Compact and Fully Integrated LED Quantum Sensor Based on NV Centers in Diamond

At a Glance

Metadata	Details
Publication Date	2024-01-24
Journal	Sensors
Authors	Jens Pogorzelski, Ludwig Horsthemke, Jonas Homrighausen, Dennis Stiegekötter, Markus Gregor
Institutions	FH Münster
Citations	28
Analysis	Full AI Review Included

Executive Summary

This work presents the smallest fully integrated, LED-based quantum sensor utilizing Nitrogen Vacancy (NV) centers in diamond microcrystals, designed for cost-effective, non-laboratory applications.

Integration and Form Factor: Achieved an extremely compact size of (6.9 × 3.9 × 15.9) mm³ (0.42 cm³), representing a factor of 7 reduction compared to the previous smallest fully integrated sensor.
Interface: Provides an all-electric interface by integrating the pump light source (LED), photodiode (PD), microwave (MW) antenna, and optical filtering onto three stacked Printed Circuit Boards (PCBs).
Performance: Demonstrated a mean sensitivity of 28.32 nT/√Hz, with a theoretical Shot Noise Limited Sensitivity (SNLS) of 2.87 nT/√Hz.
Efficiency: Operates with low power consumption, approximately 0.1 W (3.3 V, 30 mA LED current).
Thermal Management: Internal heating is well-controlled, resulting in a maximum diamond temperature increase (∆T_NVmax) of only 9.8 K above ambient.
Cost Reduction: Utilizes readily available Surface Mount Devices (SMD) and cost-effective diamond microcrystals, which are approximately 90% cheaper than equivalent Chemical Vapor Deposition (CVD) diamonds.

Technical Specifications

Parameter	Value	Unit	Context
Overall Volume	6.9 x 3.9 x 15.9 (0.42)	mm³ (cm³)	Smallest fully integrated NV sensor reported.
Measured Sensitivity (Mean)	28.32	nT/√Hz	Averaged between τ = 0.1 s and τ = 3 s.
Shot Noise Limited Sensitivity (SNLS)	2.87	nT/√Hz	Theoretical optimum sensitivity.
Minimum Detectable Field Change (∆B_min)	15.44	nT	Average minimum of Allan deviation curves.
Power Consumption	0.1	W	3.3 V at 30 mA LED current.
Internal Temperature Increase (∆T_NVmax)	9.8	K	Measured via Zero Field Splitting (ZFS) shift.
Diamond Material	HPHT Microcrystal	-	150 µm diameter, 2.5-3 ppm NV concentration.
Diamond Volume (Approx.)	0.02	mm³	Based on 170 µm sphere approximation.
LED Dominant Wavelength	525	nm	Indium Gallium Nitride LED (pump source).
Fluorescence Filter Cutoff	622	nm	Longpass filter foil used to block residual pump light.
MW Resonance Frequency (D)	2.87	GHz	Zero Field Splitting (ZFS) center frequency.
MW Antenna Trace Length	24.62	mm	Half-wavelength resonator (λ_PCB/2).
Optimal MW Power Range	5 to 10	dBm	Range achieving best SNLS performance.

Key Methodologies

The sensor was constructed using a modular, stacked design integrating commercial components for high manufacturability and low cost.

Mechanical Assembly: The sensor head consists of three stacked Printed Circuit Boards (PCBs):
- LED-PCB: Mounts the 525 nm InGaN LED.
- MW-PCB: Contains the microwave antenna structure.
- PD-PCB: Holds the SMD photodiode (VEMD1060X01) for fluorescence detection.
NV Center Integration: A 150 µm High-Pressure High-Temperature (HPHT) diamond microcrystal was fixed directly onto the epoxy resin filling the LED housing using optical adhesive (NOA61).
Microwave (MW) Antenna Design: An omega-shaped coplanar waveguide antenna was fabricated on the MW-PCB. The trace length was calculated to be 24.62 mm (half the wavelength at 2.87 GHz) to maximize the magnetic field homogeneity over the diamond volume.
Optical Filtering: A 622 nm longpass filter foil was placed between the MW-PCB and PD-PCB to separate the 637 nm NV fluorescence signal from the residual 525 nm LED pump light.
Signal Readout: The photodiode current was converted to voltage using a custom Transimpedance Amplifier (TIA). The TIA output was fed into a Lock-In Amplifier (LIA) for demodulation, using the low-frequency (f_LF) component of the Frequency Modulated (FM) microwave signal as the reference.
Thermal Characterization: The internal temperature increase (∆T_NVmax) was determined by measuring the shift in the Zero Field Splitting (ZFS) frequency (D) as a function of microwave power, referencing the known temperature coefficient of -74.2 kHz/K.
Sensitivity Optimization: The Shot Noise Limited Sensitivity (SNLS) was optimized by systematically sweeping the FM parameters: MW power (P_MW), frequency deviation (f_devi), and local oscillator frequency (f_LF). The optimal settings were found to be P_MW = [5, 10] dBm, f_devi = [1.8, 3] MHz, and f_LF = [1.5, 20] kHz.

Commercial Applications

This fully integrated, compact, and low-power NV sensor technology is suitable for widespread deployment in non-laboratory environments.

Automotive and Transportation: Current sensing, battery monitoring, and integrated magnetic field/temperature monitoring in electric vehicles and control systems.
Industrial Sensing: Robust magnetic field measurement in switching cabinets and machinery, providing an all-electric interface compatible with existing industrial infrastructure.
Portable Magnetometry: Development of handheld or drone-mounted magnetometers for geological surveys, security, or infrastructure inspection due to the small size and low power draw.
Quantum Sensing Platforms: Serving as a compact, modular building block for larger quantum systems or educational tools.
Biomedical Research: Potential use in non-contact thermometry or magnetic sensing in biological environments, leveraging the solid-state, room-temperature operation.
Quantum Computing Components: NV centers are fundamental spin systems used in solid-state quantum information processing.

View Original Abstract

Quantum magnetometry based on optically detected magnetic resonance (ODMR) of nitrogen vacancy centers in diamond nano or microcrystals is a promising technology for sensitive, integrated magnetic-field sensors. Currently, this technology is still cost-intensive and mainly found in research. Here we propose one of the smallest fully integrated quantum sensors to date based on nitrogen vacancy (NV) centers in diamond microcrystals. It is an extremely cost-effective device that integrates a pump light source, photodiode, microwave antenna, filtering and fluorescence detection. Thus, the sensor offers an all-electric interface without the need to adjust or connect optical components. A sensitivity of 28.32nT/Hz and a theoretical shot noise limited sensitivity of 2.87 nT/Hz is reached. Since only generally available parts were used, the sensor can be easily produced in a small series. The form factor of (6.9 × 3.9 × 15.9) mm3 combined with the integration level is the smallest fully integrated NV-based sensor proposed so far. With a power consumption of around 0.1W, this sensor becomes interesting for a wide range of stationary and handheld systems. This development paves the way for the wide usage of quantum magnetometers in non-laboratory environments and technical applications.

Tech Support

Original Source

DOI: https://doi.org/10.3390/s24030743

References

2021 - Integrated and Portable Magnetometer Based on Nitrogen-Vacancy Ensembles in Diamond [Crossref]
2021 - A hybrid magnetometer towards femtotesla sensitivity under ambient conditions [Crossref]
2023 - Nuclear quadrupole resonance spectroscopy with a femtotesla diamond magnetometer [Crossref]
2017 - Scanning diamond NV center probes compatible with conventional AFM technology [Crossref]
2013 - Nanoscale magnetometry with NV centers in diamond [Crossref]
2008 - Nanoscale imaging magnetometry with diamond spins under ambient conditions [Crossref]
2021 - Diamond Magnetometry and Gradiometry Towards Subpicotesla dc Field Measurement [Crossref]
2010 - Temperature Dependence of the Nitrogen-Vacancy Magnetic Resonance in Diamond [Crossref]
2013 - High-Precision Nanoscale Temperature Sensing Using Single Defects in Diamond [Crossref]