Thin-Film Oxide Transistor by Liquid Process (1): FGT (Ferroelectric Gate Thin-Film Transistor)
Abstract From this chapter to Chap. 18, applications of a liquid process for TFTs are described. We developed two types of TFTs: one is a ferroelectric gate transistor (FGT), in which the gate insulator is made from a ferroelectric material, and the other is a normal switching TFT. The FGT has a bistable function because of the hysteretic nature of ferroelectric materials. Thus, the FGT was developed for use as a memory device. In this chapter, as the first topic, we introduce our studies on the FGT. Since this TFT uses perovskite PZT as a gate insulator, fabricating a PZT thin film with a high Pr (remnant polarization), adequate Ec (coercive electric field), and good rectangular hysteresis is crucial. To fabricate a PZT film with these properties, using a good substrate to enable epitaxial growth of the PZT film is critical. In the case of the FGT, the substrate for a PZT film plays the role of a gate electrode, so it should be a conductor. We studied platinum and perovskite LaNiO3 (LNO) for this purpose; the former is made by sputtering and the latter can be made using a solution process. A noteworthy result in this chapter is the realization of an all-liquid-processed TFT (the first reported example), in which not only the semiconductor channel and gate insulator but also the gate and source and drain electrodes were all fabricated by a liquid process. This TFT is likely the first such all-liquid-processed TFT and represents an important step toward an all-printed oxide transistor. Chapter 17 describes the effect of UV irradiation on the pyrolysis of oxide precursors. In the pyrolysis process of oxide materials, heat is the conventional energy source used to decompose the starting materials to the final products (solids). However, when UV light is used in a pyrolysis process together with heat, a tremendous effect is expected. In this Chapter, we present experimental results concerning the UV irradiation under an oxygen atmosphere (UV/O3 treatment) or nitrogen atmosphere to a semiconductor precursor film. We then used these results to design a process for fabricating TFTs using only a liquid process.When the UV irradiation technology is used in combination with solvothermal synthesis of solution, which is described in Chap. 13, it enables the low-temperature solidification of oxide materials at less than 200 °C, as described in Sect. 17.3. The UV irradiation is not restricted to a tool assisting in the pyrolysis process; it can be used as a patterning tool of precursor gel films. After confirming the ability of UV light to pattern various materials, we fabricate TFTs only using UV light as a patterning method and demonstrated the operation of the TFT, as described in Sect. 17.4. Chapter 18 describes our original materials for TFTs. As semiconductor and insulator materials, we developed ZrInZnO and LaZrO films, respectively. The effect of adding Zr into the InZnO system is described in Sect. 18.1. We confirmed that addition of Zr was very effective in enhancing the InZnO material as a TFT active layer. By combining ZrInZnO with an LaZrO insulator, we developed a TFT with good properties. In Sect. 18.2, the combination of a polysilazane-based SiO2 film with a ZrInZnO active layer for a TFT is investigated. Very high mobility of 29 cm2 V−1 s−1 was obtained in this case. In Sect. 18.3, we introduce the third example of an all-solution-processed TFT. In this TFT, ZrInZnO, LaZrO, and RuO were used as the semiconductor, insulator, and conductor films, respectively. In Sect. 18.4, this original combination of materials—ZrInZnO, LaZrO, and RuO—is further extended to an all-liquid-processed active-matrix back plane (AM-BP) for an electrophoretic display (EPD). The operation of the EPD was confirmed.
KeywordsFerroelectric gate transistor (FGT) Perovskite PZT All-liquid-processed TFT
- 12.S.H. Seager, D. Mcintyre, B.A. Tuttle, J. Evans, Integr. Ferroelectr. 6, 45 (1997)Google Scholar
- 23.E. Tokumitsu, M. Senoo, T. Miyasako, Mater. Res. Soc. Symp. Proc. 830, 107 (2005)Google Scholar
- 28.W. Lu, P. Zheng, W. Du, Z. Meng, J. Mater. Sci. 15, 739 (2004)Google Scholar
- 32.P.T. Tue, B.N.Q. Trinh, T. Miyasako, P.V. Thanh, E. Tokumitsu, T. Shimoda: to be presented at Mater. Res. Soc. Spring Meet., San Francisco, (2011)Google Scholar