Invited Article: Scalable high-sensitivity optomechanical magnetometers on a chip

Abstract

The dual-resonant enhancement of mechanical and optical response in cavity optomechanical magnetometers enables precision sensing of magnetic fields. In previous working prototypes of such magnetometers, a cavity optomechanical system is functionalized by manually epoxy-bonding a grain of magnetostrictive material. While this approach allows proof-of-principle demonstrations, practical applications require more scalable and reproducible fabrication pathways. In this work, we developed a multiple-step method to scalably fabricate optomechanical magnetometers on a silicon chip, with reproducible performance across different devices. The key step is to develop a process to sputter coat a magnetostrictive film onto high quality toroidal microresonators, without degradation of the optical quality factor. A peak sensitivity of 585 pT/Hz is achieved, which is comparable with previously reported results using epoxy-bonding. Furthermore, we demonstrate that thermally annealing the sputtered film can improve the magnetometer sensitivity by a factor of 6.3.