Microstructure and optical properties of AlO x thin films grown on ZnO-deposited glass
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AlOx thin films were grown on ZnO-deposited glass substrates under different conditions using magnetron sputtering. The influence of processing parameters (mainly direct-current power and oxidizing atmosphere) on the structure and optical properties were investigated. The AlOx films for all samples in this study showed the coexistence of amorphous and polycrystalline structures. The kinetics of crystal growth could influence the dominant crystal orientation. Fast-growing planes were not the most thermodynamically stable, but were kinetically controlled under the film growth condition. Oxidizing the sample in O2 atmosphere made the AlOx film grow in random directions. The excess oxygen was chemisorbed at the interface between AlOx and ZnO. Therefore, the neighboring oxygen–oxygen distance of AlOx and that of ZnO on their closest-packed planes seriously mismatched. At high power, the particles arrived at the substrate with high kinetic energy and high rate, which led to low density due to porous structure. The transmission decreased with an increase of the pores and surface roughness of AlOx film on ZnO-deposited glass. However, the diffusion of oxygen into the grains improved transmission when the sample was oxidized in O2 atmosphere.
I. INTRODUCTION
Aluminum oxide thin films are widely used in many mechanical, optical, and microelectronic applications because of their excellent properties1 in terms of chemical inertness, mechanical strength and hardness, transparency, high abrasion and corrosion resistance, and insulating and optical properties.2 The properties of thin films are, however, dependent on the processing parameters.3 Different applications and environments demand different kinds of properties of the thin films. For optical devices, aluminum oxide is a very promising layer material4 because of its interesting optical properties. However, there is a relationship between structure and optical property, which needs to be further investigated. Aluminum oxide thin films have been produced by a variety of physical vapor deposition techniques5 such as direct current (dc) reactive sputtering,6 dual-pulsed dc magnetron sputtering,7 dc s-gun sputtering,8 and radio frequency (rf ) sputtering.9 In this paper, Al thin film was deposited on ZnO-deposited glass by dc magnetron sputtering and was then oxidized to glass/ZnO/AlOx multilayer structure. The influence of processing parameters (mainly dc power and oxidizing atmosphere) on the structure and optical properties of the AlO x thin
a)
e-mail: [email protected] J. Mater. Res., Vol. 18, No. 8, Aug 2003
http://journals.cambridge.org
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film grown on ZnO-deposited glass substrate was studied. The advantages of using glass/ZnO as substrate were described in a previous paper.10 II. EXPERIMENTAL
The ZnO-deposited glass and Al films were deposited by rf and dc magnetron sputtering, respectively. The targets used in this study were sintered stoichiometric ZnO (99.99% purity, ⭋3 × 0.25 in2, Target Materials Inc., Columbus, OH) and metallic
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