ELE8083 Assessment Style Tutorial Question MEMS accelerometer Q1. The single-axis capacitive sensing accelerometer shown in Figure 1 is to be fabricated from a 25 μm thick layer of silicon. The silicon proof mass is to be 800 μm square and the spring beams should be 2 μm wide. The spring constant of a fixed-fixed beam is given by 3 3 16 s E t w k L = (a) The accelerometer should be designed to have 3 μm deflection when subjected to an acceleration of 40 m.s -2 . Calculate the length of spring beam required. [12 marks] (b) The sense fingers at the bottom edge of the structure have an initial spacing of 5 μm and an overlap length of 80 μm. Calculate the capacitance at the lower sense fingers for zero acceleration and the change in capacitance which will occur at 40 m.s -2 acceleration. [5 marks] Figure 1 MEMS Accelerometer.
