A CMOS-MEMS BEOL 2-axis Lorentz-Force Magnetometer with Device-Level Offset Cancellation

Abstract

Lorentz-force Microelectromechanical Systems (MEMS) magnetometers have been proposed as a replacement for magnetometers currently used in consumer electronics market. Being MEMS devices, they can be manufactured in the same die as accelerometers and gyroscopes, greatly reducing current solutions volume and costs. However, they still present low sensitivities and large offsets that hinder their performance. In this article, a 2-axis out-of-plane, lateral field sensing, CMOS-MEMS magnetometer designed using the Back-End-Of-Line (BEOL) metal and oxide layers of a standard CMOS (Complementary Metal–Oxide–Semiconductor) process is proposed. As a result, its integration in the same die area, side-by-side, not only with other MEMS devices, but with the readout electronics is possible. A shielding structure is proposed that cancels out the offset frequently reported in this kind of sensors. Full-wafer device characterization has been performed, which provides valuable information on device yield and performance. The proposed device has a minimum yield of 85.7% with a good uniformity of the resonance frequency fr¯=56.8 kHz, σfr=5.1 kHz and quality factor Q¯=7.3, σQ=1.6 at ambient pressure. Device sensitivity to magnetic field is 37.6fA·μT−1 at P=1130 Pa when driven with I=1mApp.

Keywords

• MEMS
• magnetic sensor
• magnetometer
• Lorentz-force
• offset suppression
• micromachined Resonator