Integration of High-Brightness QLED-Excited Diamond Magnetic Sensor

At a Glance

Metadata	Details
Publication Date	2025-09-04
Journal	Micromachines
Authors	Pengfei Zhao, Jiangbing Du, Jinyu Tai, Zhong-Xia Shang, Xia Yuan
Institutions	North University of China
Analysis	Full AI Review Included

Executive Summary

This research presents a novel, monolithically integrated array architecture for Nitrogen-Vacancy (NV) center diamond magnetic sensors, replacing conventional bulk lasers with Quantum-Dot Light-Emitting Diodes (QLEDs) for excitation.

Core Innovation: Achieved monolithic integration of a 2 x 2 NV magnetometer array by substituting the bulky 532 nm laser source with micro/nano-fabrication compatible QLEDs.
High Integration & Low Cost: The QLED light source volume (1.5 x 1.5 x 0.2 mm) and single-chip cost (less than USD 10) offer massive advantages over traditional 532 nm lasers (volume: 142.5 x 60 x 50 mm; cost: USD 3660).
High Sensitivity: The array demonstrated a magnetic sensitivity performance below 26 nT·Hz^-1/2 (ranging from 22.8 to 25.6 nT·Hz^-1/2 across units).
Operational Range: The effective measurable range was determined to be ±120 µT within the effective bandwidth of 1-10 Hz.
Array Functionality Validated: Experimental results confirmed the array’s ability to simultaneously resolve multi-regional static magnetic fields and accurately track the spatial localization and directional variations of dynamic magnetic fields.
Device Uniformity: Conversion coefficients across the four units showed strong consistency, with maximum relative errors between theoretical and experimental values remaining below 3%.

Technical Specifications

Parameter	Value	Unit	Context
Array Configuration	2 x 2	Array	Monolithically integrated magnetometer array
Magnetic Sensitivity (Range)	22.8 to 25.6	nT·Hz^-1/2	Measured across M1-M4 units (1-10 Hz bandwidth)
Effective Measurable Range	±120	µT	Calculated based on linear regime bandwidth
Effective Bandwidth	1-10	Hz	Range selected for practical near-DC measurement sensitivity
QLED Emission Peak	532	nm	Optimized for NV center excitation
QLED FWHM	20	nm	Narrow spectral width
QLED Operating Voltage	5	V	Bias voltage for 10⁵ cd·m^-2 luminance
QLED Luminance	10⁵	cd·m^-2	Sufficient for effective NV center excitation
Array Unit Emission Area	1 x 1	mm²	Size of individually controlled QLED pixel
QLED Current Density (Range)	660-760	A·m^-2	Consistency test at 5 V bias
QLED Luminance (Range)	38,000-42,000	cd·m^-2	Consistency test at 5 V bias
Fixed Microwave Resonance Freq.	2.788	GHz	Operating frequency for CW-ODMR
Gyromagnetic Ratio (γ_e)	28	MHz/mT	Standard NV center value
ODMR Contrast (Single Peak)	0.72	%	Measured contrast of the leftmost single peak
Bias Magnetic Field (B)	3	mT	Fixed field used during conversion coefficient testing
Max Relative Error (Conversion)	Below 3	%	Between theoretical and experimental V/T coefficients

QLED Thin-Film Structure

Layer	Material	Thickness	Function
Substrate	ITO Glass	N/A	Anode
Hole Injection Layer	PEDOT:PSS	45 nm	Hole injection
Hole Transport Layer	TFB	40 nm	Hole transport
Active Layer	CdSe/ZnS QDs	20 nm	Light emission (532 nm)
Electron Transport Layer	ZnMgO	60 nm	Electron transport
Cathode	Aluminum (Al)	100 nm	Cathode

Key Methodologies

The QLED-NV magnetometer array was fabricated and characterized using a combination of micro/nano-fabrication techniques and continuous-wave optically detected magnetic resonance (CW-ODMR).

QLED Fabrication:
- Substrate Preparation: ITO film (6-8 Ω/sq) was ultrasonically cleaned and patterned using photolithography to define individual anode areas (1 x 1 mm²).
- Layer Deposition: PEDOT:PSS, TFB, QDs, and ZnMgO layers were sequentially deposited via the mature spin-coating method at a speed of 1500 r/min.
- Cathode Patterning: Aluminum (Al) electrodes were evaporated using a graphical mask to define individually addressable cathodes.
- Encapsulation: QLED devices were encapsulated in a glove box using UV-curable resin (UV glue).
Magnetometer Array Assembly:
- The QLED array was integrated with a narrowband filter (532 nm), a diamond substrate (containing NV centers), a bandpass filter (600-800 nm), and photodetectors (PDs).
- A pre-existing large-area antenna was positioned beneath the array to ensure uniform 2.87 GHz microwave driving across all four units.
CW-ODMR Detection:
- Excitation: QLEDs provided 532 nm excitation light (5 V bias, 10⁵ cd·m^-2 luminance).
- Microwave Control: A Keysight N5181B signal generator provided the microwave signal, fixed at 2.788 GHz, superimposed with a sine-wave modulation signal (500 Hz, 1 V amplitude).
- Signal Processing: A HF2LI lock-in amplifier was used for modulation and demodulation. The lock-in amplifier was locked at the zero point of the demodulation curve to ensure operation within the linear regime.
- Sensitivity Measurement: System background noise was collected for 1 hour without signal input, Fourier transformed to obtain the Amplitude Spectral Density (ASD), and used to calculate magnetic noise spectral density (η) within the 1-10 Hz effective bandwidth.
Field Validation Experiments:
- Regional Field Detection: Two collateral units were selectively activated to demonstrate spatial discrimination capability under a maximum applied field of 100 µT.
- Dynamic Field Tracking: All four units were simultaneously activated while an external magnetic field source was translated linearly (left-to-right) to quantify positional changes based on differential unit responses.

Commercial Applications

The integration of high-brightness QLEDs with NV diamond sensors creates a scalable, compact, and low-cost platform for advanced magnetic sensing arrays, enabling applications in fields requiring high spatial resolution and vector measurement capability.

Quantum Sensing and Metrology:
- Development of large-scale, high-density quantum magnetometer arrays for high-resolution field mapping.
- Scalable manufacturing of integrated quantum sensors due to QLED compatibility with micro/nano-fabrication.
Biomedical and Healthcare:
- Non-invasive monitoring and precise tracking of magnetic carriers (e.g., magnetic nanoparticles or magnetic robots) in simulated vascular environments.
- Biomedical imaging requiring ultra-high sensitivity and spatial resolution (e.g., magnetocardiography or magnetoencephalography).
Industrial Inspection and Materials Science:
- Real-time anomaly detection and high-resolution field mapping for non-destructive evaluation (NDE) of materials.
- Monitoring dynamic magnetic field variations in complex industrial environments.
Robotics and Navigation:
- Intelligent robotic navigation systems requiring robust, directionally sensitive magnetic field detection.
- Geophysical exploration and mapping of localized magnetic anomalies.

View Original Abstract

The nitrogen-vacancy (NV) center magnetic sensor, leveraging nitrogen-vacancy quantum effects, enables high-sensitivity magnetic field detection via optically detected magnetic resonance (ODMR). However, conventional single-point integrated devices suffer from limitations such as inefficient regional magnetic field detection and challenges in discerning the directional variations of dynamic magnetic fields. To address these issues, this study proposes an array- based architecture that innovatively substitutes the conventional 532 nm laser with quantum-dot light-emitting diodes (QLEDs). Capitalizing on the advantages of QLEDs—including compatibility with micro/nano-fabrication processes, wavelength tunability, and high luminance—a 2 × 2 monolithically integrated magnetometer array was developed. Each sensor unit achieves a magnetic sensitivity of below 26 nT·Hz−1/2 and a measurable range of ±120 μT within the 1-10 Hz effective bandwidth. Experimental validation confirms the array’s ability to simultaneously resolve multi-regional magnetic fields and track dynamic field orientations while maintaining exceptional device uniformity. This advancement establishes a scalable framework for the design of large-scale magnetic sensing arrays, demonstrating significant potential for applications requiring spatially resolved and directionally sensitive magnetometry.

Tech Support

Original Source

DOI: https://doi.org/10.3390/mi16091021

References

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