Sub-micron spin-based magnetic field imaging with an organic light emitting diode
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2023-03-15 |
| Journal | Nature Communications |
| Authors | Rugang Geng, Adrian Mena, William J. Pappas, Dane R. McCamey |
| Institutions | UNSW Sydney |
| Citations | 10 |
| Analysis | Full AI Review Included |
Executive Summary
Section titled âExecutive SummaryâThis research demonstrates a novel, integrated solid-state magnetic field sensor utilizing an Organic Light Emitting Diode (OLED) and a co-planar microwave resonator, offering a pathway for chip-scale quantum sensing.
- Core Value Proposition: Achieves sub-micron magnetic field mapping using spatially resolved Optically Detected Magnetic Resonance (ODMR) and Electrically Detected Magnetic Resonance (EDMR) in a single, integrated device.
- Key Performance Metric: Demonstrated magnetic field sensitivity of approximately 160 ”T Hz-1/2 ”m-2 (in the diffusion region, n=3 binning).
- Spatial Resolution: Achieved sub-micron spatial resolution of ~0.91 ”m, limited primarily by the optical diffraction limit of the microscope objective (714 nm).
- Operational Advantages: Operates at room temperature and is laser-free (unlike NV centers in diamond), enabling compatibility with mass-produced consumer electronics.
- Mechanism: Sensing relies on the spin-dependent recombination and dissociation dynamics of electron-hole polaron pairs within the Super Yellow PPV (SY-PPV) active layer.
- Manufacturability: Built on commercially relevant and manufacturable OLED technology, allowing for large-area mapping without point-to-point scanning.
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| Magnetic Field Sensitivity (Measured) | ~163.16 | ”T Hz-1/2 ”m-2 | Diffusion region, n=3 binning |
| Magnetic Field Sensitivity (Shot-Noise Limit) | 54.8 | ”T Hz-1/2 ”m-2 | Continuous Wave (CW) ODMR estimate |
| Spatial Resolution (Achieved) | ~0.91 | ”m | Super-pixel size (n=3 binning) |
| Optical Diffraction Limit | 714 | nm | For 600 nm EL wavelength |
| Gyromagnetic Ratio (γ) | 28.03 (±0.0024) | GHz/T | Experimentally determined |
| g-factor | 2.0026 (±0.00017) | - | Derived from γ |
| OLED Operating Current | 0.5 | ”A | Constant current mode (EDMR/ODMR) |
| OLED Current Density | ~10 | mA/cm2 | For 80 ”m diameter active area |
| Microwave Frequency (EDMR Peak) | ~708.5 | MHz | At B0 ~25.2 mT |
| Microwave Power | ~5 | dBm | Used in experiments |
| ODMR Modulation Frequency | 0.5 | Hz | Square-wave sequence |
| PEDOT:PSS Thickness | ~35 | nm | Hole injection layer |
| SY-PPV Thickness | ~80 | nm | Active emitting layer |
| Insulating Layer Thickness (Al2O3) | 45 | nm | Atomic Layer Deposition (ALD) |
| Top Electrode (LiF/Al) | 1 / 100 | nm | Electron injection layer |
Key Methodologies
Section titled âKey MethodologiesâThe device fabrication involves the lateral integration of a microwave resonator and a micron-sized OLED on a glass/ITO substrate, ensuring electrical isolation and optical access.
Device Fabrication (OLED and Resonator)
Section titled âDevice Fabrication (OLED and Resonator)â- Substrate Preparation: Prepatterned Indium Tin Oxide (ITO, 120 nm) on a glass substrate (30.0 x 20.0 x 0.7 mm).
- First Insulating Layer:
- Patterning via standard photolithography (MA6 system).
- Deposition of 45 nm Al2O3 using low-temperature Atomic Layer Deposition (ALD) for conformal, high-quality electrical isolation.
- Microwave Resonator:
- Patterning of the omega-shape structure via photolithography.
- Thermal deposition of Ti (10 nm) / Au (500 nm) / Ti (10 nm) metal stack, followed by lift-off.
- Second Insulating Layer: Deposition of a second 45 nm Al2O3 layer (ALD) on top of the resonator to isolate it from the subsequent OLED top electrode.
- OLED Stack Deposition:
- Hole Injection Layer: Spin coating of PEDOT:PSS (3000 rpm), followed by baking for 2 hours at 120 °C (resulting thickness ~35 nm).
- Active Layer: Spin coating of Super Yellow PPV (SY-PPV, 3 mg/ml in toluene) at 1200 rpm, followed by a post-bake for 2 hours at 60 °C (resulting thickness ~80 nm).
- Top Electrode: High vacuum deposition (<10-8 mbar) of LiF (1 nm) / Al (100 nm) using a shadow mask aligned to the active area.
- Encapsulation: Device sealed in a glove box using UV-activated epoxy and a thin glass lid containing a desiccant sheet to prevent degradation.
Measurement Techniques
Section titled âMeasurement Techniquesâ| Technique | Readout Signal | Measurement Mode | Spatial Resolution |
|---|---|---|---|
| EDMR (Electrically Detected Magnetic Resonance) | Change in device current (monitored via lock-in detection). | Bulk point sensor. | Not spatially resolved (bulk response). |
| ODMR (Optically Detected Magnetic Resonance) | Change in Electroluminescence (EL) intensity. | Spatially resolved imaging. | Sub-micron (0.91 ”m) via sCMOS camera binning. |
Spatially Resolved ODMR Process:
- The device EL is imaged onto an sCMOS camera via a microscope objective (20x, NA = 0.42).
- A square-wave microwave signal (0.5 Hz) is applied.
- The difference in EL intensity between the microwave âonâ and âoffâ cycles is recorded for every camera pixel.
- The microwave frequency is swept to obtain an ODMR spectrum for each pixel (virtual sensor).
- Camera pixels are binned (e.g., n x n) into âsuper-pixelsâ to enhance the Signal-to-Noise Ratio (SNR) at the expense of spatial resolution.
- The resonant frequency (fODMR) is extracted from the fitted spectrum of each super-pixel and converted to magnetic field strength (|B| = f/Îł) to generate the 2D magnetic field map.
Commercial Applications
Section titled âCommercial ApplicationsâThe integration of quantum sensing capabilities into a highly manufacturable, room-temperature, and laser-free platform opens doors for widespread commercial deployment.
- Ubiquitous Magnetic Sensing: Low-cost, chip-scale magnetometers for consumer electronics (e.g., compass effect compensation, environmental monitoring).
- Non-Invasive Diagnostics: Mapping magnetic fields generated by biological systems (e.g., magnetoencephalography (MEG) or magnetocardiography (MCG)) without cryogenic cooling.
- Materials Characterization: High-resolution, room-temperature imaging of magnetic domains, elements, and surfaces in materials science and semiconductor inspection.
- Quantum Magnetic Imaging: Potential applications in quantum computing and spintronics research requiring spatially resolved measurement of weak magnetic fields.
- Industrial Inspection: Fast, large-area magnetic mapping for quality control and defect detection in manufactured components.
View Original Abstract
Abstract Quantum sensing and imaging of magnetic fields has attracted broad interests due to its potential for high sensitivity and spatial resolution. Common systems used for quantum sensing require either optical excitation (e.g., nitrogen-vacancy centres in diamond, atomic vapor magnetometers), or cryogenic temperatures (e.g., SQUIDs, superconducting qubits), which pose challenges for chip-scale integration and commercial scalability. Here, we demonstrate an integrated organic light emitting diode (OLED) based solid-state sensor for magnetic field imaging, which employs spatially resolved magnetic resonance to provide a robust mapping of magnetic fields. By considering the monolithic OLED as an array of individual virtual sensors, we achieve sub-micron magnetic field mapping with field sensitivity of ~160 ”T Hz â1/2 ”m â2 . Our work demonstrates a chip-scale OLED-based laser free magnetic field sensor and an approach to magnetic field mapping built on a commercially relevant and manufacturable technology.