Effect of Different Oxygen Flow and Bilayer Gate Insulator on Electrical Performance and Bias Stability of a-IGZO TFTs

• Main Authors: LIN, TSUNG-SHENG, 林宗聖
• Other Authors: SHEI, SHIN-CHANG
• Format: Others
• Language: en_US
• Published: 2019
• Online Access: http://ndltd.ncl.edu.tw/handle/ymvu9y

碩士 === 國立臺南大學 === 電機工程學系碩博士班 === 107 === The amorphous indium gallium zinc oxide (IGZO) semiconductor has better uniformity due to the amorphous structure. Compared to the traditional using of amorphous silicon, IGZO has the higher mobility, low fabrication temperature, low fabrication cost. However, they are sensitive to oxygen, moisture, light illumination and fabrication parameters. According to many researches about IGZO, the key issue about unstable properties was caused by the variation of oxygen vacancy concentration. In this study, we fabricated the IGZO thin film transistor(TFT) on glass substrate The experiment is mainly divided into three parts. In the first part of the experiment, we discussed the argon to oxygen flow ratio of sputtering parameter which was 99/1, 98/2, 97/3, 96/4, 95/5 and 94/6 sccm. The material analysis used XRD, SEM, EDS, UV-Vis, PL and Hall Effect, and to find the optimal sputtering conditions. After analysis, we found that the best performance of devices was oxygen flow ratio of 95/5 sccm can form n-channel enhancement mode transistor, film transmittance of 91.3% in visible spectrum, suitable carrier concentration of 2.242×1012cm-3, saturation mobility of 9.25cm2/Vs, threshold voltage of 0.98V, Ion/Ioff ratio of 1.12×105 and sub-threshold swing of 0.98V/dec. In the second part of the experiment, we fabricated IGZO thin film transistors with SiO2 and SiO2/Al2O3 bilayer gate insulator, the thicknesses of were SiO2 200 nm and SiO2/Al2O3 180/20nm, 170/30nm and 160/40nm, respectively. The devices by annealing at 300℃ for one hour. After annealing, the results show that TFT with 170/30nm SiO2/Al2O3 bilayer gate insulator exhibits the best electrical performance compared to single SiO2 gate insulator based. The measured the saturation current, leakage current, insulator surface roughness, saturation mobility, threshold voltage, subthreshold swing (SS), Ion/Ioff ratio and the maximum density of surface states at the channel–insulator interface values obtained were 81.2μA, 5.42 x 10-11A/cm2, 2.95nm, 7.86cm2/Vs, 2.65V, 0.19V/dec, 4.31×1011 and 8.59×1010cm-2 respectively. In the third part of the experiment, we test device bias stability, the 170/30nm SiO2/Al2O3 bilayer gate insulator device shows a substantially smaller threshold voltage shift of 0.98V and -0.69 after a 10 and -10V gate voltage is applied for 1000s, and hysteresis ΔVTH shift 0.06V. In addition, we measure the photo responsivity of IGZO TFT, the responsivity was 200(A/W) with the illumination of 300 nm wavelength. Showing that IGZO has photosensitive properties and has the potential to be made into photo transistors.