High Power Impulse Magnetron Sputter Deposited Indium Gallium Zinc Oxide for Thin-Film Transistor

• Main Author: 柯仁程
• Other Authors: 何主亮
• Format: Others
• Language: zh-TW
• Published: 2014
• Online Access: http://ndltd.ncl.edu.tw/handle/424up8

碩士 === 逢甲大學 === 材料科學與工程學系 === 102 === Over many evolutionary generations, the display technology has become an indispensable part in our daily life. However, due to the living demand expansion, especially for the display applications, a lighter, thinner, large-sized, and low-power display has been aiming. In order to achieve these requirements, the thin-film transistor (TFT) that plays an important role in the on-off switch of the display device must be improved. The channel layer material of the TFT structure is a key factor maily influencing to display quality. Recently, the amorphous indium gallium zinc oxide (a-IGZO) has been extensively investigated and commercialized. Because IGZO has a high mobility, and its amorphous structure is uniform in large area, this material has become a noticeable material for channel layer. The study of the effects of crystallinity on IGZO found that crystalline IGZO TFT with better uniformity, higher stability and lower off-state leakage current might have more opportunities to improve the display quality. Unfortunately, it requires high temperature during post-annealing treatment for obtaining crystalline IGZO. By utilizing high power impulse magnetron sputtering (HIPIMS) of high-density plasma source, a direct deposition of crystalline IGZO on the substrate was realized, which greatly inluences to the development of the display devices. HIPIMS is different from conventional direct-current magnetron sputtering (DCMS). HIPIMS is used in the reactive sputtering process because the high ionization rate causes a high number of secondary electron accelerated towards the target surface, making an increase of current and an enhancement of the power. This study focused on two main parts. Firstly, DCMS and HIPIMS were used to deposit IGZO films under the same average power. Secondly, HIPIMS was used to deposit IGZO film with different oxygen/argon flow ratios. Microstructure of IGZO films was analysed, and electrical and optical properties were also measuared. Finally, the IGZO TFT with staggered bottom-gate structure Glass/Al/SiO2/IGZO/Al was prepared, and its device properties were investigated. Experimental results show that with different plasma sources, the structure of IGZO films is amorphous structure. HIPIMS film with the growth rate of 56 nm/min is less than that of DCMS film (100 nm/min). The results of components analysis are all rich gallium IGZO films. The optical band gap of HIPIMS film is high (approximately 3.4 eV). The mobility and electrical resistivity of HIPIMS-deposited-IGZO film are 11.9 cm2/Vs and 5.5 mΩ.cm, respectively. HIPIMS-deposited-IGZO TFT device indicates better output characteristics, say, threshold voltage of 0.7 V, off current of 1.0×10-10 A, saturated current of 5.5×10-5 A, on-off current ratio of 2.5×105, subthreshold swing of 0.6 V/decade, and field-effect mobility of 12.0 cm2/Vs. When the O2/Ar flow ratio was increased, the crystal structure of IGZO films was converted from amorphous to spinel structure, and the film growth rate was also increased. The results of components analysis are all rich gallium IGZO films, and the lowest optical band gap was seen at the O2/Ar flow ratio of 0.28. When the O2/Ar flow ratio was increased from 0.00 to 0.21, the mobility was decreased from 11.9 to 9.7 cm2/Vs, and electrical resistivity was increased from 5.5 to 8.0 mΩ.cm. The crystalline IGZO film was obtained at O2/Ar flow ratio of 0.28; however, almost oxygen vacancies were filled. The crystalline IGZO film was obtained at O2/Ar flow ratio of 0.28, threshold voltage of 3.0 V, off current of 6.2×10-11 A, saturated current of 1.3×10-6 A, on-off current ratio at 2.1×104, subthreshold swing of 1.1 V/decade, and field-effect mobility of 1.0 cm2/Vs.