31 May 2005 Micromachined infrared sensors with device-level encapsulation
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Abstract
There have been recent innovations to reduce the cost of packaging for MEMS devices, without deteriorating their performance. One such novel design for device-level encapsulation (self-packaged) of uncooled infrared (IR) microbolometers is documented here. Device-level vacuum encapsulation has the potential to eliminate some major problems associated with the bolometer performance such as high thermal conductance of the ambient atmosphere, the high cost associated with conventional vacuum packaging, and the degradation of optical transmission at different wavelengths through a conventional package window. The device-level encapsulated bolometers can also be fabricated with flexible substrates, which have the advantage of conforming to non-planar surfaces compared to Si or other rigid substrates. In addition, a flexible superstrate with low shear stress has applications in robotics, aerospace, defense and biomedicine as a "Smart skin", a name given to multisensory arrays on conformal substrates to emulate human skin functions on inanimate objects. Self-packaged uncooled microbolometer arrays of 40x40 μm2 and 60x60 μm2 are fabricated on top of Si wafer with a sacrificial layer using semiconducting Yttrium Barium Copper Oxide (YBCO) as the infrared sensing material. A two-layer surface micromachining technique in conjunction with a resonant cavity and a reflecting mirror are used for the sensor structure. The devices have demonstrated voltage responsivities of 7.9x103 V/W with a temperature coefficient of resistance of -2.5% K-1, and thermal conductivity of 2.95x10-6 W/K. The device performance was similar in air and vacuum, demonstrating vacuum integrity and a good device-level encapsulation.
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Aasutosh Dave, Zeynep Celik-Butler, Donald P. Butler, "Micromachined infrared sensors with device-level encapsulation", Proc. SPIE 5783, Infrared Technology and Applications XXXI, (31 May 2005); doi: 10.1117/12.603795; https://doi.org/10.1117/12.603795
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