The objective of this thesis is to present the design and implementation of ultra-low power radio transceivers at microwave frequencies, which are applicable to wireless sensor network (WSN) and, in particular, to the requirement of the Speckled Computing Consortium (or SpeckNet). This was achieved through quasi-MMIC prototypes and monolithic microwave integrated circuit (MMIC) with dc power consumption of less than 1mW and radio communication ranges operating at least one metre. A wireless sensor network is made up of widely distributed autonomous devices incorporating sensors to cooperatively monitor physical environments. There are different kinds of sensor network applications in which sensors perform a wide range of activities. Among these, a certain set of applications require that sensor nodes collect information about the physical environment. Each sensor node operates autonomously without a central node of control. However, there are many implementation challenges associated with sensor nodes. These nodes must consume extremely low power and must communicate with their neighbours at bit-rates in the order of hundreds of kilobits per second and potentially need to operate at high volumetric densities. Since the power constraint is the most challenging requirement, the radio transceiver must consume ultra-low power in order to prolong the limited battery capacity of a node. The radio transceiver must also be compact, less than 5×5 mm2, to achieve a target size for sensor node and operate over a range of at least one metre to allow communication between widely deployed nodes. Different transceiver topologies are discussed to choose the radio transceiver architecture with specifications that are required in this project. The conventional heterodyne and homodyne topologies are discussed to be unsuitable methods to achieve low power transceiver due to power hungry circuits and their high complexity. The super-regenerative transceiver is also discussed to be unsuitable method because it has a drawback of inherent frequency instability and its characteristics strongly depend on the performance of the super-regenerative oscillator. Instead, a more efficient method of modulation and demodulation such as on-off keying (OOK) is presented. Furthermore, design considerations are shown which can be used to achieve relatively large output voltages for small input powers using an OOK modulation system. This is important because transceiver does not require the use of additional circuits to increase gain or sensitivity and consequently it achieves lower power consumption in a sensor node. This thesis details the circuit design with both a commercial and in-house device technology with ultra-low dc power consumption while retaining adequate RF performance. It details the design of radio building blocks including amplifiers, oscillators, switches and detectors. Furthermore, the circuit integration is presented to achieve a compact transceiver and different circuit topologies to minimize dc power consumption are described. To achieve the sensitivity requirements of receiver, a detector design method with large output voltage is presented. The receiver is measured to have output voltages of 1mVp-p for input powers of -60dBm over a 1 metre operating range while consuming as much as 420μW. The first prototype combines all required blocks using an in-house GaAs MMIC process with commercial pseudomorphic high electron mobility transistor (PHEMT). The OOK radio transceiver successfully operates at the centre frequency of 10GHz for compact antenna and with ultra-low power consumption and shows an output power of -10.4dBm for the transmitter, an output voltage of 1mVp-p at an operating range of 1 metre for the receiver and a total power consumption of 840μW. Based on this prototype, an MMIC radio transceiver at the 24GHz band is also designed to further improve the performance and reduce the physical size with an advanced 50nm gate-length GaAs metamorphic high electron mobility transistor (MHEMT) device technology.

Multilevel converters have attracted a great deal of interest in recent years since they offer a number of advantages in many high voltage and high power applications, such as adjustable speed electric motor drives and power systems through Flexible Alternating Current Transmission Systems (FACTS) controllers and active harmonic filters. They can reach high voltages with low harmonics without the use of transformers or series-connected synchronised switching devices by their unique structures. Along with proper Pulse-Width Modulation (PWM) control scheme, they can also provide lower cost, higher performance, lower Electro-Magnetic Interference (EMI), and higher efficiency than the traditional PWM converters. However, switching losses become a serious issue in high power applications. In order to improve the efficiency and reliability of the system, and reduce the size of the output filter, the stresses on the semiconductors and the development and manufacturing costs, reducing the switching frequency and associated losses of multilevel PWM converters and systems needs to be properly addressed. The thesis gives an overview on multilevel converter topologies and control schemes. It then presents mathematical analysis towards further understanding of the Neutral-Point-Clamped (NPC) and the Flying Capacitor (FC) converters. The Fundamental Frequency Sinusoidal PWM (FF-SPWM) control method is examined as a potential "carrier" based approach in reducing the converter switching frequency and associated losses. The performance of multi-modular parallel connected systems based on the NPC and FC converters as a building block is reported along with the influence of the multicarrier PWM techniques. The voltage-unbalancing problem of the FC converter is addressed and a solution is provided. DSP based controllers for the three-level and the five-level FC converters have been developed and experimentally verified. Results taken from the laboratory prototype are presented to support the theoretical part of the project.

This thesis describes a comprehensive, simulation based scaling study – including device design, performance characterization, and the impact of statistical variability – on deca-nanometer bulk MOSFETs. After careful calibration of fabrication processes and electrical characteristics for n- and p-MOSFETs with 35 nm physical gate length, 1 nm EOT and stress engineering, the simulated devices closely match the performance of contemporary 45 nm CMOS technologies. Scaling to 25 nm, 18 nm and 13 nm gate length n and p devices follows generalized scaling rules, augmented by physically realistic constraints and the introduction of high-k/metal-gate stacks. The scaled devices attain the performance stipulated by the ITRS. Device a.c. performance is analyzed, at device and circuit level. Extrinsic parasitics become critical to nano-CMOS device performance. The thesis describes device capacitance components, analyzes the CMOS inverter, and obtains new insights into the inverter propagation delay in nano-CMOS. The projection of a.c. performance of scaled devices is obtained. The statistical variability of electrical characteristics, due to intrinsic parameter fluctuation sources, in contemporary and scaled decananometer MOSFETs is systematically investigated for the first time. The statistical variability sources: random discrete dopants, gate line edge roughness and poly-silicon granularity are simulated, in combination, in an ensemble of microscopically different devices. An increasing trend in the standard deviation of the threshold voltage as a function of scaling is observed. The introduction of high-k/metal gates improves electrostatic integrity and slows this trend. Statistical evaluations of variability in Ion and Ioff as a function of scaling are also performed. For the first time, the impact of strain on statistical variability is studied. Gate line edge roughness results in areas of local channel shortening, accompanied by locally increased strain, both effects increasing the local current. Variations are observed in both the drive current, and in the drive current enhancement normally expected from the application of strain. In addition, the effects of shallow trench isolation (STI) on MOSFET performance and on its statistical variability are investigated for the first time. The inverse-narrow-width effect of STI enhances the current density adjacent to it. This leads to a local enhancement of the influence of junction shapes adjacent to the STI. There is also a statistical impact on the threshold voltage due to random STI induced traps at the silicon/oxide interface.

This thesis describes the reliable design of tunnel diode and resonant tunneling diode (RTD) oscillator circuits. The challenges of designing with tunnel diodes and RTDs are explained and new design approaches discussed. The challenges include eliminating DC instability, which often manifests itself as low frequency parasitic oscillations, and increasing the low output power of the oscillator circuits. To stabilise tunnelling devices, a common but sometimes ineffective approach is the use of a resistor of suitable value connected across the device. It is shown in this thesis that this resistor tunnel diode circuit can be described by the Van der Pol model. Based on this model, design equations have been derived which enable the design of current-voltage (I-V) measurement circuits that are free from both low frequency bias oscillations and high frequency parasitic oscillations. In the conventional setup, the I-V characteristic of the tunnelling device is extracted from the measurement by subtracting from the measured current the current through the stabilising resistance at each bias voltage. In this thesis, also using the Van der Pol model, a circuit for the direct measurement of I-V characteristics is proposed. This circuit utilises a series resistor-capacitor combination in parallel with the tunnelling device for stabilisation. Experimental results show that IV characterisation of tunnel diodes in the negative differential resistance (NDR) region free from oscillations can be made. A new test set-up suitable for radio frequency (RF) characterisation of tunnel diodes over the entire NDR region was also developed. Initial measurement results on a packaged tunnel diode indicate that accurate characterisation and subsequent small-signal equivalent circuit model extraction for the NDR region can be done. To address the limitations of low output power of tunnel diode or RTD oscillators, a new multiple device circuit topology, incorporating a novel design methodology for the DC bias decoupling circuit, has been developed. It is based on designing the oscillator specifically for sinusoidal oscillations, and not relaxation oscillations which are also possible in tunnel diode oscillators. The oscillator circuit can also be described by the Van der Pol model which provides theoretical predictions of the maximum inductance, in terms of the tunnel diode device parameters, that is required to resonate with the device capacitance for sinusoidal oscillations. Each of the tunnel diodes in the multiple device oscillator circuit is decoupled from the others at DC and so can be stabilised independently. The oscillator topology uses parallel resonance but with each tunnel diode individually biased and DC decoupled making it possible to employ several tunnel diodes for higher output power. This approach is expected to eliminate parasitic bias oscillations in tunnel diode oscillators whilst increasing the output power of a single oscillator. Simulation and experimental oscillator results were in good agreement, with a two-tunnel diode oscillator exhibiting approximately double the output power as compared to that of a single tunnel diode oscillator, i.e. 3 dB higher. Another method considered for the realisation of higher output power tunnel diode or RTD oscillators was series integration of the NDR devices. A new method to suppress DC instability of the NDR devices connected in series with all the devices biased in their NDR regions was investigated. It was successfully employed for DC characterisation with integrations of 2 and 5 tunnel diodes. Even though no suitable oscillator circuit topology and/or methodology with series-connected NDR devices could be established for single frequency oscillation, the achieved results indicated that this approach may be worthy of further investigation. The final aspect of this project focussed on the monolithic realisation of RTD oscillators. Monolithic oscillators in coplanar waveguide (CPW) technology were successfully fabricated and worked at a fundamental frequency of 17.5 GHz with -21.83 dBm output power. Finally, to assess the potential of RTD oscillators for high frequency signal generation, a theoretical analysis of output power of stabilised RTD oscillators was undertaken. This analysis suggests that it may be possible to realise RTD oscillators with high output power (0 dBm) at millimetre-wave and low terahertz (up to 1 THz) frequencies.

The ultrashort pulses emitted by passive semiconductor mode-locked lasers (PSMLLs) can be applied to a wide range of applications, including modern optical communication systems, optical sampling, security, imaging or sensing. For most of these applications, it is of critical importance to gather detailed information on the mode-locked laser (MLL) dynamics as well as on the temporal intensity and phase profiles of the pulses. The pulse formation in a PSMLL is in fact a very complex mechanism that is governed by the close interplay between a number of linear and nonlinear phenomena, influenced by various semiconductor parameters. The complete characterisation of the devices as a function of the laser driving parameters, geometry and semiconductor material structure has therefore the potential to provide a deeper understanding of the PSMLL behaviour. As the available detectors are usually incapable of resolving the temporal structures of ultrashort pulses from the high repetition rate MLLs, a number of indirect measurement solutions have been developed for full pulse characterisation. However, these methods are designed for lasers with high-energy optical pulses or require pulse synchronisation or ultrafast modulation. This obviously restricts their suitability for the unsynchronised, low energy and high repetition rate pulses as those emitted by the mode-locked laser diodes. In this work, an extensive study of various dynamical regimes, such as mode-locking, self-pulsation and continuous-wave operations of the monolithically integrated AlGaInAs/InP MLLs is reported. The devices operate around 1.55 µm and emit optical pulses with sub-40 GHz repetition frequencies. The influence of the biasing conditions, laser geometry and semiconductor material on the lasers performance is analysed in detail. The complete characterisation includes the evaluation of both the phase and time profiles of pulses, using a sonogram system developed as part of this thesis. It is based on a self-referenced method, capable of ambiguity-free measurements of low power and sub-picosecond pulses. A sensitivity as low as 5mW on the pulse peak power has been achieved through the design and fabrication of a two-photon absorption (TPA) detector, optimised for polarisation insensitivity and high nonlinear response. The travelling-wave operation enables the characterisation of high-repetition rate pulses and minimises the amount of introduced dispersion. The sonogram system has been successfully employed to study the evolution of the temporal intensity and group delay profiles as a function of the laser biasing conditions and for different device geometries. The obtained results indicate a prevailing positive chirp present in the pulses, which can be reduced by a careful adjustment of the device biasing. The minimum pulse width emitted from the investigated MLLs and measured with the sonogram technique was ~500 fs.

Analog-to-digital converters play a crucial role in modern audio and communication design. Conventional Nyquist converters are suitable only for medium resolutions and require analog components that are precise and highly immune to noise and interference. In contrast, oversampling converters can achieve high resolutions (>20bits) and can be implemented using straightforward, high-tolerance analog components. In conventional oversampled modulators, negative feedback is applied in order to control the dynamic behavior of a system and to realize the attenuation of the quantization noise in the signal band due to noise shaping. However, feedback can also introduce undesirable effects such as limit cycles, jitter problems in continuous-time topologies, and infinite impulse responses. Additionally, it increases the system complexity due to extra circuit components such as nonlinear multi-bit digital-to-analog converters in the feedback path. Moreover, in certain applications such as wireless, biomedical sensory, or microphone implementations feedback cannot be applied. As a result, the main goal of this thesis is to develop sigma-delta data converters without feedback. Various new delta-sigma analog-to-digital converter topologies are explored their mathematical models are presented. Simulations are carried out to validate these models and to show performance results. Specifically, two topologies, a first-order and a second-order oscillator-based delta-sigma modulator without feedback are described in detail. They both can be implemented utilizing VCOs and standard digital gates, thus requiring only few components. As proof of concept, two digital microphones based on these delta-sigma converters without feedback were implemented and experimental results are given. These results show adequate performance and provide a new approach of measuring.

The applicability and functionality of high frequency digital and millimetre wave circuits can be enhanced by the integration of sensor elements into the circuits. It is furthermore advantageous to utilise or modify the pre–existing fabrication process flow in creating this added functionality. This thesis describes a work on magnetic field sensors based on an InP/InGaAs heterojunction bipolar transistor (HBT) which has been fabricated to be compatible with high frequency epilayer structure and processes. In this work, the complete fabrication process for the HBT magnetic sensors has been developed, using standard, transferrable process modules. Ohmic contact metallisations were optimised and D.C. electrical characterisations are also reported upon. The effects of several surface treatments on device performance have been studied and characterised. Surface passivation using two distinct sulphur containing compounds of different phases was shown to enhance performance and an ion bombardment process was developed that degraded surface quality and increased surface leakage currents for enhanced sensor performance. In order to improve the sensitivity of an HBT to magnetic field 3–dimensional magnetic structures were designed to be incorporated onto the surface of the extrinsic base. This design process was informed by simulation of magnetic field profiles of the magnetic elements and fabrication processes were created that would allow for arbitrary 3–dimensional structures. The response to magnetic field applied both parallel and perpendicular to the normal of the wafer of an as–fabricated HBT was investigated. Two different emitter structures were compared, a simple square emitter and a multiple finger emitter, and the ability of the devices to resolve applied field angle was uncovered. The effects of device bias on the field response was also looked at and the optimal bias conditions determined. An analysis of the temperature variation of the magnetic field response was conducted with lower temperatures resulting in higher sensitivity to applied field. Finally, the response of an HBT with integrated 3–dimensional magnetic structures was investigated. A passivated device was found to be less sensitive to applied magnetic field and a device treated with ion bombardment to be more sensitive to magnetic field applied parallel to the normal. The signal to noise ratio for an HBT with integrated magnetic structures was 36.4 dB with an equivalent noise of 0.002 T. The maximum magnetic field strength sensitivity was 0.339 T^(−1) and the maximum magnetic field applied angle sensitivity was 0.119 rad^(−1). The maximum change in normalised D.C. current gain was 0.019. A mathematical description of the change in current gain caused by a given magnetic field applied at a given angle was also determined.

The field of Autonomous Underwater Vehicles (AUVs) has increased dramatically in size and scope over the past two decades. Application areas for AUVs are numerous and varied; from deep sea exploration, to pipeline surveillance to mine clearing. However, one limiting factor with the current technology is the duration of missions that can be undertaken and one contributing factor to this is the efficiency of the propulsion system, which is usually based on marine propellers. As fish are highly efficient swimmers greater propulsive efficiency may be possible by mimicking their fish tail propulsion system. The main concept behind this work was therefore to investigate whether a biomimetic fish-like propulsion system is a viable propulsion system for an underwater vehicle and to determine experimentally the efficiency benefits of using such a system. There have been numerous studies into biomimetic fish like propulsion systems and robotic fish in the past with many claims being made as to the benefits of a fish like propulsion system over conventional marine propulsion systems. These claims include increased efficiency and greater manoeuvrability. However, there is little published experimental data to characterise the propulsive efficiency of a fish like propulsive system. Also, very few direct experimental comparisons have been made between biomimetic and conventional propulsion systems. This work attempts to address these issues by directly comparing experimentally a biomimetic underwater propulsion system to a conventional propulsion system to allow for a better understanding of the potential benefits of the biomimetic system. This work is split into three parts. Firstly, the design and development of a novel prototype vehicle called the RoboSalmon is covered. This vehicle has a biomimetic tendon drive propulsion system which utilizes one servo motor for actuation and has a suite of onboard sensors and a data logger. The second part of this work focuses on the development of a mathematical model of the RoboSalmon vehicle to allow for a better understanding of the dynamics of the system. Simulation results from this model are compared to the experimental results and show good correlation. The final part of the work presents the experimental results obtained comparing the RoboSalmon prototype with the biomimetic tail system to the propeller and rudder system. These experiments include a study into the straight swimming performance, recoil motion, start up transients and power consumption. For forward swimming the maximum surge velocity of the RoboSalmon was 0.18ms-1 and at this velocity the biomimetic system was found to be more efficient than the propeller system. When manoeuvring the biomimetic system was found to have a significantly reduced turning radius. The thesis concludes with a discussion of the main findings from each aspect of the work, covering the benefits obtained from using the tendon drive system in terms of efficiencies and manoeuvring performance. The limitations of the system are also discussed and suggestions for further work are included.

The International Technology Roadmap for Semiconductors (ITRS) specifies that MOSFET logic devices are to be scaled to sub-10nm dimensions by the year 2020, with 32nm bulk devices ready for production and double-gate FinFET devices demonstrated down to 5nm channel lengths. Future device generations are expected to have lower channel doping in order to reduce variability in devices due to the discrete nature of the channel dopants. Accompanying the reduced channel doping is a corresponding increase in the screening length, which is even now comparable with the channel length. Under such conditions, Coulomb scattering mechanisms become increasingly complex as the scattering potential interacts with a larger proportion of the device. Ionized impurity scattering within the channel is known to be an important Coulombic scattering mechanism within MOSFETs. Those channel impurities located close to the heavily doped source and drain or both, will induce a polarisation charge within the source and drain. These polarisation charge effects are shown in this work to increase the net screening of the channel impurities, due to the inclusion of remote screening effects, and significantly decrease the scattering rate associated with ionized impurity scattering. Remote screening can potentially reduce the control by ionized channel impurities over channel transport properties, leading to an increased sub-threshold current. A potential model has been obtained that is based on an exact solution of Poisson’s equation for an ionized impurity located close to one or both of these highly doped contact regions. The model shows that remote screening effects are evident within a few channel screening lengths of the highly doped contact regions. The resultant scattering model developed from this potential, which is based on the Born approximation, is implemented within a Monte Carlo simulator and is applied to MOSFET device simulation. The newly developed ionized impurity scattering model, which allows for remote screening, is applied in the simulation of two representative MOSFET devices: the first device being a bulk MOSFET device developed for the 32nm technology generation; the second device is an Ultra-Thin-Body Double Gate (UTB DG) MOSFET developed for the forthcoming 22nm technology generation. Thorough investigative simulations show that for both the bulk MOSFET and the UTB DG MOSFET, that remote screening of channel impurities in these devices is not a controlling effect. These results prove that the current model for ionized impurity scattering employed in Monte Carlo simulations is sufficient to model devices scaled to at least the 22nm technology node, predicted to be in production in the year 2012.

It has been of major interest in recent research to produce faster optical processing for many telecommunications applications, as well as other applications of high performance optoelectronics. The combination of one-dimensional photonic crystal structures (PhC) and narrow photonic wire (PhW) waveguides in high refractive-index contrast materials such as silicon-on-insulator (SOI) is one of the main contenders for provision of various compact devices on a single chip. This development is due to the ability of silicon technology to support monolithic integration of optical interconnects and form fully functional photonic devices incorporated into CMOS chips. The high index contrast of the combination of a silicon core with a surrounding cladding of silica and/or air provides strong optical confinement, leading to the realization of more compact structures and small device volumes. In order to obtain a wide range of device functionality, the reduction of propagation losses in narrow wires is equally important, although there are still performance limitations determined by fabrication processes. Compact single-row PhC structures embedded in PhW waveguide micro-cavities could become essential components for wavelength selective devices, especially for possible application in WDM systems. The high quality factor, Q, and confinement of light in a small volume, V, are important for optical signal processing and filtering purposes, implying large Purcell factor values. In this thesis, one-dimensional photonic crystal/photonic wire micro-cavities have been designed and modeled using both 2D and 3D versions of the finite-difference time-domain (FDTD) approach. These devices were fabricated using electron beam lithography (EBL) and reactive ion etching (RIE) for patterning of the silicon layer. The device structures were characterized with TE polarized light, using a tunable laser covering the range from 1480 nm to 1585 nm. Single-row periodic hole-type PhC mirrors consisting of identical and equally spaced holes were embedded in 500 nm wire waveguides. Two PhC hole mirrors were separated with a cavity spacer varying from 400 nm to 500 nm in length to form a micro-cavity. In contrast, several different cavity arrangements were also successfully investigated, - i.e. extended cavity and coupled micro-cavity structures. The experimental results on photonic crystal/photonic wire micro-cavity structures have demonstrated that further enhancement of the quality-factor (Q-factor) - up to approximately 149,000 at wavelengths in the fibre telecommunications range is possible. The Q factor values and the useful transmission levels achieved are due, in particular, to the combination of both tapering within and outside the micro-cavity, with carefully designed hole diameters and non-periodic hole placement within the tapered sections. On the other hand, a large resonance quality factor of approximately 18,500, together with high normalized transmission of 85% through the use of tapering on both sides of the hole-type PhC mirrors that formed the micro-cavity, has been obtained. For the extended cavity case, the multiple resonances excited within the stop band, together with substantial tuning capability of the resonances obtained by varying the cavity length has been demonstrated, together with a Q-factor value of approximately 74,000 at the selected resonance frequency with a normalised transmission of 40%. In addition, the coupled micro-cavity structures considered in this thesis have formed the basic building block for designing multiple cavity structures where the combination of several cavities splits the selected single cavity resonance frequency into a number of resonances that depends directly on the number of cavities used in the design. The coupling strength between the resonators and the Free Spectral Range (FSR) between the split resonance frequencies of the coupled cavity combination were controlled via the use of different numbers of periodic hole structures – and through the use of different aperiodic hole taper arrangements between the two cavities in the middle section of the mirrors.