Thin film magnetostrictive sensor with on-chip readout

Abstract

We report the first successful integration of magnetostrictive Metglas2605S2 (Fe78Si9B13) thin film sensor system on silicon with high resolution capacitive read-out. A deposition process for Metglas thin film has been developed to allow easy control of thin film composition. An amorphous microstructure has been achieved over a wide temperature range, and in-situ magnetic domain alignment can be accomplished at room temperature as the film is deposited. The thin film has been characterized by Inductively Coupled Plasma (ICP) analysis for composition, X-Ray Diffraction (XRD) spectrum for microstructure, magnetization measurement for domain alignment and capacitative measurement for magnetostriction. The thin film is suitable for any magnetostrictive sensor applications, in particular, for IC compatible microsensors and microactuators. We have demonstrated the subsequent process integration with IC fabrication technology. Here, the Metglas thin film has been successfully incorporated to micromechanical structures using surface micromachining with appropriate choice of sacrificial layer and low stress mechanical layers.

In addition, we present the development of a high resolution capacitative readout circuit co-integrated with the sensor. The readout circuit is based on a floating gate MOSFET configuration, requiring just a single transistor and operated at DC or low frequencies. Using the prototype developed in-house, we have successfully demonstrated a resolution capability of 10-17 F, this translates to a few A in terms of cantilever beam deflection of the sensor. The floating gate readout technique is readily applicable to any capacitive sensors with a need for on-chip readout. It is also an ideal in-situ test structure for on IC chip process characterization and parameter extraction.