The temperature coefficient of frequency (TCF), electromechanical coupling coefficient (K2) and surface acoustic wave (SAW) velocity are the major factors when choosing the substrates for surface acoustic wave devices. There exist a wide range for the designer to controll the above factors. This thesis adopted several methods to change the properties of SAW devices. First, the SAW velocity is increased using aluminum nitride (AlN) thin films deposited on z-cut LiNbO3 substrates. Besides, the ST-quartz is adopted as substrate for comparison to clarify the temperature characteristic of AlN itself. The well-known positive TCF material, silicon dioxide (SiO2), is also deposited on z-cut LiNbO3 substrates for the purpose of improving the TCF of SAW devices. Finally, the optimal piezoelectric bilayer structures will be conducted for the improvement of the properties of SAW devices on LiNbO3 substrate. AlN and SiO2 thin films are selected to be deposited on z-cut LiNbO3 and ST-cut quartz substrates using the reactive RF magnetron sputtering. The characteristics of AlN thin films are evaluated using the analyses of XRD, SEM and AFM. The optimized growth parameters of highly c-axis oriented AlN films deposited on LiNbO3 substrate are sputtering pressure of 3.5 mTorr, nitrogen concentration (N2/N2+Ar) of 60%, RF power density of 8.1 W/cm2 and substrate temperature of 400¢J. On the other hand, the optimal parameters for highly c-axis oriented AlN films deposited on quartz substrate are sputtering pressure of 15 mTorr, nitrogen concentration of 30%, RF power density of 8.1 W/cm2 and substrate temperature of 400¢J. In addition, the interdigital transducers (IDTs) are fabricated on LiNbO3, AlN/LiNbO3, SiO2/LiNbO3, quartz and AlN/quartz substrates, respectively. The characteristic parameters of SAW devices are measured by Hewlett-Packard (HP) 8720 network analyzer. For SiO2/LiNbO3 SAW devices, the SiO2 thin films reveal the compensation of TCF, but the surface wave velocity remain almost unchanged. For AlN/quartz SAW devices, the positive temperature coefficient of AlN is clarfied by taking ST-quartz substrates as comparison. For AlN/LiNbO3 SAW devices, the characteristic improvements of frequency increase and TCF compensation of LiNbO3 SAW devices are achieved at the same time.

The composition-dependent Curie temperature and bias-dependant dielectric permittivity of Barium Strontium Titanate (BST) makes it very attractive for tunable application in the RF/Microwave regime. In this research work, the performance of BST varactors fabricated on the conventional Pt/Ti/SiO2/Si bottom electrode stack were compared with those fabricated using chemical vapor deposited Nanocrystalline Diamond (NCD) as the diffusion barrier layer instead of SiO2. The varactors fabricated on NCD films displayed much better symmetry in capacitance-voltage behavior and better overall quality factors than varactors fabricated on SiO2. The improvement in performance can be attributed to existence of stable interfaces in the devices fabricated on NCD which reduced the bottom electrode losses at high frequencies. The SiO2 based BST varactors on the other hand displayed better reliability and breakdown fields. The main purpose of this research work is to develop a robust Metal Insulator Metal (MIM) structure to achieve better all round performance of BST varactors. In the second part of this research work, the prospect of developing diamond based layered Surface Acoustic Wave (SAW) devices using Ba0.8Sr0.2TiO3 as the piezoelectric layer is investigated. Structural characterization of BST thin films deposited on Si/NCD/Pt and Si/SiO2/Ti/Pt stack were performed using X-Ray Diffraction (XRD) and Atomic Force Microscopy (AFM). Cross-sectional studies on the two stacks were performed using Scanning Electron Microscopy (SEM). X-Ray Mapping (XRM) was then done to ascertain the quality of the interfaces and to check for interdiffusion between layers. MIM structures in the Coplanar Waveguide (CPW) configuration were fabricated using conventional lithography and etching techniques for high frequency measurements. The performance of the fabricated varactors was characterized from 100 MHz to 1 GHz. For the SAW application, structural characterization of Ba0.8Sr0.2TiO3 on Chemical Vapor Deposited (CVD) diamond was done and the deposition procedure was optimized to obtain thick BST films. SAW bandpass filters and resonators were designed wherein the device geometry was varied over a wide range in order to characterize the variation in device performance with geometry. Finally interdigital capacitor structures were fabricated and used for conducting Curie temperature measurements on the deposited BST films in order to determine the operation range of the deposited BST films.

Surface acoustic wave (SAW) sensors detect chemical and biological species by monitoring the shifts in frequency of surface acoustic waves generated on piezoelectric substrates. Incorporation of nanomaterials having increased surface area as sensing layer have been effective in improving the sensitivity as well as miniaturization of SAW sensors. Selectivity, sensitivity and speed of response are the three primary aspects for any type of sensor. This dissertation focuses on design and development of SAW devices with novel transducer configurations employing nanomaterial sensing layers for enhanced sensing, improved selectivity, and speed of response. The sensing mechanism in these SAW sensors is a complex phenomenon involving interactions across several different length and time scales. Surface acoustic wave propagation at the macro-scale is influenced by several kinetic phenomena occurring at the molecular scale such as adsorption, diffusion, reaction, and desorption which in turn depend on the properties of nanomaterials. This suggests the requirement of a multi-scale model to effectively understand and manipulate the interactions occurring at different length scales, thereby improving sensor design. Sensor response modeling at multiple time and length scales forms part of this research, which includes perturbation theories, and simulation techniques from finite element methods to molecular-level simulations for interpreting the response of these surface acoustic wave chemical and biosensors utilizing alloy nanostructures as sensing layers. Molecular modeling of sensing layers such as transition metal alloy nanoclusters and nanowires is carried out to gain insights into their thermodynamic, structural, mechanical and dynamic properties. Finite element technique is used to understand the acoustic wave propagation at the macroscale for sensing devices operating at MHz frequencies and with novel transducer designs. The findings of this research provide insights into the design of efficient surface acoustic wave sensors. It is expected that this work will lead to a better understanding of surface acoustic wave devices with novel transducer configurations and employing nanomaterial sensing layers.

No description available.

In this thesis, the author proposed and developed nanostructured materials based Surface Acoustic Wave (SAW) and conductometric transducers for gas sensing applications. The device fabrication, nanostructured materials synthesis and characterization, as well as their gas sensing performance have been undertaken. The investigated structures are based on two structures: lithium niobate (LiNbO3) and lithium tantalate (LiTaO3). These two substrates were chosen for their high electromechanical coupling coefficient. The conductometric structure is based on langasite (LGS) substrate. LGS was selected because it does not exhibit any phase transition up to its melting point (1470°C). Four types of nanostructured materials were investigated as gas sensing layers, they are: polyaniline, polyvinylpyrrolidone (PVP), graphene and antimony oxide (Sb2O3). The developed nanostructured materials based sensors have high surface to volume ratio, resulting in high sensitivity towards di¤erent gas species. Several synthesis methods were conducted to deposit nanostructured materials on the whole area of SAW based and conductometric transducers. Electropolymerization method was used to synthesize and deposit polyaniline nanofibers on 36° YX LiTaO3 and 64° YX LiNbO3 SAW substrates. By varying several parameters during electropolymerization, the effect on gas sensing properties were investigated. The author also extended her research to successfully develop polyaniline/inorganic nanocomposites based SAW structures for room temperature gas sensing applications. Via electrospinning method, PVP fibres and its composites were successfully deposited on 36° YX LiTaO3 SAW transducers. Again in this method, the author varied several parameters of electrospinning such as distance and concentration, and investigated the effect on gas sensing performance. Graphene-like nano-sheets were synthesized on 36° YX LiTaO3 SAW devices. This material was synthesized by spin-coating graphite oxide (GO) on the substrate and then exposin g the GO to hydrazine to reduce it to graphene. X-ray photoelectron spectroscopy (XPS) and Raman characterizations showed that the reduced GO was not an ideal graphene. This information was required to understand the properties of the deposited graphene and link its properties to the gas sensing properties. Thermal evaporation method was used to grow Sb2O3 nanostructures on LGS conductometric transducers. Using this method, different nanoscale structures such as nanorods and lobe-like shapes were found on the gold interdigitated transducers (IDTs) and LGS substrate. The gas sensing performance of the deposited nanostructured Sb2O3 based LGS conductometric sensors was investigated at elevated temperatures. The gas sensing performance of the investigated nanostructured materials/SAW and conductometric structures provide a way for further investigation to future commerciallization of these types of sensors.

Phenylalanine hydroxylase (PAH, EC: 1.14.16.1) is a non-heme iron tetrahydropterin-dependent monooxygenase that maintains phenylalanine (L-Phe) homeostasis via conversion of L-Phe to L-Tyr. PAH is an allosteric enzyme that converts from an inactive T-state to an active R-state upon addition of substrate, L-Phe. Allosteric activation is correlated with physical and structural changes within the enzyme and a large activation energy. Crystal structures of PAH have not identified the location of the allosteric effector binding site. Herein, we report computational protein mapping efforts using the FTmap algorithm and experimental site-directed mutagenesis studies designed to define and screen possible L-Phe allosteric binding sites. Mass spectroscopic analysis of PAH proteolytic fragments obtained after photo-crosslinking with 2-azido-3-phenylpropanoate overlapped with one computationally derived allosteric binding pocket containing residues 110-120 and 312-317. Ligand docking studies, fluorescence measurements, binding affinity and activity assays on wild-type and mutant enzymes further characterized the shape and specificity of this pocket. Thermodynamic studies using surface acoustic wave (SAW) biosensing determined the affinity of L-Phe for the allosteric site. Two L-Phe binding sites were observed upon SAW titrations, corresponding to the active and allosteric sites respectively ( K D,app^on 113 ± 12 µM active site, K D,app^on 680 ± 20 µM allosteric site). Site-directed mutagenesis was performed to prepare mutant enzymes containing a single tryptophan (L-Trp) residue. The fluorescence signatures of each of the three native L-Trp residues in PAH were determined by titrations with L-Phe. Trp187 primarily reports L-Phe induced allosteric conformational changes, while Trp120 reports active site L-Phe binding. Trp326 reports small signals of both active and allosteric site changes. Variable temperature stopped-flow fluorescence kinetic studies elucidated a working mechanism for L-Phe allosteric activation of PAH. Fluorescent signals from wild-type, single, and double L-Trp PAH mutants have been used to build kinetic mechanisms for the L-Phe binding in each subunit and subsequent active site reorganization or allosteric conformational change. In these mechanisms, the enzyme has reduced activity (1-2% of wtPAH) until both L-Phe induced active and allosteric site conformational changes have occurred. Failure of either activation step prevents enzyme turnover and is the chemical-based cause of the metabolic condition phenylketonuria.

This thesis focuses on the theory, fabrication, and characterization of 2-port surface acoustic wave (SAW) resonators, as well as the application of their Fabry-Pérot resonance modes for strain sensing. The thesis includes three articles. In the first article, a fabrication method for high frequency SAW devices using traditional UV photolithography equipment is developed. It is well known that SAW sensors become more sensitive at higher frequencies but realizing high frequency devices requires small features which challenge existing photolithography methods. The proposed process is a modified version of a previously reported tri-layer lift-off photolithography process intended for Si or SiO2 substrates which allows for compatibility with materials that are piezoelectric and pyroelectric, often used as the substrate in SAW devices. The process uses a lithographic tri-layer consisting of layers of lift-off resist (LOR) on the bottom, back anti-reflection coating (BARC) in the middle, and photoresist (PR) on top, improving resolution by a factor of two over traditional lift-off photolithography techniques. We demonstrate the fabrication of a SAW device with an interdigital transducer (IDT) pitch of 4 μm (minimum feature size of 1 μm) on 128o Y-X cut lithium niobate, whose operating frequency is measured as 994.5 MHz. The 2-Port SAW devices that are used in subsequent chapters are fabricated using this process. The second article proposes a method of analyzing acoustic Fabry-Pérot spectra, by analogy with optical cavities, to determine key SAW parameters. In our experiment, 2-port SAW resonators, consisting of two interdigital transducers (IDTs) laterally separated by a free surface cavity length, are used to generate SAWs on 128o Y-X lithium niobate that are trapped between the two IDTs which also act as Bragg reflectors. Fabry-Pérot cavity peaks can be observed through the electrical S11 (reflection) spectrum measured on one IDT, hence a 2-Port resonator is equivalent to an acoustic Fabry-Pérot cavity/resonator. Measurements of the free spectral range and linewidths are then fitted to linear models to obtain the free surface velocity and attenuation of SAW waves, as well as the reflection of interdigital transducers (IDTs), all of which are crucial design parameters. Our method of analyzing Fabry-Pérot spectra provides a convenient method for determining key characteristics of SAW waves and cavities. In the third article, a surface acoustic wave (SAW) strain sensor based on measuring acoustic Fabry-Pérot resonance peaks from a 2-port SAW resonator is demonstrated. A theoretical analysis is proposed to estimate the frequency sensitivity to strain of IDT and cavity resonances and to predict strain distributions in both the cavity and IDT regions of a 2-port SAW resonator bonded to a tapered cantilever beam. The frequency stability of cavity resonance peaks for fabricated 2-port SAW resonators of different cavity length are measured and analyzed to determine the cavity length which exhibits maximum frequency stability. A cross-correlation analysis technique is then introduced to improve the detection of the frequency shift of SAW resonances and enable multimode frequency shift detection. The measured frequency sensitivity to strain of the cavity resonances of a resonator 10 mm in length (operating frequency = 97.7 MHz) was found to be -103.2 ± 0.2 Hz/με while demonstrating excellent linearity (R2 = 0.9999). By considering a minimum signal to noise ratio (SNR) of 3 dB, the device exhibits a minimum strain resolution of only 234 nε.

Surface Acoustic Wave (SAW) devices have been under research for over half a century due to their excellent performance characteristics in the fields of signal processing and communications. In particular, it has been show that SAW devices can operate as sensors that are both wireless and passive. For a sensor that is wireless, it is important to develop a coding scheme that allows for the identification of an individual sensor in a multiple sensor environment. For SAW sensors, orthogonal frequency coding (OFC) has been demonstrated as a method to provide a large number of unique identification codes. This system relies on an array of frequency selective reflectors (chips) in the SAW propagation path. The reflectors are ordered such that no two SAW sensors contain an array of reflection gratings in the same frequency order. One way to increase the number of usable codes in an OFC sensor is to increase the number of OFC chips on the sensor. With this technique it is necessary to increase the delay between the transducer and the OFC chips while keeping the length of the device small. Multiple surface wave propagation tracks can be utilized to slightly increase the width of the die instead of the length. This research aims to investigate methods to extend delay time in a coded SAW device by utilizing two propagation tracks. It will be shown that the reflective multistrip coupler (RMSC) can accomplish this goal with low loss. The design, fabrication, and characterization of the RMSC will be given with applications shown in an OFC SAW device.

No description available.

Les travaux décrits dans ce mémoire ont pour but de conduire à la réalisation de capteurs et de filtres à ondes élastiques de surface (SAW) innovants, passifs et sans fil, dédiés à une utilisation en environnement sévère. Différentes structures de composants SAW sont alors étudiées. Les caractéristiques générales, telles que les pertes d’insertion ou les bandes passantes relatives atteignables, des structures usuelles (résonateurs, lignes à retard, LCRF, filtres en échelle…) sont connues de l’homme de l’art. Cependant, pour concevoir un dispositif SAW qui respecte les critères d’un cahier des charges donné, il est impératif de définir le comportement spécifique de chaque dispositif avant son envoi en production.Pour ce faire, des modèles numériques sont développés, qui incluent à la fois la possibilité d’analyser le comportement de systèmes à la géométrie complexe (filtres en échelles, transducteurs apodisés) et qui prennent en compte la présence de phénomènes perturbateurs (modes transverses, pertes liées à la nature des matériaux). La comparaison entre les calculs numériques et les mesures a mis en avant l’adéquation des résultats expérimentaux et de calculs.La mise en place de ces outils permet le développement de capteurs et filtres SAW innovants grâce à une analyse numérique rapide et fiable de leur comportement.Ainsi, l’étude de résonateurs et capteurs dédiés à une utilisation à des températures excédant les 700°C est menée. Il est démontré qu’en dépit de son inhomogénéité, le Ba2TiSi2O8 est un matériau adapté à la réalisation de SAW soumis à des températures élevées pour des fréquences de l’ordre de 300 MHz jusqu’au GHz.Par ailleurs, une structure disposant d’un transducteur à trois doigts par longueur d’ondes est utilisée dans le but de réaliser des résonateurs insensibles aux effets de la directivité lorsque la température évolue. Cette même configuration a mis en exergue la possibilité de réaliser des capteurs n’utilisant qu’un seul résonateur (contre au moins deux jusqu’à présent). Ce dernier point permet de limiter l’encombrement des composants et résout la problématique du vieillissement différentiel des structures.Un second type de capteurs, passifs et sans fil, fondés sur l’utilisation d’un seul SAW et dédiés à la mesure d’hygrométrie, a été étudié. Dans cette nouvelle configuration, un SAW de type LCRF est utilisé comme transpondeur et la zone sensible est externalisée. La sensibilité des modes (de plus d’un MHz) à la variation d’un élément capacitif ou d’une antenne dipôle a été mise en avant numériquement. En pratique, la fabrication des dispositifs a montré une variation différentielle de plusieurs centaines de kHz des résonances selon la condition électrique appliquée à l’un des ports.Finalement, des filtres, dédiés aux applications stratégiques, agiles en fréquence sont réalisés. L’objectif de faire varier la fréquence centrale des dispositifs au cours de leur fonctionnement est atteinte en modifiant les conditions électriques appliquées aux réflecteurs. Deux types de tirage en fréquence sont observés : un glissement fin, de quelques ‰ de la fréquence centrale, cyclique, et un saut de fréquences lié au glissement et à l’ouverture de la bande de Bragg des miroirs aux hautes fréquences. La fabrication des structures et leur connexion à des interrupteurs MEMS validé la faisabilité de la structure.Ces travaux mettent en lumière les capacités de prédiction du comportement des structures SAW grâce au développement de logiciels dédiés. De plus, l’étude et la réalisation de filtres et capteurs innovants ouvre la voie à de nouvelles fonctionnalités. / This thesis aims at designing innovative, passive and wireless surface acoustic waves (SAW) sensors and filters, dedicated to harsh environments. Several types of SAW components are consequently studied. The main characteristics, such as insertion losses or relative bandwidth, of usual structures (resonators, delay lines, LCRF, ladder filters…) are known by men of the art. However, to design a SAW device that respects specific requirements, the definition of the proper behavior of each device must be established before the manufacturing.For this purpose, numerical models are developed. Not only they include the possibility to analyse he beha-vior of systems with complex geometry (ladder filters, apodised transducers) but they take into account disturbing phenomena (transverse modes, losses due to the intrinsic nature of the materials). The comparison between computations and measures points out the match between experimental results and calculations.The implementation of these tools allows the development of innovative SAW sensors and filters thanks to a fast and reliable numerical analysis of their behavior.Thus, the design of resonators and sensors dedicated to a use at temperatures exceeding 700°C is studied. It is demonstrated that despite its inhomogeneity, Ba2TiSi2O8 is suitable for the manufacturing of SAW devices subject to high temperatures and in a frequency range from 300 MHz to the GHz.Furthermore, a structure composed of a three electrodes per wavelength transducer is used to produce re-sonators that are not subject to directivity effects when the temperature changes. This configuration offers the possibility to design sensors that use a single resonator (versus at least two until now). This last point makes smaller components possible and solves the question of a differential aging of the structures.A second type of sensors, also passive and wireless, dedicated to humidity measurements, based on the use of a single SAW, is studied. In this new configuration, a LCRF is used as a transponder and the sensitive area is outsourced. The mode sensitivity (of more than a MHz) to the variation of a capacitance or a dipole antenna is numerically brought to light. In practice, the device manufacturing showed a differential variation of the resonances of about 600 kHz depending on the electric condition applied to one of the ports.Finally, filters, dedicated to strategic applications, with frequency agility are designed. The purpose is to make the frequency vary depending on the electrical conditions applied to the mirrors. Two kinds of agility are identified : a slight sliding, of a few ‰ of the initial central frequency, periodic, and a frequency jump due to the shift of the Bragg band to the high frequencies. The manufacturing of some structures and their connection to MEMS switches attest the feasibility of such a structure.This work highlights the ability to predict the behavior of SAW structures thanks to the development of dedicated software. Moreover, the analysis and the manufacturing of innovative sensors and filters pave the way to new functionalities.