Browsing by Subject "MEMS"
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Item A New Approach in Tribological Characterization of High Performance Materials(2010-07-14) Fox, Grant R.This research conducts tribological investigation in three areas. The first area of research is to obtain basic understanding of tribological properties of high performance Inconel alloys. Pin-on-disk testing was conducted through a range of applied normal loads and sliding velocities in an unlubricated condition. Average friction coefficient, friction work, and specific wear rates were calculated from the data and microscopy techniques were used to observe and characterize wear mechanisms. Experimental results show a dependence of average coefficient of friction as a function of frictional work. Also shown is the wear rate dependence on frictional work, predicated by a wear mechanism change. This research gives a tribological baseline for high performance alloys. The second area of research is in the in situ spatial study of friction, complemented by monitoring changes in electrical contact resistance (ECR). Pin-on-disk testing of samples was done under low normal loads and velocities. Friction and electrical contact resistance measurements were taken spatially in the wear track during each friction cycle, giving a spatial evolution of friction and resistance change, in situ. Results show a lowering in the ECR under increased friction cycles, which was closely related to a change in the friction coefficient of the material. Using surface profilometry and X-ray Photoelectron Spectroscopy, we determined that the lowering of resistance is a result of surface modification through wear and development of a friction induced conductive tribo-film. This research provides a simple method for in situ monitoring of friction and solidifies a fundamental relationship between friction and contact resistance. The third area of research is the design of a variable force tribometer, incorporating the fundamental results demonstrated in the first two experiments. The creation of a novel testing apparatus to test materials under dynamic tribological conditions is given in detail. Simple experiments were performed on an Inconel sample and preliminary results show how dynamic normal and tangential forces affect the friction coefficient. These early results utilizing the variable force tribometer will lay the groundwork for more advanced research into the dynamic nature of friction.Item Design and analysis of a new sensing technique for casing joint validation through integrating turns measurement into a torque sensor(2012-12) Hall, Russell Ilus; Chen, Dongmei, Ph. D.Fossil fuels and their byproducts are a vital part of our economy, and society. Until renewable energy sources and energy storage technologies advance to the point where they are reliable and inexpensive, the US Economy will continue to depend upon fossil fuels. Current resources are being consumed, and the "easy to reach" reserves are becoming depleted. This leads to the requirement for more exploratory drilling, and the potential for more disasters like the recent Deepwater Horizon spill in the Gulf of Mexico. Drilling is the first of several steps in the creation of a productive oil or natural gas well. Completing a well involves casing the walls in concrete to prevent damage to the surrounding rock formations and to ensure that all of the oil or gas is captured without escaping to the surrounding environment. Ensuring the piping, which is used to case wells, is assembled correctly and to manufacturer's specifications is the focus of this study. Individual pipe sections are screwed together with a requirement for torque and number of turns. Each joint must be verified to ensure integrity, and minimize the possibility of a spill or leak. The torque measurement can be accomplished by a "torque sub", a sensor installed in-line with the drill string. The torque sub is a wireless sensor that transmits torque data to the control system for logging and display. This thesis defines the parameters required to integrate a "number of turns" measurement into an existing torque sub so that both parameters can be captured, recorded and reported using a single device. The Yost Engineering 3-Space Sensor was evaluated for use in this application. The configuration that gave the most accurate data was selected, along with the determination of some correction factors to account for site specific variation in the signals. A calibration algorithm is discussed, along with several unique methods for ensuring that the sensor output doesn't drift over the course of the joint make-up process.Item Design and Operation of Membrane Microcalorimeters for Thermal Screening of Highly Energetic Materials(2010-12-07) Carreto Vazquez, Victor 1976-Following several terrorist attacks that have occurred during this decade, there is an urgent need to develop new technologies for the detection of highly energetic materials that can represent an explosive hazard. In an effort to contribute to the development of these new technologies, this work presents the design aspects of a chip-scale calorimeter that can be used to detect an explosive material by calorimetric methods. The aim of this work is to apply what has been done in the area of chip-scale calorimetry to the screening of highly energetic materials. The prototypes presented here were designed using computer assisted design and finite element analysis tools. The design parameters were set to satisfy the requirements of a sensor that can be integrated into a portable system (handheld) for field applications. The design approach consisted of developing a sensor with thick silicon membranes that can hold micro-size samples and that can operate at high temperatures, while keeping the cost of the sensor low. Contrary to other high resolution systems based on thin-film membranes, our prototypes exhibit a contribution from addenda that is comparable to that from the sample, and hence they have lower sensitivity. However, using thick membranes offers the advantage of producing sensors strong enough for this application and that have significantly lower cost. Once the prototypes were designed, the fabrication was performed using standard microfabrication techniques. Finally, the operation of our prototypes was demonstrated by conducting thermal analysis of different liquid and solid samples.Item Design of a MEMS-based tunable graphene resonator with precision strain and force metrology(2016-05) Sun, Guoao; Cullinan, Michael; Akinwande, DejiMade of only on sheet of carbon atoms, graphene is the thinnest yet strongest material ever exist. Since its discovery in 2004, graphene have attracted tremendous research effort worldwide. Guaranteed by the superior electrical and excellent mechanical properties, graphene is the ideal building block for Nanoelectromechanical System (NEMS). However, one of the major challenges in producing highly accurate graphene-based nanoelectromechanical (NEMS) resonators is the poor fabrication repeatability of graphene-based NEMS devices due to small variations in the residual stress and initial tension of the graphene film. This has meant that graphene-based nanoelectromechanical resonators tend to have large variations in natural frequency and quality factor from device to device. However, by actively controlling the tension on the graphene resonator it is possible both to increase repeatability between devices and to increase the force/mass sensitivity of the nanoelectromechanical resonators produced. Such tension control makes it possible to produce electrometrical filters that can be precisely tuned over a frequency range of up to several orders-of-magnitude. In order to controllably strain the graphene resonator, a microelectromechanical system (MEMS) is designed and used to apply tension to the graphene. The MEMS device consists of a graphene resonator, electro-thermal actuator and two differential capacitive sensors. Using this setup, it is not only possible to tune the natural frequency of the graphene resonator, but also possible to perform high precision force and strain metrology on graphene beam. In addition to designing devices that can compensate for manufacturing errors in nanomanufactured devices, this thesis will present several methods that can greatly expand the scope and rate at which nanomaterials-based devices can be fabricated.Item Design, fabrication, and testing of a MEMS z-axis Directional Piezoelectric Microphone(2012-05) Kirk, Karen Denise; Hall, Neal A.; Neikirk, Dean P.Directional microphones, which suppress noise coming from unwanted directions while preserving sound signals arriving from a desired direction, are essential to hearing aid technology. The device presented in this paper abandons the principles of standard pressure sensor microphones, dual port microphones, and multi-chip array systems and instead employs a new method of operation. The proposed device uses a lightweight silicon micromachined structure that becomes “entrained” in the oscillatory motion of air vibrations, and thus maintains the vector component of the air velocity. The mechanical structures are made as compliant as possible so that the motion of the diaphragm directly replicates the motion of the sound wave as it travels through air. The microphone discussed in this paper achieves the bi-directionality seen in a ribbon microphone but is built using standard semiconductor fabrication techniques and utilizes piezoelectric readout of a circular diaphragm suspended on compliant silicon springs. Finite element analysis and lumped element modeling have been performed to aid in structural design and device verification. The proposed microphone was successfully fabricated in a cleanroom facility at The University of Texas at Austin. Testing procedures verified that the resonant frequency of the microphone, as expected, was much lower than in traditional microphones. This report discusses the theory, modeling, fabrication and testing of the microphone.Item Experimental study of the residual stress-induced self-assembly of MEMS structures during deposition(Texas A&M University, 2005-11-01) Kim, Sang-HyunThe possibility of using residual stresses favorably as a means of self-assembling MEMS during material deposition is experimentally investigated. Two atomic force microscope cantilevers are placed in contact at their free ends. Material is isothermally electroplated onto one (the deposition) cantilever, but no material is deposited onto the other (spring) cantilever. The deposited layer contains residual stresses that deform the deposition cantilever. The deposition cantilever in turn deforms the spring cantilever, thereby doing work in the spring cantilever and proving that the two structures can selfassemble during deposition processing. An insoluble nickel electroplating process and an all-sulfate nickel solution are used for the deposition. The deflection of the selfassembled cantilevers is measured in-situ as a function of the deposited thin film thickness through the optical method of atomic force microscopy. The experimental results are compared to an analytical model which consists of Euler-Bernoulli beam theory that is modified to account for moving boundaries as the material is deposited. The model accounts for the through-thickness variation of the intrinsic strain during the electroplating. Closed-form solutions are not possible, but numerical solutions are plotted for the cantilever deflection and work on the spring cantilever as functions of the deposition thickness.Item Methods to achieve wavelength selectivity in infrared microbolometers and reduced thermal mass microbolometers(2010-12) Jung, Joo-Yun, 1976-; Neikirk, Dean P., 1957-; Bank, Seth; Belkin, Mikhail; Hall, Neal; Rogers, Robert L.The use of a patterned resistive sheet as an infrared-selective absorber, including the effects of a mechanical support dielectric layer is discussed. Also, modified dielectric coated Salisbury Screen can improve both the wavelength selectivity and the speed of thermal response for microbolometers. These patterned resistive sheets and Modified dielectric coated Salisbury Screen are a modified form of classical Salisbury Screens that utilize a resistive absorber layer placed a quarter-wavelength in front of a mirror. These structures can show a narrower detection bandwidth when compared to conventional microbolometers. For a Modified dielectric coated Salisbury Screen for multi-spectral system, wavelength selectivity can be varied by changing the distance to the mirror, and for patterned resistive sheet, wavelength selectivity can be varied by changing the lithographically drawn parameters of the array. Hence, different pixels in a focal plane array can be designed to produce a “multi-color” infrared imaging system. Also, the thermal mass of microbolometer is reduced using patterned resistive structure.Item Micromachined in-plane acoustic pressure gradient sensors(2014-05) Kuntzman, Michael Louis; Hall, Neal A.; Champlin, Craig A; Driga, Mircea D; Hamilton, Mark F; Neikirk, Dean PThis work presents the fabrication, modeling, and characterization of two first-generation acoustic in-plane pressure gradient sensors. The first is a micromachined piezoelectric microphone. The microphone structure consists of a semi-rigid beam structure that rotates about torsional pivots in response to in-plane pressure gradients across the length of the beam. The rotation of the beam structure is transduced by piezoelectric cantilevers, which deflect when the beam structure rotates. Sensors with both 10 and 20-μm-thick beam structures are presented. An analytical model and multi-mode, multi-port network model utilizing finite-element analysis for parameter extraction are presented and compared to acoustic sensitivity measurements. Directivity measurements are interpreted in terms of the multi-mode model. A noise model for the sensor and readout electronics is presented and compared to measurements. The second sensor is a capacitive sensor which is comprised of two vacuum-sealed, pistons coupled to each other by a pivoting beam. The use of a pivoting beam can, in principle, enable high rotational compliance to in-plane small-signal acoustic pressure gradients, while resisting piston collapse against large background atmospheric pressure. A design path towards vacuum-sealed, surface micromachined broadband microphones is a motivation to explore the sensor concept. Fabrication of surface micromachined prototypes is presented, followed by finite element modeling and experimental confirmation of successful vacuum-sealing. Dynamic frequency response measurements are obtained using broadband electrostatic actuation and confirm a first fundamental rocking mode near 250 kHz. Successful reception of airborne ultrasound in air at 130 kHz is also demonstrated, and followed by a discussion of design paths toward improve signal-to-noise ratio beyond that of the initial prototypes presented. A method of localizing sound sources is demonstrated using the piezoelectric sensor. The localization method utilizes the multiple-port nature of the sensor to simultaneously extract the pressure gradient and pressure magnitude components of the incoming acoustic signal. An algorithm for calculating the sound source location from the pressure gradient and pressure magnitude measurement is developed. The method is verified by acoustic measurements performed at 2 kHz.Item Micromachined Optical and Acoustic Waveguide Systems for Advance Sensing and Imaging Applications(2014-07-08) Chang, Cheng-ChungEvolving from the IC fabrication processes, micromachining technologies allow mass production of 2D or 3D microstructures, which are otherwise difficult to achieve with traditional machining techniques. In this research, novel micromachining processes have been developed to enable new micro optical and acoustic waveguide systems for advanced optical sensing and acoustic imaging applications. The investigated applications include non-invasive cancer detection inside human body, in-field soil characterization, and time-delayed and multiplexed ultrasound and photoacoustic tomography. Micromachining technology enables miniaturized optical waveguide system for efficient light transmission. The small size and light-guiding capabilities are particularly useful for optical sensing at places deep inside the human body or underground. Two micromachined optical waveguide systems were fabricated and tested. The first one was used to conduct oblique incidence diffuse reflectance spectroscopy (OIDRS) for the determination of tumor margins on human pancreas specimens. The second one was used to conduct visible-near-infrared diffuse reflectance spectroscopy (VNIR-DRS) for extracting the compositional information of soil samples. Micromachining technology also makes it possible to utilize single-crystalline silicon as a structural material for acoustic wave propagation. It enables the development of high-performance integrated acoustic circuits and allows direct acoustic signal processing and control. The acoustic properties and propagation inside silicon waveguides were characterized, and the acoustic signal processing using micromachined acoustic waveguide system was investigated. Based on the results, two acoustic waveguide systems were designed and constructed. The first system utilized micromachined acoustic delay lines to passively delay acoustic signal thereby reducing the required transceivers and processing electronics; while the second system employed micromachined acoustic multiplexer to actively control the transmission of acoustic signals. Both techniques are expected to provide new solutions to reduce the complexity and cost of the acoustic receiver systems in ultrasound and photoacoustic imaging.Item Mitigating Wear on Surfaces Utilizing Self-Assembled Wear Passivating Films(2012-07-16) Jones, Ryan LaneControlling tribological interactions, such as friction and adhesion between contacting interfaces is critical for the advancement of technologies such as microelectromechanical systems (MEMS) devices. The challenge in MEMS device lubrication lies in the inherent nature of the material?s surface at the nanoscale as well as the nature of the surfaces typically used during experimentation. Device surfaces often display nanoscale roughness with surface asperities dictating the tribological properties between interfaces, yet the vast majority of past research has focused predominately on nanotribological studies of thin films on flat silicon substrates to model the behavior of these self-assembled wear-reducing coatings. New model surfaces have been manufactured and integrated into experiments in which surfaces with controlled asperity sizes act as more realistic models of MEMS surfaces. As friction and adhesion between real surfaces in sliding contact are dominated by the interactions of nanoscaled surface asperities, this research is an extension of previous work, moving beyond smooth surfaces by manufacturing and implementing new experimental platforms possessing controlled asperity sizes. The influence of asperity size on the tribological properties of these contacts is being studied for both native oxide and organosilane derivatized surfaces. These studies more readily mimic the conditions found at true asperity-asperity contacts. This research has aimed to develop new lubricant thin films that can effectively protect MEMS device surfaces during use with the long term goal of bringing MEMS devices out of the laboratory and into wide scale commercial use. This work investigates how self-assembled monolayers (SAMs) on curved surfaces can be utilized in manners that their analogs on flat surfaces cannot. SAMs on curved asperities can be used to trap short chain alcohols, which during contact may be released to function as an additional lubricant layer on the surface. Both atomic force microscopy and Fourier transform infrared spectroscopy have been employed to evaluate how chain disorder influences the protective function of these molecular lubricant layers on asperities. It was found that functionalized surfaces resisted wear and were able to operate under continuous scanning for longer time frames than unfunctionalized surfaces and that multicomponent films improved upon the performance of their base, single component analogs.Item Modeling and prototyping of a micromachined optical microphone(2010-12) Kuntzman, Michael Louis; Hall, Neal A.; Wilson, Preston S.A microelectromechanical systems (MEMS) optical microphone that measures the interference of light resulting from its passage through a diffraction grating and reflection from a vibrating diaphragm (JASA, v. 122, no. 4, 2007) is described. In the present embodiment, both the diffractive optical element and the sensing diaphragm are micromachined on silicon. Additional system components include a semiconductor laser, photodiodes, and required readout electronics. Advantages of this optical detection technique have been demonstrated with both omni-directional microphones and biologically inspired directional microphones. In efforts to commercialize this technology for hearing-aids and other applications, a goal has been set to achieve a microphone contained in a small surface mount package (occupying 2mm x 2mm x 1mm volume), with ultra-low noise (20 dBA), and broad frequency response (20Hz–20kHz). Such a microphone would be consistent in size with the smallest MEMS microphones available today, but would have noise performance characteristic of professional-audio microphones significantly larger in size and more expensive to produce. This paper will present several unique challenges in our effort to develop the first surface mount packaged optical MEMS microphone. The package must accommodate both optical and acoustical design considerations. Dynamic models used for simulating frequency response and noise spectra of fully packaged microphones are presented and compared with measurements performed on prototypes.Item Optimization of in-plane directional microphone(2015-08) Zha, Jingqiang; Hall, Neal A.; Masada, GlennThis report is aimed at optimization of the in-plane directional microphone. In chapter 1, a piezoelectric network model is presented. Then the network model is applied to a piezoelectric cantilever beam. Theoretical results are compared with simulation results to prove the network model. This piezoelectric cantilever beam also forms the basis of the XY directional microphone. In chapter 2, principles of XY directional microphone are explained at the beginning. Further analysis shows the expression related to signal-to-noise ratio, which is the optimization goal. ANSYS simulation is implemented to justify this expression. Based on that expression, suggestions are made to optimize the directional microphone. In chapter 3, proof of concept of a novel gyroscope directional microphone is explained. Gyroscopic effect is introduced at first. Then the result of in-plane directional microphone is presented. Finally, the expression for "amplification factor" is derived and selection of appropriate performance criterion could lead to improved sensitivity.Item Synthesis and characterization of carbon nanotubes using scanning probe based nano-lithographic techniques(2009-05-15) Gargate, Rohit VasantA novel process which does not require the traditional Chemical Vapor Deposition (CVD) synthesis techniques and which works at temperatures lower than the conventional techniques was developed for synthesis of carbon nanotubes (CNT). The substrates used for this study involved MEMS (Micro Electrical Mechanical Systems) elements and passive elements. These were coated with Fullerene using Physical Vapor Deposition or through a solution in an organic solvent. Catalyst precursors were deposited on these Fullerene coated substrates using ?wet processes?. These substrates were then heated using either the integrated microheaters or external heaters in an inert atmosphere to obtain CNT. Thus, in this process we tried to obviate the Chemical Vapor Deposition (CVD) process for synthesis of CNT (SWCNT and MWCNT). The synthesized CNT will be characterized using Scanning Electron Microscopy and Raman spectroscopy techniques. Also, conductivity measurements were carried out for the synthesized tubes using Dry (contact based) and Wet (electro-chemical) methods. This work also proves the concept for the feasibility for a portable hand held instrument for synthesis of CNT with tunable ?on demand? chirality.Item Thermodynamic and transport properties of self-assembled monolayers from molecular simulations(Texas A&M University, 2006-04-12) Aydogmus, TurkanThe purpose of the work is to employ molecular simulation to further extend the understanding of Self-Assembled Monolayers (SAMs), especially as it relates to three particular applications: organic-inorganic composite membranes, surface treatments in Micro-Electro-Mechanical Systems (MEMS) and organic-surface-modified Ordered Mesoporous Materials (OMMs). The first focus area for the work is the use of SAMS in organic-inorganic composite membranes for gas separations. These composite membranes, recently proposed in the literature, are based on the chemical derivatization of porous inorganic surfaces with organic oligomers. Our simulations achieve good qualitative agreement with experiment in several respects, including the improvement in the overall selectivity of the membrane and decrease in the permeance when increasing the chain length. The best improvement in the overall solubility selectivity is reached when the chains span throughout the pore. The second application focus is on the use of SAMs as coatings in MEMS devices. The work focuses on the modeling of adhesion issues for SAM coatings at the molecular level. It is shown that as the chain length is increased from 4 to 18 carbon atoms, the adhesion forces between two monolayers at the same separations decreases. The third application focus is on the use of SAMs for tailoring surface and structural properties of OMMs, in particular, porous silicas. A molecular study of structural and surface properties of a silica material with a 5 nm pore size, modified via chemical bonding of organosilanes with a range of sizes (C4, C8 and C18) is presented. Grand canonical MC simulations are employed to obtain nitrogen adsorption isotherms for unmodified and modified MCM-41 material models. Furthermore, the density profiles of alkyl chains and nitrogen molecules are analyzed to clarify the differences in the adsorption mechanisms in unmodified and modified materials. The position of the capillary condensation steps gradually shifted to lower pressure values with the increase in size of the bonded ligands, and this shift was accompanied by a gradual disappearance of the hysteresis loop. As the length of the bonded ligands is increased, a systematic decrease in the pore diameter is observed and the multi-layer adsorption mechanism in modified model materials diminishes.