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The potential of algal biofuels has been technically and experimentally confirmed with laboratory- and pilot-scale studies in past literature. However, the most important factor now is to confirm that algal cultivation for biofuels and other end-products is economically feasible on the large, commercial scale. The ALGADISK project aimed to produce a novel biofilm-based photo-bioreactor with the aims of CO2 capture and making valuable products such as biofuel, economically viable. This thesis aimed to investigate and provide substrates in which algae biofilm is stimulated and increased. Polyelectrolyte (PE) coatings adsorbed onto cost-effective polymers were investigated, based on the strategy of electrostatic attraction. It was found that the algae species charge density and cell wall functional groups composition affected attachment onto charged PE coatings. Two coatings labeled C1 and C3 were selected due to their promising growth results with the strains C.sorokiniana, C.vulgaris and S.obliquus. Harvesting growth results showed inconsistent regrowth due to the lack of textured structure. Sandpapering the surface with certain grades was found to improve regrowth and consistency. Surface roughness did not show correlation to initial attachment of algae or strength of attachment. It was shown instead that surface roughness improved long-term growth As part of the aims of the ALGADISK project, the coatings large scale potential and cost was optimized. It was found that airbrushing rather than dip-coating, reduced the amount of PE solution needed drastically. Furthermore, photo-cross- linking with UV exposure enhanced the strength of C1 according to scratch and wear data. Lastly, the physico-chemical properties of both algae and substrates were examined in order to examine the thermodynamic model for algae adhesion prediction. It was found that the two thermodynamic approaches tested did not predict algae adhesion results with good accuracy. However, it was revealed that there could be a possible link between the substrate physico-chemistry and lipid content found in the biofilm attached. It was found that the less favorable the predicted thermodynamic conditions the higher the lipid content.

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.

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.

Energy harvesting; that is, harvesting small amounts of energy from environmental sources such as solar, air flow or vibrations using small-scale (≈1cm 3 ) devices, offers the prospect of powering portable electronic devices such as GPS receivers and mobile phones, and sensing devices used in remote applications: wireless sensor nodes, without the use of batteries. Numerous studies have shown that power densities of energy harvesting devices can be hundreds of µW; however the literature also reveals that power requirements of many electronic devices are in the mW range. Therefore, a key challenge for the successful deployment of energy harvesting technology remains, in many cases, the provision of adequate power. This thesis aims to address this challenge by investigating two methods of enhancing the power output of a piezoelectric-based vibration energy harvesting device. Cont/d.

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.

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.

Patch 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.

This 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 thin-film dielectrics were grown by sol-gel and RF magnetron sputtering, respectively. The effects of different bottom electrodes were also investigated. Capacitors in metal-insulator-metal (MIM) structure have been fabricated to characterise the dielectric films at low frequency (to 300 kHz). Finding alternative higher permittivity dielectrics to SiO2 for various capacitor and isolation layer applications can be a challenge. Trials were conducted that looked at using amorphous BZT and nano-crystalline/crystalline BZN as a low-k dielectric insulator. Dielectric constants of ~50 were typical for BZN, but much lower permittivity was achieved for amorphous BZT, between 2 and 15 when deposited on Cr/Au bottom electrode. Breakdown strength of amorphous BZT was extremely high (2.0 MV/cm) and far superior to that of BZN (0.35 MV/cm). The dielectric strength of BZN was increased to 0.56 MV/cm when BZN was grown on a BZT seed layer due to a change in the microstructure of the BZN film from granular to columnar. The development of a suitable dielectric BZN for use with polymer substrate was also investigated and MIM capacitors fabricated by sputter deposition. Preliminary results for nano-crystalline BZN thin film growth on gold coated liquid crystal polymer (LCP) substrates appeared encouraging with dielectric constant of 27 and loss 0.005. Crystallised BZT thin films can be used to good effect as lead-free dielectric material in tunable devices. For BZT in the ferroelectric phase, excellent tunabilities of 80% were realised when deposited on platinised silicon. This wasfound not to be the case for BZT in the paraelectric phase where tunabilities tended to be ~60% at best. The dielectric properties of thin-film MIM capacitors can be enhanced by the use of lower resistivity bottom electrode such as gold. Previous research has failed to demonstrate growth and crystallisation of BZT on gold electrode due to the fact that it is technically difficult using the sol-gel method. Films tend to crack after annealing. I have found that films can be stabilised, and the tunability of BZT thin film in the paraelectric phase can be increased significantly, by growing BZT on gold bottom electrode using a BZN buffer layer 25nm thick. A peak tunability of 83% was achieved while maintaining a low dielectric loss of ~0.01. Novel BZT multilayer structures incorporating both ferroelectric and paraelectric compositions were grown on platinised silicon resulting in a tunability of 82% at a bias field 600 kV/cm. Based on the success of growing good quality BZN thin films on gold bottom electrode, it was decided to use BZN thin film as one of the high-k dielectrics in the zipping varactor, a miniature MEMS tunable device. Trials were performed that looked at depositing BZN on thick (800nm) gold coated silicon and glass. This was successful on small sample pieces but failed when scaled up to full device wafer size (100 mm diameter) due to Cr/Au diffusion into the dielectric layer. To overcome this, a 300nm thick BZN film was sputter deposited on Ti/Pt and Ti/Au/Pt coated 100 mm glass device wafers and processed to form the dielectric layer and bottom electrode of the capacitor. As part of the process the BZN layer required patterning. Wet etching of the small features was inappropriate due to undercutting of the structure; dry etching was therefore necessary. Prior to this work there had been nothing reported on the dry etching of BZN, only wet etched using a 1:10 HF-deionised H2O solution. In this work, thin-film BZN was reactively ion etched in Ar/CHF3 plasma at a rate of 6nm per minute with excellent selectivity over platinum of 10:1. Fabrication of the curved top electrode, final assembly and device testing were undertaken by a group at Imperial College London who were collaborators on a work programme entitled, “Integrated Functional Materials for System-in-Package Applications”.

Ferroelectric perovskite thin films for voltage tunable applications, namely (Ba,Sr)TiO3 (Barium Strontium Titanate or BST) and (Pb,Sr)TiO3 (Lead Strontium Titanate or PST), are synthesized via the so-called sol-gel route. While BST shows the tendency to severe film cracking, PST can be grown crack free onto platinised Si standard substrates and even directly onto SiO2, SiNx or bare Si. The growth kinetics of PST on platinised SiO2/Si and directly on SiO2/Si are studied in detail using X-ray diffractometry (XRD), scanning electron and atomic force microscopy, SEM and AFM respectively. It is shown that PST begins to crystallise at 500°C on Ti/Pt and 550°C directly on SiO2. After a thermal treatment of 650°C for 15 min both films are fully crystallised with random (100) and (110) orientation and a smooth surface. The dielectric properties, e.g. dielectric constant, loss and tunability, of PST 50/50 are measured using a standard Ti/Pt bottom electrode with Cr/Au top electrodes and a TiW/Cu bottom electrode on which the PST thin film was bonded with TiW/Cu top electrodes. The Cu/PST/Cu system shows an enhanced performance in terms of loss resulting in a larger device quality factor and a figure of merit (FOM) of 18.25 compared to 16.6 for the configuration using a Pt bottom electrode. The maximum tunability is 73% with an applied voltage of 35V and the dielectric constant at zero bias is ~ 420 with a loss < 4 %. (Pb0.4Sr0.6)(MnxTi1-x)O3 (Mn doped PST 40/60) thin films with x = 0, 0.01, 0.03, and 0.05 are grown on Ti/Pt coated SiO2/Si substrates. The surface morphologies, dielectric and tunable properties of these films are investigated as a function of Mn content (x). It is found that the grain size/roughness, dielectric constant, loss, tunability and figure of merit are affected by the Mn doping level. Further on it is found that the ferroelectricity and the transition temperature between the cubic paraelectric and tetragonal ferroelectric state increase with Mn content. The dielectric constant at zero bias reaches a maximum of 1100 and the maximum FOM is 23.96 with 3 mol% Mn; whereas the maximum value of the tunability is 76.72% at 10 V with 1 mol% Mn. A detailed understanding of the effect of Mn doping is developed and presented. It is found and explained that a doping level of 2 mol% Mn results in optimal properties in terms of tunability and loss. Auger spectroscopy is used to study the compositional change in the interfacial region between PST and PZT thin films and SiO2/Si substrates to understand the growth kinetics of PST directly onto SiO2 in more detail. The thin films from both materials are annealed under the same conditions (temperature and time). It is found that strontium stops the lead diffusion into SiO2 by forming SrSiO3/Sr2SiO4 and/or SrO, maintaining a well defined SiO2 region, while PbSiO3 is formed in the PZT/SiO2 system. It is shown that SrO covalently saturates all Si dangling bonds by forming SrSiO3 and/or Sr2SiO4. This provides the necessary ionic template towards the perovskite SrO-terminated SrTiO3, on which PST can grow further on. A single layer of PST is finally used as a buffer layer for the growth of piezoelectric PZT directly onto SiO2 to replace the common Ti/Pt bottom electrode. The initial characterisation of PZT device structures shows that PZT films with PST as a diffusion buffer had fully crystallized in the perovskite phase exhibiting good dielectric and ferroelectric behaviour. Although the piezoelectric coefficients of the PZT films were not measured directly in this study, it is envisaged from the experimental data of the dielectric constant and hysteresis loop that the PZT/PST composite has the potential to provide good and comparable piezoelectric performances as typically observed in PZT device structures grown on commonly used Ti/Pt.

This research presents the design and microfabrication of a novel pyroelectric IR array detector. Micromachined concentrators are incorporated in the device to focus incoming radiation. Patterning of the sensing elements is introduced to reduce thermal losses. According to the physical theory of IR detection, these improvements can enhance the response of a pyroelectric detector. The device is designed to be fabricated using state of the art micro systems technology. The design and fabrication route build partially on a previous primitive version of the device, which has been used as a case study. An array of 3 - d structured non-imaging collectors is coupled to the sensing array. A survey of concentrators identified the most suitable contours, which were subsequently analysed. An original series of "suspended" collectors were especially developed for incorporation in this device. The calculations demonstrated that, generally, the Compound Parabolic Concentrator outperforms any other system. In all cases, truncated or suspended systems would show lower efficiency than the respective full systems. The search for a viable microfabrication route focussed on methodologies based on Deep Reactive Ion Etching. Experimental trials, using both 3 - d sacrificial masks and conventional binary masks demonstrated a range of interesting structures, some of which had not been previously showed in literature. Long etching cycles in pure SFg could only approximate a tenth of the ideal contour and lacked flexibility, but demonstrated the lowest surface roughness (300 nm to 2 /rm), highest reliability and are easy to implement and optimise. Being the processes of choice, these were analysed further and chosen as a quick route for producing working prototypes of the device. A chemical model of the process was built, based on mass balance considerations. Calculations demonstrated that, by isolating each sensing element of the array on a spiral microbridge, the responsivity of the device could be increased up to 100 times. Conventional Reactive Ion Etching was used for patterning the entire active layer (pyroelectric material and electrodes). Suspended spiral elements were successfully incorporated in the final prototypes. To produce the final device, two wafers (250 /rm thick) were stacked to approximate a collector with 37 % truncation, leading to a maximum theoretical collection efficiency of 2.36. The electrical properties and response from the prototypes were measured and the results compared with the theoretical performance of the device, calculated using rough approximations in 2-d. Using a home made testing rig, the best responses obtained were between 5 to 25 mV. Unfortunately, the model used is not sophisticated enough to allow straightforward comparison with the experimental results. Recently, better agreement has been demonstrated using a 3-d model.