Design,fabrication,characterization and reliability study of CMOS-MEMS Lorentz-force magnetometers

摘要

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.