Effects of Excimer Laser Annealing on InGaZnO4 Thin-Film Transistors Having Different Active-Layer Thicknesses Compared with Those on Polycrystalline Silicon

Excimer laser annealing (ELA), which can raise the temperature of InGaZnO4 (IGZO) films for a desired very short time, is effective for obtaining good transfer characteristics in IGZO thin-film transistors (TFTs) on plastic substrates. In this study, we investigate the dependence of the effects of ELA on IGZO-TFTs in comparison with that of its effects on low-temperature polycrystalline silicon (LTPS) for various film thicknesses. We show that the optimum laser energy density with respect to TFT performance decreases with increasing IGZO thickness. Results for IGZO film properties such as carrier density and Hall mobility show the same tendency. This is contrary to the tendency for the ELA of LTPS, in which the threshold energy density for micro crystallization increases with increasing film thickness. In order to gain an insight into the mechanisms at work here, we have numerically estimated the rise in temperature of the IGZO and Si films on the basis of a heat-flow equation. Unlike the case for LTPS, the calculated maximum temperature in IGZO films increases with increasing film thickness. We show that this discrepancy is influenced significantly by the difference in penetration depth between the IGZO film (roughly 70 nm) and Si film (roughly 6 nm) for excimer laser light. To improve the IGZO-TFT characteristics, it is necessary to take into account IGZO penetration depth when determining a suitable IGZO thickness and laser energy density.

[1]  M. Matsumura,et al.  A Novel Phase-Modulated Excimer-Laser Crystallization Method of Silicon Thin Films , 1998 .

[2]  R. McLean,et al.  Transparent ZnO thin-film transistor fabricated by rf magnetron sputtering , 2003 .

[3]  Hideo Hosono,et al.  Defect passivation and homogenization of amorphous oxide thin-film transistor by wet O2 annealing , 2008 .

[4]  Benjamin J. Norris,et al.  ZnO-based transparent thin-film transistors , 2003 .

[5]  M. Nakata,et al.  Comparison of Ultraviolet Photo-Field Effects between Hydrogenated Amorphous Silicon and Amorphous InGaZnO4 Thin-Film Transistors , 2009 .

[6]  Pedro Barquinha,et al.  Wide-bandgap high-mobility ZnO thin-film transistors produced at room temperature , 2004 .

[7]  Hideo Hosono,et al.  Trap densities in amorphous-InGaZnO4 thin-film transistors , 2008 .

[8]  Masashi Kawasaki,et al.  High Mobility Thin Film Transistors with Transparent ZnO Channels , 2003 .

[9]  M. Nakata,et al.  Effects of Thermal Annealing on ZnO Thin-Film Transistor Characteristics and the Application of Excimer Laser Annealing in Plastic-Based ZnO Thin-Film Transistors , 2009 .

[10]  M. Matsumura,et al.  A New Nucleation-Site-Control Excimer-Laser-Crystallization Method , 2001 .

[11]  Setsuo Kaneko,et al.  Flexible High-Performance Amorphous InGaZnO4 Thin-Film Transistors Utilizing Excimer Laser Annealing , 2009 .

[12]  H. S. Bae,et al.  ZnO-based thin-film transistors of optimal device performance , 2004 .

[13]  H. Ohta,et al.  Amorphous Oxide Semiconductors for High-Performance Flexible Thin-Film Transistors , 2006 .

[14]  M. Nakata,et al.  Temperature-Dependent Transfer Characteristics of Amorphous InGaZnO4 Thin-Film Transistors , 2009 .

[15]  Setsuo Kaneko,et al.  Improvement of InGaZnO4 Thin Film Transistors Characteristics Utilizing Excimer Laser Annealing , 2009 .

[16]  H. Ohta,et al.  Room-temperature fabrication of transparent flexible thin-film transistors using amorphous oxide semiconductors , 2004, Nature.

[17]  Ryoichi Ishihara,et al.  Effects of Light Pulse Duration on Excimer-Laser Crystallization Characteristics of Silicon Thin Films , 1995 .

[18]  M. Nakata,et al.  Dual-Gate Characteristics of Amorphous $ \hbox{InGaZnO}_{4}$ Thin-Film Transistors as Compared to Those of Hydrogenated Amorphous Silicon Thin-Film Transistors , 2009, IEEE Transactions on Electron Devices.

[19]  T. Kamiya,et al.  High-mobility thin-film transistor with amorphous InGaZnO4 channel fabricated by room temperature rf-magnetron sputtering , 2006 .

[20]  Hideo Hosono,et al.  Ionic amorphous oxide semiconductors: Material design, carrier transport, and device application , 2006 .

[21]  M. Nakata,et al.  Effect of Zinc Oxide Film Deposition Position on the Characteristics of Zinc Oxide Thin Film Transistors Fabricated by Low-Temperature Magnetron Sputtering , 2008 .

[22]  J. W. Metselaar,et al.  Advanced excimer-laser crystallization process for single-crystalline thin film transistors , 2003 .

[23]  Hideo Hosono,et al.  Modeling of amorphous InGaZnO4 thin film transistors and their subgap density of states , 2008 .