Optimization of IGZO/Cu/IGZO Multilayers as Transparent Composite Electrode on Flexible Substrate by Room-temperature Sp
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Optimization of IGZO/Cu/IGZO Multilayers as Transparent Composite Electrode on Flexible Substrate by Room-temperature Sputtering and Post-Deposition Anneals Aritra Dhar1 and T. L. Alford1,2 1
Department of Chemistry and Biochemistry,
2
School for Engineering of Matter, Transport, and Energy,
Arizona State University, Tempe, Arizona 85287
ABSTRACT Highly transparent composite electrodes made of multilayers of In- and Ga-doped ZnO and Cu (IGZO/Cu/IGZO) thin films (30/3-9/30 nm thick) are deposited onto flexible substrates at room temperature and by using radio frequency magnetron sputtering. The effect of Cu thickness on the electrical and optical properties of the multilayer stack has been studied in accordance with the Cu morphology. The optical and electrical properties of the multilayers are studied with the UV–Vis spectrophotometry, Hall measurement and four point probe analyses. Results are compared with those from a single IGZO layered thin film. The average optical transmittance and sheet resistance both decreases with increase of copper thickness and has been optimized at 6 nm Cu middle layer thickness. The Haacke figure of merit (FOM) has been calculated to evaluate the performance of the films. The highest FOM achieved is 6 x 10-3 Ω-1 for a Cu thickness of 6 nm with a sheet resistance of 12.2 Ω/sq and an average transmittance of 86%. The multilayered thin films are annealed upto 150 oC in vacuum, forming gas and O2 environments and the optical and electrical properties are studied and compared against the as-deposited samples. Thus IGZO/Cu/IGZO multilayer is a promising flexible electrode material for the nextgeneration flexible optoelectronics. INTRODUCTION Transparent conducting oxides (TCOs) are widely used in the optoelectronic industry for organic light emitting diodes (OLEDs), flat panel displays and solar cells etc. TCOs are characterized by the combination of high electrical conductivity and high transmittance in the visible region. TCOs can be broadly divided into two categories based on their constituents: single-component systems (e.g., zinc oxide, tin oxide) and multi-component systems like indium-tin oxide, indium-zinc oxide (IZO), and aluminium-gallium-zinc oxide etc. Singlecomponent TCOs such as zinc oxide [1-3] and tin oxide [4] have been studied extensively for the last few decades. Recently, there has been increasing interest in multi-component TCOs with multiple cation oxides such as indium tin oxide [5], indium zinc oxide [6], zinc tin oxide [7] etc. Among them, amorphous indium gallium zinc oxide (a-IGZO) has emerged as a promising candidate due to high-mobility (~10 cm2/Vs) and their prospective applications as channel layer materials in transparent thin film transistors (TTFT) in flexible electronics [8]. The ease of manufacturability at room-temperature makes amorphous materials very attractive. Moreover, at such low temperatures, the oxides show smooth surfaces, which is advantageous
for process integration. Also, the problem of having grain boundaries can also be avoided. Th
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