A Miniaturized On-Chip Electron Paramagnetic Resonance Sensor

Electron paramagnetic resonance (EPR) spectrometers have a wide range of applications. The conventional EPR spectrometers are bulky and heavy, restricting their use to laboratories. Recently, miniaturization of the majority of the components of the spectrometers, except magnets which generate dc magnetic field, has been reported. Lack of completely miniaturized on-chip EPR spectrometers has become deterrent for on-field applications. This article describes the design and development of an on-chip miniaturized EPR sensor for on-field applications. The miniaturization is achieved by replacing the bulky external magnets with on-chip permalloy micro magnetic patterns to generate dc magnetic field. These patterns are placed inside a broadband micro coil which acts as an electromagnetic field source in a wide frequency range of 0.1–15 GHz. Unlike in conventional EPR spectrometers, where dc magnetic field is swept, here, frequency is swept to obtain electron spin resonance, with a constant dc magnetic field. 1,1-Diphenyl-2-picrylhydrazyl (DPPH) is used to demonstrate the EPR principle. EPR is observed at a frequency of 1.722 GHz at 300 K. The sensitivity achieved is
${1.1} \,\,\times {10}^{{8}}\,\,\text {spins}/\sqrt {\text {Hz}} $
. The proposed sensor enables a monolithic solution for EPR spectrometers which would be light, cheap, and completely portable.