TABLE OF CONTENTS With the demand from automotive and other industries in the latter 1980s, several sensor manufacturers developed micromachined silicon ICs for sensing acceleration. Today several component manufacturers such as IC Sensors, Analog Devices, and Motorola have families of silicon accelerometers. Basic sensor elements as well as signal conditioned versions are available.
The principles of acceleration sensing were simulated using a weight and spring connected to a frame to develop silicon accelerometers by using the piezoresistive properties of silicon and building capacitive structures with variation of effective capacitance between plates attached to a seismic mass of silicon. To simulate the basic mechanical analogy of accelerometers and minimise secondary effects that complicate the measuring process [25, 26] required several improvements in silicon-processing technology.
One such improvement was the advent of silicon fusion bonding [26]. Fusion bonding, which allows the bonding of two wafers while preserving the crystalline structure of silicon, permits the creation of complex three-dimensional structures without introducing mechanical discontinuities or thermal dependent stress. This structuring ability allows accelerometer manufacturers to capture the seismic mass with a sealed cavity by bonding a cap and a base plate to the frame. By controlling the space between the mass and cavity, vendors can use the air sealed inside the cavity as a viscous damping fluid for the system's motion.
Silicon fusion bonding also provides an answer to another limitation: shock resistance. Simply falling off a desk can produce a 200 g shock when the sensor...
