Significant tunneling electroresistance and ultralow resistance-area product in asymmetric In 2 S 3 / Cu 2 Se ferroelectric tunnel junctions

Conventional ferroelectric tunnel junctions (FTJs) face inherent limitations in simultaneously achieving both a high tunneling electroresistance ratio (TER) and a low resistance-area product (RAP), hindering high-density, low-power, nonvolatile memory applications. This study overcomes this challenge by designing asymmetric FTJs based on a two-dimensional ${\mathrm{In}}_{2}{\mathrm{S}}_{3}/{\mathrm{Cu}}_{2}\mathrm{Se}$ heterostructure. Utilizing first-principles calculations with quantum transport simulations, we demonstrate that ferroelectric polarization switching in ${\mathrm{In}}_{2}{\mathrm{S}}_{3}$ reversibly modulates the heterostructure's band alignment between type-III (metallic) and type-II (semiconducting) states. Exploiting this, we engineered asymmetric ${\mathrm{In}}_{2}{\mathrm{S}}_{3}/{\mathrm{Cu}}_{2}({\mathrm{Se}}_{0.9}{\mathrm{S}}_{0.1})$ and ${\mathrm{In}}_{2}{\mathrm{S}}_{3}/{\mathrm{Cu}}_{2}({\mathrm{Se}}_{0.9}{\mathrm{Te}}_{0.1})$ electrodes flanking a central ${\mathrm{In}}_{2}{\mathrm{S}}_{3}/{\mathrm{Cu}}_{2}\mathrm{Se}$ barrier. The asymmetric FTJ achieves a TER of $9.95\ifmmode\times\else\texttimes\fi{}{10}^{8}%$, which is 5 orders of magnitude higher than that of symmetric FTJs ($1.28\ifmmode\times\else\texttimes\fi{}{10}^{3}%$), while maintaining an ultralow RAP of $0.11\phantom{\rule{0.16em}{0ex}}\mathrm{\ensuremath{\Omega}}\phantom{\rule{0.16em}{0ex}}\textmu{}{\mathrm{m}}^{2}$. Crucially, these optimal performance metrics (TER $\ensuremath{\sim}{10}^{9}%$, $\mathrm{RAP}<0.2\phantom{\rule{0.16em}{0ex}}\mathrm{\ensuremath{\Omega}}\phantom{\rule{0.16em}{0ex}}\textmu{}{\mathrm{m}}^{2}$) persist robustly even under variations in channel width ($N=1$ to $N=9$, $\ensuremath{\sim}0.7--6.3\phantom{\rule{0.16em}{0ex}}\mathrm{nm}$) or electrode doping concentration (5%--15%). These findings highlight the superior performance and exceptional robustness of the asymmetric ${\mathrm{In}}_{2}{\mathrm{S}}_{3}/{\mathrm{Cu}}_{2}\mathrm{Se}$-based FTJ, which holds significant promise for high-density, low-power, nonvolatile memory applications.