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Title: A study of dielectric thin film materials for display applications
Author: Nam, Taesung
ISNI:       0000 0001 3439 3525
Awarding Body: Nottingham Trent University
Current Institution: Nottingham Trent University
Date of Award: 2006
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By advances in information and telecommunication technology (ICT), a display device is one of the most important information technologies. In particular, flat panel displays and technologies have been considered as the centre of a next generation engine in society, academia, business, and other communities. This thesis is based on an inorganic alternative current thin film electroluminescent (ACTFEL) device which is one of the flat panel display technologies. Investigation of electrical and dielectric properties of Bao.5Sro.5Ti0 3 (BST) thin film to enhance device stabiUty and reduce a driving voltage of the TFEL device was carried out. In addition, yttrium oxide dielectric thin film, yellow emitting ZnS:Mn and blue emitting SrS:Cu,Ag phosphors are also discussed. These thin films and TFEL devices were fabricated by rf-magnetron sputtering method except for the aluminium(Al) electrode, which was deposited by thermal evaporation. Various characterisations techniques were apphed to the candidate dielectric thin films and the EL devices. These were performed by fabricating Metal-lnsulator-Semiconductor (MIS) capacitors and lateral- and surface emitting- TFEL devices, respectively. Meanwhile, materials and device engineering included laser annealing and barrier layers were utiHsed. In this study the optimum growth conditions for rf-sputtered barium strontium titanate (BST) thm films were estabhshed. The substrate temperature, sputtering pressure, oxygen ratio, and rf power were 300 to 350 °C, 10 mTorr, 10% O₂ mixture, and 100 watts, respectively. Also, it is found that an additional post-annealing process was necessary to improve BST thin films. Thus, BST thin films prepared in the optimum conditions showed a high dielectric constant of 32.4 and a high breakdown field of 8 MV/cm. Thus, the charge storage capacity of 100 nm-thick BST thin films is as high as 22.95 μC/cm², which is 8 times larger than the minimum requirement of charge storage capacity in selecting candidate dielectric material. Leakage current was as low as 1.58 μA/cm² at 80 V. In device structures, BaₓSr₁₋ₓTiO₃ (BST)/ZnS:Mn/Y₂O₃ EL devices exhibited far better performance in turn-on characteristics, luminance and device stability compared to other BaₓSr₁₋ₓTiO₃ (BST)/ZnS:Mn/ BaₓSr₁₋ₓTiO₃(BST) and Y₂O₃/ZnS:Mn/Y₂O₃ EL devices. For blue emitting SrS:Cu,Ag EL devices, the device performance had a high correlation with barrier layer thickness. A 10 nm-thick barrier layer and 5-laser pulse at 1.8 J/cm² laser annealing process were the optimum conditions for the barrier layers. Meanwhile, high laser fluence (> 2.0 J/cm²) may cause a "laser ablation" effect on the surface of the samples and as a result, a lower performance was observed. Therefore, overall improvement of EL emission could be achieved by combination of the device and materials engineering.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available