Present status of transparent conducting oxide thin-film development for Indium-Tin-Oxide (ITO) substitutes

Abstract This paper describes the present status and prospects for further development of transparent conducting oxide materials for use as Indium-Tin-Oxide (ITO) substitutes in the thin-film transparent electrodes of liquid crystal displays (LCDs), currently the largest use of ITO, and, thus, of indium. The best substitute material for the ITO transparent electrodes used in LCDs is impurity-doped ZnO, e.g., Al- and Ga-doped ZnO (AZO and GZO). From resource and environmental points of view, AZO is the best candidate. The most important problems associated with substituting impurity-doped ZnO for the ITO used in LCDs have already been resolved in laboratory trials. Under the present circumstances, (rf and dc)-magnetron sputtering (rf + dc-MS) deposition, both with and without H 2 gas introduction, has been found to be the best deposition method to prepare impurity-doped ZnO thin films for practical use; AZO thin films with a resistivity on the order of 10 − 4  Ω cm were prepared on glass substrates with an approximately uniform resistivity spatial distribution and a thickness above 100 nm. In order to improve the resistivity stability, AZO and GZO thin films co-doped with another impurity have been newly developed. A 50 nm-thick V-co-doped AZO (AZO:V) thin film was stable enough to be acceptable for use in practical transparent electrode applications. However, it seems likely that obtaining a stability comparable to that of ITO using impurity-doped ZnO will be difficult for thin films with a thickness below approximately 30 nm.

[1]  Tadatsugu Minami,et al.  Transparent and conductive multicomponent oxide films prepared by magnetron sputtering , 1999 .

[2]  T. Miyata,et al.  Transparent conducting impurity-co-doped ZnO:Al thin films prepared by magnetron sputtering , 2001 .

[3]  H. Hartnagel,et al.  Semiconducting Transparent Thin Films , 1995 .

[4]  T. Miyata,et al.  STABILITY OF TRANSPARENT CONDUCTING OXIDE FILMS FOR USE AT HIGH TEMPERATURES , 1999 .

[5]  J. Seto.  The electrical properties of polycrystalline silicon films , 1975 .

[6]  H. Nanto,et al.  Electrical and optical properties of zinc oxide thin films prepared by rf magnetron sputtering for transparent electrode applications , 1984 .

[7]  T. Yuasa,et al.  Influence of Energetic Oxygen Bombardment on Conductive ZnO Films , 1985 .

[8]  Takashi Mouri,et al.  Preparations of ZnO:Al transparent conducting films by d.c. magnetron sputtering , 1990 .

[9]  Yoshifumi Ota,et al.  Low resistivity indium–tin oxide transparent conductive films. II. Effect of sputtering voltage on electrical property of films , 1990 .

[10]  T. Miyata,et al.  Electrical Conduction Mechanism of Highly Transparent and Conductive ZnO Thin Films , 2001 .

[11]  David L. Young,et al.  Characterization of Transparent Conducting Oxides , 2000 .

[12]  H. Nanto,et al.  The stability of aluminium-doped ZnO transparent electrodes fabricated by sputtering , 1986 .

[13]  T. Miyata,et al.  Transparent conducting Al-doped ZnO thin films prepared by magnetron sputtering with dc and rf powers applied in combination , 2007 .

[14]  Shinzo Takata,et al.  Conduction mechanism of highly conductive and transparent zinc oxide thin films prepared by magnetron sputtering , 1992 .

[15]  S. Kawai,et al.  Control of electrical conductivity in laser deposited SrTiO3 thin films with Nb doping , 1994 .

[16]  T. Minami.  New n-Type Transparent Conducting Oxides , 2000 .

[17]  H. Nanto,et al.  Effect of applied external magnetic field on the relationship between the arrangement of the substrate and the resistivity of aluminium-doped ZnO thin films prepared by r.f. magnetron sputtering , 1988 .

[18]  Shinzo Takata,et al.  Group III Impurity Doped Zinc Oxide Thin Films Prepared by RF Magnetron Sputtering , 1985 .

[19]  S. Nakamura,et al.  ZnO:Ga conducting-films grown by DC arc-discharge ionplating , 2001 .

[20]  B. Szyszka,et al.  Properties of aluminum-doped zinc oxide films deposited by high rate mid-frequency reactive magnetron sputtering , 2001 .

[21]  Sho Shirakata,et al.  Electrical and optical properties of large area Ga-doped ZnO thin films prepared by reactive plasma deposition , 2006 .

[22]  Shinzo Takata,et al.  Highly Conductive and Transparent Aluminum Doped Zinc Oxide Thin Films Prepared by RF Magnetron Sputtering , 1984 .

[23]  Y. Shigesato,et al.  Al-Doped ZnO Films Deposited by Reactive Magnetron Sputtering in Mid-Frequency Mode with Dual Cathodes , 2002 .

[24]  Akio Suzuki,et al.  Low resistivity transparent conducting Al-doped ZnO films prepared by pulsed laser deposition , 2003 .

[25]  K. Tominaga,et al.  Radiation Effect due to Energetic Oxygen Atoms on Conductive Al-Doped ZnO Films , 1988 .

[26]  T. Minami.  Transparent conducting oxide semiconductors for transparent electrodes , 2005 .

[27]  T. Miyata,et al.  High rate deposition of transparent conducting oxide thin films by vacuum arc plasma evaporation , 2002 .

[28]  T. Hitosugi,et al.  Ta-doped Anatase TiO2 Epitaxial Film as Transparent Conducting Oxide , 2005 .

[29]  T. Miyata,et al.  Transparent conducting V-co-doped AZO thin films prepared by magnetron sputtering , 2003 .

[30]  J. Webb.  Conductivity imaging of the erosion pattern for ZnO prepared by planar R.F. magnetron sputtering , 1986 .

[31]  Shinzo Takata,et al.  The stability of zinc oxide transparent electrodes fabricated by R.F. magnetron sputtering , 1984 .

[32]  T. Miyata,et al.  Origin of electrical property distribution on the surface of ZnO:Al films prepared by magnetron sputtering , 2000 .

[33]  T. Miyata,et al.  New Transparent Conducting Al-doped ZnO Film Preparation Techniques for Improving Resistivity Distribution in Magnetron Sputtering Deposition , 2006 .

[34]  R. Cebulla,et al.  Al-doped zinc oxide films deposited by simultaneous rf and dc excitation of a magnetron plasma: Relationships between plasma parameters and structural and electrical film properties , 1998 .

[35]  T. Miyata,et al.  Effect of thickness on the stability of transparent conducting impurity‐doped ZnO thin films in a high humidity environment , 2007 .

[36]  Taro Hitosugi,et al.  A transparent metal: Nb-doped anatase TiO2 , 2005 .

[37]  T. Miyata,et al.  Highly transparent and conductive rare earth-doped ZnO thin films prepared by magnetron sputtering , 2000 .