Bulk micromachined capacitive accelerometers

• Bulk anisotropic etching of silicon is a well-developed technology

• Comparing to pressure sensors, accelerometers require more sophisticated anisotropic etching (double-sided etching)

• Size of bulk micromachined accelerometers is typically a few millimetres

 

Surface micromachined capacitive accelerometers

• Proof mass and its suspensions are fabricated by techniques using LPCVD or electroplating

• Sacrificial spacing layer is removed after the structural film is deposited to release the structure from the substrate

• Sensors are typically few hundreds of micrometers on each side, with the thickness of each layers determined
  by the deposition times of those layers

• Performance of these devices depends critically on

  • Uniformity and mechanical properties of the deposited layers

  • Effects of residual stress in the films

• Interface electronics are often integrated on the same chip because the sensing element is small and on only one side
  of the wafer

• Different variations of the basic capacitive principles employ lateral, transversal, or torsional movement
  of either one movable electrode or of a set of interdigitated electrodes.