Wafer-Level Vacuum Packaging of Microbolometer-Based Infrared Imagers

Abstract: Microbolometer focal plane arrays (FPAs) require an ambient with a total pressure of less than 10 mTorr for optimum sensitivity. A wafer-level vacuum packaging process greatly reduces the cost of the FPA component and makes the packaged device lighter and smaller in comparison with the traditional one-die-at-a-time packaging approach. To meet the package requirements of microbolometer FPAs, we have developed a wafer-to-wafer bonding technique based on Cu-Sn solid-liquid interdiffusion (SLID). By bonding microbolometer FPA wafers with silicon window wafers that were coated with thin-film getters and anti-reflective films, arrays of micro vacuum chambers were created in parallel. The SLID based vacuum-packages demonstrated electro-optical performance consistent with the performance of the FPAs in traditional die-level vacuum packages. The developed bonding process may be also be applicable to other smart sensor microsystems, as they are transitioning from multi-chip configurations to system-on-chip architectures that reduce size, weight, power, and cost.