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.



































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