Toshikazu Irisawa

The total thickness scaling of electrodes and the (Al _0.9 Sc _0.1 )N layer is evaluated for ferroelectric memory applications. The good crystal orientation and large remanent polarization ( P _r ) above 100 µC cm ⁻² are obtained for 160‐nm‐thick (Al _0.9 Sc _0.1 )N films even when the Pt bottom electrode is reduced to a thickness of 5 nm. The (Al _0.9 Sc _0.1 )N film integrated on a 5‐nm‐thick Pt bottom electrode maintains a saturated P _r value above 100 µC cm ⁻² at a thickness of 30 nm. Furthermore, the (Al _0.9 Sc _0.1 )N film exhibits improved crystal orientation by the post‐heat‐treatment of the Pt bottom electrode, and a saturated large P _r value above 100 µC cm ⁻² is obtained at a thickness of 20 nm. Moreover, a P _r value of 90 µC cm ⁻² is obtained at a (Al _0.9 Sc _0.1 )N thickness of 10 nm. No significant degradation in the P _r characteristics is detected when the thickness of the Pt top electrode is reduced to 5 nm. Finally, the total thickness is successfully scaled down to 30 nm for a Pt (top electrode, 5 nm)/(Al _0.9 Sc _0.1 )N (20 nm)/Pt (bottom electrode, 5 nm) stack. This work presents guidelines for the thickness scaling of the (Al,Sc)N‐based stacks for ferroelectric memory applications, including ferroelectric thin films and electrodes.

Impacts of post-heat treatment in a H2-contained (97% Ar and 3% H2) atmosphere on the switching kinetics of (001)-oriented AlScN capacitors are investigated. Fully saturated polarization can be obtained for all capacitors at frequencies of 50 Hz–50 kHz. In contrast to other ferroelectric materials, the domain wall movement behavior does not change after the heat treatment with frequency. The switching behavior follows the Kolmogorov–Avrami–Ishibashi (KAI) model, and the dimension of domain growth, n, values are ∼1–2 for all films before and after the H2-contained heat treatment. The domain nucleation and lateral domain growth in both the electric field- and time-dependent domain dynamics visualized by piezoresponse force microscopy are consistent with the KAI model. The activation energy increases slightly for the film after the heat treatment. This highly resilient switching behavior brings the AlScN films one step closer to realizing the next generation of nonvolatile memory technologies.

The changes in the crystal structure and ferroelectric properties of (Al0.8Sc0.2)N films sandwiched between Pt and TiN electrodes were investigated by subjecting the films to post-heat-treatment at various temperatures up to 600 °C in both H2 and Ar gases. The remanent polarization underwent slight change, whereas the coercive field strengthened by approximately 9% as a result of the post-heat-treatment up to 600 °C irrespective of the atmosphere and electrode material. This change is much smaller than that reported for ferroelectric (Hf,Zr)O2 films as well as for Pb(Zr,Ti)O3 and SrBi2Ta2O9 films for a wide temperature range from 400 to 600 °C and is almost independent of the Pt and TiN electrodes. The high stability of (Al,Sc)N films with both Pt and TiN electrodes under H2 atmosphere is highly promising to stabilize the properties through the device fabrication process.