2022 Fiscal Year Research-status Report
Elucidating carrier transport mechanism in disordered amorphous oxide semiconductors to realize flexible fully solution processed oxide transistors
| Project/Area Number |
22K14291
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| Research Institution | Nara Institute of Science and Technology |
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Principal Investigator |
Bermundo J.P.S 奈良先端科学技術大学院大学, 先端科学技術研究科, 助教 (60782521)
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| Project Period (FY) |
2022-04-01 – 2024-03-31
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| Keywords | oxide semiconductors / fully solution TFT / low temperature process / reliability / flexible devices / carrier concentration |
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| Outline of Annual Research Achievements |
We have successfully improved both performance and stability of fully solution processed oxide thin-film transistors by optimizing UV irradiation combined with low heating. Aside from optimizing oxygen vacancy (VO) amount, it is necessary to consider the metal oxide formation in both functionalized electrode and channel. Thus, we sought alternative methods instead of photonic process and found that Ar plasma irradiation also induces better stability. Aside from modulating VO to control carrier concentration, Ar plasma enhanced the semiconductor film density through reduction of voids/impurities which improved carrier transport. We also applied the concept of carrier concentration control on a solution processed ultrawide bandgap oxide insulator to transform it into a semiconductor film.
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| Current Status of Research Progress |
Current Status of Research Progress
1: Research has progressed more than it was originally planned.
Reason
We improved the performance and stability of fully solution processed oxide thin-film transistor (TFT) in both positive bias stress (PBS) and negative bias stress (NBS) ahead of schedule. Ar plasma irradiation yielded better PBS and NBS stability especially compared with UV irradiation and laser treatment. We have found that the Ar plasma not only affects the exposed regions but also unexpectedly affects the channel and enhances the film density which is likely why it is superior to UV treatment. Fully solution TFTs have also been realized on flexible substrates. The buffer layer between the channel and flexible substrate is being optimized to prevent delamination/layer damage. We have since used carrier concentration control methods to transform an oxide insulator to a semiconductor.
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| Strategy for Future Research Activity |
We plan to improve the performance and stability of fully solution processed TFT on flexible substrates by improving buffer layer deposition and considering alternative surface modification treatments, electrode functionalization process, and high-k gate insulators. Currently, we are using solid state laser irradiation (343 nm) as a cost-effective alternative to excimer laser annealing. As for the stability improvement mechanism, we will continue performing comprehensive characterization especially at the functionalized electrode and channel regions. We have since expanded the use of carrier concentration control on ultrawidebandgap materials and are using machine learning methods such as supervised learning to predict properties such as the Fermi level from experimental parameters.
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