Ferroelectric-to-paraelectric phase engineering for 2D layered ultra-high-κ dielectrics

Area of Science:

• Materials Science
• Condensed Matter Physics
• Nanotechnology

Background:

• Two-dimensional (2D) electronic devices require advanced dielectric layers with high dielectric constants, minimal leakage, and atomically smooth interfaces.
• Existing 2D ferroelectrics offer high dielectric constants but suffer from remnant polarization and hysteresis, hindering their use in digital electronics.
• Landau theory explains the ferroelectric-paraelectric transition, where the paraelectric phase above the Curie temperature (T_C) eliminates remnant polarization and hysteresis.

Purpose of the Study:

• To engineer robust van der Waals (vdW) dielectric materials from 2D ferroelectrics by suppressing ferroelectricity while retaining desirable dielectric properties.
• To investigate the potential of cation-substituted CuInP₂S₆ as hysteresis-free paraelectric dielectrics for advanced electronic applications.

Main Methods:

• Cationic substitution at Copper (Cu) sites in 2D ferroelectric CuInP₂S₆ to disrupt long-range dipolar order and suppress ferroelectricity.
• Synthesis of centimeter-scale single crystals of Cu_1-xM'_xInP₂S₆ (where M' represents substituting cations) and exfoliation into atomically flat nanoflakes.
• Characterization of the dielectric properties, including dielectric constant, leakage current, and breakdown field, of the modified materials.

Main Results:

• The cationic substitution successfully transformed the 2D ferroelectric into a hysteresis-free paraelectric dielectric material at room temperature.
• The paraelectric Cu_0.8Ag_0.2InP₂S₆ achieved a record-high dielectric constant (κ ≈ 108) among vdW dielectrics, with ultralow leakage (∼10^-12 A) and high breakdown field (∼2.6 MV/cm).
• These novel dielectrics formed trap-free interfaces with MoS₂, enabling transistors with low operating voltage (0.5 V), high ON/OFF ratio (10⁸), and excellent subthreshold swing (62 mV/dec).

Conclusions:

• Cationic substitution is an effective strategy to convert 2D ferroelectrics into high-performance, hysteresis-free vdW dielectrics.
• The developed paraelectric materials offer a promising solution for next-generation 2D electronic devices requiring superior dielectric performance.
• These findings pave the way for the integration of advanced dielectric layers in high-performance, low-power 2D electronics.