We present a voltage-controlled oscillator (VCO)-based electron paramagnetic resonance (EPR) sensor featuring an enhanced sensing area for a high concentration sensitivity and improved homogeneity compared to conventional, chip-integrated planar sensors. Prior designs have relied on VCO-array configurations to expand the sensing area, which comes at the cost of increased power consumption. Here, the relatively small diameters of the individual coil elements limit the homogeneous region in the direction perpendicular to the chip surface. To address these limitations, we propose the use of inductance-capacitance (LC) VCO-based EPR detectors with large coil diameters with a laser-fabricated hole to create a large sensitive volume with high homogeneity of the microwave B1field inside the coil. Despite the enlarged coil diameter and the correspondingly large inductance, the VCO-based detector achieves a low phase noise (PN) of -116 dBc/Hz at a 1 MHz offset from a center frequency of 6.75 GHz, and a 10 % frequency tuning range. The presented sensor frontend incorporates the VCO-based EPR detector inside an integer-N phase-locked loop (PLL), enabling precise phase and frequency control from an external low-frequency reference. The C-band operation of the presented VCO-based EPR detector is compatible with the static magnetic fields achievable with compact permanent magnets. The proposed sensor is electrically characterized and validated in the target EPR application using standard EPR samples of BDPA (α, γ-bisdiphenylene-β-phenylallyl) and TEM-POL (2,2,6,6-tetramethyl-4-hydroxy-piperidine-1-oxyl), achieving a spin sensitivity of 5 × 109spins/(G Hz1/2) and concentration sensitivity of 15.6 µM/(G Hz1/2), respectively.

The excellent performance of quantum magnetometers based on nitrogen-vacancy (NV) centers in diamond, including their high sensitivity, their wide dynamic range, and the possibility for a calibration-free operation, renders them a very promising alternative to classical magnetic field sensors. However, existing lab prototypes of NV center sensors still suffer from a large volume and non-scalable manufacturing technologies. To mitigate this problem, in this paper, we present a miniaturized and scalable microwave electronics platform for quantum magnetometry based on an S-band SiGe BiCMOS transmitter (TX) chip and a custom-designed resonator manufactured on a microwave printed circuit board. The fabricated TX chip can deliver a high saturated output power of 19dBm at a center frequency of 2.87GHz over a wide relative bandwidth of 38.3% of the center frequency to a 50Ω load while occupying a compact die area of 0.593mm2. To manipulate the spin state of NV centers efficiently, we use two of the presented TX chips to drive a newly proposed differential resonator, which provides microwave magnetic fields of B1=179μT over a large active area of 18.48×104μm2. Continuous-wave and pulsed optically detected magnetic resonance (ODMR) measurements are used to verify the excellent performance of the proposed platform compared to the state-of-the-art. In these experiments, the presented platform produced Rabi frequencies up to 5.81MHz.

In this paper, we present a miniaturized chip-based Overhauser dynamic nuclear polarization (ODNP) platform for enhancing detection sensitivity and, thereby, improving the achievable limit of detection. The presented system uses three custom-designed ASICs for the excitation and the detection of the NMR signal as well as the generation and preamplification of the required microwave (MW) signal. A commercial baredie GaN power amplifier is used in addition to achieve the driving strength of up to 26 dBm at 7 GHz required for the target ODNP application. Moreover, the wide bandwidth of the custom-designed, printed MW Alderman-Grant (AG) resonator allows for an indirect measurement of the electron spin resonance (ESR) signal of the utilized DNP agent without the need for an additional ESR spectrometer. Overall, the presented system achieves an ODNP enhancement factor of 50 with an active volume of 500 nL, the latter number improving the state-of-the-art in chip-based ODNP platforms by a factor of 500×.