Film bulk acoustic resonator pressure sensor with self temperature reference

A novel film bulk acoustic resonator (FBAR) with two resonant frequencies which have opposite reactions to temperature changes has been designed. The two resonant modes respond differently to changes in temperature and pressure, with the frequency shift being linearly correlated with temperature and pressure changes. By utilizing the FBAR's sealed back trench as a cavity, an on-chip single FBAR sensor suitable for measuring pressure and temperature simultaneously is proposed and demonstrated. The experimental results show that the pressure coefficient of frequency for the lower frequency peak of the FBAR sensors is approximately −17.4 ppm kPa−1, while that for the second peak is approximately −6.1 ppm kPa−1, both of them being much more sensitive than other existing pressure sensors. This dual mode on-chip pressure sensor is simple in structure and operation, can be fabricated at very low cost, and yet requires no specific package, therefore has great potential for applications

Integration of sol-gel frequency agile materials for tunable RF devices

This thesis focuses on the use of high permittivity tunable dielectrics and more specifically sol-gel ferroelectric thin films for low cost, high performance tunable devices such as varactors and filters at RF and microwave frequencies. The top- ics covered include measurement techniques for the characterization of tunable dielectrics at low and microwave frequencies, fabrication processes, electrical and acoustic modeling of thin film ferroelectric varactors, performance optimization using conductive electrodes, realization of tunable microwave circuits and inte- gration of tunable dielectrics with conventional bulk acoustic wave resonators (FBAR). A lead strontium titanate (PST) sol-gel ferroelectric varactor is designed, elec- trically and acoustically modeled and fabricated, displaying dielectric tunability of "'-'75%. A two port automatic extraction technique using MATLAB allowing the de-embedding of parasitic connecting transmission lines, as well as parasitic pads has been developed and presented, yielding accurate dielectric permittivity values in good agreement with literature. The potential factors that may compro- mise the electrical performance of the ferroelectric tunable varactor are analyzed and a novel Au/Ti02 bottom electrode stack process is proposed and shown to improve the RF performance of the tunable varactor lowering the overall metaliza- tion resistance and improving performance, compared to the commonly used Pt electrodes. To establish the possibility of tunable microwave systems integrating sol-gel ferroelectric tunable varactors the following novel microwave devices are designed, modeled and fabricated: A ferroelectric varactor-based RF resonant switch, integrating a thin film sol- gel PST ferroelectric varactor with a high Q micro-machined inductor is fabri- cated. An insertion loss of ",1.5 dB and isolation of ",18 dB have been achieved for a single 7 GHz resonant switch with a device area of 0.6 mm x 1 mm. The intrinsic performance limitations of this type of device due to the ferroelectric thin film are discussed and the implementation of cascaded switches and state-of-the- art ferroelectric materials for further improvement of performance of this device, have been considered and simulated. Tunable band-stop resonators and notch filters using sol-gel PST ferroelectric varactors in a coplanar waveguide (CPW) defected ground structure are fabricated and measured. The PST varactors tune single resonators and 3-pole band-stop filters, operating at the center frequency of 4 and 8 GHz, having a maximum rejection of more than 13.8 dB at the stop band, while the insertion loss at the pass band is less than 3 dB. Full-wave analysis is performed to identify the critical points, where PST varactors are implemented to adjust the resonance frequency of the devices. An optimized fabrication process allows for fabrication of a 3-stage filter with a maximum rejection of 28 dB, albeit with a reduced tuning range, possibly due to DC bias path leakage. Finally, a fabrication approach where a ferroelectric varactor is integrated with a conventional zinc oxide (ZnO) acoustic wave resonator is presented. The approach avoids the piezoelectric thin film degradation due to the ferroelectric annealing by first fabricating the ferroelectric varactor and superimposing the conventional FBAR on top of it. The tuning of the series resonant frequency of a conventional ZnO FBAR with a ferroelectric varactor is demonstrated. Field induced deformation limits the maximum shift of the resonance to 0.45% at 1.5 GHz, for 41% tunability of the ferroelectric varactor, suggesting a big scope for possible improvements in performance by improving the design and fabrication. VIII.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Analysis and Fabrication of MEMS Tunable Piezoelectric Resonators

Piezoelectric MEMS resonators are being used with increased frequency for many applications, operating as frequency sources in sensors, actuators, clocks and filters. Compensation for the effects of manufacturing variation and a changeable environment, as well as a desire for frequency-hopping capabilities, have brought forth a need for post-process tuning of the resonant frequency of at these devices, in particular clocks and filters manufactured at the MEMS scale. This work applies a shunt capacitor tuning concept to three different types of piezoelectric MEMS resonators: bending beam devices, surface acoustic wave devices, and film bulk acoustic wave devices, in order to solve this tuning need across a wide range of the frequency spectrum (single Kilohertz to tens of Gigahertz). Questions about how the material and design parameters of these resonators affect the resonant frequencies and tunability of the devices are further discussed for each of the designs. In addition to the theoretical modeling, the fabrication steps necessary for processing the piezoelectric MEMS bending devices, specifically utilizing PZT thin films and an interdigitated design, are developed. Results of many fabrication trials are discussed, and finalized process plans for fabricating quality thin film PZT and PZT interdigitated devices are provided

In-liquid bulk acoustic wave resonators for biosensing applications

Gravimetric sensors based on thin-film bulk acoustic wave (BAW) resonators operating between 1-5 GHz have tremendous potential as biosensors because they are inexpensive, label-free, fast and highly sensitive. The two main challenges in this objective are: the conventional longitudinal mode resonance in $\textit{c}$-axis oriented piezoelectric films suffers from more than 90% damping in liquid; the alternative is the shear mode resonance, with lower damping in liquid but which requires an inclined $\textit{c}$-axis piezoelectric film, a process that is still not fully scalable. In this thesis, seed layers such as AlN with mainly (103) orientations are used to promote the growth of homogeneously inclined $\textit{c}$-axis ZnO (inclination of up to $\sim$45$^{\circ}$) films without significant equipment modifications. Sputtered Al electrodes with controlled roughness are then substituted for the parasitic AlN seed layers to improve the electromechanical performance. At a substrate temperature, T$_{s}$ = 100 $^{\circ}$C, an optimum surface roughness of 9.2 nm yields homogeneously inclined $\textit{c}$-axis ZnO films with angles $\sim$25$^{\circ}$. Solidly mounted resonators (SMRs) operating in a shear mode at $\sim$1.1 GHz with the Al electrodes have resonant quality factors (Q$_{r}$) higher than 150 and effective electromechanical coupling coefficients, k$^{2}$$_{eff}$, of 2.9-3.4%, which are improved from only 2.2% with the AlN seed layers. This shear mode of the ZnO SMRs has mass sensitivities, S$_{m}$ of (4.9 $\pm$ 0:1) kHz$\cdot$cm$^{2}$/ng and temperature coefficients of frequency (TCF) of -(66$\pm$2) ppm/K. Viscosity sensing is carried out with different ethanol-water compositions; the SMRs are functionalised and successfully used in the detection of Rabbit Immunoglobin G. To mitigate the longitudinal mode damping in water, multi-wall carbon nanotube (CNT) forests are grown by chemical vapour deposition (CVD) at 600 $^{\circ}$C using Fe/Al layers on the active area of inclined $\textit{c}$-axis AlN SMRs designed for improved thermal and chemical stability. The dense CNT forest (with 0.5/8 nm Fe/Al) of $\sim$15 μm height provides an acoustic isolation to DI water with only 50-70% drop in the longitudinal mode Q$_{r}$ compared to 99% in SMRs without the CNTs. Mass loading is still detected and demonstrated by detecting bovine serum albumin (BSA) in water whereas with forest heights of $\sim$30 μm and no significant frequency shifts due to mass attachment are observed. With the CNTs the longitudinal mode is shown for the first time to be more sensitive to mass ($\sim$7x) than the shear mode in liquid, highlighting the potential of CNTs for the large scale use of the longitudinal mode for in-liquid sensing

Monolithically Integrated Acoustic Resonators on CMOS for Radio-Frequency Circuit Applications

Wireless communication circuits rely on the use of high-quality passive elements (inductor-capacitor resonant tanks) for the implementation of selective filters and high-purity frequency references (oscillators). Typically available CMOS, on-chip passives suffer from high losses, primarily inductors, and consume large areas that cannot be populated by transistors leading to a significant area penalty. Mechanical resonators exhibit significantly lower losses than their electrical counterparts due to the reduced parasitic loss mechanisms in the mechanical domain. Efficient transduction schemes such as the piezoelectric effect allow for simple electrical actuation and read-out of such mechanical resonators. Piezoelectric thin-film bulk acoustic resonators (FBARs) are currently among the most promising and widely used mechanical resonator structures. However, FBARs are currently only available as off-chip components, which must be connected to CMOS circuitry through wire-bonding and flip-chip schemes. The use of off-chip interfaces introduces considerable parasitics and significant limitations on integration density. Monolithic integration with CMOS substrates alleviates interconnect parasitics, increases integration density and allows for area sharing whereby FBARs reside atop active CMOS circuitry. Close integration of FBARs and CMOS transistors can also enable new circuit paradigms, which simultaneously leverage the strengths of both components. Described here, is a body of work conducted to integrate FBAR resonators with active CMOS substrates (180nm and 65nm processes). A monolithic fabrication method is described which allows for FBAR devices to be constructed atop the backend small CMOS dies through low thermal-budget (< 300°C) post-processing. Stand-alone fabricated devices are characterized and the extracted electrical model is used to design two oscillator chips. The chips comprise amplifier circuitry that functions along with the integrated FBARs to achieve oscillation in the 0.8-2 GHz range. The chips also include test structures to assess the performance of the underlying CMOS transistors before and after the resonator post-processing. A successful FBAR-CMOS oscillator is demonstrated in 65nm CMOS along with characterization of FBARs built on CMOS. The approach presented here can be used for experimenting with more complex circuits leveraging the co-integration of piezoelectric resonators and CMOS transistors

Advances in piezoelectric thin films for acoustic biosensors, acoustofluidics and lab-on-chip applications

Recently, piezoelectric thin films including zinc oxide (ZnO) and aluminium nitride (AlN) have found a broad range of lab-on-chip applications such as biosensing, particle/cell concentrating, sorting/patterning, pumping, mixing, nebulisation and jetting. Integrated acoustic wave sensing/microfluidic devices have been fabricated by depositing these piezoelectric films onto a number of substrates such as silicon, ceramics, diamond, quartz, glass, and more recently also polymer, metallic foils and bendable glass/silicon for making flexible devices. Such thin film acoustic wave devices have great potential for implementing integrated, disposable, or bendable/flexible lab-on-a-chip devices into various sensing and actuating applications. This paper discusses the recent development in engineering high performance piezoelectric thin films, and highlights the critical issues such as film deposition, MEMS processing techniques, control of deposition/processing parametres, film texture, doping, dispersion effects, film stress, multilayer design, electrode materials/ designs and substrate selections. Finally, advances in using thin film devices for lab-on-chip applications are summarised and future development trends are identified.The authors acknowledge support from the Innovative electronic Manufacturing Research Centre (IeMRC) through the EPSRC funded flagship project SMART MICROSYSTEMS (FS/01/02/10), Knowledge Transfer Partnership No KTP010548, EPSRC project EP/L026899/1, EP/F063865/1; EP/F06294X/1, EP/P018998/1, the Royal Society-Research Grant (RG090609) and Newton Mobility Grant (IE161019) through Royal Society and NFSC, the Scottish Sensing Systems Centre (S3C), Royal Society of Edinburgh, Carnegie Trust Funding, Royal Academy of Engineering-Research Exchange with China and India, UK Fluidic Network and Special Interest Group-Acoustofluidics, the EPSRC Engineering Instrument Pool. We also acknowledge the National Natural Science Foundation of China (Nos. 61274037, 51302173), the Zhejiang Province Natural Science Fund (No. Z11101168), the Fundamental Research Funds for the Central Universities (No. 2014QNA5002), EP/D03826X/1, EP/ C536630/1, GR/T24524/01, GR/S30573/01, GR/R36718/01, GR/L82090/01, BBSRC/E11140. ZXT acknowledges the supports from the National Natural Science Foundation of China (61178018) and the NSAF Joint Foundation of China (U1630126 and U1230124) and Ph.D. Funding Support Program of Education Ministry of China (20110185110007) and the NSAF Joint Foundation of China (Grant No. U1330103) and the National Natural Science Foundation of China (No. 11304209). NTN acknowledges support from Australian Research Council project LP150100153. This work was partially supported by the European Commission through the 6th FP MOBILIS and 7th FP RaptaDiag project HEALTH-304814 and by the COST Action IC1208 and by the Ministerio de Economía y Competitividad del Gobierno de España through projects MAT2010-18933 and MAT2013-45957R

Based acoustic waves microsensor for the detection of bacteria in complex liquid media

Cette thèse s’inscrit dans le cadre d’une cotutelle internationale entre l’Université de Bourgogne Franche-Comté en France et l’Université de Sherbrooke au Canada. Elle porte sur le développement d'un biocapteur miniature pour la détection et la quantification de bactéries dans des milieux liquides complexes. La bactérie visée est l’Escherichia coli (E. coli), régulièrement mise en cause dans des épidémies d'infections alimentaires, et parfois meurtrière. La géométrie du biocapteur consiste en une membrane en arséniure de gallium (GaAs) sur laquelle est déposé un film mince piézoélectrique d’oxyde de zinc (ZnO). L'apport du ZnO structuré en couche mince constitue un réel atout pour atteindre de meilleures performances du transducteur piézoélectrique et consécutivement une meilleure sensibilité de détection. Une paire d'électrodes déposée sur le film de ZnO permet de générer, sous une tension sinusoïdale, des ondes acoustiques se propageant dans le GaAs, à une fréquence donnée. La face arrière de la membrane, quant à elle, est fonctionnalisée avec une monocouche auto-assemblée (SAM) d'alkanethiols et des anticorps contre l’E. coli, conférant la spécificité de la détection. Ainsi, le biocapteur bénéficie à la fois des technologies de microfabrication et de bio-fonctionnalisation du GaAs, déjà validées au sein de l’équipe de recherche, et des propriétés piézoélectriques prometteuses du ZnO, afin d’atteindre potentiellement une détection hautement sensible et spécifique de la bactérie d’intérêt. Le défi consiste à pouvoir détecter et quantifier cette bactérie à de très faibles concentrations dans un échantillon liquide et/ou biologique complexe. Les travaux de recherche ont en partie porté sur les dépôts et caractérisations de couches minces piézoélectriques de ZnO sur des substrats de GaAs. L’effet de l’orientation cristalline du GaAs ainsi que l’utilisation d’une couche intermédiaire de Platine entre le ZnO et le GaAs ont été étudiés par différentes techniques de caractérisation structurale (diffraction des rayons X, spectroscopie Raman, spectrométrie de masse à ionisation secondaire), topographique (microscopie à force atomique), optique (ellipsométrie) et électrique. Après la réalisation des contacts électriques, la membrane en GaAs a été usinée par gravure humide. Une fois fabriqué, le transducteur a été testé en air et en milieu liquide par des mesures électriques, afin de déterminer les fréquences de résonance pour les modes de cisaillement d’épaisseur. Un protocole de bio-fonctionnalisation de surface, validé au sein du laboratoire, a été appliqué à la face arrière du biocapteur pour l’ancrage des SAMs et des anticorps, tout en protégeant la face avant. De plus, les conditions de greffage d’anticorps en termes de concentration utilisée, pH et durée d’incubation, ont été étudiées, afin d’optimiser la capture de bactérie. Par ailleurs, l’impact du pH et de la conductivité de l’échantillon à tester sur la réponse du biocapteur a été déterminé. Les performances du biocapteur ont été évaluées par des tests de détection de la bactérie cible, E. coli, tout en corrélant les mesures électriques avec celles de fluorescence. Des tests de détection ont été réalisés en variant la concentration d’E. coli dans des milieux de complexité croissante. Différents types de contrôles ont été réalisés pour valider les critères de spécificité. En raison de sa petite taille, de son faible coût de fabrication et de sa réponse rapide, le biocapteur proposé pourrait être potentiellement utilisé dans les laboratoires de diagnostic clinique pour la détection d’E. coli.Abstract: This thesis was conducted in the frame of an international collaboration between Université de Bourgogne Franche-Comté in France and Université de Sherbrooke in Canada. It addresses the development of a miniaturized biosensor for the detection and quantification of bacteria in complex liquid media. The targeted bacteria is Escherichia coli (E. coli), regularly implicated in outbreaks of foodborne infections, and sometimes fatal. The adopted geometry of the biosensor consists of a gallium arsenide (GaAs) membrane with a thin layer of piezoelectric zinc oxide (ZnO) on its front side. The contribution of ZnO structured in a thin film is a real asset to achieve better performances of the piezoelectric transducer and consecutively a better sensitivity of the detection. A pair of electrodes deposited on the ZnO film allows the generation of acoustic waves propagating in GaAs under a sinusoidal voltage, at a given frequency. The backside of the membrane is functionalized with a self-assembled monolayer (SAM) of alkanethiols and antibodies against E. coli, providing the specificity of the detection. Thus, the biosensor benefits from the microfabrication and bio-functionalization technologies of GaAs, validated within the research team, and the promising piezoelectric properties of ZnO, to potentially achieve a highly sensitive and specific detection of the bacteria of interest. The challenge is to be able to detect and quantify these bacteria at very low concentrations in a complex liquid and/or biological sample. The research work was partly focused on the deposition and characterization of piezoelectric ZnO thin films on GaAs substrates. The effect of the crystalline orientation of GaAs and the use of a titanium/platinum buffer layer between ZnO and GaAs were studied using different structural (X-ray diffraction, Raman spectroscopy, secondary ionization mass spectrometry), topographic (atomic force microscopy), optical (ellipsometry) and electrical characterizations. After the realization of the electrical contacts on top of the ZnO film, the GaAs membrane was micromachined using chemical wet etching. Once fabricated, the transducer was tested in air and liquid medium by electrical measurements, in order to determine the resonance frequencies for thickness shear mode. A protocol for surface bio-functionalization, validated in the laboratory, was applied to back side of the biosensor for anchoring SAMs and antibodies, while protecting the top side. Furthermore, different conditions of antibody immobilization such as the concentration, pH and incubation time, were tested to optimize the immunocapture of bacteria. In addition, the impact of the pH and the conductivity of the solution to be tested on the response of the biosensor has been determined. The performance of the biosensor was evaluated by detection tests of the targeted bacteria, E. coli, while correlating electrical measurements with fluorescence microscopy. Detection tests were completed by varying the concentration of E. coli in environments of increasing complexity. Various types of controls were performed to validate the specificity criteria. Thanks to its small size, low cost of fabrication and rapid response, the proposed biosensor has the potential of being applied in clinical diagnostic laboratories for the detection of E. coli