Design consideration for three-axis MEMS accelerometers using an asymmetric proof mass

This paper presents three different designs of three-axis accelerometers using a thick epitaxial surface micromachining process. The designs have a common serpentine spring topology, providing a resonant frequency of around 1.5 kHz, with a spring length of 350 μm and have capacitive sensitivities in the region of 5 to 10 fF/g for the X and Y sensing. The Z-axis sensing is performed by means of torsional springs of 370 μm in length. The sensing techniques include varying gap differential combs for the XY-axes; varying gap differential electrodes and varying overlap area for the Z-axis. The acceleration range for all designs is ±10 g and the overall sensitivity was increased by having a large nominal capacitance.