advanced MEMS components and MEMS packages. Using OELIM, sub-micron deformations of MEMS structures are readily measured with nanometer accuracy and very high spatial resolution over a range of environmental and functional conditions. This greatly facilitates characterization of dynamic and thermomechanical behavior of MEMS components, packages for MEMS, and other complex material structures. In this paper, the OELIM methodology, which allows noninvasive, remote, full-field-of-view measurements of deformations in near real-time, is presented and its viability for development of MEMS is discussed. Using OELIM methodology, sub-micron displacements of sensors can be readily observed and recorded over a range of operating conditions, Fig. 2.