Surface micromachined capacitive accelerometer with torsionally movable electrode
(off-plane accelerations):

Basic features:

• Upper capacitor plate is attached to pedestal via a torsional bar having the axis in x direction
• Asymmetric proof mass structure has a centre of mass that is offset from the axis of the torsional bar
• Acceleration along the z-axis produces a moment around the torsional bar axis
• On the substrate surface, beneath the sense element wing, two conductive capacitor plates are symmetrically located on each side of the torsional bar axis
• Upper wing and the two lower capacitor plates on the substrate form two air-gap variable capacitors with a common node, creating a fully active capacitance bridge
• Sense element may be built out of nickel and its alloys using selective electroforming
• Approximate dimensions of the sense element are 1000 μm of length, 600 μm of width and 5 to 10 μm of thickness
• Wing to substrate spacing of about 5 μm results in a capacitance of about 0.15 pF.