MEMS microbridge deflection monitoring using integrated spin valve sensors and micromagnets

Summary form only given. In this work, the deflection of a microelectromechanical systems microbridge is determined with nm resolution using magnetoresistive field sensors, measuring the fringe field coming out of integrated micromagnets placed on the moving bridge structure. A spin valve sensor (10/spl times/2 /spl mu/m/sup 2/, MR=6.5%) was placed 3 /spl mu/m away and 2.8 /spl mu/m below the central region of an a-Si:H bridge, with a 1.2 /spl mu/m air gap. The bridge movement, resulting from an electrical force, was controlled by an applied voltage between gate and bridge. In the un-deflected state, a Co/sub 78/Pt/sub 22/ micromagnet (0.2 /spl mu/m/spl times/18 /spl mu/m/spl times/15 /spl mu/m, M/sub r/t=12.5 memu/cm/sup 2/), deposited on top of the bridge, and saturated in an external field, creates a fringe field in the spin valve sensor shifting the transfer curve. An external bias field was then used to linearize the sensor response. Final sensor output vs. bridge gate voltage was obtained using a low frequency square-wave gate excitation voltage (1 Hz). Bridge deflections from few nm to 0.23 /spl mu/m were then calculated according to the measured sensor output voltage. The microbridge deflection is being measured with an alternative external optical technique, in order to compare both methods.