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Vacuum Micropackaging Technology for MEMS
Keywords: Vacuum packaging, MEMS, Infrared microbolometers
Vacuum wafer-level packaging is a key issue in the technology development path to low-cost, high volume production of a number of Micro-Optical-ElectroMechanical Systems (MOEMS). In the case of uncooled microbolometer detectors used for infrared imaging applications, vacuum packaging is essential to minimize the thermal conductance through residual gas in the package. INOs low-cost, wafer-level micropackaging1,2 technology allows for the solder bonding at low temperatures (<200C) of known good dies and various infrared windows onto a spacer wafer, using conventional flip-chip bonding equipment operated in air. Consequently, cavity volumes of several tens of microliters can be achieved for enhanced long-term vacuum integrity. The technology also offers the advantages of dicing through only one wafer as well as dissociated assembly and vacuum sealing steps where the device is baked-out under vacuum and sealed using a solder ball placed at the vacuum port. Fluxless processes were developed for steps involving the MEMS chip. The wafer-scale fabrication of ceramic spacers and antireflection coated-IR windows equipped with a solderable layer is based on a combination of selective electroplating and laser micromachining techniques. To monitor in-situ pressure changes within the package cavity, micromachined integrated pressure sensors were fabricated. This paper reports on the vacuum integrity of micropackaged 160x120 pixel focal plane array (FPA) dies based on vanadium oxide, submitted to accelerated testing at various temperatures with or without the incorporation of a non-refireable getter. Results show that cavity pressures of 100 mTorr or less can be obtained after vacuum sealing. Typically, a noise equivalent temperature difference (NETD) of 90 mK can be achieved for a micropackaged 160x120 pixel FPA die. References [1] P. Topart, S. Leclair, C. Alain and H. Jerominek, Proceedings SPIE, Vol. 5342, 26, (2004). [2] P. Topart, C. Alain, L. Le Noc, S. Leclair, Y. Desroches, B. Tremblay and H. Jerominek, Proc. SPIE, Vol. 5783, 544, (2005).
Patrice Topart, Researcher

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