Effect of dielectric/organic interface properties on the performance of the organic thin film transistors
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Effect of dielectric/organic interface properties on the performance of the organic thin film transistors Ronak Rahimi1 and D. Korakakis1 1
Lane Department of Computer Science and Electrical Engineering, West Virginia University, Morgantown, WV 26506 ABSTRACT In order to manufacture organic electronic devices with high performance, more detailed studies of the structure and the morphology of the organic materials as well as the underlying physical charge transport mechanisms are warranted. For instance, high efficiency organic thin film transistors (OTFTs) require materials with high charge carrier mobility [1, 2]. The parameters that determine the charge carrier mobility of the device include the structure of the first organic layer at the organic-dielectric interface as well as the morphology and the structural order of the other organic layers. Therefore, fundamental questions about structural properties of organic materials should be answered in order to optimize device performance [2-4]. In this work, several bilayer structures of LiF/PTCDI-C8 and LiF/pentacene were prepared and their morphology and molecular structure were characterized using X-ray reflectivity (XRR) technique. In order to study the effects of the films’ structures and dielectric/organic interfacial properties on the device performance, OTFTs based on these bilayers were fabricated and characterized. It has been observed that PTCDI-C8 thin films have higher molecular packing in the LiF/PTCDI-C8 bilayer structure, which results in superior electrical characteristics for OTFTs based on this organic material. Devices with LiF/PTCDI-C8 bilayer exhibit about one order of magnitude higher output current (Ids) at a constant drain-source voltage (Vds) compared to the devices with LiF/pentacene bilayer. The observed differences in the electrical characteristics of these devices can be attributed to the effects of the dielectric/organic interface and the molecular structure of the organic layers. INTRODUCTION For the past several decades, organic materials including polymers, oligomers and small molecules have been of great interest for their various applications in the electronics and the semiconductor industry. The most appealing advantages of organic materials compared to their inorganic counterparts are their compatibility with flexible substrates and amenability to lowtemperature and low-cost fabrication processes such as evaporation, spin-coating and printing [5, 6]. Moreover, the ability to be utilized in fabrication of lightweight and large-area devices is among other reasons for popularity of organic materials. A large number of studies have reported on various aspects of the development and optimization of organic electronics such as organic light emitting diodes (OLEDs), solar cells (OSCs) and thin film transistors (OTFTs). Although significant progress has been made during this period, some of the intrinsic electrical properties of organic materials such as low carrier mobility have continued to hinder the full development and maturation of
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