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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.

The miniaturisation and reduction in cost of acceleration sensors led to the increase of use of said sensors in a large number of devices. Such include: Inertial Measurement Units (IMUs), air-bag deployment mechanism and consumer electronic devices. This paper presents three alternative designs of capacitive sensing MEMS 2-axis accelerometers. All designs have a common fabrication process but each design features different characteristics in terms of spring design and layout. A novel design methodology was devised such that the three designs have approximately the same characteristics such that crosscomparisons can be done. The resonant frequency was designed to be about 1.5 kHz and the accelerometers have a sensitivity of 400 aF/ms -2 . Behavioural Model Simulations using Saber ® Simulator and Finite Element Method (FEM) analysis were performed on these three designs. A comparison between the two different types of simulators was performed. This resulted in the conclusion that both simulators have comparable results and the variation between theoretical and simulation results can be attributed to the assumptions and inaccuracies of the mathematical model used in the theoretical computation.

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