This thesis analyses the design strategies used to protect RF circuits that are implemented in CMOS technologies. It investigates, in detail, the physical mechanisms involved when a ggNMOS structure is exposed to an ESD event and undergoes snapback. The understanding gained is used to understand why the performance of the current RF ESD clamp is poor and suggestions are made as to how the performance of ggNMOS clamps can be improved beyond the current body of knowledge. The ultimate aim is to be able to design effective ESD protection clamps whilst minimising the effect the circuit has on RF I/O signals. A current ggNMOS based RF ESD I/O protection circuit is analysed in detail using a Transmission Line Pulse (TLP) tester. This is shown to be a very effective diagnostic tool by showing many characteristics of the ggNMOS during the triggering and conducting phase of the ESD event and demonstrate deficiencies in the clamp design. The use of a FIB enhances the analysis by allowing the isolation of individual components in the circuit and therefore their analysis using the TLP tester. SPICE simulations are used to provide further commentary on the debate surrounding the specification required of a TLP tester for there to be a good correlation between a TLP test and the industry standard Human Body Model (HBM) ESD test. Finite element simulations are used to probe deeper in to the mechanisms involved when a ggNMOS undergoes snapback especially with regard to the contribution parasitic components within the ggNMOS make to the snapback process. New ggNMOS clamps are proposed which after some modification are shown to work. Some of the finite element experiments are repeated in a 0.18μπ7. process CMOS test chip and a comparison is made between the two sets of results. In the concluding chapter understanding that has been gained from previous chapters is combined with the published body of knowledge to suggest and explain improvements in the design of a ggNMOS for RF and standard applications. These improvements will improve homogeneity of ggNMOS operation thus allowing the device size to be reduced and parasitic loading for a given ESD performance. These techniques can also be used to ensure that the ESD current does not take an unintended path through the chip.

This thesis describes a study of pentacene-based organic electronic devices with poly(methyl methacrylate) (PMMA) and cross-linked PMMA (cPMMA) gate dielectrics. The electrical characteristics of pentacene-based organic thin-film transistors (OTFTs) using PMMA as the gate dielectric are reported. Uniform pinhole-free and crack-free films of PMMA could be obtained by spin-coating, with a lower limit to the thickness of about 150 nm. The effects of the insulator thickness and channel dimensions on the performance of the devices has been investigated. Leakage currents, which are present in many devices using polymeric gate dielectrics, were reduced by patterning the pentacene active layer. The resulting transistors exhibited minimal hysteresis in their output and transfer characteristics with an acceptable performance (a field-effect mobility of 0.33 cm2 V−1 s−1, a threshold voltage of -11 V, an on/off current ratio of 1.2X106 and a subthreshold slope of 1.5 V per decade). A bootstrapped inverter incorporating optimised pentacene OTFT structures, with PMMA as the gate dielectric, has been designed, fabricated and tested. The inverter uses capacitive coupling and bootstrapping effects, and exhibits superior performance to the normal diode-connected load inverter. The circuit has a 30 us rise time and 450 us fall time, at an operating frequency of 1 kHz and 30 V drive voltage. Pentacene-based OTFTs incorporating a PMMA gate insulator usually possess a large operating voltage, related to the thickness of the PMMA layer. A physical method, in particular ion-beam irradiation, to produce ultra-thin cross-linked layers of PMMA (33 nm) is introduced. It is demonstrated that physical cross-linking of the PMMA gate dielectric can be used to produce OTFTs with improved performance (a field-effect mobility of 1.1 cm2 V−1 s−1, a threshold voltage of -1 V, an on/off current ratio of 1.0X106 and a subthreshold slope of 220 mV per decade) and operating at low voltages, < 10 V. Low voltage memory transistors based on various charge storage elements (gold nanoparticles, ultra-thin aluminium and silver films) with cPMMA as the gate dielectric, have been investigated. Solution-processed OTFTs based on 6,13-bis(triisopropylsilylethynyl) (TIPS) pentacene with PMMA and cPMMA as the gate dielectric were also studied.

Existing equivalent circuit models of bipolar transistors are reviewed together with techniques for the evaluation of suitable values of the model elements. A method enabling the optimisation of the element values of any particular model in order to match the measured S parameters of a device that is to be modelled is described. This method uses a modified Gauss Newton algorithm to minimise an objective function defined as the sum of the squares of the weighted errors between the required S parameters and those of the model. Details are then given of a new modelling algorithm for the development of accurate equivalent circuit models which was developed from this original optimisation method. The new modelling algorithm requires some S parameter measurements of the device to be modelled' over an appropriate range of frequencies, together with a potentially suitable model. The initial model elements are optimised and then, if necessary, suitable topological changes, involving the addition or deletion of both elements and nodes, are made until a model having the. required accuracy or complexity is obtained. A number of examples are given of small-signal equivalent circuit models of bipolar transistors developed using the algorithm. These particular transistors were operating at frequencies up to lGHz .A further example is given of the use of the modelling algorithm in the development of a bias dependent small-signal model of two similar bipolar transistors operating at frequencies up to 2GHz . Additional S parameter data for the same two transistors is also used to demonstrate that the algoritim can be used successfully for the development of non-linear models.

Dispersion of particles in multiphase-flows can be both quantitatively and qualitatively characterised using modern optical or nonintrusive devices. The development of a nonintrusive particle sizer (NPS) is performed. This device employs a high intensity pulsed laser as a light source and a digital camera to capture the particle images. The dynamic image analysis (DIA) software is designed to analyse the captured images and control the inputs and outputs of the data. The NPS has the ability to operate using shadow sizing, direct illumination (DI) and particle mixture shadow (PMS) techniques. The architecture and working principles of each technique are described in detail. A novel technique, which is Particle Mixture Shadow has been developed for the characterisation of solid/liquid mixture dispersed in air. The capability of the technique to distinguish and size the solid and liquid particles is demonstrated. The sensitivities of laser intensity, image magnification factor and scattering angle on the accuracy of particle size have been investigated. In order to evaluate the repeatability and the accuracy of the NPS device, the measurements of certified microsphere particle sizes are repeated several times. The results are then validated against proprietary particles with specification data provided by the manufacturer. The particle size error of the developed device confirms that it has a good repeatability in sizing the particles. The device is applied to solid and liquid particles dispersed in fluid media using shadow and DI techniques. The results comparison between these techniques is also demonstrated.

Scanning electrical probe-based storage using phase change materials is considered as a promising data storage technology due to its potential to meet future needs for ultra-high areal density, low-power, non-volatility, and rewritability. It is therefore important to understand and model the write, read and erase processes of this new technology, so that likely performance limits can be predicted and recording media and recording systems designed. Thus, this thesis presents a theoretical framework and associated computational model for write, read, and erase processes in electrical probe storage on phase change materials (Ge2Sb2Te5). Investigations of the write performance in this thesis are mainly focused on writing crystalline bits in an amorphous background, which is investigated using a parametric approach to assess the role of the electrical, thermal, and thickness properties of the media stack and probe tip on the size and shape of recorded bits, and on the write voltage and power required. In addition, advanced modeling techniques including heterogeneous nucleation, threshold switching, contact resistance and surface roughness are also introduced into the writing simulation in order to mimic more closely a practical recording environment. Based on these investigations, the design of an optimal media stack is proposed, which comprises a thin Ge2Sb2Te5 layer sandwiched by a thin capping layer with fairly high electrical conductivity and low thermal conductivity and a thick underlayer with a high electrical conductivity and fairly low thermal conductivity. Readout performance is evaluated in this thesis by extending the previous 2-D model to 3D, aiming to pursue a realistic read current and understand effects of the noise on the read process. It is found that isolated crystalline bits extending through the amorphous matrix exhibits a better reading contrast than either crystalline bits embedded in the amorphous matrix or amorphous bits on top portion of the crystalline matrix. Isolated amorphous bits on the crystalline matrix give the narrowest read pulse width, the largest peak-peak readout signal, and the least noise effect, but the writing of amorphous bits is difficult due to the high field and temperature in the capping/underlayer. This thesis also investigated the erasure of both crystalline bits and amorphous bits in a scanning probe phase change memory. The amorphous bit in a crystalline matrix can be easily erased (re-crystallized), but the erasing of crystalline bits in an amorphous matrix is problematic and always accompanied by the formation of an unwanted crystalline ‘ring’ surrounding the originally recorded bit. Two novel approaches, i.e. patterned Ge2Sb2Te5 media in an SiO2 matrix and slow ‘growth’ material are proposed in order to overcome such a ‘ring’ effect. It was found that patterned Ge2Sb2Te5 media can entirely remove the ‘ring’, but the thermal conductivity of the capping/underlayer needs to be chosen carefully to avoid high temperature appearing in these two layers. The fabrication of such patterned media on the nanoscale dimensions needed for ultra-high density storage is however problematic. The use of ‘slow-growth’ material improves the erase performance of continuous (i.e. unpatterned) Ge2Sb2Te5 films, but without a complete removal of the ‘ring’. Finally, using the optimized design of media stack and a suitable probe tip the feasibility of writing and reading at an areal density of 10Tbit/inch2 has been demonstrated, with a much lower power/energy (1.08pJ/bit) than in any previous work.

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This thesis describes the design and construction of a differential absorption lidar system for the measurement of ambient levels of sulphur dioxide in agricultural environments. Chapter 1 discusses the effects of sulphur dioxide in the environment together with the most common methods used for analysis. The principles of the lidar technique are presented in Chapter 2. Chapter 3 describes in detail the instrumental system design including the laser transmitter, the telescope receiver, the transient signal digitizer and the microcomputer used for experimental control and data handling. The electronic control circuitry and computer programs are described in Chapters 4 and 5. An account of preliminary experimental results is given in Chapter 6 and the error involved in the measurement of the spatial distribution of sulphur dioxide is investigated in Chapter 7. Appendices I and II give schematic electronic circuit diagrams and computer program flow charts.

This thesis reports on work undertaken to analyse, design, optimise, and fabricate a high-Quality factor mechanical resonant magnetometer, based on a Xylophone Bar Resonator (XBR). The principle of operation is based on the use of nodal supports to mechanically isolate a transverse beam vibrating in its fundamental mode. A control model is developed for the device, incorporating the effect of electromechanical parametric amplification. The device response and performance is shown to be strongly dependent on the Q factor of the sense element. The need for a quantitative model of XBR dynamics in order to design an optimal XBR is thus established. Using a Rayleigh-Ritz based approach, a model of the modal dynamics of an XBR is developed for the first time. In order to examine the efficacy of the nodal supports, a new model for support loss for resonators with two supports is developed and presented. Analytical models for other sources of dissipation are adapted for the first time to the XBR case. Combining these developments with a system level model allows for the development of a quantitative predictor of the fundamental and electronic noise limits on performance for an XBR. The model is solved over the operational range of geometric parameters, yielding optimisation criteria for the geometry. Corresponding predictions for the force and magnetic field sensitivity are presented. Based on the results, an optimised XBR design is exhibited for a macroscopic metal flexural XBM to be fabricated via Wire EDM. The fabricated devices are characterised, constituting the first demonstration of a macroscopic flexural XBR. The resulting Q factors and sensitivities are shown to be in agreement with the predictions. Fruitful directions for further work are suggested throughout the thesis and summarised in the conclusions. The original contribution to knowledge made by the thesis can be summarised as the development of an original and detailed theory of the principles of XBR optimisation for high Q, and demonstration of an operational macroscopic flexural XBM for the first time.