Browsing by Author "Kirby, Paul B."
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Item Open Access Are the 1D and 2D constitutive equations of piezoelectric materials right?(2007-06-14T00:00:00Z) Zhu, Meiling; Kirby, Paul B.Item Open Access Design and development of a polymer patch clamping device(Cranfield University, 2010) Wilson, Sandra; Kirby, Paul B.; Saile, VolkerPatch clamping is considered the gold standard in measuring the bioelectrical activity of a cell. It is used to detect and measure ion transport through ion channels located throughout a cell membrane. Ion movement is crucial to cell viability and cell-to-cell communication. Pharmaceutical companies increasingly target ion channels because of their significance in disease and to help design better targeted drugs. However, the traditional method of patch clamping is cumbersome and is being replaced by planar high throughput screening (HTS) systems. These systems are reaching their limits due to materials and cost of processing; cell handling methods and small varieties of applicable cell types are also issues to be addressed. In this work, the core components of a new kind of planar patch clamping device have been designed and developed, after analysis of currently available HTS systems. This design approaches patch clamping using polymers to overcome some of the limitations in current systems, specifically cell handling and positioning, by using a simple modification technique to provide distinct attractive areas for cell binding. This uniquely allows the culture of both single cells and cell networks to increase the range of cell types that can be measured and circumvents challenges from using suction to pull cells onto measurement holes. The components of the design are a 10 x 10 array of small holes drilled in a polymer then aligned modifications for precise cell placement are added and a planar electrode array for individual addressing of each cell. A study of methods to produce a leak-tight seal required between microfluidic chambers was done. Cell adhesion parameters for the modification techniques were established. The principle viability of this approach was confirmed using the modification technique to culture cells over holes and measure their resistance using a rig developed for this work.Item Open Access Design study of piezoelectric micro-machined mechanically coupled cantilever filters using a combined finite element and microwave circuit analysis.(Elsevier Science B.V., Amsterdam., 2006-02-01T00:00:00Z) Zhu, Meiling; Kirby, Paul B.A new mechanical filter structure is presented which comprises two silicon cantilevers mechanically coupled by a silicon linkage with thin film piezoelectric transducers providing electrical input and output signals. The resonance behaviour of such a structure results in a band-pass filter response, having a band-width determined by the frequency separation between the closely spaced in-phase and out-of-phase vibrational modes of the two coupled cantilevers. A detailed configuration design analysis, filter simulation and optimisation of performance is undertaken using a new modelling approach combining microwave circuit theory and finite element analysis to evaluate the generalised (A, B, C and D) and scattering (S) circuit parameters of the filter. Two significant features of the filters have emerged from the derived analyses and simulations: (1) with correct design filter Q-values can reach several thousand which is much higher than the Q-values (80) of uncoupled cantilevers, (2) the Q-value is determined by the configuration of the silicon linkage and so is under the designer's control. The position and length of the linkage that give optimum Q and minimum insertion loss are determined.Item Open Access Development aspects of an integrated pyroelectric array incorporating a thin PZT film and radiation collectors(Taylor and Francis, 2004) Shaw, Christopher P.; Landi, Spartaco; Whatmore, Roger W.; Kirby, Paul B.Abstract Work is being undertaken to produce an uncooled pyroelectric infra-red detector array which incorporates within its structure, an array of radiation collectors made by the bulk micro-machining of silicon. Development aspects of the processing route are presented here.Item Open Access Development of high concentrated aqueous silver dispersion for inkjet printing on ceramic substrates(2012-02-15T00:00:00Z) Kosmala, A.; Zhang, Q.; Wright, R.; Kirby, Paul B.In this paper, the formulation of a high Ag loading (45 wt %) aqueous ink and its subsequent printing on three different ceramic substrates were reported. Monodispersed Ag nanoparticles with a size down to 10 nm were successfully synthesized in aqueous medium. These nanoparticles were then successfully dispersed up to 45 wt% in aqueous medium with the aid of a co-polymer, Pluronic F127. The printed tracks show the electrical conductivity of 3μΩcm close to the value of silver bulk (1.6 μΩcm). The use of high solid loading inks reduces the number of printed layers required for thick, dense and conductive film thus leading to the reduction of the costs, and high efficiency of the printing process. High solid loading also results in the finer printed features. The effect of substrates, printing temperature and dot spacing on the size and morphology of printed silver features was investigated. Increasing the dot spacing together with the substrates temperature resulted in the limited ink spreading, hence narrow printed line and improved geometry of printed patteItem Open Access Development of high loading Ag nanoparticle inks for inkjet printing and Ag nanowire dispersions for conducting and transparent coatings(Cranfield University, 2012-03) Kosmala, A.; Zhang, Qi; Kirby, Paul B.The work presented in this thesis focuses on the synthesis of nanomaterials, formulation and printing of Ag nanoparticle and nanowire inks for two distinct applications: a) inkjet printing of Ag nanoparticle films on ceramic substrates with the aim of providing a smaller size of printed feature at lower cost than that can be obtained with the conventionally used screen printing, and b) Ag nanowires films prompted by the wide quest of electronics industry for materials with increased flexibility, lower cost and higher transmittance to replace indium tin oxide. Ag nanoparticles with a size of 50 nm were successfully synthesized and dispersed in aqueous medium. Two preparation routes were compared in order to distinguish the effects of solvents treatment of particles and their influence on the suspension characteristics including Ag loading, rheology, surface tension and later the electrical film properties. The co-polymer Pluronic F127 was found to be an effective as a stabiliser leading to the formulation of high silver loading in inks. The processing and characterization of silver films was performed. The aim was to reduce the number of layers in the silver nanoparticles film by increasing the thickness of a single layer with the goal of obtaining a dense and conductive film. An increase in the Ag loading, from 5 wt % to 45 wt % favoured the achievement of denser and thicker film with one layer printing. Addition of SiO2 to the ink formula resulted in denser structure and better adhesion of the printed track then the one without SiO2. A new method for improving the morphology of inkjet printed tracks has been proposed by printing the ink into the structured channels with predefined topography. Silver nanowires were synthesised and dispersed in methanol with help of copolymer F127. They were subsequently deposited on plastic and glass substrates forming conductive and transparent films.Item Open Access Development of lead-free thin-film dielectrics for capacitor applications(Cranfield University, 2010) Darbyshire, David Anthony; Kirby, Paul B.; Zhang, QiThis PhD project aims to develop lead-free thin-film dielectric materials for fixed value, voltage tunable and high-k zipping variable capacitors using growth techniques that can be scaled for silicon batch fabrication. The thesis specifically details the growth and characterisation of barium zirconate titanate (BZT) and bismuth zinc niobate (BZN) dielectric thin films. Fixed value and tunable capacitors have been realised through the use of low and high permittivity dielectric thin film materials in both the amorphous and crystalline states. Planar devices fabricated using BZT and BZN dielectric thin films were grown by sol-gel and RF magnetron sputtering, respectively. The effects of different bottom electrodes were also investigated. Capacitors in a metal-insulator-metal (MIM) [metal-ferroelectric-metal (MFM) for BZT] structure have been fabricated to characterise the dielectric films at low frequency to 300 kHz. Cont/d.Item Open Access Development of mechanical reliability testing techniques with application to thin films and piezo MEMS components(Cranfield University, 2010-04) Gkotsis, Petros; Kirby, Paul B.This work focuses on the development of a method for probing the mechani- cal response of thin film materials based on miniature tensile testing. A number of mechanisms that may compromise the performance and potentially limit the operational lifetime of MEMS devices which incorporate functional ferroelectric ceramics were also identified and investigated. Reliability of piezo MEMS com- ponents was studied at a wafer and at a device level through the development of appropriate techniques based on miniature tensile testing, time- resolved mi- cro RAMAN spectroscopy and laser Doppler vibrometry. Micro tensile testing was further used for the extraction of the elastic properties of various thin film materials. A miniature tensile stage was developed in common with DEBEN UK for the mechanical characterization of functional thin film materials like PZT and ZnO ceramics, which are commonly used in MEMS fabrication. The stage is of- fered with a piezo electric motor which can be fitted with interchangeable heads. These can be combined with di.erent types of mounting jaws, enabling both con- ventional tensile testing and compression testing to be performed. Strains and displacements were measured in- situ using an optical, non destructive method based on CCD imaging. The elastic constants of polymer (LCP), LCP-Au bi- layers and electroplated Ni were defined in good agreement with the literature. However yield of successfully released ceramic samples was rather poor so a col- laboration with IMTEK at Germany was established. Using their facilities batch processing of a large number of wafers was possible. Cont/d.Item Open Access Electrode optimisation for piezoelectric MEMS transfer bonded devices(Cranfield University, 2008-09) Raymont, Jeffery; Kirby, Paul B.Optimisation can be viewed in many ways including that which is new and improvements to the materials, or methods that are already in place. Therefore we can define the two specific areas that make up the investigation relating to this work; those pertaining to new materials which may improve performance, and an analysis of the methods, and results, with regard to adhesion of the dissimilar materials incumbent in the present structures. In this work, two candidate materials have been identified in order to improve the performance of the electrode structures present in MEMS devices used for piezoelectric applications. These are the conductive oxides, Lanthanum Nickel Oxide and Ruthenium Oxide, which have shown considerable promise because of their reported improvements in fatigue properties with PZT applications. They have been investigated as potential top layer electrodes as the literature has indicated that substantive improvements can be made in piezoelectric performance when conductive oxides are used as a top electrode. The results for LNO as a top electrode using deposition through CSD yielded no crystalline presence when examined with XRD. However, the results indicate a possible amorphous presence when subjected to a strict cleaning regime and crystallisation using rapid thermal annealing. LNO deposition through CSD, when used as a top electrode with PZT has not been previously reported. This warrants further investigation as a basis for future work. Conductive ruthenium oxide has been deposited through sputtering using a ruthenium target source and an 80/20 argon/oxygen mix. The results for ruthenium oxide deposited on to glass slides indicate that resistivity improves with annealing temperature. The results indicate successful ruthenium deposition on to PZT 30/70 but have produced mixed results when subjected to annealing because of the thickness of the ruthenium oxide deposited. Two methods for measuring adhesion have been evaluated for their suitability in relation to thin metal films. The multi pass wear scratch test proved unsuitable for producing meaningful results with films deposited on to PZT. The pull test produced some results which mean that comparative analyses are possible for the thin film systems making up the electrode structure. The stressed overlayer technique has been used as a means to evaluate the work of fracture for the metal electrodes making up the present structure. A model has been used on the blister structures resulting from the stressed overlayer. In addition, the method has enabled qualitative judgments of the electrode structures submitted for analysis.Item Open Access Evaluation of the optical switching characteristics of erbium-doped fibres for the development of a fibre Bragg grating sensor interrogator(SPIE, 2014-06-02) Rigas, E.; Correia, Ricardo N.; Stathopoulos, N. A.; Savaidis, S. P.; James, Stephen W.; Bhattacharyya, Debabrata; Kirby, Paul B.; Tatam, Ralph P.A polling topology that employs optical switching based on the properties of erbium-doped fibres (EDFs) is used to interrogate an array of FBGs. The properties of the EDF are investigated in its pumped and un-pumped states and the EDFs’ switching properties are evaluated by comparing them with a high performance electronically controlled MEM optical switch. Potential advantages of the proposed technique are discussed. © (2014) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.Item Open Access Fabrication of PZT actuated cantilevers on silicon-on-insulator wafers for a RF microswitch.(International Society for Optical Engineering - SPIE, 2003) Jiang, Hong Wen; Kirby, Paul B.; Zhang, QiA processing scheme for fabricating Pb(ZrxTi1-x)O3 thin film actuated silicon cantilevers using silicon-on-insulator wafers is described. Such piezoelectrically actuated cantilevers are being investigated for RF microswitches. The microswitch design specification requires the Pb(ZrxTi1-x)O3 thin film to be at least 1μm thick to achieve the adequate deflection at an operating voltage of 10V. A two-stage dry-wet etching process was developed to reliably pattern the 1μm Pb(ZrxTi1-x)O3 film. To release the Pb(ZrxTi1-x)O3 cantilevers on silicon-on-insulator wafers it is necessary to perform deep silicon etching from both sides of the wafer. The Pb(ZrxTi1-x)O3 thin film was prepared by sol-gel method. The piezoelectric coefficient d31 was calculated as 14pC/N.Item Open Access Fabrication, development and analysis of film bulk acoustic resonators on flexible polymer substrates(Cranfield University, 2010) Hakemi, Ghazal; Kirby, Paul B.It is the focus of this project to explore the possibility of achieving Radio Fre¬quency (RF) micro-devices on flexible polymer substrates. To this end standard MEMS fabrication methods have been tailored to allow the integration of func¬tional materials and device patterning for production of RF MEMS devices with flexible organic substrates. Material quality, device yield, performance and re-liability are critical aspects of our study. The project encompasses the use of a direct integration method for the creation of Film Bulk Acoustic Resonators (FBARs) on Liquid Crystal Polymer (LCP) substrates. An FBAR is a passive component used for resonance and filtering purposes. Its production on organic substrates would lead to a number of ad-vantages including: overall cost savings, size reduction and ability of the device to be directly integrated on the printed circuit board (PCB) front-end with the other essential components (i.e. antenna) without the use of wiring and inter-connections. New fabrication process flows have been developed to allow the creation of FBAR microwave devices on LCP. First of all pre-processing of the polymer substrate is carried out to make it rigid and smooth. Substrate smoothness and stiffness are necessary in order to obtain functioning devices and for the substrate to comply to the standard fabrication methods. Rigidity is achieved through a backing method whereby silicon or glass are attached to LCP with an intermediate adhesive layer. The best way to achieve smoothness was found to be Chemical Mechanical Polishing (CMP). Standard fabrication techniques were then employed to deposit the metal and piezoelectric material and pattern them. Both bulk and surface micromachining were used and, in some cases, tailored to suit the new substrates (LCP) tolerance limits (such as temperature and flexibility). Zinc Oxide (ZnO) piezoelectric is the preferred functional material and it is chosen due to its relatively low deposition temperature re¬quirements (below 300C) and its high frequency characteristics. The creation of a front-to-back processed FBAR on LCP is successfully carried out at relatively low temperatures since the Zinc oxide (ZnO) functional mate¬rial is proven to yield good crystallinity at a deposition temperature of 100C and also because micromachining temperatures do not generally exceed 115C. The final device is characterized through RF measurements, compared with sim¬ulations and standard FBARs and the polymer/ceramic integration reliability for device creation is briefly addressed. In conclusion FBARs are successfully created on LCP with only minor compli¬cations related to LCP surface roughness and RIE etch of the polymer. The project lays promising prospects for RF MEMS devices on compliant organic substrates.Item Open Access Growth and high frequency characterization of Mn doped sol-gel Pb xSr1-xTiO3 for frequency agile applications(American Institute of Physics, 2009-06) Fragkiadakis, Charalampos; Luker, Arne; Wright, Robert V.; Floyd, L.; Kirby, Paul B.In pursuit of thin film ferroelectric materials for frequency agile applications that are both easily adapted to large area deposition and also high performance, an investigation has been carried out into sol-gel deposition of 3% Mn doped (Pb0.4Sr0.6)TiO3. Large area capability has been demonstrated by growth of films with good crystallinity and grain structure on 4 in. Si wafers. Metal-insulator-metal capacitors have also been fabricated and development of an improved de-embedding technique that takes parasitic impedances fully into account has enabled accurate extraction of the high frequency dielectric properties of the PbxSr1−xTiO3 films. Practically useful values of ε ∼ 1000, tan δ ∼ 0.03, and tunability ∼ 50% have been obtained in the low gigahertz range (1–5 GHz). Peaks in the dielectric loss due to acoustic resonance have been modeled and tentatively identified as due to an electrostrictive effect with an electromechanical coupling coefficient of ∼ 0.04 at an electric field of 240 kV/cm which is potentially useful for tunable thin film bulk acoustic wave devices.Item Open Access High frequency thin-film bulk acoustic wave resonators for gas- and bio-analytical applications(2000-10) Ashley, Greg M.; Kirby, Paul B.; Cullen, David C.Thin Film Bulk Acoustic Wave Resonators (FBAR) are mechanical micro scale devices that operate in the UHF/Microwave frequency range. This high frequency of operation potentially offers increased sensitivity to the addition of surface mass loading as implied by the famous Sauerbrey equation. FBAR was shown to be responsive to physical and chemical changes in the environment and was further adapted to act as bio-sensor. Thus indicating a universal platform from which to launch an enhanced sensing technology. This thesis follows the research and development of a prototype chemical and biological sensor based on FBAR FBAR devices were fabricated in a clean room and on die RF measurements were made to identify the units with performance characteristics of high enough quality to be useful as sensors. The FBAR design was then adapted so that it could be environmentally isolated, and microwave circuitry was devised to allow the FBAR to remain in electrical contact with the outside world during its isolation. This allowed for controllable environments in which to test FBAR responses to chemical and biological agents free from interfering signals. A software suite was written to specifically address the requirements for accurate and sensitive data processing of FBAR responses to measured analytes in real time. The isolation assembly and software was tested thoroughly, and the ultimate limits of resolution and sensitivity for the instrumentation were found using temperature change as the variable input parameter. A gas delivery apparatus was constructed and the FBAR was coated with hygroscopic polymer layers to sensitise the device to water vapour. Changes in the concentration of water vapour in a gas stream were tracked and the range of detection was established along with stability and resolution of the chemically sensitised FBAR. FBAR device gold surfaces were coated with biological antibodies, these made the devices ultra specific to measurand. Direct experimental comparisons between the FBAR and the relative performance of well established but lower frequency acoustic wave immunosensor technology systems were made and the relative increase in sensitivity was established for the FBAR based immunosensor. Optical methods were used to compliment the acoustic ones in determining the thickness and density of the protein layers adsorbed to equivalent gold surfaces. The thesis concludes with a section of speculative ideas for future work, with the experimental results for a potential rheological probe device shown. A brief demonstration of the FBAR performance when submerged in semi-infinite liquid environments is shown. Arrays of FBAR devices are software modelled in a novel way and demonstration of their possible applications are presented.Item Open Access In-plane excitation of thin silicon cantilevers using piezoelectric thin films(American Institute of Physics, 2007-10) Leighton, Glenn J. T.; Kirby, Paul B.; Fox, Colin H. J.This paper deals with the actuation of in-plane and out-of-plane motions of silicon cantilevers, using a single thin film of lead zirconate titanate with a divided electrode configuration. In-plane actuation is demonstrated practically, and excellent agreement is obtained between theoretically predicted and experimentally measured resonant amplitudes, for the fundamental out-of-plane and in-plane modes of vibration of the fabricated test cantilevers.Item Open Access In-plane excitation of thin silicon cantilevers using piezoelectric thin films(American Institute of Physics, 2007-10-29T00:00:00Z) Leighton, Glenn J. T.; Kirby, Paul B.; Fox, Colin H. J.This paper deals with the actuation of in-plane and out-of-plane motions of silicon cantilevers, using a single thin film of lead zirconate titanate with a divided electrode configuration. In-plane actuation is demonstrated practically, and excellent agreement is obtained between theoretically predicted and experimentally measured resonant amplitudes, for the fundamental out-of-plane and in-plane modes of vibration of the fabricated test cantilevers.Item Open Access Integration of sol-gel frequency agile materials for tunable RF devices(Cranfield University, 2012-01) Fragkiadakis, Charalampos; Kirby, Paul B.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 topics 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 integration of tunable dielectrics with conventional bulk acoustic wave resonators (FBAR). Cont/d.Item Open Access Integration of thin film bulk acoustic resonators onto flexible liquid crystal polymer substrates(Elsevier Science B.V., Amsterdam., 2011-06-30T00:00:00Z) Wright, Robert V.; Hakemi, Ghazal; Kirby, Paul B.Thin film bulk acoustic resonators (FBARs) have been directly integrated on liquid crystal polymer (LCP) substrates for application to the field of flexible electronics. Particular developments required were chemo-mechanical polishing for LCP roughness reduction to enable growth of high quality ZnO films and a through substrate deep reactive ion etch process. Q values of up to 126 and 78 for series and parallel resonances combined with an electromechanical coefficient ∼ 6.7% were achieved. Further device development is needed but this performance is already sufficient for some chemical/biological sensing applications.Item Open Access Laser transfer of sol-gel ferroelectric thin films using an ITO release layer(Elsevier Science B.V., Amsterdam., 2011-02-01T00:00:00Z) Bansal, A.; Hergert, R.; Dou, G.; Wright, Robert V.; Bhattacharyya, Debabrata; Kirby, Paul B.; Yeatman, E. M.; Holmes, A. S.A new laser transfer process is reported which allows damage-free transfer of ferroelectric thin films from a growth substrate directly to a target substrate. The thin film ferroelectric material is deposited on a fused silica growth substrate with a sacrificial release layer of ITO (indium tin oxide). Regions of the film that are to be transferred are then selectively metallised, and bonded to the target substrate. Separation from the growth substrate is achieved by laser ablation of the ITO release layer by a single pulse from a KrF excimer laser, with the laser light being incident through the growth substrate. The residual ITO on the transferred ferroelectric layer is electrically conducting, and may be suitable for incorporation into the final device, depending on the application. The new process has been demonstrated for 500 nm-thick layers of sol-gel PZT which were thermosonically bonded to a silicon target substrate prior to laser release. The transferred films show ferroelectric behaviour and have a slightly reduced permittivity compared to the as-depositItem Open Access Mechanical design aspects of a tri-axial accelerometer(2004-06) Hatt, Joseph M.; Kirby, Paul B.This work describes the development of computer models for the design of a novel three-axis silicon accelerometer with thin-film PZT piezo-electric sensing. Theoretical and finite element methods are used to predict the resonant frequencies, resonant mode shapes, and charge sensitivity of the accelerometers. The strengths of each analytical method are used to allow the identification of trends in geometrical affects, and to optimise the design with respect to specification objectives for a commercial device. The theoretical models have been developed and refined in conjunction with practical fabrication trials. This has allowed the material properties to be derived, specific to the thin-film deposition method used, and incorporated onto the models. The practical fabrication process has raised a number of unforeseen issues, and these have led to changes from the original design. These changes have been analysed with the theoretical models, and revised performance predictions produced. The practical findings are consistent with the revised predictions, and achieve close to the desired performance specification.