Patent Number: 6,167,757

Title: Single-side microelectromechanical capacitive accelerometer and method of making same

Abstract: A high sensitivity, Z-axis, capacitive microaccelerometer having stiff sense/feedback electrodes and a method of its manufacture on a single-side of a semiconductor wafer are provided. The microaccelerometer is manufactured out of a single silicon wafer and has a silicon-wafer-thick proof mass, small and controllable damping, large capacitance variation and can be operated in a force-rebalanced control loop. One of the electrodes moves with the proof mass relative to the other electrode which is fixed. The multiple, stiffened electrodes have embedded therein damping holes to facilitate force-rebalanced operation of the device and to control the damping factor. Using the whole silicon wafer to form the thick large proof mass and using thin sacrificial layers to form narrow uniform capacitor air gaps over large areas provide large capacitance sensitivity. The manufacturing process is simple and thus results in low cost and high yield manufacturing. In one preferred embodiment, the fixed electrode includes a plurality of co-planar, electrically-isolated, conductive electrodes formed by thin polysilicon deposition with embedded vertical stiffeners. The vertical stiffeners are formed by refilling vertical trenches in the proof mass and are used to make the fixed electrode stiff in the sense direction (i.e. Z or input axis). The moving electrode is dimensioned and supported for movement on the proof mass so as to be stiff in the sense direction. In another embodiment both of the electrodes are electroplated. In yet another embodiment four support beams support the proof mass at an upper portion thereof and four support beams support the proof mass at a lower portion thereof.

Inventors: Yazdi; Navid (Scottsdale, AZ), Najafi; Khalil (Ann Arbor, MI)

Assignee: The Regents of the University of Michigan

International Classification: G01P 15/13 (20060101); G01P 15/125 (20060101); G01P 15/08 (20060101); G01P 015/125 ()

Expiration Date: 01/02/2018