Wafer-level reliability characterization for wafer-level-packaged microbolometer with ultrasmall array size

For the development of a small and low-cost microbolometer, wafer-level reliability characterization techniques for vacuum-level packaged wafers are introduced. Amorphous-silicon-based microbolometer-type vacuum sensors fabricated on an 8-inch wafer are bonded with a cap wafer by using an Au-Sn eutectic solder. Membrane deflection and integrated vacuum sensor techniques are independently used to characterize the hermeticity at the wafer level. For a packaged wafer with a membrane thickness below 100 mu m, it is possible to determine the hermeticity via a screening test performed using an optical detector. An integrated vacuum sensor having the same structure as a bolometer pixel shows a vacuum level below 100 mTorr. All steps from the packaging process to the fine hermeticity test are implemented at the wafer level to verify that high-volume and low-cost production of the microbolometer is possible.