Sealed Cavity Pressure Evaluation from 1 Pa to Over 10 KPA Using Thin Diaphragm for MEMS Vacuum Packaging

This article reports a wide range vacuum evaluation system for a sealed cavity of packaged micro-devices. The measurement is based on the zero-balance method, which encompasses the measurement from its resolution to near the atmospheric pressure. The key improvement for high vacuum evaluation is the use of an intentionally tensile stressed thin Si diaphragm using high concentration boron doping to minimize the initial deflection of the diaphragm. During the pressure change operation of the zero-balance method, no diaphragm buckling which prevents high accuracy vacuum measurement is confirmed, because the flat diaphragm has a single zero-balance point, i.e. mono-stable. Such feature results in single digit Pa measurement accuracy.