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

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

Gallium Nitride Integrated Microsystems for Radio Frequency Applications.

The focus of this work is design, fabrication, and characterization of novel and advanced electro-acoustic devices and integrated micro/nano systems based on Gallium Nitride (GaN). Looking beyond silicon (Si), compound semiconductors, such as GaN have significantly improved the performance of the existing electronic devices, as well as enabled completely novel micro/nano systems. GaN is of particular interest in the “More than Moore” era because it combines the advantages of a wide-band gap semiconductor with strong piezoelectric properties. Popular in optoelectronics, high-power and high-frequency applications, the added piezoelectric feature, extends the research horizons of GaN to diverse scientific and multi-disciplinary fields. In this work, we have incorporated GaN micro-electro-mechanical systems (MEMS) and acoustic resonators to the GaN baseline process and used high electron mobility transistors (HEMTs) to actuate, sense and amplify the acoustic waves based on depletion, piezoelectric, thermal and piezo-resistive mechanisms and achieved resonance frequencies ranging from 100s of MHz up to 10 GHz with frequency×quality factor (f×Q) values as high as 1013. Such high-performance integrated systems can be utilized in radio frequency (RF) and microwave communication and extreme-environment applications.PHDElectrical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/135799/1/azadans_1.pd

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

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

Fabrication and characterization of AlN thin film bulk acoustic wave resonator

This dissertation presents the fabrication and characterization of the AlN thin film bulk acoustic wave resonator (FBAR). The bulk acoustic wave (BAW) resonators and filters have been considered the most promising devices used in the frequency control and wireless communication field when the performance frequency is up to GHz range. AlN is a piezoelectric material with hexagonal crystal structure. Some of its properties such as high longitudinal acoustic wave velocity (~11000m/s), high thermal conductivity, and high thermal and chemical stability make it a suitable material to fabricate the thin film bulk acoustic wave resonator.In this study, first, the background that includes the concepts of the FBAR resonators and filters, the piezoelectricity, the material properties of some of the piezoelectric materials and the MEMS techniques is introduced. Following the introduction, the fabrication and characterization of the AlN thin film, the composite BAW resonator and membrane type FBAR are presented. AlN thin films deposited under various sputtering deposition conditions have been investigated and characterized. X-ray diffraction (XRD) and scanning electron microscopy (SEM) characterization results show that the highly c-axis oriented AlN thin films have been deposited on the Si and sapphire substrate at the appropriate conditions. The effective piezoelectric coefficient d33eff and the mechanical properties such as the hardness and the reduced elastic constant of the AlN thin film in the four-layer composite resonator have been measured by the single beam laser interferometer and nano-indentation methods, respectively. Then, the transfer matrix method is developed to characterize the impedances and electromechanical properties of the multilayer FBAR and composite BAW resonator. The effects of the type and thickness of the electrodes and support layers on the resonance frequency and effective electromechanical coupling coefficient are discussed. The resonance frequency control and tuning methods including the connection to the external circuits and the incorporation of the support SiO2 layer are also discussed. In addition, the vector network analyzer has been utilized to measure the resonance frequency response of the four-layer composite BAW resonator and the material properties have been characterized from the experimental data. Lastly, the accomplishments of this study are summarized and future perspectives are provided