Browsing by Author "Cheng, Hua-Chi"

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Cation-mediated effects on zinc oxide films formed by chemical bath deposition
(2007-07-01)
Cheng, Hua-Chi
;
Chen, Chia-Fu
;
Tsay, Chien-Yie
;
材料科學與工程學系
;
Department of Materials Science and Engineering
Crvstalline ZnO films with a densely packed morphology were grown on a silicon oxide (SiOx) glass substrate by chemical bash deposition (CBD) in an aqueous-solution bath containing magnesium nitrate [Mg(NO3)(2)center dot 2H(2)O] used as a cation-mediation compound. zinc nitrate [Zn(NO3)2 center dot 6H(2)O], and dimethylarnineborane (DMAB) at 65 degrees C. Grains of ZnO films grown in nonmediated solution preferentially grew on the (002) plane. In the cation-mediated-solution bath, the films were compressed into a compact morphology by the increased tendency for films to grow in the (002) prefer orientation. The crystalline ZnO film exhibits good optical transmittance of over 90%. Additionally, the direct band-gap value was 3.22 eV, which is less than 3.38 eV, which was obtained using a nonmediated-solution bath. This was due to the lattice constant variation caused by cation mediation.
Effect of Sn-doped on microstructural and optical properties of ZnO thin films deposited by sol-gel method
(2008-12-01)
Tsay, Chien-Yie
;
Cheng, Hua-Chi
;
Tung, Yen-Ting
;
Tuan, Wei-Hsing
;
Lin, Chung-Kwei
In this study, transparent thin films of Sn-doped ZnO (ZnO:Sn) were deposited onto alkali-free glass substrates by a sol-gel method; the effect of Sri doping on crystallinity, microstructural and optical properties was investigated. The atomic percentages of dopant in ZnO-based sols were Sn/Zn = 0, 1, 2, 3, and 5 at.%. The as-deposited films were pre-heated at 300 degrees C for 10 min and then annealed in air at 500 degrees C for 1 h. The results show that Sn-doped ZnO thin films demonstrate obviously improved surface roughness, enhanced transmittance in the 400-600 nm wavelength range and reduced average crystallite size. Among all of the annealed ZnO-based films in this study, films doped with 2 at.% Sn concentration exhibited the best properties, namely an average transmittance of 90%, an RMS roughness value of 1.92 nm and a resistivity of 9.3 x 10(2) Omega-cm. (C) 2008 Elsevier B.V All rights reserved.
High oriented ZnO films by sol-gel and chemical bath deposition combination method
(2009-05-05)
Cheng, Hua-Chi
;
Chen, Chia-Fu
;
Tsay, Chien-Yie
;
Leu, Jih-Perng
;
材料科學與工程學系
Poly-crystalline ZnO films with high oriented columnar grains were deposited on ZnO-coated seed layers by chemical bath deposition (CBD) in an aqueous-solution bath containing zinc nitrate [Zn(NO(3))(2)center dot 6H(2)O], and dimethylamineborane (DMAB) at 60 degrees C without pre-activation especially. Sol-gel ZnO films on glass substrates were used as the seed layers which the mean size of the crystals in seed layer increased from several to approximately 80nm at temperature from 150 degrees C to 550 degrees C. The deposited ZnO films on the ZnO-coated seed surfaces are preferentially on the (0 0 2) plane and exhibit increased from several 10 nm to 150 nm with increasing seed layer grain size. (C) 2008 Elsevier B.V. All rights reserved.
Performance of sol-gel deposited Zn1-xMgxO films used as active channel layer for thin-film transistors
(2007-12-15)
Tsay, Chien-Yie
;
Cheng, Hua-Chi
;
Wang, Min-Chi
;
Lee, Pee-Yew
;
Chen, Chia-Fu
ZnO thin-film transistors (TFTs) have attracted considerable R&D interest due to their high transparency and low photosensitivity compared with typical a-Si:H TFTs. The electrical characteristics of ZnO thin films may be controlled by doping with ternary element, for instance Al, Ga, In, Mg, Zr, etc. In this study, Zn1-x ,MgxO (x= 0 to 0.36) thin films were deposited on glass substrates by spin coating. The as-deposited films were baked at 300 degrees C for 10 min and then annealed at 500 degrees C for I h in air. The results show that, addition of Mg-species in ZnO films markedly enhanced the uniformity of film thickness and improved optical properties. The Zn0.8Mg0.2O film exhibited the best transparency of 92%, an increase of similar to 15% over a pure ZnO film, and the rms roughness value decreased to 1.63. The Zn1-x .,MgxO TFTs were demonstrated to have n-type enhancement behavior. The optimum device with Zn0.8Mg0.2O channel layer had a field-effect mobility of 0.1 cm(2) /V s, a threshold voltage of 6.0 V, and an on/off ratio more than 10(7). (c) 2007 Elsevier B.V. All rights reserved.
Transparent ZnO thin film transistor fabricated by sol-gel and chemical bath deposition combination method
(2007-01-01)
Cheng, Hua-Chi
;
Chen, Chia-Fu
;
Tsay, Chien-Yie
;
材料科學與工程學系
;
Department of Materials Science and Engineering
Top-gate thin film transistors with n-type ZnO active channel were performed under 230 degrees C. Especially, ZnO film was deposited by a combined method of sol-gel and chemical bath deposition without any preactivation for film growth. Silicon nitride and indium tin oxide were used as the gate insulator and the conducting electrodes (source, drain, and gate). These transistors were highly transparent in the visible spectrum, with transmittance as high as 75% to approximately 85% at wavelength from 500 to 700 nm. The optimum device has field-effect mobility of 0.67 cm(2)/V s and an on-off ratio more than 10(7).