A Bulk Micromachined Si-on-glass Tunneling Accelerometer with Out-of-plane Sensing Capability

A bulk micromachined tunneling accelerometer on Pyrex 7740 glass substrate is reported in this paper, which is capable of out-of-plane sensing and intended for highly sensitive inertial measurements. Low stress in single crystal Si (SCS) proof mass-suspension structure and low thermal incompatibility between SCS structural layer and substrate can minimize low frequency noise of the device. Double-face ICP etchings are utilized to define the movable proof mass and suspension: one made on the face with the tip to partially defines the movable structure before anodic bonding, and another made to releases the movable structure after the bonding. The process can avoid severe blades, as found on beams of samples fabricated with previous process. A 3-order closed loop control circuit is used to keep the tip staying close to the optimal operation position and to ensure favorable linearity over the measuring range. Theoretical analysis and design of the control electronics are presented. The device is tested in low noise environment and the result shows an excellent low frequency resolution of 0.015mg/rtHz (@1~100Hz), and nonlinearity < 2% over plusmn10g input (<1% over plusmn 1g).