Integrated magnetic sensing of electrostatically actuated thin-film microbridges

The movement of electrostatically actuated microbridges is measured by sensing the field of a permanent magnet, deposited and patterned on top of the microbridge, with a spin valve magnetic sensor fabricated beside the bridge at the level of the substrate. The spin valve sensor is sensitive to the position of the magnet and thus to the position of the bridge. The thin-film microbridges are fabricated using thin-film technology and surface micromachining at low temperatures (≤100°C) on glass substrates. The bridges are electrostatically actuated by applying a voltage between the bridges and a gate counter electrode placed beneath them. The deflection of the bridge is at the same time characterized optically by focusing a laser on the structure and monitoring the position of the reflected beam with a photodetector. A comparison of the bridge position sensing using the optical and magnetic methods is made. The absolute movement of the structures is measured with a precision close to 0.1 Å using the integrated magnetic sensor. The deflection of the electrostatically actuated structures is studied as a function of the applied gate voltage and length of the bridges. The experimental results show qualitative agreement with an electromechanical model.