Pentacene-Based Organic Thin Film Transistors for Ammonia Sensing

Dept. of Photonics, Nat. Chiao Tung Univ., Hsinchu, Taiwan
IEEE Sensors Journal (Impact Factor: 1.76). 04/2012; 12(3):594 - 601. DOI: 10.1109/JSEN.2011.2121901
Source: IEEE Xplore


Non-invasive ammonia sensors are attractive alternatives for the diagnoses of a variety of chronic diseases such as liver cirrhosis and renal failure. A low cost pentacene-based organic thin film transistor (OTFT) fabricated by a novel and simple process was demonstrated to be highly sensitive and specific for ammonia gas. Various measurement parameters that reflected OTFT device characteristics for ammonia detection were investigated. Significant variations of the turn-on current, intrinsic mobility, and threshold voltage ( V th) were observed while subthreshold swing ( S . S .) was almost unchanged to the alteration of ammonia concentration. The OTFT device detected 0.5 ~ 5 ppm concentration ammonia gas at room temperature, which is in the critical range that can distinguish between healthy person and paticents with liver cirrhosis and renal failure. The sensitivity of the device was further enhanced following a simple UV irradiation treatment to modify the functional groups on poly(methyl methacrylate) (PMMA) dielectric layer. Possible interference for ammonia detection such as humidity effect and selectivity among nitrogen, alcohol, carbon dioxide, acetone, methane and ammonia were also examined. We concluded that the proposed pentacene-based OTFT is a promising device for the future application in non-invasive medical diagnoses.

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    • "Furthermore, hydroxyl groups in polymers have been reported to have the ability to interact with ammonia to form structure like ammonia water, thus the trapped ammonia at the dielectric surface may not be removed easily under the environment of dry air [32]. For PMMA dielectric, the dipole moment of the –COOCH 3 has the ability to absorb NH 3 molecules [31], while such interactions will not happen between ammonia and benzene rings. In addition, the polarities of PVA, PMMA and PVP are all higher than that of PS, which indicates dipole–dipole interactions can occur much more frequently between the above three dielectrics and polar ammonia. "
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