Magnetolastic Smart Tags Using Electroformed Cobalt Iron Boron

Abstract

Microfabricated magnetoelastic resonators forming the basis for a new, passive, wireless tagging technology platform have been developed. These magnetoelastic tags operate on the principle of Joule magnetostriction (i.e., a large change in material shape induced by an applied AC magnetic field) to produce magnetic signals and are an alternative technology to existing inductive RF tags. Lithographically patterned and electrochemically deposited (ECD) cobalt iron boron (CoFeB) alloy films are used to create the longitudinal mode magnetoelastic resonators. Due to the greater thickness and low-stress nature of electrodeposited films, these resonators can be released like other MEMS devices via a sacrificial layer to form free-standing structures. This batch fabrication technique also allows for multiple resonators of varying lengths and magnetic bias angles resulting in a multi-frequency signal that becomes the tag identity. Hysteresis curves to measure fundamental material magnetic properties that affect tag performance such as magnetic saturation, coercivity, and susceptibility were measured. Process flows for microfabricating resonators along with resonator design, modeling and characterization results will be presented. Future design concepts for tags with environmental sensing functions using this novel material set will be briefly discussed.