A next generation TCO Material for display systems: Molybdenum doped Indium oxide thin films
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A next generation TCO Material for display systems: Molybdenum doped Indium oxide thin films E. Elangovan, A Marques, R Martins, and E Fortunato Materials Science Department, New University of Lisbon, CENIMAT/FCT/UNL, Campus de Caparica, Caparica, 2829-516, Portugal ABSTRACT Thin films of indium molybdenum oxide (IMO) were rf sputtered onto glass substrates at room temperature. The films were studied as a function of sputtering power (ranging 40 – 180 W) and sputtering time (ranging 2.5 – 20 min). Thickness of the films found varied between 50 – 400 nm. The films were characterized for their structural (XRD), electrical (Hall measurements) and optical (Transmittance spectra) properties. XRD studies revealed that the films are amorphous for the sputtering power ≤ 100 W and deposition time ≤ 5 min. All the other films are polycrystalline and the strongest refection along (222) plane showing a preferential orientation. A minimum bulk resistivity of 2.65 × 10-3 Ω-cm and a maximum carrier concentration of 4.16 × 1020 cm-3 have been obtained for the films sputtered at 180 W (10 min). Whereas maximum mobility (19.5 cm2 V-1 s-1) has been obtained for the films sputtered at 80 W (10 min). A maximum visible transmittance of 90 % (500 nm) has been obtained for the films sputtered at 80 W (10 min) with a minimum of 27 % for those sputtered at 180 W. The optical band gap of the films found varying between 3.75 and 3.90 eV for various sputtering parameters. INTRODUCTION In recent years, there has been significant research investment in the development of a flexible flat panel display (FFPD) technology [1]. To enable FFPD, a flexible substrate (either plastic or thin glass) must replace the conventional glass substrates. FFPDs which offer many potential advantages, such as very thin profiles, lightweight and robust display, and ability to flex, curve, conform, roll and fold can potentially result in many compelling applications not satisfied by a rigid glass-based display. Anticipating a new market opportunity, the display industry has been developing display materials targeted specifically at FFPD requirements which include transparent conducting oxides (TCOs) [2, 3]. Since the flexible substrate represents the fundamental starting component for the display, flexible substrates arguably face the greatest challenges, like room or low temperature processing, in terms of compatibility with all other necessary display layers that need to be integrated onto them. For display applications, indium oxide materials are almost extensively used due to their superior combination of environmental stability, low electrical resistivity and high visible transmittance [1]. Indium tin oxide (ITO) is the typical conducting layer used in display technologies. However, the process temperatures required for ITO on glass is incompatible with polymeric substrates. A possible crack of ITO deposited on polymer due to tensile strain can cause catastrophic failure for a display application [1a]. Further ITO has reached a performance plateau and
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