Silicon fusion bonding can be used

Silicon fusion bonding can be used to reduce the size of a micromachined structure. As shown in Figure 2.5(b), the anisotropically etched cavity can be much smaller, yet the diaphragm area is identical for an SFB pressure sensor compared to a conventional pressure sensor. The bottom wafer with the ani-sotropically etched cavity is silicon fusion bonded to a top wafer. After bond-ing, the top wafer is etched back to form a thin diaphragm and the bottom wafer is ground and then polished to open the access to the diaphragm. For absolute pressure sensors, such as the units in Figure 2.5(b), a support wafer is attached to the structure containing the diaphragm produced by any of the pre-viously described methods.