Strong Temperature Effect on the Ferroelectric Properties of CuInP₂S₆ and Its Heterostructures

Van der Waals (vdW) ferroelectric insulator CuInP₂S₆ (CIPS) has attracted intense research interest due to its unique ferroelectric and piezoelectric properties. In this paper, we systematically investigate the temperature and frequency dependence of the ferroelectric properties of CIPS. We find that there is a large imprint in the CIPS capacitor, which can be attributed to the fixed dipoles induced by defects. At high temperatures and low frequencies, the amplitude and direction of the imprint become tunable by the preset pulse, as the copper ions are more mobile and these dipoles become switchable. When the polarization in CIPS changes direction, the graphene/CIPS/graphene ferroelectric diode exhibits switchable resistance since the Fermi level in graphene is modulated by the polarization in CIPS. For CIPS/MoTe₂ dual-gate transistor, a temperature-dependent nonvolatile memory window is observed, which can be attributed to the interplay between ferroelectric polarization and interface traps. This research provides experimental groundwork for vdW ferroelectric materials, expands the understanding of ferroelectricity in CIPS, and opens up exciting opportunities for novel electronic devices based on vdW ferroelectric materials.