Thickness scaling of (Al<sub>0.8</sub>Sc<sub>0.2</sub>)N films with remanent polarization beyond 100 μC cm<sup>−2</sup> around 10 nm in thickness
Ryoichi Mizutani, Shinnosuke Yasuoka, Takahisa Shiraishi, Takao Shimizu, Masato Uehara, Hiroshi Yamada, Morito Akiyama, Osami Sakata, Hiroshi Funakubo
Abstract
The temperature dependence of ferroelectric properties was investigated for (Al0.8Sc0.2)N films 9–130 nm thick prepared on (111)Pt/TiOx/SiO2/Si substrates. The coercive fields (Ec) of these films decreased with increasing measurement temperature up to 523 K, irrespective of film thickness, thus realizing polarization switching because the applicable maximum electric field is beyond Ec. As a resultant, remanent polarization (Pr) above 100 μC cm−2 was ascertained for 9 nm thick films at 373 and 423 K, which is more than 5 times larger than those of HfO2-based films of the same thickness. The Pr value was almost independent of film thickness when an electric field is applied for switching. In addition, Ec showed a smaller thickness dependence than conventional ferroelectrics, including Pb(Zr,Ti)O3. The large Pr value beyond 100 μC cm−2 for around 10 nm thick films with small degradation against film thickness, as well as the diminished increase in Ec with decreasing film thickness. This showed that (Al0.8Sc0.2)N film is a promising candidate for nonvolatile memory applications requiring high-density and low-voltage operation, including capacitor-type memories and ferroelectric tunnel junction-type memories that consist of metal–ferroelectric–metal structure.