Metal oxides as functional semiconductors. An inkjet approach
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Metal oxides as functional semiconductors. An inkjet approach Anna Vilà1, Alberto Gomez1, Luis Portilla1, Marti Cirici1 and Juan Ramon Morante1,2 1 M2E-IN2UB, Electronics Department, Marti i Franques 1, 08028-Barcelona, Spain. 2 Institute for Research on Energy of Catalonia, Jardins de les Dones de Negre 1, 08930-Sant Adria de Besos, Spain. ABSTRACT Inkjet printing provides an interesting technology for electronic devices, as it is a versatile minimum-waste cost-effective technique for direct writing on almost every surface without need of masks or sacrificial layers. Among the fields in which it has been tested, transparent and flexible electronics offer a variety of applications ranging from large-area roll-toroll (such as OLEDs for lighting or solar cells) to small low-consumption biocompatible devices such as biosensors. This work aims to present some advances in the field of semiconductors synthesized by sol-gel and patterned by inkjet printing. Chemical routes are used to obtain suitable inks, based on salts of Ga, In, Zn, Cu and Sn and solvents as methoxyethanol. Inkjet printing provides thin layers 20-300nm thick, with morphology strongly depending on the materials. Different thermal treatments are tested, and some chemical and optical characterization of the obtained layers allows optimizing the technology for each material. The effectiveness of the inks and the technique is demonstrated by the electronic behavior of thin-film transistors fabricated by the proposed technology. The different devices are compared, suggesting the properties of the different materials analyzed, as a step ahead in the development of a complete logic for such promising applications of the flexible electronics. INTRODUCTION Inkjet-printing is an interesting technique for fabrication of electronic devices mainly due to the fact that it is a direct-write method. Patterning and deposition can be accomplished in the same step without the need of a mask and a lift-off step used in most conventional techniques such as photolithography, vapor deposition and sputtering [1]. Therefore, the needed material and resources can be reduced drastically, and the process complexity is diminished, leading to a more flexible process, lesser waste generation and lower overall costs. These characteristics are of particular interest in the large-area electronics industry when deposition of material is required only at specific positions [2]. In recent years there has been a rapid development in the area of inorganic transparent electronics using metal oxides as the channel material [3]. In particular, important advances have been reported in ZnO-based semiconductors, which with additives such as In or Ga are proposed to provide better electrical properties and chemical stability respectively [4]. However, most metal oxide semiconductors are n-type conducting, and only little success has been reported for transparent p-type conducting films [5]. For instance, previous studies have shown that undoped SnO2 exhibits high n-type conductivity and a direct ban
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