Glass microbubble on-chip packaged ferrofluid based magnetoviscous magnetometer

We present a new packaging method for improving the lifetime of ferrofluid-based magnetoviscous magnetometer. The concept of a ferrofluid based magnetometer has been previously reported where the viscoelastic response of a thin interfacial ferrofluid layer loaded atop a high frequency shear wave quartz resonator to applied magnetic field is monitored. The magnetic field can be sensitively quantified by the changes in the at-resonance admittance characteristics of the resonator. However, under open conditions, continuous evaporation of the ferrofluid compromises the long term performance of the magnetometer. In this work, we integrate glass hemispherical microbubbles, used as vessels of ferrofluid, on the resonator chip to seal and prevent the evaporation of the ferrofluid liquid and drying out. A layer of high relative permeability thin film Metglas (Fe
₈₅
B
₅
Si
₁₀
) is deposited on the resonator chip to improve the sensitivity. Using these improvements, a minimum detectable field of 650 nT/yHz at 1 Hz is achieved. Moreover, comparing with the unsealed ferrofluid device, the lifetime of the glass microbubble integrated chip packaged device improved significantly from only few hours to over a month and continuing.