XPS spectra of Zr, In, Zn ions with respect to the Zr content, and pre-annealing temperature was shown in the Figure 4.11. The Zr 3d5/2, In 3d5/2, Zn 2p3/2, centered at 183.4, 445.6, and 1022.8 eV, which indicated Zr-O, In-O, and Zn-O bonds, respectively.
First, we investigated the effect of the Zr content. As expected the intensity of the Zr 3d5/2 peak decreased the decreasing Zr content. The peak of Zr 3d5/2 centered at 183.4 eV was attributed to the fully oxidized zirconium. When the Zr content was decreased, it could cause a shift in the lower binding energy of In 3d5/2 and Zn 2p3/2
peaks from 445.6 and 1022.8 eV to 445.2 and 1022.2 eV, respectively.
Finally, we investigated the effect of the exposure to the atmosphere. In Figure 4.12, we observed that the binding energy of the peaks for the device prepared with the ratio of Zr: In: Zn = 0.5: 5: 5 was different than others after 2 days. According to Figure 4.4, we observed that the transfer performances became stable after 8 day. We inferred that the chemical reaction had not been completed yet. Therefore, the XPS pattern was similar to that of the device. On the other hand, after 7th day, the Zr 3d5/2, In 3d5/2 and Zn 2p3/2 peaks shifted from 181.8, 444.2 and 1021.2 eV to 183.4, 445.6 and 1022.8 eV respectively. The shifted peaks indicated that a chemical reaction occured.
According the pattern of XPS, we calculated the real ratio of Zr: In: Zn = 0: 5: 5, 0.1: 5: 5, 0.5: 5: 5was 0: 3: 2, 1: 2: 2, 4: 11: 5, respectively.
Figure 4.13 shows the O 1s region of the XPS spectra with respect to Zr content.
The O 1s peak could be deconvoluted into two peaks centered at 531.3 and 532.9 eV, determined by Gaussian fitting. The O 1s peak could be explained with the binding state of oxygen with metals. The lower energy oxygen peaks was defined as OI, the higher as OII. OI represented the O2- ions combined with Zr, In and Zn ions in the ZIZO system. OII was associated with oxygen vacancies in the ZIZO compound. Ototal
denoted the total O 1s peak area. When increasing the Zr content, the OII/Ototal value representing the ratio of oxygen vacancies gradually decreased from 0.486 to 0.289.
Not only OII/Ototal but also OII/OI was decreased from 0.967 to 0.6310. Therefore, incorporating Zr reduced oxygen vacancies, indicating that Zr acted as a carrier suppressor effectively.
Table 4.4 Variation in the area ratio of O 1s
Zr:In:Zn
Binding Energy (eV)
Ratio Area OII/OI
0:5:5
531.3 OI/Ototal 0.502
0.967 532.9 OII/Ototal 0.486
0.1:5:5
531.3 OI/Ototal 0.516
0.6337 532.9 OII/Ototal 0.327
0.5:5:5
531.3 OI/Ototal 0.458
0.6310 532.9 OII/Ototal 0.289
Chapter 5 Conclusion
In conclusion, we have demonstrated a solution-processable approach for manufacturing high-performance ZrInZnO (ZIZO) thin film transistors (TFTs). We studied Zr as a candidate material for carrier suppressor in the IZO systems in place of other common suppressors, such as Ga. The ZIZO TFTs exhibited a field effect mobility of 3.8 cm2/Vs, an on-off ratio of ~107. The threshold voltage (Vth) was 0.44 V and the subthreshold swing was 0.42 V/dec. The threshold voltage became stable under the bias stress. Further, ZIZO thin film was amorphous. When the pre-annealing temperature increased, the crystallization was improved. Analysis of the O 1s peak in the XPS spectra showed decreasing the O2- ions related to the variation in the concentration of oxygen vacancies which can supply free electrons.
By adding NaOH, we could speed up the hydroxylation reaction. Overall the device performance is almost comparable with that of the device made by conventional cosputtering methods. Our method offers another possible way to low-cost, high-through manufacture for next generation TFTs for display applications.
Reference
[1] J.-H. Lee, D.-H. Kim, D.-J. Yang, S.-Y. Hong, K.-S. Yoon, P.-S.Hong,C.-O. Jeong, H.-S. Park, S. Y. Kim, S. K. Lim, and S. S. Kim, “World’s Largest (15-inch) XGA AMLCD Panel Using IGZO Oxide TFT,” SID Symposium Digest Tech Papers, 625, 2008.
[3] H. Hosono, “Ionic amorphous oxide semiconductors: Material design, carrier transport, and device application,” J. Non-Crystalline Solids 352, 851 (2006)
[4] H. Hosono, “Working hypothesis to explore novel wide band gap electrically conducting amorphous oxides and examples,” J. Non-Crystalline Solids, 198–200, 165–169 (1996).
[5] J. F. Wager, “Applied Physics Transparent Electronics,” Science, 300, 1245 (2003).
[6] P. F. Carcia, R. S. Mclean, M. H. Reilly, and G. Lunes, “Transparent ZnO thin-film transistor fabricated by rf magnetron sputtering,” Jr. Appl. Phys. Lett., 82, 1117 (2003).
[7] K. L. Chopra, S. Major, and K. Pandya, “Highly transparent and conducting indium-doped zinc oxide films by spray pyrolysis,” Thin Solid Films, 102,1 (1983).
[8] Y. Ohya, T. Niwa, T. Ban, and Y. Takahashi, “Thin Film Transistor of ZnO Fabricated by Chemical Solution Deposition,” Jpn. J. Appl. Phys., 40, 297 (2001).
[9] K. Nomura, A. Takagi, T. Kamiya, H. Ohta, M. Hirano, and H.Hosono, “Amorphous Oxide Semiconductors for High-Performance Flexible Thin-Film Transistors,” Jpn. J.
Appl. Phys., 45, 4303-4308 (2006).
[10] H. Yabuta, M. Sano, K. Abe, T. Aiba, T. Den, H. Kumomi, K.Nomura, T. Kamiya, and H. Hosono, “High-mobility thin-film transistor with amorphous InGaZnO4 channel fabricated by room temperature rf-magnetron sputtering,” Appl. Phys. Lett., 89, 112123 (2006).
[11] N. F. Mott, “Silicon dioxide and the chalcogenide semiconductors; similarities and differences,” Adv.Phys., 26, 363–391 (1977).
[12] K. Nomura, H. Ohta, A. Takagi, T. Kamiya, M. Hirano, and H. Hosono,
“Room-temperature fabrication of transparent flexible thin film transistors using amorphous oxide semiconductors,” Nature, 432, 488 (2004).
[13] P. Barquinha, A. Pimentel, A. Marques, L. Pereira, R. Martins and E. Fortunato, “Influence of the semiconductor thickness on the electrical properties of transparent TFTs based on indium zinc oxide,” J. Non-Cryst. Solids, 352, 1749 (2006).
[14] P. Gorrn, P. Holzer, T. Riedl, W. Kowalsky, J. Wang, T. Weimann, P. Hinze and S.
Kipp, “Stable of transparent zinc tin oxide transistors under bias stress, ”Appl. Phys. Lett., 90, 063502 (2007).
[15] J.S. Park, K. S. Kim, Y. G. Park, Y. G. Mo, H. D. Kim, and J. K. Jeong, “Novel ZrInZnO Thin-film Transistor with Excellent Stability,” Adv. Mater 21, 329-333 (2009).
[16] E. Fortunato, P. Barquinha, A. Pimentel, A. Goncalves, A. Marques, L.
Pereira, R. Martins, “Fully transparent ZnO thin-film transistor produced at room
[18] R. L. Hoffman, B. H. Norrs, J. F. Wager, “ZnO-based transparent thin film transistors, “Room temperature deposited indium zinc oxide thin film transistors,”
Appl. Phys. Lett. 82, 733 (2003).
[19] Y.-L. Wang, F. Ren, W. Lim, D. P. Norton, S. J. Pearton, I. I. Kravchenko, J.
M. Zavada, “Room temperature deposited indium zinc oxide thin film transistors,”
Appl. Phys. Lett. 90, 232103 (2007).
[20] B. Yaglioglu, H. Y. Yeom, R. Beresford, D. C. Paine, “Magnetotransport properties of Ge channels with extremely high compressive strain,” Appl. Phys. Lett.
89, 062103 (2006).
[21] C. G. Choi, S.-J. Seo, B.-S. Bae, Electrochem. “Solution-processed indium zinc oxide transparent thin-film transistors,” Solid-State Lett 11, H7 (2008).
[22] H. Yabuta, M. Sano, K. Abe, T. Aiba, T. Den, H. Kumomi, K. Nomura, T.
Kamiya, H. Hosono, “Control of p- and n-type conductivities in Li-doped ZnO thin films,” Appl. Phys. Lett. 89, 112123 (2006).
[23] M. Kim, J. H. Jeong, H. J. Lee, T. K. Ahn, H. S. Shin, J. S. Park, J. K. Jeong, Y.
G. Mo, H. D. Kim, “High mobility bottom gate InGaZnO thin film transistors with SiOx etch stopper,” Appl. Phys. Lett. 90, 212114 (2007).
[24] J. S. Park, J. K. Jeong, Y. G. Mo, H. D. Kim, “Improvements in the device characteristics of amorphous indium gallium zinc oxide thin-film transistors by Ar plasma treatment,” Appl. Phys. Lett. 90, 262106 (2007).
[25] J. K. Jeong, J. H. Jeong, H. W. Yang, J.-S. Park, Y.-G. Mo, H. D. Kim, “High performance thin film transistors with cosputtered amorphous indium gallium zinc oxide channel,” Appl. Phys. Lett. 91, 113505 (2007).
[26] J. H. Jeong, H. W. Yang, J.-S. Park, J. K. Jeong, Y.-G. Mo, H. D. Kim, J. Song, C. S. Hwang, “Origin of subthreshold swing improved in amorphous indium gallium zinc oxide transistor,” Electrochem. Solid-State Lett. 11, H157 (2008).
[27] K. Nomura, H. Ohta, A. Takagi, T. Kamiya, M. Hirano, H. Hosono,
“Room-temperature fabrication of transparent flexible thin-film transistors using amorphous oxide semiconductors,” Nature 432, 488 (2004).
[28] G. H. Kim, W. H. Jeong, B. D. Ahn, H. S. Shin, H. J. Kim, H. J. Kim. M. -K.
Ryu, K. –B. Park, J. –B. Seon, and S. –Y. Lee, “Investigation of the effects of Mg incorporation into InZnO for high-performance and high-stability solution-processed thin film transistors,” Appl. Phy. Lett 96,163506 (2010).
[29] W. H. Jeong, G. H. Kim, H. S. Shin, B. D. Ahn, H. J. Kim, M, -K. Rye, K. -B.
Park, J. -B. Seon, and S. -Y. Lee, “Investigating addition effect of hafnium in InZnO thin film transistors using a solution process,” Appl. Phy. Lett. 96, 093503 (2010).
[30] Y. Choi, G. Kim, W. Jeong, J. Bae, H. Kim, J. Hong, J. Yu, “Carrier-suppressing effect of scandium in InZnO systems for solution-processed thin film transistor,”
Appl. Phys Lett. 97, 162102 (2010).
[31] D. N. Kim, D. L. Kim, G. H. Kim, S. J. Kim, Y. S. Rim, W. H. Jeong, and H. J.
Kim, “The effect of La in InZnO systems for solution-processed amorphous oxide thin-film transistors,” Appl. Phys Lett. 97, 192105 (2010).
[32] S. Kobayashi, T. Nishikawa, T. Takenobu, S. Mori, T. Shimoda, T. Mitani, H.
Shimotani, N. Yoshimoto, S. Ogawa, and Y. Iwasa, “Control of carrier density by self-assembled monolayers in organic field-effect transistors,” Nat. Mater. 3, 317 (2004).
[33] K. P. Pernstich, S. Haas, D. Oberhoff, C. Goldmann, D. J. Gundlach, B. Batlogg, A. N. Rashid, and G. Schitter, “Threshold voltage shift in organic field effect transistors by dipole monolayers on the gate insulator,” J. Appl. Phys. 96, 6431
[35] G. Horowitz, F. Dellofre, F Garnier, R. Hajlaoui, M. Hmyene, and A. Yassar, Synth, “All-organic field-effect transistors made of π-conjugated oligomers and polymeric insulators,” Met. 54, 435 (1993).
[36] Jin-Seong Park, KwangSuk Kim, Yong-Gil Park, Yeon-Gon Mo, Hye Dong Kim, and Jae Kyeong Jeong, “Novel ZrInZnO Thin-film Transistor with Excellent Stability,” Adv. Mater. 2009, 21, 329–333