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15 December 2000 Development of Si monolithic (Ba, Sr)TiO3 thin film ferroelectric microbolometers for uncooled chopperless infrared sensing
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We have been developing a total monolithic microbolometer technology for uncooled thermal sensing along the route from fabricating pixels of thin-film ferroelectric bolometers on micromachined Si substrates. Toward achieving this objective, sensor material of (Ba0.75Sr0.25)TiO3 (BST) has been prepared into thin-film form and been investigated to obtain a large temperature coefficient of dielectric constant (TCD) within the ambient temperature region. Operated in our proposed dynamic pulse-biased mode, the infrared responsivity (Rv) of sensor pixels is analyzed to reflect how those materials properties of BST film dominate the ultimate array performances. This new ferroelectric bolometer is expected to provide value-added merits of chopperless operation and high sensitivity enhanced by pulsed bias. In this paper, pixels of C-C balanced BST thin-film microbolometers have been fabricated by integrating Si-bulk micromachining and ferroelectric thin-film processing. Both pulsed laser deposition (PLD) and metal organic decomposition (MOD) methods have been employed in preparing BST films on those micromachined silicon substrates. Both the films show similar insufficient bolometric behavior with TCD-values smaller than 1%/K. Under pulsed bias, chopperless operation of pixels of so- fabricated microbolometers was confirmed. PLD enabled low- temperature preparation of high-quality films at 520 degree(s)C, so renders it for cutting-edge investigations to attain the TCD-value that demonstrated in BST ceramic plate by preparing large-grained, stress-free, micrometers -thick films. Meanwhile, MOD provides us those advantages of low-cost, large-area deposition and good uniformity compared to PLD method, films with TCD-value about -0.3%/K have been developed by MOD and are being geared to fabricate arrays. Finally, the future direction towards prototyping ferroelectric arrays was formulated based on the practical view of our development expeditions.
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Huaping Xu, Kazuhiko Hashimoto, Tomonori Mukaigawa, Hong Zhu, Ryuichi Kubo, Tatsuro Usuki, Hiroyoki Kishihara, Minoru Noda, Yoshihiko Suzuki, and Masanori Okuyama "Development of Si monolithic (Ba, Sr)TiO3 thin film ferroelectric microbolometers for uncooled chopperless infrared sensing", Proc. SPIE 4130, Infrared Technology and Applications XXVI, (15 December 2000);

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