Highly sensitive hydrogenated amorphous silicon (a-Si:H) microbolometer arrays have been developed that take advantage of the high temperature coefficient of resistance (TCR) of aSi:H and its relatively high optical absorption coefficient. TCR is an important design parameter and depends on material properties such as doping concentration. Ultra-thin (∼2000 Å) aSiNx:H/a-Si:H/ a-SiNx:H membranes with low thermal mass suspended over silicon readout integrated circuits are built using RF plasma enhanced chemical vapor deposition (PECVD) and surface micromachining techniques. The IR absorptance of the bolometer detectors is enhanced by using quarter-wave resonant cavity structures and thin-film metal absorber layers. To ensure high thermal isolation the microbolometer arrays are vacuum packaged using wafer level vacuum packaging. Imaging applications include a 120×160 a-Si:H bolometer pixel array IR camera operating at ambient temperature. Non-imaging applications are multi-channel detectors for gas sensing systems.
Vacuum packaging of high performance infrared (IR) MEMS uncooled detectors and arrays, inertial MEMS accelerometers and gyros, and radio frequency (rf) MEMS resonators is a key issue in the technology development path to low cost, high volume MEMS production. Wafer-level vacuum packaging transfers the packaging operation into the wafer fab. It is a product neutral enabling technology for commercialization of MEMS for home, industry, automotive, and environmental monitoring applications. 4 in. wafer-level vacuum packaging has been demonstrated using IR MEMS bolometers and results will be presented in this article. In addition to the wafer-level packaging results, vacuum package reliability results obtained on component-level ceramic vacuum packages will also be presented.
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