Size-Controlled Polarization Retention and Wall Current in Lithium Niobate Single-Crystal Memories

Area of Science:

• Materials Science
• Condensed Matter Physics
• Nanotechnology

Background:

• Ferroelectric domain walls in LiNbO3 (LNO) thin films offer high conductivity for ferroelectric domain wall random access memory (DWRAM).
• Downscaling memory cells to the nanoscale raises concerns about polarization retention and electrical performance.

Purpose of the Study:

• To investigate the size-dependent electrical performance of LNO thin film memory cells.
• To understand the critical size for optimal polarization retention and readout currents in nanoscale DWRAM.

Main Methods:

• Fabrication of lateral mesa-like cells on X-cut LNO thin films bonded to SiO2/Si wafers.
• Electrical characterization using current-voltage measurements.
• In-plane piezoresponse force microscopy (PFM) imaging.
• One-dimensional thermodynamic calculations and phase-field simulations.

Main Results:

• A critical cell size (l0) of 105 nm was identified, below which domain wall current is enhanced.
• Cells larger than l0 exhibited poor polarization retention in inner areas due to lower coercive fields (Ec = 150 kV/cm).
• Outer periphery domains (70 nm) showed good retention but required higher Ec (785 kV/cm), attributed to phase reconstruction from released strain.

Conclusions:

• Nanoscale LNO memory cells exhibit size-dependent electrical properties critical for DWRAM performance.
• Optimizing cell size below l0 enhances readout currents and improves retention, enabling higher storage densities.
• Understanding strain-induced phase reconstruction is vital for designing reliable nanoscale ferroelectric memory devices.