Indium gallium zinc oxide

Indium gallium zinc oxide (IGZO) is a semiconducting material, consisting of indium (In), gallium (Ga), zinc (Zn) and oxygen (O). IGZO thin-film transistor (TFT) is used in the TFT backplane of flat-panel displays (FPDs). IGZO-TFT was developed by Hideo Hosono's group at Tokyo Institute of Technology and Japan Science and Technology Agency (JST) in 2003 (crystalline IGZO-TFT)[1][2] and in 2004 (amorphous IGZO-TFT).[3] IGZO-TFT has 20–50 times the electron mobility of amorphous silicon, which has often been used in liquid-crystal displays (LCDs) and e-papers. As a result, IGZO-TFT can improve the speed, resolution and size of flat-panel displays. It is currently used as the thin-film transistors for use in organic light-emitting diode (OLED) TV displays.

IGZO-TFT and its applications are patented by JST.[4] They have been licensed to Samsung Electronics[4] (in 2011) and Sharp[5] (in 2012).

In 2012, Sharp was first to start production of LCD panels incorporating IGZO-TFT.[6] Sharp uses IGZO-TFT for smartphones, tablets, and 32" LCDs. In these, the aperture ratio of the LCD is improved by up to 20%. Power consumption is improved by LCD idling stop technology, which is possible due to the high mobility and low off current of IGZO-TFT.[7] Sharp has started to release high pixel-density panels for notebook applications.[8] IGZO-TFT is also employed in the 14" 3,200x1,800 LCD of an ultrabook PC supplied by Fujitsu,[9] also used in the Razer Blade 14" (Touchscreen Variant) Gaming Laptop and a 55" OLED TV supplied by LG Electronics.[10]

IGZO's advantage over zinc oxide is that it can be deposited as a uniform amorphous phase while retaining the high carrier mobility common to oxide semiconductors.[11] The transistors are slightly photo-sensitive, but the effect becomes significant only in the deep violet to ultra-violet (photon energy above 3 eV) range, offering the possibility of a fully transparent transistor.

The current impediment to large-scale IGZO manufacturing is the synthesis method. The most widely used technique for Transparent Conducting Oxide (TCO) synthesis is Pulsed Laser Deposition (PLD).[12] In PLD, a laser is used to focus on nano-sized spots on solid elemental targets. Laser pulse frequencies are varied between the targets in ratios to control the composition of the film. IGZO can be deposited onto substrates such as quartz, single-crystal silicon, or even plastic due to its ability for low-temperature deposition. The substrates are placed in a PLD vacuum chamber, which controls oxygen pressure in order to ensure favorable electrical properties. After synthesis, the film is annealed, or gradually exposed to air to adjust to the atmosphere.

While PLD is a useful and versatile synthesis technique, it requires expensive equipment and plenty of time for each sample to adjust to regular atmospheric conditions. This is not ideal for industrial manufacturing.

Solution Processing is a more cost effective alternative. Specifically, combustion synthesis techniques can be used. Kim et al. used a metal nitrate solution with an oxidizer to create an exothermic reaction.[13] One common type of combustion synthesis is spin coating,[14] which involves depositing In and Ga solution layers onto a hot plate and annealing at temperatures roughly between 200 and 400 degrees C, depending on the target composition. The films can be annealed in air, which is a large advantage over PLD.

Combustion processing has potential as a new synthesis method, but more research is required to assess its viability. The Bedzyk Group at Northwestern University is currently comparing properties such as the crystallization temperature and electron mobility between IGO films made by PLD and combustion processing.

References
  1. Nomura, K; Ohta, H; Ueda, K; Kamiya, T; Hirano, M; Hosono, H (2003-05-23). "Thin-Film Transistor Fabricated in Single-Crystalline Transparent Oxide Semiconductor". Science. 300: 1269–1272. doi:10.1126/science.1083212. PMID 12764192.
  2. "To whom interested in Research & Development and/or Business Development of IGZO-based Oxide Semiconductor TFT". Jst.go.jp. Retrieved 2015-11-01.
  3. Nomura, K; Ohta, H; Takagi, A; Kamiya, T; Hirano, M; Hosono, H (Nov 2004). "Room-temperature fabrication of transparent flexible thin-film transistors using amorphous oxide semiconductors". Nature. 432: 488–492. doi:10.1038/nature03090. PMID 15565150.
  4. "JST Signs Patent License Agreement with Samsung for High Performance Thin Film Transistor Technology". Jst.go.jp. July 20, 2011. Retrieved 2015-11-01.
  5. "シャープとJSTが酸化物半導体に関するライセンス契約を締結 | ニュースリリース：シャープ". Sharp.co.jp. Retrieved 2015-11-01.
  6. "Sharp Begins Production of World's First LCD Panels Incorporating IGZO Oxide Semiconductors | Press Releases | Sharp Global". Sharp-world.com. 2012-04-13. Retrieved 2015-11-01.
  7. "機能・サービス｜docomo NEXT series AQUOS PHONE ZETA SH-02Eトップ｜docomoラインアップ ｜AQUOS：シャープ". Sharp.co.jp. Retrieved 2015-11-01.
  8. "Sharp to Produce 3 Types of IGZO LCD Panels for Notebook PCs | Press Releases | Sharp Global". Sharp-world.com. 2013-05-14. Retrieved 2015-11-01.
  9. "Fujitsu Launches New Lineup of FMV Series PCs with Four New Models - Fujitsu Global". Fujitsu.com. Retrieved 2015-11-01.
  10. "LG DISPLAY SAYS UHD OLED TV PANEL PRODUCTS IN VARIOUS SIZES AND DESIGNS IN 2015 - Flat Panel TV and Display World-2 液晶・業界・動向". Flat-display-2.livedoor.biz. 2013-05-27. Retrieved 2015-11-01.
  11. Chiao-Shun Chuang. "P-13: Photosensitivity of Amorphous IGZO TFTs for Active-Matrix Flat-Panel Displays" (PDF). Eecs.umichy.edu. Retrieved 2015-11-01.
  12. Jin, B.J; Im, S; Lee, S.Y (May 2000). "Violet and UV luminescence emitted from ZnO thin films grown on sapphire by pulsed laser deposition". Thin Solid Films. 366 (1–2): 107–110. doi:10.1016/S0040-6090(00)00746-X.
  13. Kim, Myung-Gil; Kanatzidis, Mercouri G.; Facchetti, Antonio; Marks, Tobin J. (17 April 2011). "Low-temperature fabrication of high-performance metal oxide thin-film electronics via combustion processing". Nature Materials. 10 (5): 382–388. doi:10.1038/nmat3011.
  14. Mitzi, David B.; Kosbar, Laura L.; Murray, Conal E.; Copel, Matthew; Afzali, Ali (March 2004). "High-mobility ultrathin semiconducting films prepared by spin coating". Nature. 428 (6980): 299–303. doi:10.1038/nature02389.
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