Enhanced Chip Scale Piezoelectric MEMS Magnetic Field Sensors: High Sensitivity and Wide Bandwidth

Description

This proposal aims to advance the state-of-art for chip scale Microelectromechanical Systems (MEMS) magnetometers in terms of both resolution and bandwidth by investigating alternative device concepts. Magnetometers, which measure magnetic fields, are now in every smartphone (2 billion sold annually) along with other sensors that make up the inertial measurement unit (IMU). These other sensors that measure acceleration, yaw rate and pressure are fabricated with MEMS technology that is compatible with semiconducting manufacturing. But the magnetometer is made from materials incompatible with semiconducting manufacturing. As such, IMUs comprise discrete sensors in discrete packages, instead of an integrated system with a tiny footprint. This presents a problem as integration is a key enabler of increasingly complex systems in the age of internet-of-things. Capacitive MEMS magnetometers have dominated the research field. A state-of-art MEMS magnetometer would have 100nT-level resolution and 50Hz bandwidth. But their performance is highly-dependent on operating pressure, requiring sealing the device in high quality vacuum (not a common service). Capacitive MEMS magnetometers also have limited dynamic range (±10mT) due to higher susceptibility of nonlinearity when optimizing sensitivity. These tradeoffs between sensitivity, bandwidth and dynamic range are intrinsic to the physics of capacitive devices and thus cannot be addressed from optimization. Over the past three years, the PI has worked on alternative transducers based on piezoelectric devices to overcome the dependency on vacuum. To date, he has demonstrated on par resolution performance in ambient pressure conditions with dynamic range beyond the magnitude of fields possible in the lab (100mT) and low power 100μW-level. These basic device concepts have reached a performance bottleneck too. This proposal seeks to breakthrough the existing bottleneck by investigating more advanced device concepts that are far less straight-forward to implement on actual devices. We mitigate risks by leveraging our work in high performance Very High Frequency (VHF) band resonators, active-Q enhancement in capacitive resonators, and experience with piezoelectric LFMs.  More specifically, we plan to investigate implementing higher order vibration modes in piezoelectric LFMs with the aim to scale up operating frequency, quality factor, sensitivity and bandwidth simultaneously. These goals are described in Objective 1 and 2 of this proposal: Objective 1 targets vibration modes for in-plane field detection while Objective 2 targets vibration modes for out-of-plane field detection. Objective 3 aims to actively boost Q beyond the material limit. We aim to deliver 100 times improvement over the state-of-art in sensitivity, resolution (0.1- 1nT), and bandwidth (1kHz).