In this study, we fabricated bolometer-type uncooled infrared focal plane allays (IRFPAs) of 640 × 480 pixels with high-purity semi-conducting single-walled carbon nanotubes (SWCNTs) as detection materials for the first time. The thermal isolation structure of the IRFPAs for high responsivity was realized by creating a cavity between the contact electrode and the infrared detection part and by connecting them with beam wiring. The infrared detection part was formed in the order of SiNx film, semiconducting SWCNT network film, SiO2 film, and SiNx film from the bottom. Especially the SWCNT network film was only formed by a printing process except for the fabrication process in micro electro mechanical systems (MEMS). Here, our semi-conducting SWCNTs, which is a dispersion containing a nonionic surfactant, formed a high-density film with locally-oriented structure by the coating process. The responsivity and thermal time constant of typical element in long-wave IR region showed over 105 (V/W) @0.2 V and 5 ms, respectively. Assuming the thermal conductance and infrared absorption rate, temperature coefficient of resistance (TCR) was estimated as above -5%/K. The TCR value was similar with that of semi-conducting SWCNT network film prepared on Si substrate and about three times larger than that of conventional vanadium oxide film. Therefore, we found that semi-conducting SWCNTs become a promising bolometer material that can achieve high sensitivity.
Uncooled bolometer-type infrared detector's performance is strongly limited by temperature coefficient of resistance (TCR) of the resistor. Single-walled carbon nanotubes (SWCNTs) are expected as promising materials with high TCR, and high chemical stability. In a preliminary experiment TCR of semiconducting CNT networks extracted by using non-ionic surfactants was confirmed to be -6%/K. Electric properties of SWCNT networks were strongly affected by its morphology. Optimization of SWCNT network morphology is important to maximize the detectability of SWCNT bolometers.
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