Failure behaviour of AZO/Ag/AZO multilayers on PEN substrates for flexible electronic devices

Mohammed, Dilveen W.; Elhamali, S.; Koutsogeorgis, D.; Bowen, James and Kukureka, Stephen N. (2015). Failure behaviour of AZO/Ag/AZO multilayers on PEN substrates for flexible electronic devices. In: 42nd International Conference on Metallurgical Coatings and Thin Films, 20-24 Apr 2015, San Diego, USA.



Requirements of transparent conductive oxide (TCO) films for optoelectronic applications are mainly focussed on their low electrical resistivity, optical transmittance of above 85% in the visible region and mechanical stability on flexible polymer substrates. Examples of applications include flat-panel displays, solar cells, and thin film transistors (TFTs). Indium tin oxide (ITO) is widely used in transparent conductive electrodes in such devices, but high costs and brittleness have limited its applications. The electrical conductivity and mechanical stability of a single aluminium-doped zinc oxide (AZO) layer for flexible optoelectronic applications is still relatively limited. In this study we prepared AZO (35 nm)/Ag/AZO (35 nm) films using RF magnetron sputtering at room temperature. In order to satisfy the requirements of TCO films for flexible electronic device applications, Ag thin films with thicknesses 8, 10, and 12 nm were used as intermediate metal layers. The effect of Ag thickness on the electrical and optical properties is reported and discussed. The mechanical properties of AZO/Ag/AZO multilayer film compared with the single-layered AZO sample were investigated using cyclic bending fatigue and twisting tests. Changes in electrical resistance were monitored in situ. Scanning electron microscopy and atomic force microscopy were used to provide surface characterisation of the mechanically-tested samples. The effective embedment of the Ag layer between upper and lower AZO films led to metallic conductivity, high optical transparency, and superior flexibility to the single AZO electrode, due to the high failure strain of the ductile Ag layer. Furthermore, AZO/Ag/AZO showed similar performance compared with ITO films. These results indicate that flexible AZO/Ag/AZO multilayer electrodes grown by RF magnetron sputtering are a promising candidate for use as an indium-free flexible anode for optoelectronic devices.

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