Sub-micron spin-based magnetic field imaging with an organic light emitting diode

At a Glance

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

Technical Documentation & Analysis: MPCVD Diamond for Integrated Quantum Sensing

Reference: Geng et al., Sub-micron spin-based magnetic field imaging with an organic light emitting diode, Nature Communications (2023)14:1441.

Executive Summary

This research demonstrates a highly integrated, solid-state magnetic field sensor based on an Organic Light Emitting Diode (OLED) utilizing electrically detected magnetic resonance (EDMR) and optically detected magnetic resonance (ODMR). This approach offers a pathway toward commercially scalable, chip-integrated quantum sensing.

Core Achievement: Demonstrated sub-micron magnetic field mapping (spatial resolution ~0.91 µm) using spatially resolved ODMR.
Sensitivity: Achieved a field sensitivity of ~160 µT Hz^-1/2 µm^-2 in the diffusion region.
Scalability & Integration: The device architecture integrates the sensor (OLED) and the microwave resonator on a single substrate, enabling chip-scale, room-temperature, and laser-free operation.
Methodology: Magnetic field strength is determined by measuring the resonant frequency shift (f = γB₀) via frequency-swept EDMR/ODMR.
Quantum Comparison: The work explicitly positions the OSC-based sensor as an alternative to established quantum platforms, specifically Nitrogen-Vacancy (NV) centers in diamond, which typically require complex optical pumping and cryogenic temperatures.
Future Direction: The discussion highlights the need for improved sensitivity, longer spin phase coherence times (T₂), and advanced device architecture for vector field detection—areas where high-quality MPCVD diamond excels.

Technical Specifications

Parameter	Value	Unit	Context
Magnetic Field Sensitivity	~163.16	µT Hz^-1/2 µm^-2	Measured in the diffusion region (n=3 binning)
Spatial Resolution	~0.91(5)	µm	Super-pixel size (n=3 binning)
Theoretical Sensitivity (Shot-Noise-Limited)	54.80	µT Hz^-1/2 µm^-2	Continuous Wave (CW) ODMR estimate
Gyromagnetic Ratio (γ)	28.03 (±0.0024)	GHz/T	Derived from linear fit of resonant frequency vs. B₀
Resonant Frequency (f_EDMR)	708.5	MHz	Measured at B₀ ≈ 25.2 mT
OLED Active Area Diameter	80	µm	Defined by photolithography
OLED Operating Current Density	~10	mA/cm²	At 500 nA current
PEDOT:PSS Film Thickness	~35	nm	Hole injection layer
Al₂O₃ Insulating Layer Thickness	45	nm	Deposited via ALD
Microwave Power Used	~5	dBm	Used to minimize power broadening effects

Key Methodologies

The integrated device fabrication relies on precise thin-film deposition and patterning techniques to achieve electrical isolation between the microwave resonator and the OLED.

Substrate Preparation: Prepatterned Indium Tin Oxide (ITO) (120 nm) on glass substrates (30.0 x 20.0 x 0.7 mm) was used as the bottom electrode.
First Insulating Layer: Aluminum Oxide (Al₂O₃) (45 nm) was deposited via low-temperature Atomic Layer Deposition (ALD) and patterned using standard photolithography (MA6 system) and lift-off.
Microwave Resonator Fabrication: An omega-shape resonator was defined using a metal stack of Ti (10 nm)/Au (500 nm)/Ti (10 nm) deposited via thermal deposition, with Ti acting as the adhesion layer.
Second Insulating Layer: A second Al₂O₃ layer (45 nm) was deposited via ALD on top of the resonator to electrically isolate it from the subsequent top OLED electrode.
OLED Active Layer Deposition:
- PEDOT:PSS (35 nm) was spin-coated and baked at 120 °C.
- Super Yellow Poly(p-phenylene-vinylene) (SY-PPV) copolymer (80 nm) was spin-coated and baked at 60 °C.
Top Electrode & Encapsulation: LiF (1 nm)/Al (100 nm) was deposited using a shadow mask in a high vacuum chamber (<10^-8 mbar). The device was encapsulated with a glass lid and UV-activated epoxy in a glove box (O₂ < 0.5 ppm, H₂O < 0.5 ppm).
Spatially Resolved ODMR: Measurements utilized an optical imaging system (20x objective, NA = 0.42) and an sCMOS camera to capture electroluminescence (EL) intensity changes, enabling pixel binning (n x n super-pixels) to trade spatial resolution for enhanced Signal-to-Noise Ratio (SNR).

6CCVD Solutions & Capabilities

The research highlights the potential of solid-state magnetic sensors while noting that established quantum platforms, such as NV centers in diamond, offer superior sensitivity but face integration challenges. 6CCVD specializes in providing the high-quality MPCVD diamond materials and custom engineering required to overcome these integration hurdles, enabling the next generation of high-sensitivity, chip-scale NV-based quantum sensors.

Research Requirement / Challenge (Paper Context)	6CCVD Solution & Capability	Technical Advantage for Quantum Sensing
High-Sensitivity Quantum Platform (NV centers require ultra-pure material)	Optical Grade Single Crystal Diamond (SCD)	Provides ultra-low strain and low-nitrogen concentration substrates, essential for maximizing NV center spin coherence times (T₂) and achieving the picotesla-level sensitivity benchmark. Polishing to Ra < 1 nm ensures optimal surface quality for subsequent thin-film deposition.
Chip-Scale Integration & Miniaturization	Custom Dimensions & Thin SCD/PCD Wafers	We offer SCD and PCD plates from 0.1 µm up to 500 µm thick, and substrates up to 10 mm. Custom dimensions up to 125 mm (PCD) allow for scalable fabrication of integrated sensor arrays, addressing the need for miniaturization cited in the paper.
Integrated Microwave Delivery (Resonators, Microwires)	In-House Metalization Services	We provide custom deposition of critical metals (Au, Pt, Pd, Ti, W, Cu) directly onto diamond surfaces. This capability is vital for fabricating the on-chip microwave structures (e.g., coplanar waveguides or strip lines) necessary for high-frequency EDMR/ODMR excitation in integrated diamond devices.
Vector Field Detection (Requires complex, perpendicular metallic strip lines)	Precision Laser Cutting & Etching	Our advanced laser cutting and etching services enable the creation of complex geometries and micro-structures in diamond, facilitating the integration of multi-axis microwave delivery systems without compromising the crystal lattice quality.
Addressing Sensitivity Limitations (Need for longer T₂ and optimized SNR)	Engineering Consultation & Material Selection	6CCVD’s in-house PhD team provides expert support in selecting the optimal diamond material (e.g., high-purity SCD for NV centers or Boron-Doped Diamond (BDD) for electrochemical applications) to minimize intrinsic noise and maximize the performance of similar Magnetic Field Imaging projects.

For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.

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 µT Hz −1/2 µm −2 . 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.

Tech Support

Original Source

DOI: https://doi.org/10.1038/s41467-023-37090-y