Organic Thin-Film Transistor Sensors: Interface Dependent and Gate Bias Enhanced Responses
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Organic Thin-Film Transistor Sensors: Interface Dependent and Gate Bias Enhanced Responses Maria C. Tanese1; Daniel Fine2; Ananth Dodabalapur2; Luisa Torsi1 Dipartimento di Chimica and Centro di Eccellenza TIRES - Università degli Studi di Bari Bari (Italy) 2 University of Texas at Austin , Microelectronics Research Center, Austin, Texas (USA) 1
ABSTRACT Organic Thin Film Transistors are a new class of sensors potentially capable of outperforming chemiresistors. They can be operated at room temperature, offer the advantage of remarkable response repeatability and can function as multi-parameter sensors. In this paper evidence of OTFT response dependence on important parameters such as the chemical nature of the organic semiconductor active layer and the gate-dielectric/organic-semiconductor interface are produced. A sizable response enhancement of an OTFT sensor operated in the enhancement mode is also presented indicating that an OTFT can in principle lead to a lower detection limit than a resistortype sensor with the same organic semiconductor. INTRODUCTION The field of organic thin-film transistor (OTFT) sensors is a relatively new research area that was born in the late eighties, [1-3] only a few years after the first working OTFT had been proposed [4]. In the last four years it has grown thanks to the advancements achieved by different groups [5-24]. Particularly, OTFTs have been recently proposed as multi-parameter sensors, [18] introducing the idea of exploiting OTFTs as sensors potentially capable of outperforming chemiresistors. Such sensors offer the advantage of remarkable response repeatability [10], evidenced by their response reproduction, within 2%, for hundreds of subsequent exposures to the analyte. The full device recovery, indeed, can be achieved by a strategic use of the gate bias, while operating the OTFTs at room temperature. Selectivity is being pursued by choosing ad hoc chemically or biologically functionalized semiconducting polymer active layers [16, 25] opening wide horizons for the use of OTFTs in compact sensing systems or even in bio-chips [10, 13, 21, 23]. In this work we show the critical role played by the chemical nature of the organic semiconductor active layers, the organic-semiconductor/gate-dielectric interface and the gate bias in determining the sensing mechanism of the OTFT sensors. Evidence of how OTFTs responses can be modulated, and in most cases even enhanced, by properly choosing the device operating gate voltages will also be produced. This can be an important advancement in sensing technology, as the results show that a response intensity modulation of more than one order of magnitude can be attained. EXPERIMENTAL DETAILS Bottom gate OTFT sensors [10], whose structure is shown in figure 1, were fabricated using a highly conductive n-doped silicon substrate covered by a gate dielectric layer
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comprising either thermally grown silicon dioxide (SiO2) or silicon dioxide coated by an organic glass resin (GR/SiO2). Organic anal yte
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