MEMS microbridge vibration monitoring using spin-valve sensors

Spin-valve sensors were used to measure on chip, the vibration of microelectromechanical systems microbridges excited by dc + ac voltages. A spin-valve sensor (10 /spl times/ 2 /spl mu/m/sup 2/, MR = 6.5%) was placed 3 /spl mu/m away and 2.6 /spl mu/m below the central region of an a-Si:H/Al bridge, with a 1-/spl mu/m air gap. This sensor detects the fringe field created by a Co/sub 78/Pt/sub 22/ micromagnet deposited on top of the bridge. The bridge movement was controlled by an applied voltage on the gate. An unforeseen capacitance coupling effect was found between the control gate and the spin-valve sensor, affecting all ac measurements. Once this coupling was isolated and taken into account, bridge oscillation at joint dc + ac excitation voltages was monitored. Bridge vibration amplitudes of several tens of angstroms peak to peak were detected for dc and ac gate voltages up to 30 V.