Decoupling polarization and coercive field in AlScN/AlN/AlScN stack for enhanced performance in ferroelectric thin-film transistors.

AlScN emerges as a promising material for ferroelectric field-effect transistors due to its high coercive field (>6 MV/cm). However, its high remanent polarization (>100 μC/cm) can degrade memory window and retention, limiting its use in memory applications. This study introduces an AlScN/AlN/AlScN multi-layer designed to decouple the polarization and coercive field, thereby increasing the coercive field while maintaining polarization value. The AlN layer switches ferroelectrically in response to the AlScN layer's switching, even though a single AlN layer is piezoelectric. The lower dielectric constant of AlN compared to AlScN increases the coercive field of the stack, while the AlScN layer primarily determines the polarization. This study shows that increasing the AlN ratio in the multi-layer significantly enhances the memory window and retention performance of ferroelectric thin-film transistors with amorphous indium-gallium-zinc-oxide channels. A maximum memory window of 15 V is achieved, enabling the development of a penta-level cell for next-generation storage.