44 research outputs found

    Analytical Modeling for the Bending Resonant Frequency of Multilayered Microresonators with Variable Cross-Section

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    Multilayered microresonators commonly use sensitive coating or piezoelectric layers for detection of mass and gas. Most of these microresonators have a variable cross-section that complicates the prediction of their fundamental resonant frequency (generally of the bending mode) through conventional analytical models. In this paper, we present an analytical model to estimate the first resonant frequency and deflection curve of single-clamped multilayered microresonators with variable cross-section. The analytical model is obtained using the Rayleigh and Macaulay methods, as well as the Euler-Bernoulli beam theory. Our model is applied to two multilayered microresonators with piezoelectric excitation reported in the literature. Both microresonators are composed by layers of seven different materials. The results of our analytical model agree very well with those obtained from finite element models (FEMs) and experimental data. Our analytical model can be used to determine the suitable dimensions of the microresonator’s layers in order to obtain a microresonator that operates at a resonant frequency necessary for a particular application

    Dynamic Characteristics of Electrostatically Actuated Shape Optimized Variable Geometry Microbeam

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    Modeling and Control of MEMS-based Multi-layered Prestressed Piezoelectric Cantilever Beam

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    Piezoelectric materials are the preferred smart materials for sensing and actuation in the form of micro and nano-engineering structures like beams and plates. Cantilever beams play a significant role as key components in atomic force microscopy and bio and chemical sensors. Adding an active layer such as lead zirconate titanate (PZT) thin-film to form smart cantilever beams with sensing and actuation capabilities is highly desirable to facilitate miniaturization, enhance performance and functionali- ties such as enabling on-chip high-speed parallel AFM. During the micro-fabrication process, residual stresses develop in the different layers of the cantilever beam, causes initial deflection. The residual stress in the different layers of the cantilever beam and the application of voltage to the PZT thin-film affects their dynamics. This the- sis investigates the dynamic behaviour and develops a control technique and a novel charge readout circuit to improve the performance of a micro-fabricated multi-layer prestressed piezoelectric cantilever beam as an actuator and a deflection sensor. Firstly, the fabrication process of a unimorph PZT cantilever beam is explained. A low thermal budget Ultra-high vacuum e-beam evaporated polysilicon thin-film (UHVEEpoly) process is used for the fabrication of multi-layered PZT cantilever beam in d31 mode. The sharp peaks at resonant frequencies in the frequency response of the PZT cantilever beam show very little damping and a large settling time of the cantilever beam. Secondly, the dynamic behaviour of the prestressed PZT cantilever beam is in- vestigated subjected to change in driving voltage. Experimental investigations show a shift in resonant frequencies of a PZT cantilever beam. However, there is no reported mathematical model that predicts the shift in resonance frequencies of a multi-layered prestressed piezoelectric cantilever beam subjected to a change in driving voltage. This work developed a mathematical model with experimental val- idation to estimate the shift in resonance frequencies of such cantilever beams with the change in the driving voltage. A very good agreement between the model predic- tions and experimental measurements for the frequency response of the cantilever beam at different driving voltages has been obtained. A novel linear formulation has been developed to predict the shift in resonance frequencies of the PZT can- i tilever beam for a wide range of driving voltages. The formulation shows that the shift in resonance frequencies of a multi-layered prestressed piezoelectric cantilever beam per unit of applied voltage is dependent on geometric parameters and material properties. Thirdly, a robust resonant controller has been designed and implemented to re- duce the settling time of a highly vibrating PZT cantilever beam. The controller design is based on a mixed negative-imaginary, passivity, and a small-gain approach. The motivation to design a resonant controller using the above-mentioned analyti- cal framework is its bandpass nature and the use of velocity feedback, as the charge collected from a vibrating PZT cantilever beam gives the velocity information of the beam. The proposed controller design results in finite gain stability for a pos- itive feedback interconnection between two stable linear systems with a large gain and phase margin. Experimental results demonstrate that the designed resonant controller is able to effectively damp the first resonant mode of a cantilever, signifi- cantly reducing settling time from 528 ms to 32 ms. The robustness of the designed resonant controller is tested against changes in the cantilever beam dynamics due to residual stress variation and or stress variation due to driving voltage. Finally, to facilitate the miniaturization of on-chip sensors and parallel high- speed AFM, a single layer of a PZT thin-film in a cantilever beam is used as a deflection sensor and an actuator instead of bulky optical deflection sensors. A novel charge readout circuit is designed for deflection sensing by capturing the electrical charge generated due to the vibration of the PZT beam. The signal-to-noise ratio and sensitivity analysis of the readout circuit shows similar results compared to the commercially available optical deflection sensors. Our work highlights very important aspects in the dynamic behaviour and perfor- mance of a multi-layered prestressed piezoelectric cantilever beam. The agreement between the proposed theoretical formulation and experimental investigations in modeling, control design, and a novel readout circuit will provide the platform for further the development and miniaturization of microcantilever-based technologies, including on-chip parallel HS-AFM

    PLATE AND MICRO-SCALE STRUCTURES: ANALYSIS AND EXPERIMENTS

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    Within this work, plate and micro-scale structures are studied. Methodologies are developed to analyze the laminate stiffness, residual forces, moments and stresses, and deformations in these thin composite laminate structures to facilitate better designs, enable device characterization, and enhance device performance. Specific devices studied in this work are cantilevered and clamped-clamped PZT resonators of various lengths, widths, and laminate thicknesses. In order to better understand the behavior of these devices, analytical and experimental methods have been developed. The analytical methods are based on linear and nonlinear beam and plate models, with reduced-order models developed to study dynamic behavior. Parameter identification techniques have been applied to characterize residual stress induced deformation of micro-scale structures. Extensive data has been collected through careful experiments to aid the development of identification techniques and to determine device deflections and individual device residual stress values. An analytical model has been developed to describe the behavior of thin composite laminate plate-like structures. Since an exact solution for plate mode shapes does not exist for all boundary conditions, appropriate combinations of orthogonal functions are assumed for the mode shapes of a plate with all edges simply supported or all edges clamped. These functions make the development of reduced-order models possible for these boundary conditions. In addition, these plate-like structures are asymmetric isotropic laminates. A procedure was applied to calculate the stiffness, forces and moments for a laminate comprised of multiple isotropic layers regardless of symmetry. Parametric identification techniques were developed to identify system parameters and to characterize residual stress induced deformation in plate and micro-scale structures. These techniques are based on linear and nonlinear beam models and reduced-order methodologies, and they enable the first characterization of residual stress in PZT micro scale devices post-fabrication and release processing. The obtained results indicate that post-release residual stress measurements in devices can be considerably different from the corresponding measurements made before release

    A long-period fibre grating sensor for respiratory monitoring

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    In the current clinical practice of non-invasive mechanical ventilation (NIV), continuous monitoring of respiratory volumes is based on the measurement of air flow through an oronasal mask or mouthpiece. Errors in respiratory-volumes monitoring and patientventilator asynchrony due to the inevitable air leaks from the mask may lead to insufficient ventilation and/or damage of the airway system. Therefore, clinician’s observations of the chest wall expansions are required, but they are subjective, time consuming and strongly dependent on clinician’s experience [1]. We present and validate a method for the measurement of respiratory volumes by a single long period fibre-grating (LPG) sensor of bending. This method is grounded on the hypothesis that the volume of the inhaled air can be correlated with the change in a local torso curvature in a ribs area with stiff underlying tissues. Here, we explain the working principle of the LPG sensors, a monochromatic interrogation scheme, a two-step calibration-test measurement procedure and present results that establish a linear correlation between the change in the local rib-cage curvature and the change in the lung volume. Results also show good sensor accuracy in measurements of tidal and minute respiratory volumes for all clinically relevant breathing volumes [2]. Additionally, we examine the possibility of using the rib-cage movement signal measured by a single LPG sensor as a new way to provide a trigger to the ventilator. Our preliminary results on healthy volunteers provide the statistical evidence of the 200 ms lag of the pneumotechometer with respect to the fibre-optic signal. The proposed single-sensor method is non-invasive, simple, low-cost and easy to implement. Moreover this method does not suffer from the flaws of air-flow measurements, it eliminates the need for chest movement observation by clinicians and can be implemented on both male and female patients. The preliminary results are promising and indicate that the method proposed here could be used in NIV.V International School and Conference on Photonics and COST actions: MP1204, BM1205 and MP1205 and the Second international workshop "Control of light and matter waves propagation and localization in photonic lattices" : PHOTONICA2015 : book of abstracts; August 24-28, 2015; Belgrad

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

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    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

    Geometry and Material Nonlinearity Effects on Static and Dynamics Performance of MEMS

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    Nonlinear behavior of micro-mechanical systems is an interesting and little explored area of research. Although, micro-system technologies is new and fast developing area, there is little work carried out on modeling and simulation of MEMS devices which concerns their non-linear behavior. Nonlinear modeling of MEMS devices is based on observations related to the micro-systems performance which is often far away from linearity in MEMS devices. There are two types of components that are extensively used in MEMS design: micro-beams (cantilever type) and micro-plates. Manufacturing as well as usage of these components are advantageous to MEMS applications. The main applications of such structures include micro-sensors and micro-actuators. Large deflection of micro-cantilever beams under electrostatic force is studied. Pull in voltage as a phenomenon was widely studied in conjunction with MEMS. Large deflection of micro-cantilever beams under electrostatic field with the application of a voltage very close to pull in voltage is studied in this thesis and it is shown that pull in voltage provided by the nonlinear analysis is different from the one yielded by the linear analysis and more accurate when compared to the experimental values. Large deflection of curved micro-cantilever beams sometimes encountered as AFM probes was studied to investigate the variation of sensitivity under large deflection of originally curved micro-cantilever beams. Results show that curved or straight beams experience same sensitivity which decreases with the increase of deflection. Micro-plate pressure sensors are widely used in industrial applications. Deposition of several different layers creates residual stress in those layers. The residual stress is measured indirectly by Stoney equation. It is shown that Stoney equation yields under normal circumstances up to 40% error in the value of the predicted stress and the experimental results do not match any numerical analysis. An extraction method was developed to calculate the stress distribution in each layer based on the experimentally measured deflection. In summary, the work proves on few general configurations that the non-linear analysis of microstructures yields results that are closer to the results of the experimental investigations when compared to the ones yielded by the linear analyses. Analytical solutions of the differential equations were sought using Lie symmetry method

    Modelling and Characterization of Guiding Micro-structured Devices for Integrated Optics

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    In this thesis we show several modelling tools which are used to study nonlinear photonic band-gap structures and microcavities. First of all a nonlinear CMT and BPM were implemented to test the propagation of spatial solitons in a periodic device, composed by an array of parallel straight waveguides. In addition to noteworthy theoretical considerations, active functionalities are possible by exploiting these nonlinear regimes. Another algorithm was developed for the three-dimensional modelling of photonic cavities with cylindrical symmetry, such as microdisks. This method is validated by comparison with FDTD. We also show the opportunity to confine a field in a region of low refractive index lying in the centre of a silicon microdisk. High Q-factor and small mode volumes are achieved. Finally the characterization of microdisks in SOI with Q-factor larger than 50000 is presente

    A Whispering Gallery Mode Microlaser Biosensor

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    A biological sensor, commonly referred to simply as a biosensor, is a transducing device that allows quantitative information about specific interactions, analytes or other biological parameters to be monitored and recorded. The development of biosensors that are low-cost, reliable and simple to use stand to facilitate fundamental breakthroughs and revolutionize current medial diagnostic methods. Notably, there remains an unmet need for developing in-vivo biosensors, allowing insights to be directly gained from the precise location of biological interactions within the human body. Over the last two decades, whispering gallery modes (WGM) within microresonators have emerged as a promising technology for developing highly sensitive and selective biosensors, among many other applications. However, significant work remains to allow WGM sensors to make the transition from primarily being used within purely research environments to real-world applications. Specifically, one of the key limiting factors is the requirement of an external phase-matched coupling scheme (such as a tapered or angle polished optical fiber, prism or waveguide) to excite the WGMs, despite these devices displaying tremendous sensing performance. One way to lift this dependency on complex interrogation schemes is introduce a gain medium, such as a fluorescent dye or coating the resonator with quantum dots for example, thereby rendering it active and allowing remote excitation and collection of the WGM spectrum. Using active WGM resonators has allows the creation of novel sensing opportunities such as tagging, tracking and monitoring forces from insides living cells. Applications like these could not have been realized using external phase-matched coupling schemes. The biosensing platform presented here is based on combining WGM within active microspherical resonators with microstructured optical fibers (MOF). The MOF enables both the excitation and collection method for the WGM spectrum while simultaneously providing a robust and easy to manipulate dip sensing architecture that has the potential to address the unmet need for real time labelfree in-vivo sensing by combining with a catheter. The platform is investigated fundamentally as well as experimentally, beginning with the development of an analytical model that is able to generate the WGM spectrum of active microspherical resonators. This provides the opportunity to pinpoint the optimal choice of resonator to be used for undertaking refractive index based biosensing. Specifically by being able to extract the quality (Q) factor, a measure of the resonance linewidth, and refractive index sensitivity from the WGM spectrum, the optimal combination of resonator parameters (diameter and resonator refractive index) can be identified for optimizing the resonators sensing performance. Further, the availability, biocompatibility and cost, as well as fabrication requirements can be also considered when selecting the ideal resonator. Next, the inherently lower Q-factors observed in active resonators compared to their passive counterparts (i.e. resonators without a gain medium) is examined using a combination of theoretical, experimental and imaging methods. Through this examination process, the inherent asphericity of the resonator is identified as being the limiting factor on the Q-factor of active resonators, with its effect most notably being observed for measurements made in the far field. Experimentally, the first demonstration of this platform operating as a biosensor is presented by monitoring the well-documented specific interaction of Biotin/neutravidin in pure solutions. Including identifying ways to improve sensing performance and lower the detection limit, such as operating the resonator above its lasing threshold. Although, it is noted that in its current form, this platform is best suited for the monitoring of protein, preferably occurring in higher concentrations, until further improvements to the sensing performance can be implemented. However, the robust design coupled with its ability to provide access to previously difficult to obtain locations provides an insight into its potential future application capabilities. Finally, the extension of the platform to operating in complex samples, namely undiluted human serum, is outlined. By self-referencing the platform, through the addition of a second, almost identical resonator (only varying in its surface functionalization) into one of the remaining vacant holes on the tip of the fiber, the effects of non-specific binding as well as changes in local environmental conditions (i.e. temperature fluctuations), can be eliminated.Thesis (Ph.D.) -- University of Adelaide, School of Physical Sciences, 201
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