Design, Fabrication, Characterization and Reliability Study of CMOS-MEMS Lorentz-Force Magnetometers

TL;DR

This paper details the design, fabrication, and testing of CMOS-MEMS Lorentz-force magnetometers, demonstrating high yield, competitive performance, and robustness through innovative design techniques and comprehensive characterization.

Contribution

It introduces novel CMOS-compatible design and fabrication methods for high-yield, reliable Lorentz-force magnetometers with performance comparable to or better than existing solutions.

Findings

Yields above 95% achieved with proper design techniques

Performance metrics are similar or superior to commercial magnetometers

Reliability tests show robustness against harsh conditions

Abstract

This article presents several design techniques to fabricate micro-electro-mechanical systems (MEMS) using standard complementary metal-oxide semiconductor (CMOS) processes. They were applied to fabricate high yield CMOS-MEMS shielded Lorentz-force magnetometers (LFM). The multilayered metals and oxides of the back-end-of-line (BEOL), normally used for electronic routing, comprise the structural part of the MEMS. The most important fabrication challenges, modeling approaches and design solutions are discussed. Equations that predict the Q factor, sensitivity, Brownian noise and resonant frequency as a function of temperature, gas pressure and design parameters are presented and validated in characterization tests. A number of the fabricated magnetometers were packaged into Quad Flat No-leads (QFN) packages. We show this process can achieve yields above 95 % when the proper design techniques are adopted. Despite CMOS not being a process for MEMS manufacturing, estimated performance (sensitivity and noise level) is similar or superior to current commercial magnetometers and others built with MEMS processes. Additionally, typical offsets present in Lorentz-force magnetometers were prevented with a shielding electrode, whose efficiency is quantified. Finally, several reliability test results are presented, which demonstrate the robustness against high temperatures, magnetic fields and acceleration shocks.