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.

Ferromagnetic Resonance Assisted Optomechanical Magnetometer

“…The field sensitivity presented in Fig. 2(e) is similar to the best sensitivity obtained in previous cavity OMM studies [6][7][8][9]. In those references, a magnetostrictive material (Terfenol-D) was used due to its high magnetostrictive coefficient [25].…”

“…Stimuli readout experiments based on such platforms have already reached the state of the art for force sensors [4] and accelerometers [5]. In addition, the interaction of mechanical elements with magnetic fields also makes OM devices high-performance magnetometers, i.e., room temperature OM magnetometer (OMM) of small size [6,7], high sensitivity [8], and large dynamic range [9]. The ability to measure small magnetic fields over a broad frequency range is important for numerous applications playing a key role in areas such as geology [10], space exploration [11], biology [12], and medical imaging [13].…”

Ultrasensitive Magnetic Field Sensors for Biomedical Applications

“…Hz [142] (at room temperature) is the cavity optomechanical magnetometer [143]. This magnetometer is commonly based on microtoroidal cavities (the schematic image is shown in the panel (b) of Figure 9) and implemented on a silicon chip.…”

“…Due to the modern tendency of device miniaturization, there is a high demand for highly localized magnetic field sensors. One type of magnetic field sensor having linear dimensions of tenths of micrometers [141], and the lowest detection level of the order of about 100 pT/√Hz [142] (at room temperature) is the cavity optomechanical magnetometer [143]. This magnetometer is commonly based on microtoroidal cavities (the schematic image is shown in the panel (b) of Figure 9) and implemented on a silicon chip.…”

Ultrabroadband and sensitive cavity optomechanical magnetometry

“…Cavity optomechanical magnetometers are particulary attractive, promising stateof-the-art sensitivity without the need for cryogenics, with only microwatt power consumption [11][12][13][14]16], and with silicon chip based fabrication offering scalability [15]. For instance, cavity optomechanical magnetometers working in the megahertz frequency range have been demonstrated by using a magnetostrictive material Terfenol-D, either manually deposited onto a microcavity [11,12,14] with a reported peak sensitivity of 200 pT/ √ Hz [12], or sputter coated onto the microcavity with a reported peak sensitivity of 585 pT/ √ Hz [15]. Efforts have also been made to improve the sensitivity at the hertz-to-kilohertz frequency range, which is relevant to many applications.…”