Effects of Device Architecture on the Performance of Organic Thin Film Transistors
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Effects of Device Architecture on the Performance of Organic Thin Film Transistors X.J. Zhou, K.E Mutkins, D. Elkington, K. Sirois, W. Belcher, P.C. Dastoor Centre for Organic Electronics, University of Newcastle, Callaghan, NSW 2308, Australia.
ABSTRACT The impact of device dimension and architecture on the device performance of an all−solution fabrication organic thin film transistor (OTFT) has been investigated. The saturation drain current is inversely proportional to the channel length, indicating that a characteristic of field−effect like transistor has been obtained. In contrast, the drain current is independent of the thickness of polyvinylphenol (PVP) dielectric layer and a large leakage current is observed at the gate electrode indicating that the device also shows electrochemical transistor characteristics. Although separate conductance measurements of a single poly(3−hexylthiophene) (P3HT) layer and a P3HT/PVP layer reveal that the conductance is proportional to the thickness of the layer, the maximum achieved drain current in the fabricated OTFT is inversely proportional to the P3HT thickness. Using this data, an interface of P3HT/PVP or a maximum P3HT thickness for a working transistor of approximately 160 ± 16 nm can be extracted. The mechanism of operation of these devices is discussed.
INTRODUCTION Sandberg et al. has reported a novel hygroscopic insulator field−effect transistor (HIFET) incorporating a hygroscopic dielectric layer [1,2,3,4]. These HIFET devices exhibited enhanced performance under humid environments and operated at low voltages (< 1V) and thus appear well−suited to bio−sensing applications requiring hydrophillic conditions [5]. Such all−polymer devices can be fabricated by low−cost spin−coating and printing technology thus offering the potential for affordable and disposable non-reversible bio sensing devices for medical applications [5]. Previous work showed that HIFETs are not truly electrical field modulated transistors because the source−drain current is actually modulated by gate potential rather than gate field [2]. Furthermore, the HIFET characteristics more closely resemble the behaviour of organic electrochemical transistors (OECTs), as suggested by Herlogsson [6], in which the gate potential controls the doping/dedoping of the semi−conducting polymer via ion migration from the dielectric layer into the active channel. However, like conventional field effect transistors, the device characteristics of electrochemical transistors are also subject to modulation by the device architecture. In this work, the effects of device dimension and architecture upon device performance of these hygroscopic insulator structures (referred to more generally as organic thin film transistors (OTFTs)) are reported and discussed in the context of the prevailing models for device operation. EXPERIMENTAL SETUP Figure 1 depicts the structural configuration of OTFT devices and the measurement circuit. All OTFT devices were fabricated on pre−patterned indium tin oxide (ITO) coated gl
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