Design of a 2-axis MEMS accelerometer

Abstract

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.

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

“…Resonant Frequency (radians/s) As illustrated in [6] the capacitive sensitivity is non-linear since the capacitive change with respect to the displacement is inversely proportional. All the designs were designed to have their sensitivity between 5 and 10 fF/g.…”