Inertial MEMS (Micro Electro Mechanical System) sensors are normally sealed in hermetic enclosures. Some are
assembled in hermetic packages but wafer level packaging has become much more important in recent years. Anodic
bonding can be used to achieve wafer level seals between silicon and glass but most suppliers of inertial sensors screen
print glass frit onto silicon cap wafers. After removing the organic vehicle, these patterned cap wafers are sealed to
device wafer prior to wafer singulation and plastic packaging. Anodic and glass frit bonding are both cost-effective.
However, they impose size, quality and performance limitations. Wafer level sealing with a metal removes some of
these limitations but introduces other concerns. This paper will review the current wafer level hermetic processes
followed by a description of a thermocompression metal seal technology that is compatible with IC fabrication.
Stiction is a major failure mechanism during the operation of accelerometers and hence it is important to know the stiction force that the structures encounter during use. We explore the possibility of devising an electrical technique for the direct measurement of in use stiction force. We have designed and fabricated three terminal test structures to measure both vertical and horizontal in use stiction. The measurement is not visual and is based on I-V data with the possibility of automation in the future. The structure consists of cantilever beams of different lengths each with an actuating pad and a detection pad. We measure the pull in voltage applied to the actuating pad, VPI , required to bring the cantilever beam in contact with the detection pad and the pull out voltage, VPO, at which the contact is broken. Using the Finite Element tool, ANSYS, a coupled electromechanical model is developed to determine the stiction force from the pull-in and pull-out voltages. We discuss the measurements in terms of the advantages and the shortcomings. We also discuss the sensitivity of the model to various material and geometric parameters and to the accuracy of the measurement.
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