Intrinsic Room Temperature Ferroelectricity in Thin Layered CuInP₂S₆

Van der Waals layered copper indium thiophosphate (CuInP₂S₆, CIPS) has emerged as a perfect 2D ferroelectric material; however, precise tuning of its polarization of ferroelectric domains remains challenging due to the dominant Cu-ion migration that often obscures ideal ferroelectric switching. Here, we present an atomic force microscopy (AFM)–based measurement platform integrated with a ferroelectric tester, enabling direct nanoscale probing of the intrinsic ferroelectric properties using current–voltage, capacitance–voltage, polarization–electric field (P–E), and PUND characteristics of exfoliated CIPS thin flakes (<80 nm). The experimental configuration employs a conductive AFM tip electrically coupled to an external ferroelectric measurement circuit. A few-layer graphene (FLG) flake is transferred onto the CIPS flake serving as the top electrode and Au-coated SiO₂/Si substrate acts as the bottom contact. This approach enables reliable polarization detection in the presence of mobile Cu⁺ ions. The measured P–E hysteresis loops exhibit robust opening and frequency-tunable remanent polarization. At the same trend, the current-voltage measurement loops reveal the a dominant ferroelectric transition without resistive effect. Furthermore, the PUND measurements confirm the intrinsic switchable ferroelectric domains within the exfoliated layers which are tunable as a function of pulse delay and pulse width. These findings demonstrate an effective strategy to characterize intrinsic ferroelectric switching in 2D van der Waals systems, providing a versatile route for exploring and engineering nanoscale ferroelectric phenomena in several layered ferroelectric materials.