Polymer-Clay Hybrid Dielectric Layer for Flexible Organic Thin Film Transistors
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0939-O03-18
Polymer-Clay Hybrid Dielectric Layer for Flexible Organic Thin Film Transistors Sei Uemura, Koji Suemori, Manabu Yoshida, Satoshi Hoshino, Takehito Kodzasa, and Toshihide Kamata Photonics Research Institute, National Institute of Advanced Industrial Science and Technology, Central 5, 1-1-1 Higashi, Tsukuba, Ibaraki, 305-8565, Japan
ABSTRACT A polymer field-effect transistor (FET) was fabricated with poly(3-hexylthophene) [P3HT] as an active layer and poly(methyl-methacrylate) [PMMA] gate dielectric modified with poly(vinyl alcohol) [PVA]. The influences of air atmosphere on the FET property were investigated. Under the air atmosphere, FET properties such as modulation of drain current by gate bias, leakage current and threshold voltage shift were strongly influenced by humidity. The influence was investigated by temperature dependence of FET properties. It cleared the relationship between the FET property and intrinsic mobile ion in the gate dielectric. An influence of humidity on the FET property can be prevented by insertion of a clay mineral layer, which clogs motion of ion transport in gate dielectric layer.
INTRODUCTION An organic FET has been investigated extensively from the standpoint of flexibility and processability in a large area device. Polymer materials are particularly promising materials for flexible and low-cost fabrication with wet-process such as spin coating, spray coating, and printing1. As other advantage, organic materials can be applied on wide variety of use because of much kind. However, it is difficult to layer organic films alternately because most organic materials are dissolved in organic solvent. It leads to mixture or fusion between layers. For example, typical conducting polymer such as poly(alkyl-thiophene), poly(alkyl-fluorene) and its derivatives are soluble in non-polar solvent such as chloroform and THF.1 Typical polymer insulator such as polystyrene and PMMA are also dissolved in similar non-polar solvents. It indicates that the combination of typical polymer insulator and conducting polymer to fabricate FET is impossible. It indicates that the diversity of choices is restricted by the mixture problem of layers. In order to improve the problem, polymer insulator such as poly(vinyl phenol) and PVA, which are dissolved in polar solvent, is commonly used in stead of the typical polymer insulator2. However, it can be expected that such polymers are easily influenced by water and/or oxygen, which are included in air. Influence to a FET property of oxygen in the air was reported by several researchers.3 The influence to the FET property is observed as threshold shift and increase of leakage current. On the other hand, as for the influence, it was reported that it was moisture rather than atmospheric oxygen.4 Those were studied as an influence to semiconductor layer of organic FET fabricated on SiO2. In the FET fabricated with polymer gate dielectric, it is important to investigate with taking into account the influence of the air on the electric properties of insulator
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