2022 Fiscal Year Research-status Report
Controlling the polarity of ScAlN via formation of cation/anion vacancy
| Project/Area Number |
21K04168
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| Research Institution | National Institute of Advanced Industrial Science and Technology |
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Principal Investigator |
Anggraini SriAyu 国立研究開発法人産業技術総合研究所, エレクトロニクス・製造領域, 研究員 (80784123)
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| Project Period (FY) |
2021-04-01 – 2024-03-31
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| Keywords | ScAlN / piezoelectric / polarity inversion / sputtering / thin films / AlN / nitride |
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| Outline of Annual Research Achievements |
Previously, we have confirmed that the addition of element such as Si or Ge could inverse the polarity of ScAlN from Al-polar to N-polar. However, addition of Carbon (C) could not inverse the polarization direction of ScAlN, which is suspected to be due to the presence of nitrogen vacancy (Vn). The role of Vn on polarity is confirmed in this fiscal year by addition of element that theoretically can generate nitrogen vacancy such as magnesium (Mg) or zinc (Zn). It was found that addition of Mg or addition of Zn into ScAlN yielded in thin films with Al-polarity, which means that addition of either element was unable to inverse the polarity of ScAlN from Al-polar to N-polar. Increase in concentration of Mg or Zn added into ScAlN was only resulted in a decrease in wurtzite phase stability which led to lower piezoelectric d33 response. These results further confirm that the presence of nitrogen vacancy could not induce polarity inversion in nitride. Also, our presentation in JSAP Spring meeting 2023 was also nominated to receive best poster award.
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| Current Status of Research Progress |
Current Status of Research Progress
2: Research has progressed on the whole more than it was originally planned.
Reason
Carbon is part of group IVB element and is expected to create aluminum vacancy (Val) and induce polarity inversion. Therefore, the inability of carbon to inverse polarity of ScAlN was an unexpected result but simultaneously gave us an encouragement to think that nitrogen vacancy (Vn) cannot inverse the polarity of nitride-based piezoelectric thin films, particularly ScAlN. After obtaining this result, the addition of Mg or Zn is suspected to incapable of inversing the polarity of ScAlN and that hypothesis was later confirmed via experimental results.
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| Strategy for Future Research Activity |
This fiscal year, we have confirmed that addition of element that induced aluminum vacancy (Val) can cause polarity inversion while addition of element that induced nitrogen vacancy (Vn) cannot cause polarity inversion. The biggest question would be “why the presence of Val could lead to polarity inversion? And why Vn could not cause polarity inversion?”. Efforts to answer those questions will be done via material characterization of ScAlN. In FY 2023, polarity distribution of the thin films will be done by conducting piezo force microscopy (PFM). Aluminum or nitrogen vacancy is expected to cause changes in bond coordination, and this will be examined by using Raman spectroscopy and FTIR. Furthermore, the inversion domain boundary (IDB) will also be examined via STEM analysis. By thoroughly analyzing ScAlN that has Al-polar and N-polar, the role of Val and Vn on governing polarization direction can be clarified.
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| Causes of Carryover |
The remaining unused budget was occur due to the cost of business trip was slightly lower than expected. The remaining budget will be used this year to buy the necessary items for material characterization experiment.
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