Room Temperature Deposition of Highly Transparent n-ZnO on PET and ZnO Semiconductor FET
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Room Temperature Deposition of Highly Transparent n-ZnO on PET and ZnO Semiconductor FET Alessandro Neri 1 , Riccardo Lotti 1, Dmitry Yarmolich1, Petr Nozar 2, Santiago Quiroga1, Eugenio Lunedei 2 and Carlo Taliani 1,2 1 Organic Spintronics Srl, Via P. Gobetti 52/3, 40129 Bologna, Italy 2 Consiglio Nazionale delle Ricerche – Istituto per lo Studio dei Materiali Nanostrutturati (CNRISMN), Via P. Gobetti 101, 40129 Bologna, Italy ABSTRACT In this paper we report on the fabrication of n-doped ZnO and semiconducting n-ZnO at room temperature by a new ablation deposition technology that makes use of electron/plasma ablation sources named Pulsed Plasma Deposition (PPD) developed by Organic Spintronics Srl. The oxygen vacancies n-doped ZnO PPD grown thin film is deposited on PET and shows a resistivity of 3 x 10-4 ohm cm. The n-ZnO TCO is compact, smooth and highly transparent in the UV-VIS (better than 90 T%) as well as in the near IR spectral range and it is remarkably temperature stable. Typical ZnO deposition rate of the PPD is 500 nm/min. The RT deposited semiconductor ZnO shows a very large Hall electron mobility up to 1000 cm2/Vs approaching that of the single crystal. Preliminary results of Si/SiO2 based bottom gate and contact FET test pattern structures with a 50 nm overlaying ZnO thin film shows an ON/OFF ratio of 50000 and a FET mobility of 1 cm2/Vs. Further implementation on appropriate FET design will be performed to explore the possibility to achieve a larger FET mobility. The PPD proves to be an enabling technology that makes it possible the advent of flexible OLED displays. INTRODUCTION ZnO is, in principle, a plentiful material for making thin film transistors (TFT) and transparent conductive oxide thin films (TCO), for applications on flexible optoelectronics and electronics on plastic substrates. Several reviews cover the recent developments in this field [1-4].The crucial parameter for making it a perfect material for TFT and flexible OLED is the possibility to deposit at room temperature (RT) on low cost plastic substrates. In fact plastic substrates are highly sensitive to temperature and cannot be processed at temperatures higher than the glass transition temperature (Tg). The substrate of choice for the best properties vs cost ratio is polyethylene terephtalate (PET), having a Tg of only 80°C. Pulsed laser deposition (PLD) has shown to be a feasible RT technology [5, 6] also on plastic substrates [7 ,8] but PLD lacks the possibility to become an industrial tool for the high cost of installation and maintenance of the laser sources and for the difficulty to scale the process to large areas. Ablation by Pulsed Plasma Deposition (PPD) developed by Organic Spintronics (OS), as we show in this paper, allows to fabricate both TCO and semiconductor n-ZnO thin films at RT and has the potential to become industrial for the simplicity and the low cost of the PPD sources. The PPD technology was previously used by Huang et.al. [9] to fabricate a TCO based on molybdenum doped indium oxide (IMO) .
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