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

Tesi en modalitat de compendi de publicacionsToday, the most common form of mass-production semiconductor device fabrication is Complementary Metal-Oxide Semiconductor (CMOS) technology. The dedicated Integrated Circuit (IC) interfaces of commercial sensors are manufactured using this technology. The sensing elements are generally implemented using Micro-Electro-Mechanical-Systems (MEMS), which need to be manufactured using specialized micro-machining processes. Finally, the CMOS circuitry and the MEMS should ideally be combined in a single package. For some applications, integration of CMOS electronics and MEMS devices on a single chip (CMOS-MEMS) has the potential of reducing fabrication costs, size, parasitics and power consumption, compared to other integration approaches. Remarkably, a CMOS-MEMS device may be built with the back-end-of-line (BEOL) layers of the CMOS process. But, despite its advantages, this particular approach has proven to be very challenging given the current lack of commercial products in the market. The main objective of this Thesis is to prove that a high-performance MEMS, sealed and packaged in a standard package, may be accurately modeled and manufactured using the BEOL layers of a CMOS process in a reliable way. To attain this, the first highly reliable novel CMOS-MEMS Lorentz Force Magnetometer (LFM) was successfully designed, modeled, manufactured, characterized and subjected to several reliability tests, obtaining a comparable or superior performance to the typical solid-state magnetometers used in current smartphones. A novel technique to avoid magnetic offsets, the main drawback of LFMs, was presented and its performance confirmed experimentally. Initially, the issues encountered in the manufacturing process of MEMS using the BEOL layers of the CMOS process were discouraging. Vapor HF release of MEMS structures using the BEOL of CMOS wafers resulted in undesirable damaging effects that may lead to the conclusion that this manufacturing approach is not feasible. However, design techniques and workarounds for dealing with the observed issues were devised, tested and implemented in the design of the LFM presented in this Thesis, showing a clear path to successfully fabricate different MEMS devices using the BEOL.Hoy en día, la forma más común de producción en masa es una tecnología llamada Complementary Metal-Oxide Semiconductor (CMOS). La interfaz de los circuitos integrados (IC) de sensores comerciales se fabrica usando, precisamente, esta tecnología. Actualmente es común que los sensores se implementen usando Sistemas Micro-Electro-Mecánicos (MEMS), que necesitan ser fabricados usando procesos especiales de micro-mecanizado. En un último paso, la circuitería CMOS y el MEMS se combinan en un único elemento, llamado package. En algunas aplicaciones, la integración de la electrónica CMOS y los dispositivos MEMS en un único chip (CMOS-MEMS) alberga el potencial de reducir los costes de fabricación, el tamaño, los parásitos y el consumo, al compararla con otras formas de integración. Resulta notable que un dispositivo CMOS-MEMS pueda ser construido con las capas del back-end-of-line (BEOL) de un proceso CMOS. Pero, a pesar de sus ventajas, este enfoque ha demostrado ser un gran desafío como demuestra la falta de productos comerciales en el mercado. El objetivo principal de esta Tesis es probar que un MEMS de altas prestaciones, sellado y empaquetado en un encapsulado estándar, puede ser correctamente modelado y fabricado de una manera fiable usando las capas del BEOL de un proceso CMOS. Para probar esto mismo, el primer magnetómetro CMOS-MEMS de fuerza de Lorentz (LFM) fue exitosamente diseñado, modelado, fabricado, caracterizado y sometido a varias pruebas de fiabilidad, obteniendo un rendimiento comparable o superior al de los típicos magnetómetros de estado sólido, los cuales son usados en móviles actuales. Cabe destacar que en esta Tesis se presenta una novedosa técnica con la que se evitan offsets magnéticos, el mayor inconveniente de los magnetómetros de fuerza Lorentz. Su efectividad fue confirmada experimentalmente. En los inicios, los problemas asociados al proceso de fabricación de MEMS usando las capas BEOL de obleas CMOS resultaba desalentador. Liberar estructuras MEMS hechas con obleas CMOS con vapor de HF producía efectos no deseados que bien podrían llevar a la conclusión de que este enfoque de fabricación no es viable. Sin embargo, se idearon y probaron técnicas de diseño especiales y soluciones ad-hoc para contrarrestar estos efectos no deseados. Se implementaron en el diseño del magnetómetro de Lorentz presentado en esta Tesis, arrojando excelentes resultados, lo cual despeja el camino hacia la fabricación de diferentes dispositivos MEMS usando las capas BEOL.Postprint (published version

Closed-form equation for natural frequencies of beams under full range of axial loads modeled with a spring-mass system

A new simple closed-form equation that accurately predicts the effect of an arbitrarily large constant axial load, residual stress or temperature shift on the natural frequencies of an uniform single-span beam, with various end conditions, is presented. Its accuracy and applicability range are studied by comparing its predictions with numerical simulations and with the approximate Galef’s and Bokaian’s formulas. The new equation may be understood as a refinement or extension of these two approximate formulas. Significant accuracy and applicability range improvements are achieved, especially near the buckling point and for large and moderate axial load. The new closed-form equation is applicable in the full range of axial load, i.e., from the buckling load to the tensioned-string limit. It also models well the beam-to-string transition region for the eight boundary conditions studied. It works remarkably well in the free-free and sliding-free cases, where it is a near-exact solution. In addition, it yields the natural frequencies of a 1-D spring-mass system that may be used to model tensioned beams, and potentially, more complex systems.Peer ReviewedPostprint (published version

Curvature of BEOL cantilevers in CMOS-MEMS processes

© 2017 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes,creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.This paper presents the curvature characterization results of released back-end-of-line 5 µm-wide cantilevers for two different 0.18-µm 1P6M complementary metal-oxide semiconductor microelectromechanical systems processes. Results from different runs and lots from each foundry are presented. The methodology and accuracy of the characterization approach, based on optical measurements of test cantilever curvature, are also discussed. Special emphasis is given to the curvature average and variability as a function of the number of stacked layers. Analythical equations for modeling the bending behavior of stacked cantilevers as a function of the tungsten (W) vias that join the metal layers are presented. In addition, the effect of various post-processing conditions and design techniques on the curvature of both single and stacked cantilevers is analyzed. In particular, surpassing certain time-dependent temperature stress conditions after release lead to curvature shifts larger than one order of magnitude. Also, the W via design was found to strongly affect the curvature of the test cantilevers.Peer ReviewedPostprint (author's final draft

A mixed-signal control system for Lorentz-force resonant MEMS magnetometers

This paper presents a mixed-signal closed-loop control system for Lorentz force resonant MEMS magnetometers. The control system contributes to 1) the automatic phase control of the loop, that allows start-up and keeps self-sustained oscillation at the MEMS resonance frequency, and 2) output offset reduction due to electrostatic driving by selectively disabling it. The proposed solution proof-of-concept has been tested with a Lorentz force-based MEMS magnetometer. The readout electronic circuitry has been implemented on a printed circuit board with off-the-shelf components. Digital control has been implemented in an FPGA coded with VHDL. When biased with 1 V and a driving current of 300 µArms, the device shows 9.75 pA/µT sensitivity and total sensor white noise of 550 nT/vHz. Offset when electrostatic driving is disabled is 793 µT, which means a 40.1% reduction compared when electrostatic driving is enabled. Moreover, removing electrostatic driving does not worsen bias instability, which is lower than 125 nT in both driving cases.Peer ReviewedPostprint (published version

A test setup for the characterization of Lorentz-force MEMS magnetometers

© 2021 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes,creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.Lorentz-force MEMS magnetometers are interesting candidates for the replacement of magnetometers in consumer electronics products. Plenty of works in the literature propose MEMS magnetometers, their readout circuits and modulations. However, during the standalone characterization of such MEMS devices, a great variety of instruments and strategies are used, making it very complex to compare results from different works in the literature. For this reason, this article proposes a test setup to characterize Lorentz-force MEMS magnetometers. The proposed setup is based around the use of an impedance analyzer for the driving of voltage and Lorentz-current of the MEMS in-phase and in quadrature, which allows the device Amplitude Modulation and Frequency Modulation characterization. The proposed solution is validated by using the designed circuit to characterize two CMOS-MEMS magnetometers with very different characteristics.This work was supported in part by the Spanish Ministry of Science, Innovation and Universities, the State Research Agency (AEI) under Project RTI2018-099766-B-I00, and in part by the European Social Fund (ESF).Peer ReviewedPostprint (published version

Monolithic sensor integration in CMOS technologies

© 2023 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes,creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.Besides being mainstream for mixed-signal electronics, CMOS technology can be used to integrate micro-electromechanical system (MEMS) on a single die, taking advantage of the structures and materials available in feature sizes around 180 nm. In this article, we demonstrate that the CMOS back-end-of-line (BEOL) layers can be postprocessed and be opportunistically used to create several kinds of MEMS sensors exhibiting good or even excellent performance, such as accelerometers, pressure sensors, and magnetometers. Despite the limitations of the available mechanical and material properties in CMOS technology, due to monolithic integration, these are compensated by the significant reduction of parasitics and system size. Furthermore, this work opens the path to create monolithic integrated multisensor (and even actuator) chips, including data fusion and intelligent processing.This work was supported in part by Baolab Microsystems; in part by the Spanish Ministry of Science, Innovation and Universities (MCIN); in part by the State Research Agency (AEI); in part by the European Social Fund (ESF) under Project RTI2018-099766-B-I00; in part by MCIN/AEI/10.13039/501100011033 under Grant PID2021-123535OB-I00; and in part by ERDF, “A way of making Europe.” The associate editor coordinating the review of this article and approving it for publication was Prof. Jean-Michel Redoute.Peer ReviewedPostprint (author's final draft

MUSiC : a model-unspecific search for new physics in proton-proton collisions at root s=13TeV

Results of the Model Unspecific Search in CMS (MUSiC), using proton-proton collision data recorded at the LHC at a centre-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 35.9 fb(-1), are presented. The MUSiC analysis searches for anomalies that could be signatures of physics beyond the standard model. The analysis is based on the comparison of observed data with the standard model prediction, as determined from simulation, in several hundred final states and multiple kinematic distributions. Events containing at least one electron or muon are classified based on their final state topology, and an automated search algorithm surveys the observed data for deviations from the prediction. The sensitivity of the search is validated using multiple methods. No significant deviations from the predictions have been observed. For a wide range of final state topologies, agreement is found between the data and the standard model simulation. This analysis complements dedicated search analyses by significantly expanding the range of final states covered using a model independent approach with the largest data set to date to probe phase space regions beyond the reach of previous general searches.Peer reviewe

Measurement of prompt open-charm production cross sections in proton-proton collisions at root s=13 TeV

The production cross sections for prompt open-charm mesons in proton-proton collisions at a center-of-mass energy of 13TeV are reported. The measurement is performed using a data sample collected by the CMS experiment corresponding to an integrated luminosity of 29 nb(-1). The differential production cross sections of the D*(+/-), D-+/-, and D-0 ((D) over bar (0)) mesons are presented in ranges of transverse momentum and pseudorapidity 4 < p(T) < 100 GeV and vertical bar eta vertical bar < 2.1, respectively. The results are compared to several theoretical calculations and to previous measurements.Peer reviewe

Observation of the Production of Three Massive Gauge Bosons at root s=13 TeV

The first observation is reported of the combined production of three massive gauge bosons (VVV with V = W, Z) in proton-proton collisions at a center-of-mass energy of 13 TeV. The analysis is based on a data sample recorded by the CMS experiment at the CERN LHC corresponding to an integrated luminosity of 137 fb(-1). The searches for individualWWW, WWZ, WZZ, and ZZZ production are performed in final states with three, four, five, and six leptons (electrons or muons), or with two same-sign leptons plus one or two jets. The observed (expected) significance of the combinedVVV production signal is 5.7 (5.9) standard deviations and the corresponding measured cross section relative to the standard model prediction is 1.02(-0.23)(+0.26). The significances of the individual WWW and WWZ production are 3.3 and 3.4 standard deviations, respectively. Measured production cross sections for the individual triboson processes are also reported

Measurement of B-c(2S)(+) and B-c*(2S)(+) cross section ratios in proton-proton collisions at root s=13 TeV

Peer reviewe