Current Flow Mapping in Conducting Ferroelectric Domain Walls Using Scanning NV‐Magnetometry
At a Glance
Section titled “At a Glance”| Metadata | Details |
|---|---|
| Publication Date | 2025-06-26 |
| Journal | Advanced Electronic Materials |
| Authors | Conor J. McCluskey, James Dalzell, Amit Kumar, J. M. Gregg |
| Institutions | Queen’s University Belfast |
| Analysis | Full AI Review Included |
Current Flow Mapping in Conducting Ferroelectric Domain Walls Using Scanning NV-Magnetometry
Section titled “Current Flow Mapping in Conducting Ferroelectric Domain Walls Using Scanning NV-Magnetometry”Executive Summary
Section titled “Executive Summary”This technical analysis focuses on the application of advanced diamond-based quantum sensing to fundamentally characterize current transport in ferroelectric domain wall memristors, highlighting the critical role of high-quality diamond materials in enabling this breakthrough.
- Core Achievement: Direct, in situ mapping of 2D current density vectors in Lithium Niobate (LNO) domain wall memristors using Scanning Nitrogen-Vacancy (NV) Magnetometry.
- Methodology: Utilized a diamond scanning probe tip containing a single NV- defect to measure Oersted fields generated by current flow, followed by Biot-Savart law inversion to reconstruct current density maps.
- Key Finding (Channeling): The current flow is highly non-uniform and channeled, revealing that a strikingly small fraction (f’DW $\approx$ 0.22) of the total domain wall network is responsible for the majority of conduction.
- Scientific Correction: This insight forces a two-order-of-magnitude correction to the previously inferred 2D carrier density, raising the corrected value to n’2D $\approx$ 1.9 x 107 cm-2.
- Material Implication: The observed high mobility (up to 3700 cm2V-1s-1) combined with low carrier density confirms that domain wall transport exhibits characteristics indicative of semiconducting behavior.
- 6CCVD Relevance: The core measurement technique relies entirely on the precise engineering of high-purity Single Crystal Diamond (SCD) material, a specialty of 6CCVD, for the NV-center scanning probe.
Technical Specifications
Section titled “Technical Specifications”| Parameter | Value | Unit | Context |
|---|---|---|---|
| Ferroelectric Film Material | Lithium Niobate (LNO) | - | Ion-sliced, z-cut orientation |
| Film Thickness | $\approx$ 500 | nm | Dielectric layer thickness |
| Top Electrode Material | Platinum (Pt) | - | Sputtered, square geometry |
| Electrode Side Length | $\approx$ 110 | µm | Area (A) = 1.21 x 10-8 m2 |
| Switching Voltage (VSW) | $\approx$ 26 | V | Voltage required to initiate domain wall conduction |
| Read Current (I) | $\approx$ 132 | µA | Measured at 10 V bias |
| Conductance Increase | $\approx$ 8 | orders of magnitude | Observed after domain wall injection |
| Assumed Domain Wall Thickness (tDW) | 1 | nm | Used for initial area calculation |
| Initial Domain Wall Fraction (fDW) | $\approx$ 0.24 | - | Estimated from PFM amplitude map |
| Corrected Active DW Fraction (f’DW) | $\approx$ 0.22 | - | Based on NV-magnetometry current channeling |
| Corrected 2D Carrier Density (n’2D) | $\approx$ 1.9 x 107 | cm-2 | Corrected by factor of $\approx$100 |
| Carrier Mobility ($\mu$) | 3700 | cm2V-1s-1 | Implied by geometric magnetoresistance measurements |
| Expected Screening Density (nscreen) | 1.8 x 1014 | cm-2 | Based on full polar discontinuity screening |
| NV Scanning Current | $\approx$ 400 | µA | Constant current supplied during magnetic field mapping |
| NV Tip-Sample Delta Height | 50 | nm | Used during KPFM potential measurement |
Key Methodologies
Section titled “Key Methodologies”The experiment combined advanced thin-film fabrication with specialized scanning probe techniques, critically relying on the high-precision diamond NV-center sensor.
- Capacitor Fabrication: Square Platinum (Pt) electrodes ($\approx$110 µm side length) were sputtered onto 500 nm thick z-cut ion-sliced Lithium Niobate (LNO) films (Au-Cr bottom electrode).
- Domain Wall Injection: A triangular voltage pulse (up to $\approx$50 V) was applied to the top electrodes to partially reverse polarization and inject conducting domain walls, creating the memristor state.
- Electrical Characterization: I-V curves and read current (at 5 V) were measured using a Keysight B2910BL Source Measure Unit.
- Microstructural Analysis (PFM/c-AFM): Piezoresponse Force Microscopy (PFM) mapped domain structure, while Conductive AFM (c-AFM) spatially correlated enhanced conductivity with domain wall locations, using Pt-Ir coated Si tips.
- In Situ Potential Mapping (KPFM): Kelvin Probe Force Microscopy (KPFM) confirmed the equipotential nature of the electrode surface under bias (1 V), utilizing FIB-deposited Pt interconnects to supply current without obscuring the active area.
- Current Density Mapping (NV-Magnetometry): A commercially available scanning NV magnetometer (ProteusQ, Qnami AG) was used. The core sensor, a diamond tip with a single NV-defect, was raster-scanned over the sample while supplying a constant current of $\approx$400 µA.
- Data Reconstruction: The 2D current density vectors were quantitatively reconstructed from the measured Oersted magnetic field maps by inverting the Biot-Savart law using MATLAB.
6CCVD Solutions & Capabilities
Section titled “6CCVD Solutions & Capabilities”This research demonstrates the power of diamond-based quantum sensing (NV-Magnetometry) to solve fundamental problems in ferroelectric device physics. 6CCVD is uniquely positioned to supply the foundational diamond materials and custom engineering required to replicate, extend, and commercialize this type of advanced quantum research.
| Research Requirement | 6CCVD Solution & Capability | Technical Advantage |
|---|---|---|
| NV-Center Sensing Platform | Optical Grade Single Crystal Diamond (SCD) | SCD wafers (up to 500 µm thick) with ultra-low nitrogen content and low strain are the essential precursors for high-coherence NV-center implantation, maximizing quantum sensing fidelity and coherence time. |
| Custom Probe Geometry | Custom Dimensions & Laser Cutting | The NV-microscope relies on precisely engineered diamond pillars/tips. 6CCVD offers high-precision laser cutting and shaping services for SCD material, enabling the fabrication of custom scanning probe geometries. |
| Electrode & Interconnect Integration | In-House Metalization Services | The study utilized Pt, Au, and Cr for electrodes and FIB interconnects. 6CCVD offers internal deposition capabilities for Au, Pt, Pd, Ti, W, and Cu, ensuring seamless, high-quality integration of metallic contacts onto diamond or other substrates for complex device architectures. |
| High-Quality Surface Finish | Precision Polishing (Ra < 1 nm) | Achieving reliable contact and maintaining the critical tip-sample distance for NV-magnetometry requires extremely flat surfaces. 6CCVD guarantees Ra < 1 nm polishing on SCD material, crucial for minimizing measurement noise and maximizing spatial resolution. |
| Scaling & Replication | Polycrystalline Diamond (PCD) Substrates | For scaling up related thin-film or memristor research, 6CCVD offers large-area PCD wafers up to 125 mm in diameter, polished to Ra < 5 nm, providing robust, thermally stable substrates for high-throughput device fabrication. |
Engineering Support
Section titled “Engineering Support”6CCVD’s in-house PhD team can assist researchers and engineers with material selection, orientation, and surface preparation for similar Quantum Sensing and Ferroelectric Integration projects. We ensure that the SCD material properties (purity, orientation, thickness) are optimized to maximize NV coherence time and device performance.
For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.
View Original Abstract
Abstract The electrical conductivity of parallel plate capacitors, with ferroelectric lithium niobate as the dielectric layer, can be extensively and progressively modified by the controlled injection of conducting domain walls. Domain wall‐based memristor devices result. Microstructures, developed as a result of partial switching, are complex, and so simple models of equivalent circuits, based on the collective action of all conducting domain wall channels acting identically and in parallel, may not be appropriate. Here, the current density in ferroelectric domain wall memristors is directly mapped in situ by mapping Oersted fields, using nitrogen vacancy center microscopy. Current density maps are found to directly correlate with the domain microstructure, revealing that a strikingly small fraction of the total domain wall network is responsible for the majority of the current flow. This insight forces a two order of magnitude correction to the carrier densities, previously inferred from standard scanning probe or macroscopic electrical characterization.