Integrated sensors for process monitoring and health monitoring in microsystems

This thesis presents the development of integrated sensors for health monitoring in Microsystems, which is an emerging method for early diagnostics of status or “health” of electronic systems and devices under operation based on embedded tests. Thin film meander temperature sensors have been designed with a minimum footprint of 240 m × 250 m. A microsensor array has been used successfully for accurate temperature monitoring of laser assisted polymer bonding for MEMS packaging. Using a frame-shaped beam, the temperature at centre of bottom substrate was obtained to be ~50 ºC lower than that obtained using a top-hat beam. This is highly beneficial for packaging of temperature sensitive MEMS devices. Polymer based surface acoustic wave humidity sensors were designed and successfully fabricated on 128° cut lithium niobate substrates. Based on reflection signals, a sensitivity of 0.26 dB/RH% was achieved between 8.6 %RH and 90.6 %RH. Fabricated piezoresistive pressure sensors have also been hybrid integrated and electrically contacted using a wire bonding method. Integrated sensors based on both LiNbO3 and ZnO/Si substrates are proposed. Integrated sensors were successfully fabricated on a LiNbO3 substrate with a footprint of 13 mm × 12 mm, having multi monitoring functions for simultaneous temperature, measurement of humidity and pressure in the health monitoring applications

Microfabricated Optofluidic Ring Resonators for Sensitive, High-Speed Detection of Volatile Organic Compounds

The development of microfabricated sensors and sensor arrays for volatile organic compounds (VOC) and their evaluation as detectors in micro-scale gas chromatographic (μGC) instrumentation are described. Initial efforts explored the discrimination of VOCs with arrays of chemiresistors (CR) employing interface layers of thiolate-monolayer-protected gold nanoparticles (MPNs) or tin-oxide nanowires (NWs). The response diversity of several possible MPN-CR arrays was found to exceed that of the NW-CR array, and was not enhanced by combining the former with the latter. The next study demonstrated that the response diversity of MPN-CR arrays could be enhanced moderately by combining them with arrays of mass-sensitive MPN-coated thickness-shear-mode resonators. However, the analysis of binary VOC mixtures was not satisfactory even with the best of these multi-transducer arrays. A new type of optical vapor sensor was then created: the microfabricated optofluidic ring resonator (μOFRR). This sensor combines vapor sensing and fluidic transport functions in a monolithic microstructure comprising a hollow, vertical SiOx cylinder (250 μm i.d.) with a central quasi-toroidal mode-confinement section, grown and partially released from a Si substrate. It also integrates fluidic-interconnection and fiber-optic probe alignment features. High-Q whispering gallery modes (WGM) generated with a tunable near-IR laser exhibited shifts in resonant wavelength, λWGM, from polymer swelling and refractive index changes as vapors reversibly partitioned into the thin sorptive-polymer film lining the cylinder. Remarkably high sensitivity and rapid responses were obtained with this μOFRR sensor installed downstream from a single μGC separation column and a two-dimensional μGC subsystem. Since MPN films exhibit localized surface plasmon resonance (LSPR) they also have the potential to serve as interface layers in optical sensor arrays. Indeed, it was shown that VOC discrimination was possible by probing an MPN film at just two wavelengths flanking its LSPR absorbance maximum in a custom-built reflectance measurement system. In a first attempt to adapt multi-wavelength plasmonic sensing to the μOFRR platform, measured shifts in λWGM from an MPN coated μOFRR sensor were shown to be proportional to concentration for several VOCs. Results suggest that arrays of MPN-coated μOFRR sensors show great promise as detectors in single- and multi-dimensional μGC systems.PHDApplied PhysicsUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/111492/1/keesc_1.pd

Vacuum and Hermetic Packaging of MEMS using Solder

This work explores the use of solder as a material for wafer-level vacuum packaging of MicroElectroMechanicalSystems (MEMS). Two bonding techniques were developed and characterized: a standard solder bond and an advanced solder bond based on transient liquid phase (TLP) bonding. Solder was also used as a release layer as well as bond layer for forming transferred thin-film packages. Several different standard solder alloy / under bump metallization combinations were used for wafer bonding. Only the Au-Sn solder alloy, with its low tin content, proved to be compatible with the thermal limitations of commercial wafer bonders. The bond is formed at 300 °C in under an hour and has a shear strength of 28 MPa. It was used to create packages (2.3 mm X 2.3 mm X 0.5 mm) with integrated Pirani gauges. The pressures were as low as 200 mTorr and showed a worst-case leak rate of 1.5.10-15 atm.cc.s-1. TLP solder bonding was investigated because it is more compatible with the long thermal time-constant of commercial wafer bonders. Au-In and Ni-Sn TLP solder bonds were used to create vacuum packages (2.3 mm X 2.3 mm X 0.5 mm) with integrated Pirani gauges. The Ni-Sn and Au-In packages were formed at 300 °C and 200 °C, have measured shear strengths of 12.4 and 24.4 MPa, showed package pressures of 200 mTorr and 150 mTorr, and worst-case leak rates of 1.7.10-15 atm.cc.s-1 and 0.1.10-15 atm.cc.s-1. The design rules for creating bonds with these techniques are presented. Outgassing and getter activation were studied. Package pressures were reduced to 20 mTorr by outgassing for 24 hours before bonding. It was shown that titanium getters can be activated at 200 °C, enabling a MEMS vacuum packaging process with a maximum temperature of 200 °C. Solder was used to transfer thin-film electroplated nickel packages as small as 250 μm wide, 250 μm long, and 20 μm thick. A thin nickel film was electroplated over a lead-free solder transfer layer on a carrier wafer and then simultaneously bonded and transferred to a device wafer at 300 °C for 1 hour with a yield of greater than 99%.Ph.D.Electrical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/58520/1/welchw_1.pd

Simulation and Fabrication of Three Novel Micromechanical Sensors

This work focuses on the simulation, fabrication and characterization of novel microdevices for chemical and biological sensors for improved sensitivity, enhanced performance and applicability. Specifically, microbridge and microcoil sensors have been fabricated via advanced microfabrication technologies. Due to the potential application in chemical and biological sensing, the growth of gold and platinum nanowires during an electrolysis process have also been investigated. A microbridge can be considered as the head-to-head fusion of two cantilevers and the middle of the bridge would deform in a way similar to a microcantilever. The microbridge sensing device is more stable than the microcantilever, especially in turbulent or vibrational conditions, since both ends are fixed. The trade-off is the low ΔR/R change (sensitivity) of the microbridge compared to that of the microcantilever. Simulation of the microbridge has been conducted via Finite Element Analysis (FEA). The width, thickness and doping level of the piezoresistor play an important part in the sensitivity of the microbridge. Based on the simulation results and following standard microfabrication technology, microbridges have been fabricated. The detection of Hg2+ based on the microbridge platform was investigated for sensor validation. The microcoil hygrometer can be used as a universal tool for the detection of chemical species by depositing a chemical specific coating on one side of the coil. The coil movement can be readily observed by the human eye and it advances as a cost-effective and power-free device. A micro- or nano-scale sized coil provides an outstanding sensor platform with improved dynamic response, greatly reduced size, and the integration of micromechanical components with on-chip electronic circuitry. Following standard microfabrication techniques, an SiO2/Si/SU-8 microcoil has been fabricated. After surface modification by treating the coil with aminopropyltriethoxysilane (APS), the microcoil was exposed to acetic acid vapor in air for characterization. This microcoil device has a potential to be used as a novel microsensor for the detection of chemical and biological species both in air and in solutions. A self-assembled approach to grow gold and platinum nanowires across the gap of two electrodes on a surface using an electrolysis process has been investigated. In this process, the anode electrode is oxidized to form nanowires on the cathode. The DC offset, AC signal frequency and the space between the two electrodes all play important roles in the growth of the nanowires

FLEXIBLE LOW-COST HW/SW ARCHITECTURES FOR TEST, CALIBRATION AND CONDITIONING OF MEMS SENSOR SYSTEMS

During the last years smart sensors based on Micro-Electro-Mechanical systems (MEMS) are widely spreading over various fields as automotive, biomedical, optical and consumer, and nowadays they represent the outstanding state of the art. The reasons of their diffusion is related to the capability to measure physical and chemical information using miniaturized components. The developing of this kind of architectures, due to the heterogeneities of their components, requires a very complex design flow, due to the utilization of both mechanical parts typical of the MEMS sensor and electronic components for the interfacing and the conditioning. In these kind of systems testing activities gain a considerable importance, and they concern various phases of the life-cycle of a MEMS based system. Indeed, since the design phase of the sensor, the validation of the design by the extraction of characteristic parameters is important, because they are necessary to design the sensor interface circuit. Moreover, this kind of architecture requires techniques for the calibration and the evaluation of the whole system in addition to the traditional methods for the testing of the control circuitry. The first part of this research work addresses the testing optimization by the developing of different hardware/software architecture for the different testing stages of the developing flow of a MEMS based system. A flexible and low-cost platform for the characterization and the prototyping of MEMS sensors has been developed in order to provide an environment that allows also to support the design of the sensor interface. To reduce the reengineering time requested during the verification testing a universal client-server architecture has been designed to provide a unique framework to test different kind of devices, using different development environment and programming languages. Because the use of ATE during the engineering phase of the calibration algorithm is expensive in terms of ATE’s occupation time, since it requires the interruption of the production process, a flexible and easily adaptable low-cost hardware/software architecture for the calibration and the evaluation of the performance has been developed in order to allow the developing of the calibration algorithm in a user-friendly environment that permits also to realize a small and medium volume production. The second part of the research work deals with a topic that is becoming ever more important in the field of applications for MEMS sensors, and concerns the capability to combine information extracted from different typologies of sensors (typically accelerometers, gyroscopes and magnetometers) to obtain more complex information. In this context two different algorithm for the sensor fusion has been analyzed and developed: the first one is a fully software algorithm that has been used as a means to estimate how much the errors in MEMS sensor data affect the estimation of the parameter computed using a sensor fusion algorithm; the second one, instead, is a sensor fusion algorithm based on a simplified Kalman filter. Starting from this algorithm, a bit-true model in Mathworks Simulink(TM) has been created as a system study for the implementation of the algorithm on chip

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