Effects of metal content on electrical and physical properties in solution-processed IGZO thin films

Takaaki Morimoto, Yicheng Yang, Yusuke Ochiai, Nobuko Fukuda, Yoshimichi Ohki

Research output: Contribution to journalArticlepeer-review

Abstract

The on-current of indium gallium zinc oxide (IGZO) thin-film transistors (TFTs) fabricated by solution process with low-temperature post-annealing increases monotonically with the decrease in the Ga content. This trend is different from that of IGZO fabricated by a solution process, which shows the maximum electron mobility at a Ga content of 33%. To clarify its cause, effects of Ga and In contents in solution-processed IGZO post-annealed at a low-temperature on their oxygen deficiency and band structures were investigated with spectroscopic methods such as X-ray photoelectron spectroscopy, ultraviolet photoelectron spectroscopy, photoluminescence, and ultraviolet–visible absorption. When the Ga content is low, the oxygen vacancy becomes less abundant. The increase in In content exhibits similar effects on the oxygen vacancy. We have reported that Ga is not oxidized sufficiently at low temperatures, which should cause the generation of oxygen vacancies. By this theory, the above-mentioned decrease in oxygen vacancies can be explained. Furthermore, when these films are actually used as TFT channels, the on-current increases with the decrease in Ga content. From this, in solution-processed IGZO post-annealed at a low temperature, oxygen vacancies mainly act as electron traps that decrease the on-current, rather than acting as donors. In manufacturing flexible devices, even when we decrease the process temperature low enough to suppress the damage to polymer substrates, the devices must maintain good performance. Our results suggest that an optimal metal ratio different from that of a typical vacuum process is necessary to improve the performance of IGZO TFTs fabricated by the low-temperature solution process.

Original languageEnglish
Article number388
JournalApplied Physics A: Materials Science and Processing
Volume126
Issue number5
DOIs
Publication statusPublished - 2020 May 1

Keywords

  • IGZO
  • Metal ratio
  • Oxygen vacancy
  • TFT
  • X-ray photoelectron spectroscopy

ASJC Scopus subject areas

  • Chemistry(all)
  • Materials Science(all)

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