Sensitivity Enhancement of Lorentz Force MEMS Resonant Magnetometers via Internal Thermal-Piezoresistive Amplification

This letter presents sensitivity enhancement of MEMS resonant magnetometers using the thermal-piezoresistive internal amplification effect in silicon microstructures. Preliminary results show up to ~15 X improvement in sensitivity per bias current for a resonator operated as a Lorentz force magnetometer. Magnetometer sensitivity figure-of-merit, defined as sensitivity (mV/T) over sensor dc bias current, has increased from 0.29 Ω/T(mV/Tesla/mA) to 4.22 Ω/T via internal thermal-piezoresistive amplification that also led to resonator effective quality factor (Q) increasing from its intrinsic value of 1140 to 16900 (in air). Previous work on the thermal-piezoresistive amplification effect suggests that amplification factors up to 3-4 orders of magnitude can be achieved using optimally designed structures, which can lead to ultra-high sensitivities for the presented sensors. It should be noted that the main focus of this letter is not to demonstrate a highly sensitive magnetometer, but rather to demonstrate the ability to improve magnetometer sensitivity as the resonator internal Q-amplification kicks-in. Although the resonant structure in this letter has not been optimized to operate as a magnetometer, sensitivities as high as 262 mV/T in air (minimum detectable field in the μT range) have been achieved.