In recent years there has been a huge increase in the growth of communication systems such as mobile phones, wireless local area networks (WLAN), satellite navigation and various other forms of wireless data communication that have made analogue frequency control a key issue. The increase in frequency spectrum crowding and the increase of frequency into microwave region, along with the need for minimisation and capacity improvement, has shown the need for the development of high performance, miniature, on-chip filters operating in the low to medium GHz frequency range. This has hastened the need for alternatives to ceramic resonators due to their limits in device size and performance, which in turn, has led to development of the thin film electro-acoustics industry with surface acoustic wave (SAW) and bulk acoustic wave (BAW) filters now fabricated in their millions. Further, this new technology opens the way for integrating the traditionally incompatible integrated circuit (IC) and electro-acoustic (EA) technologies, bringing about substantial economic and performance benefits. In this thesis the compatibility of aluminium nitride (AlN) to IC fabrication is explored as a means for furthering integration issues. Various issues have been explored where either tailoring thin film bulk acoustic resonator (FBAR) design, such as development of an improved solidly mounted resonator (SMR) technology, and use of IC technology, such as chemical mechanical polishing (CMP) or nickel silicide (NiSi), has made improvements beneficial for resonator fabrication or enabled IC integration. The former has resulted in major improvements to Quality factor, power handling and encapsulation respectively. The later has provided alternative methods to reduce electro- or acoustomigration, reduced device size, for plate waves, supplied novel low acoustic impedance material for high power applications and alternative electrodes for use in high temperature sensors. Another method to enhance integration by using the piezoelectric material, AlN, in the IC side has also been explored. Here methods for analysing AlN film contamination and stoichiometry have been used for analysis of AlN as a high-k dielectric material. This has even brought benefits in knowledge of film composition for use as a passivation material with SiC substrates, investigated in high power high frequency applications. Lastly AlN has been used as a buried insulator material for new silicon-on-insulator substrates (SOI) for increased heat conduction. These new substrates have been analysed with further development for improved performance indicated. / wisenet

En studie i hur känsligheten avtar från ytan hos biosensorer med höga frekvenser presenteras. Med ny teknologi som avancerade elektroakustiska tunnfilms komponenter, så kallade FBARs, blir tidigare outforskade områden som decay längden möjliga att studera. För att undersöka hur frekvenssvaret och känsligheten påverkas av interaktioner långt ut från en sensoryta används proteinkemi. Ett protokoll har optimerats innehållande aktivering med EDC/NHS och fibrinogen för att säkerställa en jämn tjocklek och fördelning av ett adsorberat proteinlager över en yta. Dessa ytor kontrollerades först med hjälp av ellipsometri och sedan i ett QCM instrument. Alla experiment med de högfrekventa FBAR sensorerna utfördes vid Ångströmslaboratoriet i Uppsala där pågående forskning inom området finns. Resultaten bekräftar teorin om en avtagande känslighet i och med ett ökat avstånd från ytan. En experimentell genomförd och beräknad tjocklek för decay längden uppskattades som inte helt stämde överens med den teoretiskt beräknade. En ny term föreslås då frekvenssvaret hos en biosensor planar ut. Detta är en effekt som sker vid dubbla tjockleken av den teoretisk beräknade tjockleken av decay längden och har fått namnet; detection length. Efter denna längd eller gräns observeras en inverterad signal som det än så länge inte finns någon förklaring till. / A study of the sensitivity decrease of biosensors working at high frequencies is presented. With new technology such as film bulk acoustic resonators (FBAR), issues like the decay length is no longer irrelevant theory but may cause limitation in the system as well as it offers new detection possibilities. To investigate the frequency response and sensitivity, layer-on-layer construction chemistry was used. A protocol involving activation with EDC/NHS and coupling chemistry with fibrinogen was optimized to ensure accurate thickness and uniformly distribution of each layer over the surface. Surfaces were characterized using null ellipsometry and the protocol was tested in a traditional quartz crystal microbalance (QCM). Experiments with the FBAR were preformed at the Ångström laboratory in Uppsala were there is ongoing research and development in FBAR technology. The results confirmed the theory of decreasing frequency and sensitivity further out from the surface. An experimental and estimated thickness was calculated which to some extent correlates to the theoretically calculated decay length. A new terminology is suggested when the frequency levels off. It occurs approximately at twice the distance and thickness of the theoretically calculated decay length and is given the name; detection length. Beyond the detection length an inverted signal is observed which cannot yet be explained for.

Thin film technology is of great significance for a variety of products, such as electronics, anti-reflective or hard coatings, sensors, solar cells, etc. This thesis concerns the synthesis of thin functional films, reactive magnetron sputter deposition process as such and the physical and functional characterization of the thin films synthesized. Characteristic for reactive sputtering processes is the hysteresis due to the target poisoning. One particular finding in this work is the elimination of the hysteresis by means of a mixed nitrogen/oxygen processing environment for dual sputtering of Alumina-Zirconia thin films. For a constant moderate flow of nitrogen, the hysteresis could be eliminated without significant incorporation of nitrogen in the films. It is concluded that optimum processing conditions for films of a desired composition can readily be estimated by modeling. The work on reactively sputtered SiO2–TiO2 thin films provides guidelines as to the choice of process parameters in view of the application in mind, by demonstrating that it is possible to tune the refractive index by using single composite Six/TiO2 targets with the right composition and operating in a suitable oxygen flow range. The influence of the target composition on the sputter yield is studied for reactively sputtered titanium oxide films. It is shown that by using sub-stoichiometric targets with the right composition and operating in the proper oxygen flow range, it is possible to increase the sputter rate and still obtain stoichiometric coatings. Wurtzite aluminum nitride (w-AlN) thin films are of great interest for electro-acoustic applications and their properties have in recent years been extensively studied. One way to tailor material properties is to vary the composition by adding other elements. Within this thesis (Al,B)N films of the wurtzite structure and a strong c-axis texture have been grown by reactive sputter deposition. Nanoindentation experiments show that the films have nanoindentation hardness in excess of 30 GPa, which is as hard as commercially available hard coatings such as TiN. Electrical properties of w-(Al,B)N thin films were investigated. W-(Al,B)N thin films are found to have a dielectric strength of ~3×106 V/cm, a relatively high k-value around 12 and conduction mechanisms similar to those of AlN. These results serve as basis for further research and applications of w-(Al,B)N thin films. An AlN thin film bulk acoustic resonator (FBAR) and a solidly mounted resonator (SMR) together with a microfluidic transport system have been fabricated. The fabrication process is IC compatible and uses reactive sputtering to deposit piezoelectric AlN thin films with a non-zero mean inclination of the c-axis, which allows in-liquid operation through the excitation of the shear mode. The results on IC-compatibility, Q-values, operation frequency and resolution illustrate the potential of this technology for highly sensitive low-cost micro-biosensor systems for applications in, e.g. point-of-care testing.

In this study, gas sensing systems that are based on piezoelectric smart material and structures are proposed, designed, developed, and tested, which are mainly aimed to address the temperature dependent CO2 gas sensing in a real environment. The state-of-the-art of gas sensing technologies are firstly reviewed and discussed for their pros and cons. The adsorption mechanisms including physisorption and chemisorption are subsequently investigated to characterize and provide solutions to various gas sensors. Particularly, a QCM based gas sensor and a C-axis inclined zigzag ZnO FBAR gas sensor are designed and analyzed for their performance on room temperature CO2 gas sensing, which fall into the scope of physisorption. In contrast, a Langasite (LGS) surface acoustic wave (SAW) based acetone vapor sensor is designed, developed, and tested, which is based on the chemisorption analysis of the LGS substrate. Moreover, solid state gas sensors are characterized and analyzed for chemisorption-based sensitive sensing thin film development, which can be further applied to piezoelectric-based gas sensors (i.e. Ca doped ZnO LGS SAW gas sensors) for performance enhanced CO2 gas sensing. Additionally, an innovative MEMS micro cantilever beam is proposed based on the LGS nanofabrication, which can be potentially applied for gas sensing, when combined with ZnO nanorods deposition. Principal component analysis (PCA) is employed for cross-sensitivity analysis, by which high temperature gas sensing in a real environment can be achieved. The proposed gas sensing systems are designated to work in a high temperature environment by taking advantage of the high temperature stability of the piezoelectric substrates.

The explosive development of the telecom industry and in particular wireless and mobile communications in recent years has lead to a rapid development of new component and fabrication technologies to continually satisfy the mutually exclusive requirements for better performance and miniaturization on the one hand and low cost on the other. A fundamental element in radio communications is time and frequency control, which in turn is achieved by high performance electro-acoustic components made on piezoelectric single crystalline substrates. The latter, however, reach their practical limits in terms of performance and cost as the frequency of operation reaches the microwave range. Thus, the thin film electro-acoustic technology, which uses thin piezoelectric films instead, has been recently developed to alleviate these deficiencies. This thesis explores and addresses a number of issues related to thin film synthesis on the one hand as well as component design and fabrication on other. Specifically, the growth of highly c-axis textured AlN thin films has been studied and optimized for achieving high device performance. Perhaps, one of the biggest achievements of the work is the development of a unique process for the deposition of AlN films with a mean c-axis tilt, which is of vital importance for the fabrication of resonators operating in contact with liquids, i.e. biochemical sensors. This opens the way for the development of a whole range of sensors and bio-analytical tools. Further, high frequency Lamb wave resonators have been designed, fabricated and evaluated. Performance enhancement of FBAR devices is also addressed, e.g. spurious mode suppression, temperature compensation, etc. It has been demonstrated, that even without temperature compensation, shear mode resonators operating in a liquid still exhibit an excellent performance in terms of Q (200) and coupling (~1.8%) at 1.2 GHz, resulting in a mass resolution better than 2 ng cm-2 in water, which excels that of today’s quartz sensors.

Union between top-down and bottom-up assembly is inevitable when scaling down physical, chemical, and biological sensors and probes. Current sensor/probe-based technologies are firmly founded on top-down manufacturing, with limitations in cost of production, manufacturing methods, and material constraints. As an alternative to such limitations, contemporary synthesis techniques for one-dimensional nanostructures have been combined with established methods of micro-fabrication for the development of novel tools and techniques for nanotechnology. More specifically, this dissertation is a systematic study of the synthesis and characterization of ZnO nanostructures for piezoelectric applications. Within this study the following goals have been achieved: 1) rational design and control of a diversity of novel ZnO nanostructures, 2) improved understanding of polar-surface-dominated (PSD) phenomena among Wurtzite crystal structures, 3) confirmation of Taskers Rule via the synthesis, characterization, and modeling of polar-surface-dominated nanostructures, 4) measurement of the surface-charge density for real polar surfaces of ZnO, 5) confirmation of the electrostatic polar-charge model used to describe polar-surface-dominated phenomena, 6) dispersion of ZnO nanobelts onto the selective layers of surface acoustic wave (SAW) devices for gas sensing applications, 7) manipulation of ZnO nanostructures using an atomic force microscope (AFM) for the development of piezoelectric devices, 8) fabrication of bulk acoustic resonator (BAR) and film bulk acoustic resonator (FBAR) devices based on the integrity of individual ZnO belts, 9) electrical characterization of a ZnO belt BAR device, 10) prediction and confirmation of the electrical response from a BAR device using a one-dimensional Krimholt-Leedom-Matthaei (KLM) model, and 11) development of a finite element model (FEM) to accurately predict the electrical response from ZnO belt BAR and FBAR devices in 3D.

Small and affordable CO2 sensors are in high demand for modern applications, such as smart buildings, smartphones, electrical cars or medicine. The thin-film bulk acoustic resonator (FBAR) presents a promising platform to fulfil these demands by functionalising its surface with materials that reversibly interact with CO2. In this thesis, aminopolysiloxane-coated FBARs are prepared and analysed regarding their CO2-sensing performance. It is found that they can reach high CO2 sensitivity with resolutions up to 50 ppm in a dynamic range between 400 ppm and 5000 ppm. It is also shown that common cross-sensitivities, such as changing humidity, can be separated from the CO2 signal. These are promising results on the way to develop a new generation of CO2 sensors. However, it is also found that the sensor sensitivity decreases over time. Analytical examinations show that the main degradation product in aminopolysiloxanes is urea, which forms preferrably in softer polymers and at temperatures above 80 °C. This degradation is found in all analysed compositions of aminopolysiloxanes that were aged for more than one year showing the stability limitations of this sensor concept.:1 Introduction 9 1.1 Motivation for new CO2 sensors . . . . . . . . . . . . . . . . . . . . . . . . . . 9 1.2 The FBAR as a high-potential sensor device . . . . . . . . . . . . . . . . . . . 10 1.3 Content of this work . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 2 Fundamentals 13 2.1 Gas Sensors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 2.1.1 De_nition, History and Classi_cation . . . . . . . . . . . . . . . . . . . 13 2.1.2 Gas sensor characteristics . . . . . . . . . . . . . . . . . . . . . . . . . 15 2.1.3 State-of-the-art CO2 sensors . . . . . . . . . . . . . . . . . . . . . . . . 16 2.2 FBAR Fundamentals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 2.2.1 Acoustic resonator theory . . . . . . . . . . . . . . . . . . . . . . . . . 20 2.2.2 The Mason Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 2.2.3 Sensing theory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 2.2.4 Film resonance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 2.3 CO2-sensitive materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28 2.3.1 General Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . 28 2.3.2 Classes of CO2 sorbents . . . . . . . . . . . . . . . . . . . . . . . . . . 29 2.3.3 Suitabe materials for the functionalisation of the FBAR . . . . . . . . 35 3 Experimental details 37 3.1 FBAR designs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37 3.1.1 Passive FBARs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37 3.1.2 Active FBARs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38 3.2 Gas measurement setup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39 3.2.1 Passive FBARs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39 3.2.2 Active FBARs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39 3.3 Development of the sensitive layer . . . . . . . . . . . . . . . . . . . . . . . . 40 3.3.1 Material choice . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40 3.3.2 Material preparation . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43 3.3.3 Deposition methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44 3.3.4 Annealing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45 3.4 Analytical techniques . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46 3.4.1 Fourier-transform infrared spectroscopy . . . . . . . . . . . . . . . . . 46 3.4.2 Raman spectroscopy . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47 3.4.3 X-ray photoelectron spectroscopy . . . . . . . . . . . . . . . . . . . . . 47 3.4.4 Nuclear magnetic resonance spectroscopy . . . . . . . . . . . . . . . . 47 3.4.5 Acoustic measurements . . . . . . . . . . . . . . . . . . . . . . . . . . 47 4 Results and discussion 49 4.1 FBARs functionalised with ethyl cellulose . . . . . . . . . . . . . . . . . . . . 49 4.1.1 Acoustic characterisation . . . . . . . . . . . . . . . . . . . . . . . . . 49 4.1.2 Humidity sensing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55 4.1.3 Stability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58 6 Contents 4.2 FBARs with aminopolysiloxanes . . . . . . . . . . . . . . . . . . . . . . . . . 59 4.2.1 Acoustic characterisation . . . . . . . . . . . . . . . . . . . . . . . . . 59 4.2.2 Humidity and CO2 sensing . . . . . . . . . . . . . . . . . . . . . . . . 63 4.2.3 Stability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67 4.3 Degradation mechanisms in aminopolysiloxanes . . . . . . . . . . . . . . . . . 69 4.3.1 Stability evaluation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69 4.3.2 Analytical characterisation . . . . . . . . . . . . . . . . . . . . . . . . 70 4.3.3 Degradation hypothesis . . . . . . . . . . . . . . . . . . . . . . . . . . 78 4.4 CO2 sensing with an active FBAR array . . . . . . . . . . . . . . . . . . . . . 82 4.4.1 Presentation of the functionalised sensor chip . . . . . . . . . . . . . . 82 4.4.2 Sensor characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83 4.4.3 Selective Multigassensing . . . . . . . . . . . . . . . . . . . . . . . . . 89 5 Summary 93 6 Outlook 95 7 Appendix 97 7.1 Additional tables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97 7.2 Additional pictures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98 Bibliography 103

The fields of health care and environment control have an increasing demand for sensors able to detect low concentrations of specific molecules in gaseous or liquid samples. The recent introduction of microfabricated devices in these fields gave rise to sensors with attractive properties. A cutting edge technology is based on guided acoustic waves, which are perturbed by events occurring at the nanometer scale. A first part of the thesis investigates the Love mode waveguide, a versatile structure in which a thin film is guiding the acoustic wave generated in a piezoelectric substrate. A systematic analysis of its sensitivity was obtained using a transmission line model generalized to discriminate the rigid or viscous nature of the probed layers. We developed a novel integrated combination of the Love mode device with a Surface Plasmon Resonance optical sensor to quantify the thickness and the composition of soft layers. The electromagnetic interferences in the recorded signal were modeled to determine the phase velocity in the sensing area and to provide new mechanisms for an enhanced sensitivity. The experimental aspects of this work deal with the fabrication, the important issue of the packaging and the sensitivity calibration of the Love mode biosensor. A second part of the thesis investigates nanocrystalline diamond under the form of a thin film membrane suspended to a rigid silicon frame. The high mechanical and chemical resistance of nanocrystalline diamond, close to single-crystal diamond, open ways to membrane based acoustic sensors such as Flexural Plate Wave and thin Film Bulk Acoustic Resonators (FBAR). A novel dynamic characterization of the thin film is reported and the properties of composite FBAR devices including a diamond thin film membrane and a piezoelectric aluminum nitride layer are assessed using the perturbation theory. This study is applied to evaluate the high sensing potential of the first prototype of an actual diamond-based composite FBAR.

The fields of health care and environment control have an increasing demand for sensors able to detect low concentrations of specific molecules in gaseous or liquid samples. The recent introduction of microfabricated devices in these fields gave rise to sensors with attractive properties. A cutting edge technology is based on guided acoustic waves, which are perturbed by events occurring at the nanometer scale. A first part of the thesis investigates the Love mode waveguide, a versatile structure in which a thin film is guiding the acoustic wave generated in a piezoelectric substrate. A systematic analysis of its sensitivity was obtained using a transmission line model generalized to discriminate the rigid or viscous nature of the probed layers. We developed a novel integrated combination of the Love mode device with a Surface Plasmon Resonance optical sensor to quantify the thickness and the composition of soft layers. The electromagnetic interferences in the recorded signal were modeled to determine the phase velocity in the sensing area and to provide new mechanisms for an enhanced sensitivity. The experimental aspects of this work deal with the fabrication, the important issue of the packaging and the sensitivity calibration of the Love mode biosensor. A second part of the thesis investigates nanocrystalline diamond under the form of a thin film membrane suspended to a rigid silicon frame. The high mechanical and chemical resistance of nanocrystalline diamond, close to single-crystal diamond, open ways to membrane based acoustic sensors such as Flexural Plate Wave and thin Film Bulk Acoustic Resonators (FBAR). A novel dynamic characterization of the thin film is reported and the properties of composite FBAR devices including a diamond thin film membrane and a piezoelectric aluminum nitride layer are assessed using the perturbation theory. This study is applied to evaluate the high sensing potential of the first prototype of an actual diamond-based composite FBAR.

Les systèmes publics de santé nécessitent des capteurs miniaturisés pour l'amélioration des diagnostics médicaux. Dans ce contexte, l'objectif de cette thèse était de simuler, réaliser et caractériser des résonateurs à ondes acoustiques de volume à base de couches minces, vibrant en mode de cisaillement à 800 MHz et montés sur miroir acoustique (SMR), et de démontrer leur capacité à fonctionner comme capteurs gravimétriques en milieu liquide.<br /><br />Trois procédés de dépôt par pulvérisation de couches de ZnO à axe c incliné ont été développés. De telles couches sont nécessaires pour l'excitation d'ondes de cisaillement et essentielles pour un fonctionnement en milieu liquide. Des inclinaisons jusqu'à 16° ont été obtenues avec une incidence oblique des particules en utilisant des caches additionnels. Des couches homogènes ont été déposées sur la surface entière d'un wafer 4“. Des outils de simulation et de caractérisation ont permis d'optimiser les SMRs, améliorant le coefficient de couplage de 0.012 à 0.149 et le facteur de qualité de 3.5 à 230. Leur application dans des solutions de glycérol a montré qu'ils se prêtent à la détection gravimétrique et comme viscosimètres. Des mesures de liaisons anticorps-antigènes en milieu liquide ont été réalisées avec succès. Comparées à des microbalances à quartz vibrant à 10 MHz, la sensibilité est 1000 fois plus grande et la résolution est 4 fois meilleure.<br /><br />Les SMRs sont hautement sensibles, peuvent être intégrés à des systèmes électroniques, et permettent des mesures quantitatives avec de bonnes résolutions. Ces nanobalances à couche piézoélectrique pourront former le noyau de systèmes portables et bon marché pour le diagnostic médical.