| AVS 58th Annual International Symposium and Exhibition | |
| Transparent Conductors and Printable Electronics Focus Topic | Thursday Sessions |
| Session TC+EM+NS-ThA |
| Session: | Transparent / Printable Electronics Part 2 |
| Presenter: | Keisuke Ide, Tokyo Institute of Technology, Japan |
| Authors: | K. Ide, Tokyo Institute of Technology, Japan K. Nomura, Tokyo Institute of Technology, Japan T. Kamiya, Tokyo Institute of Technology, Japan H. Hosono, Tokyo Institute of Technology, Japan |
| Correspondent: | Click to Email |
Amorphous oxide semiconductors (AOSs) represented by amorphous In-Ga-Zn-O (a-IGZO) are expected for large-area high-performance flexible electronic devices, because AOSs have large electron mobilities greater than 10 cm2(Vs)-1 even if fabricated at room temperature (RT). In particular, a-IGZO has good controllablities of carrier concentration, and their thin-film transistors (TFTs) exhibit superior properties including long-term stability.
In this study, we investigated effects of oxidation on operation characteristics of a-IGZO TFTs. Bottom gate, top-contact a-IGZO TFTs were fabricated on SiO2/c-Si substrates by RF magnetron sputtering. Sputtering conditions were the RF power of 70 W and the total pressure of 0.55Pa. Two oxidation treatments were examined; (i) ozone annealing and (ii) varying a mixing gas ratio of Ar : O2 from 18 : 2 to 19.8 : 0.2 in standard cc per minute (sccm) during the channel deposition.
For the ozone annealed TFTs, annealing at ≤ 250oC produced good TFTs, while those annealed at 300oC caused large hysteresis and S slope. After applying a high VGS larger than 40 V, the transfer characteristics showed the large Vth of 40V and the small hysteresis. Trap state around Fermi level of the large S state and the large Vth state were ~4x1017 and ~1x1017 cm-3eV-1, which were estimated by C-V analysis. The large Vth state is very stable in the dark, but the TFT recovers to the initial large S state by light illumination. The photoresponse measurements revealed that deep trap states were formed at 2.3 eV below the conduction band minimum by applying a high VGS. Thermal desorption spectra showed that weakly-bonded excess oxygens were incorporated in the a-IGZO layer. From these results, we built a subgap DOS model of the trap states of the excess oxygens. We also confirmed similar behaviors in a-IGZO TFTs fabricated in high oxygen pressure conditions.
This study reveals that the control of oxygen stoichiometry is important for obtaining good performance and stability of AOS TFTs.