Polarization-Induced Transport: A Comparative Study of Ferroelectric and Non-Ferroelectric Dielectric-Gated Organic Fiel
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Polarization-Induced Transport: A Comparative Study of Ferroelectric and NonFerroelectric Dielectric-Gated Organic Field-Effect Transistors Amrit Laudari,1 Shubhra Gangopadhyay,2 and Suchismita Guha1 1 Department of Physics and Astronomy, University of Missouri, Columbia, MO 65211 2 Department of Electrical and Computer Engineering, University of Missouri, Columbia, MO 65211 ABSTRACT A comparative study of ferroelectric and non-ferroelectric-gated organic field-effect transistors (FETs) have been carried out by using a small molecule semiconductor 6,13 bis(triisopropylsilylethynyl) pentacene (TIPS-pentacene) to understand the fundamental aspects of carrier transport in FET architectures. Temperature-dependent current-voltage characteristics from non-ferroelectric dielectric-gated FETs show a clear activated transport, independent of the dielectric constant. While using the ferroelectric dielectric polymer poly(vinylidene fluoridetrifluoroethylene) (PVDF-TrFE), where the dielectric constant may be tuned by changing the temperature, a negative temperature coefficient of the carrier mobility is observed beyond 200 K. The polarization fluctuation dominant transport inherent to a ferroelectric dielectric in conjunction with the discrete nature of traps in TIPS-pentacene results in an effective de-trapping of the shallow trap states into more mobile states. INTRODUCTION Charge transport in organic field-effect transistors (FETs) is usually discussed within the framework of hopping between disordered-localized states. With carrier mobilities > 1 cm2/Vs, band-like transport in organic FETs has been observed in several classes of organic semiconductors [1,2]. This further illustrates that the mechanism of transport may have several competing factors: intermolecular interactions forming extended band states, off-diagonal thermal disorder terms resulting in localized states, and the crystallinity of the semiconducting material. Additionally, the polymer-dielectric interface plays a large role in the performance of FETs, and specifically the charge carrier mobility (μ). As a result, the same organic semiconductor in an FET architecture may show a hopping transport as a function of temperature (T) with dμ/dT > 0 or a band-like transport with dμ/dT < 0, depending on the choice of the dielectric. An advantage of ferroelectric dielectrics such as poly (vinylidene fluoride-tri-fluoroethylene) (PVDF-TrFE) is that its dielectric constant (κ) may be tuned by a factor of five from 100 K to its ferroelectric-paraelectric phase transition temperature at ~ 400 K [3]. Also, such dielectrics emphasize polarization fluctuation dominant transport which may result in screening; combined with the nature of traps in the semiconductor, 6,13 bis (triisopropyl-silylethynyl) pentacene (TIPS-pentacene) FETs show dμ/dT 0 over the entire temperature range. With PVDF-TrFE, beyond 240 K, a clear decrease in carrier mobility is observed, signaling band-like transport. As noted, the device geometry in Figure 1 (c) allows using either CYTOP or PVDF-TrFE as t
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