Scalable Two-Dimensional α-In₂Se₃ Thin Films and Ferroelectric Memory Array

Non-volatile memories based on ferroelectric materials are one of the most competitive next-generation memories due to their low power consumption, fast read and write speed, non-volatility, and compatibility with CMOS manufacturing processes. However, the high-density integration of ferroelectric memories is tightly blocked by the depolarization-field caused by critical dimension effect of conventional ferroelectric thin films. Meanwhile, the emerging 2D Van der Waals (vdW) ferroelectric materials with robust ferroelectricity in ultrathin scale offer the great potential in the miniaturization of the device and screen the depolarization field in ultrathin form to bypass the limitations of conventional ferroelectric materials. Wherein, α-In₂Se₃ is recognized as one of the most promising 2D ferroelectrics due to its stable layered structure at room temperature, high Curie temperature (&gt;200 °C) and special dipole-locked in-plane (IP) and out-of-plane (OOP) ferroelectricity at the monolayer limit. However, the coexistence of multiple phases during the growth of In₂Se₃thin films remains as a challenge to growing uniform and pure α phase In₂Se₃ in large area. In addition, there have been few studies thus far aimed at investigating the epitaxial growth properties of α-In₂Se₃ films and there is still lack of array demonstration of ferroelectric device based on as-grown 2D α-In₂Se₃ films.<br/>Herein, we demonstrate a controllable synthesis of centimeter-scale α-In₂Se₃ from monolayer to multilayer films by adjusting the thickness of the boundary layer over the substrate in a chemical vapor deposition (CVD) process. Raman spectroscopy, transmission electron microscopy (TEM) and second harmonic generation (SHG) were carried out to identify the uniform alpha phase across the whole film. The α-In₂Se₃ triangular domains grow epitaxially on mica surface with mainly two orientations and epitaxial relationship over large area is further confirmed by in-plane XRD. In the meantime, piezoresponse force microscopy (PFM) measurements demonstrate the robust ferroelectricity and good stability of the polarization of as-grown α-In₂Se₃films at room temperature. In addition, we demonstrate the transportmechanism for ferroelectric resistive switching, endurance and retention characteristics by constructing a crossbar ferroelectric semiconductor junction (FSJ) array based on α-In₂Se₃continuous films for next-generation memory.