Anisotropic transport and ferroelectric polarization of van der Waals heterostructure for multistate nonvolatile memory

The demand for high-density memory drives the development of multistate nonvolatile memory devices. However, switching to an assigned intermediate memory state requires additional steps in multistate memories such as ferroelectric tunnel junctions (FTJs). Here, we design in-plane FTJs by utilizing ferroelectric control of the metal-semiconductor transition in \ensuremath{\alpha}-tellurene$/{\mathrm{In}}_{2}{\mathrm{Se}}_{3}$ van der Waals heterostructures. The tunnel electroresistance ratio of in-plane FTJs exhibits more pronounced differences in two transport directions with the increase in channel length, and it can remain above 5 \ifmmode\times\else\texttimes\fi{} ${10}^{4}$% at low bias voltage. Furthermore, synergistic anisotropic transport and ferroelectric polarization can induce four independent storage states, enabling direct switching between the four states without requiring the erasing step. This work simplifies operations and offers an alternative approach for implementing multistate nonvolatile memory.