Process Integration of Electroformed MEMS Variable Capacitors for Magnetostriction Measurements

Abstract

Electrochemically deposited CoFe and CoFeB films are being studied for use as wireless remote sensors. Coded signals can be achieved through passive devices and interrogated to produce electronic signatures that are nearly impossible to replicate or counterfeit. A MEMS variable capacitor is being fabricated from a novel electroformed process with CoFe and CoFeB magnetostrictive films. This approach to MEMS fabrication is being used to incorporate electroplated ferric alloys into a variable capacitor, to study Joule magnetostriction. Such alloys are capable of a large change in material shape when subjected to a magnetic field. Integrating these films with a variable capacitor MEMS device allows for a unique approach to provide accurate microstrain measurements in low magnetic fields up to saturation, to provide feedback for the optimization without the use of expensive commercial setups. This process is unique to MEMS device fabrication and is differentiated by the use of a planar layered approach. Maintaining planarity by manipulating oxides to form electroplating molds, as well as provide a sacrificial material, results in an electrochemically deposited cantilever structure with an integrated magnetostrictive sensing element. This presentation will discuss the fabrication process of these devices. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000