The MIT Faculty has made this article openly available. Please share how this access benefits you. Your story matters. CitationKim, Donggyu et al. "A CMOS-integrated quantum sensor based on nitrogen-vacancy centres."

The simultaneous imaging of magnetic fields and temperature (MT) is important in a range of applications, including studies of carrier transport 1-3 , solid-state material dynamics 1-6 , and semiconductor device characterization 7,8 . Techniques exist for separately measuring temperature (e.g., infrared (IR) microscopy 9 , micro-Raman spectroscopy 9 , and thermo-reflectance microscopy 9 ) and magnetic fields (e.g., scanning probe magnetic force microscopy 10 and superconducting quantum interference devices 11 ). However, these techniques cannot measure magnetic fields and temperature simultaneously. Here, we use the exceptional temperature 12,13 and magnetic field 14,15 sensitivity of nitrogen vacancy (NV) spins in conformally-coated nanodiamonds to realize simultaneous wide-field MT imaging. Our "quantum conformally-attached thermo-magnetic" (Q-CAT) imaging enables (i) wide-field, high-frame-rate imaging (100 -1000 Hz); (ii) high sensitivity; and (iii) compatibility with standard microscopes. We apply this technique to study the industrially important problem 8,16-18 of characterizing multifinger gallium nitride high-electron-mobility transistors (GaN HEMTs). We spatially and temporally resolve the electric current distribution and resulting temperature rise, elucidating functional device behavior at the microscopic level. The general applicability of Q-CAT imaging serves as an important tool for understanding complex MT phenomena in material science, device physics, and related fields.The NV center in diamond has attracted great interest because of its exceptional spin properties at room temperature, which exhibit outstanding nanoscale sensitivity to magnetic fields 14,19-23 and temperature 12,13 . NV centers located within nanodiamonds (NVNDs) have gained particular interest for applications including drug delivery 24 , thermal measurements of biological systems [25][26][27][28][29] , and scanning magnetometer tips 30,31 . The NVND's small size allows direct measurement of their local MT environment. These applications have motivated studies of NVND properties such as strain, magnetic and thermal sensitivity, and coherence time 32,33 . However, NVND properties differ for a given fabrication process 32 or surface treatment 34 . This variability of nanodiamond material parameters and orientations has presented challenges for wide-field imaging studies using NVNDs. In this work, we (i) develop a model that describes the optically detected magnetic resonance (ODMR) 35,36 spectrum of NVND ensembles as a function of magnetic field and temperature; (ii) perform statistical characterization of NVND parameters, specifically the variation in NVND thermal response with implications for NVND temperature sensing; (iii) use this NVND model and our statistical characterization to extend the capabilities of NV sensing by enabling wide-field imaging with deposited coatings of NVNDs (Q-CAT imaging); (iv) demonstrate our technique's capabilities by imaging the dynamic phenomenon of electromigration; and (v) perform wide-field MT...

Nitrogen-vacancy (NV) quantum magnetometers offer exceptional sensitivity and long-term stability. However, their use to date in distributed sensing applications, including remote detection of ferrous metals, geophysics, and biosensing, is limited due to the need to combine optical, microwave (MW), and magnetic excitations into a single system. Existing approaches have yielded localized devices but not distributed capabilities. In this study, a continuous system-in-a-fiber architecture is reported, which enables distributed magnetic sensing over extended lengths. Key to this realization is a thermally drawn fiber that has hundreds of embedded photodiodes connected in parallel and a hollow optical waveguide that contains a fluid with NV diamonds. This fiber is placed in a larger coaxial cable to deliver the required MW excitation. This distributed quantum sensor is realized in a water-immersible 90-m-long cable with 102 detection sites. A sensitivity of 63 ± 5 nT Hz −1/2 per site, limited by laser shot noise, is established along a 90 m test section. This fiber architecture opens new possibilities as a robust and scalable platform for distributed quantum sensing technologies.Current distributed fiber sensors have high sensitivity to temperature, [1,2] strain, [3][4][5] and pressure, [6][7][8] but not to magnetic fields. [9][10][11] Here, we add distributed spin-based quantum magnetometry to the sensing capabilities of distributed fiber sensors through the integration of NV ensembles. Recent years have seen the rapid advancement of NV solid-state quantum sensors because of their excellent sensitivity to magnetic fields, [12][13][14][15] with sub-nT Hz −1/2 sensitivity in the dc limit, [16,17] high dynamic range vector resolution, [18,19] and remarkable long-term stability. [20,21] Recent advances toward component integration have achieved magnetometry point probes consisting of micro-diamonds on fiber facets [22] or nanodiamonds on tapered fibers. [23] However, practical devices will require compact and stable architectures

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Magnetometers based on quantum mechanical processes enable high sensitivity and long-term stability without the need for re-calibration, but their integration into fieldable devices remains challenging. This paper presents a CMOS quantum vector-field magnetometer that miniaturizes the conventional quantum sensing platforms using nitrogen-vacancy (NV) centers in diamond. By integrating key components for spin control and readout, the chip performs magnetometry through optically detected magnetic resonance (ODMR) through a diamond slab attached to a custom CMOS chip. The ODMR control is highly uniform across the NV centers in the diamond, which is enabled by a CMOS-generated ∼2.87 GHz magnetic field with <5% inhomogeneity across a large-area current-driven wire array. The magnetometer chip is 1.5 mm 2 in size, prototyped in 65-nm bulk CMOS technology, and attached to a 300×80 µm 2 diamond slab. NV fluorescence is measured by CMOS-integrated photodetectors. This on-chip measurement is enabled by efficient rejection of the green pump light from the red fluorescence through a CMOS-integrated spectral filter based on a combination of spectrally dependent plasmonic losses and diffractive filtering in the CMOS back-end-of-line (BEOL). This filter achieves ∼25 dB of green light rejection. We measure a sensitivity of 245 nT/Hz 1/2 , marking a 130× improvement over a previous CMOS-NV sensor prototype, largely thanks to the better spectral filtering and homogeneous microwave generation over larger area.