abstract: This thesis presents approaches to develop micro seismometers and accelerometers based on molecular electronic transducers (MET) technology using MicroElectroMechanical Systems (MEMS) techniques. MET is a technology applied in seismic instrumentation that proves highly beneficial to planetary seismology. It consists of an electrochemical cell that senses the movement of liquid electrolyte between electrodes by converting it to the output current. MET seismometers have advantages of high sensitivity, low noise floor, small size, absence of fragile mechanical moving parts and independence on the direction of sensitivity axis. By using MEMS techniques, a micro MET seismometer is developed with inter-electrode spacing close to 1μm, which improves the sensitivity of fabricated device to above 3000 V/(m/s^2) under operating bias of 600 mV and input acceleration of 400 μG (G=9.81m/s^2) at 0.32 Hz. The lowered hydrodynamic resistance by increasing the number of channels improves the self-noise to -127 dB equivalent to 44 nG/√Hz at 1 Hz. An alternative approach to build the sensing element of MEMS MET seismometer using SOI process is also presented in this thesis. The significantly increased number of channels is expected to improve the noise performance. Inspired by the advantages of combining MET and MEMS technologies on the development of seismometer, a low frequency accelerometer utilizing MET technology with post-CMOS-compatible fabrication processes is developed. In the fabricated accelerometer, the complicated fabrication of mass-spring system in solid-state MEMS accelerometer is replaced with a much simpler post-CMOS-compatible process containing only deposition of a four-electrode MET structure on a planar substrate, and a liquid inertia mass of an electrolyte droplet encapsulated by oil film. The fabrication process does not involve focused ion beam milling which is used in the micro MET seismometer fabrication, thus the cost is lowered. Furthermore, the planar structure and the novel idea of using an oil film as the sealing diaphragm eliminate the complicated three-dimensional packaging of the seismometer. The fabricated device achieves 10.8 V/G sensitivity at 20 Hz with nearly flat response over the frequency range from 1 Hz to 50 Hz, and a low noise floor of 75 μG/√Hz at 20 Hz. / Dissertation/Thesis / Ph.D. Electrical Engineering 2014

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Neural probes are a promising tool in understanding the brain, alleviating symptoms of various diseases like Parkinson’s Disease and allowing for applications like controlling prosthetics directly using the mind. However, current probes suffer from deleterious glial tissue buildup, poor insulation and low electrode yield. In this work, to improve upon current probes, ultra-compliant probes are fabricated and integrated with biodissolvable needles. Mechanically compliant probes allow for reduction in the body’s immune response chronically whereas biodissolvable needles provide sufficient stiffness during insertion. To achieve this, contributions are made in the categories of probe design concepts, device level processes, and processes in support of final probe assembly. Major contributions include incorporation of interleaved atomic layer deposited ceramics to create hybrid materials that provide better insulation properties, reducing the distance between the electrode and the site-of-interest by developing a gray scale lithography based technique to fabricate protruding electrodes and creating probes that improve electrode yield by integrating liquid crystal polymers into the parylene-C probe structure, which allows the parylene-C probe to actuate. To allow for integration of the biodissolvable needle with the probe, a peel-based process is developed that controls the adhesion between parylene-C to Si using different HMDS conditions and a transfer based process is developed that enables hightemperature annealing. In addition, a generalized design of neural probes using meandering interconnect structures is developed, allowing for rapid mechanical design of probes. This is key for neural probes because of the application specific nature of neural probe design.

Over the past several years, rapid advances in the field of integrated photonics coupled with nanofabrication capabilities have enabled studies of the interaction of light with the mechanics of a variety of physical structures. Concurrently, mechanical resonators have been extensively studied in the MEMS community due to their high quality factors, and have been implemented in a variety of RF filters and oscillators. The combination of MEMS with integrated optomechanical structures can generate a variety of novel devices that can be used for applications in RF-Photonics, timing and optical switching. While there are several demonstrations of electrostatic devices integrated with optomechanical structures, fewer examples exist in the piezoelectric domain. In particular, photonic integration in a piezoelectric material can benefit from some of the traditional strengths associated with this type of actuation, such as the ability to easily scale to higher frequencies of operation by patterning lateral features, the ability to interface with 50Ω electronics and strong electromechanical coupling. In addition, it enables a platform to produce new architectures for photonic-based electronic frequency reference oscillators that incorporate multiple degrees of freedom. This thesis presents the development of a piezoelectrically-actuated acousto-optic modulator in the aluminum nitride (AlN) material system. The process of implementing this device is carried out in five principal stages. First, light coupling from optical fibers to the AlN thin film is demonstrated with the use of on-chip grating couplers, exhibiting a peak insertion loss of -6.6 dB and a high 1 dB bandwidth of 60 nm for operation in the telecommunications C- and L-bands. This is followed by characterization of photonic whispering gallery mode microdisk and microring resonators with optical quality factors on the order of 104. Next, a robust fabrication method combining optical and electron-beam lithography is developed to produce a fully-integrated device preserving the critical features for acoustic and photonic resonators to be colocalized in the same platform. Acousto-optic modulation is demonstrated with the use of a contour mode resonator which drives displacements in the photonic resonator at 653 MHz, corresponding to the mechanical resonance of the composite structure. The modulator is then implemented in an opto-acoustic oscillator loop, for which an initial phase noise of -72 dBc/Hz at 10 kHz offset from the carrier is recorded with a large contribution from thermal noise at the photodetector. Finally, some possibilities to improve the modulator efficiency and oscillator phase noise are provided along with prospects for future work in this area.

Dans cette thèse, les diodes Schottky pour des applications en ondes millimétriques et aux fréquences térahertz sont étudiées. Une méthodologie de conception et d'optimisation est proposée pour améliorer la performance de telles diodes. La conception et les simulations sont effectuées à l'aide d'un programme basé sur un modèle analytique. Les différentes méthodes de calcul de la fréquence de coupure de la diode sont définies, étudiées et classifiées selon les applications potentielles. En utilisant un modèle de diode générique et général, une nouvelle approche pour calculer la fréquence de coupure est suggérée pour les applications de mélangeur / multiplicateur. Cette approche permet d'évaluer la tension seuil avec une précision beaucoup plus grande et proche de la réalité. En outre, la conception d’une diode Schottky en tenant compte dès le départ l’application visée (détecteur direct, mélangeur ou multiplicateur) est étudiée. Cette thèse montre que l'ingénierie de la structure épitaxiale a un impact important lorsque l’on utilise une conception de diode basée sur l’application finale comme proposée. Un procédé de microfabrication a été entièrement développé et caractérisé. Une méthode de planarisation unique est introduite pour permettre de connecter la diode par des ponts à air en minimisant les effets parasites. Afin d'éviter une coûteuse lithographie par faisceau électronique, une anode en forme de T est produite en utilisant une technique de photolithographie. Ce procédé est fiable et répétitif, est de faible coût et offre une grande souplesse en matière de conception en plus de répondre au besoin d‘une production de masse, pour laquelle la lithographie par faisceau d’électrons n’est guère possible. Le procédé final nécessite simplement deux étapes de métallisation, nombre minimal possible que nous avons atteint. En raison des exigences de recuit du contact ohmique, il est impossible d’avoir moins de deux étapes de métallisation. Le processus de planarisation proposé repose sur l'utilisation de différents taux de gravure plasma de deux résines couramment utilisées. Pour les travaux réalisés dans cette thèse, une épitaxie GaAs HBT disponible au sein du laboratoire a été utilisée. Les résultats de caractérisation de diodes réalisés dérivés des mesures DC et RF sont rapportés et comparés avec les résultats de la simulation. Les résultats de mesure montrent une réduction significative de la capacité parasite de la diode à moins de 20% de sa capacité totale. Par conséquent, le procédé de conception et de fabrication de ce travail peut fournir des diodes qui peuvent fonctionner au-delà du térahertz avec des dimensions pour l’anode plus grandes que les diodes trouvées dans la littérature et qui peuvent donc être fabriquées uniquement par des techniques de photolithographie optique. / Abstract: In this thesis, Schottky diodes for millimeter waves and terahertz application are scrutinized. A design and optimization methodology is proposed to improve the diode performance. Design and simulations are performed by using an analytical model based code. Diode cut-off frequency calculation methods are studied and classified for different applications. Considering general diode equivalent circuit model, a new approach for calculating the cut-off frequency is suggested for mixer/multiplier applications. This approach provides cut-off much closer to its practical value. Also, the diode design based on its application, direct detector and mixer/multiplier, is studied. It is shown that the epitaxial structure engineering has impact on diode application based design. For diode realization a microfabrication process is developed. Unique planarization method is introduced which provides necessary substruction for the airbridges. In order to avoid expensive e-beam lithography, a T-shaped anode is produced by employing photolithography technique. This process is repeatable, reliable, low cost, gives high flexibility in design terms, and suitable for mass production. The final process merely requires two metallization steps which is minimum possible number due to annealing requirement of ohmic contact. The proposed planarization process is based on using different plasma etching rates of two common resists. In the diode fabrication an available GaAs HBT epitaxial wafer is used. The realized diode characterization results derived from DC and RF measurements are reported and compared with the simulation results. The measurement results showed significant reduction in parasitic capacitance of the diode to under twenty percent of its total capacitance. Therefore, the design and fabrication method of this work can provide diodes to operate over one terahertz with larger anode area (that can be produced by photolithography techniques).

Cette thèse porte sur l'exploration des propriétés de l'interface entre les deux cuprates supraconducteurs La1.85Sr0.15CuO4 et Pr1.85Ce0.15CuO4 réunis selon l'axe c sous la forme d'une bicouche. En particulier, on y démontre l'existence d'un phénomène de transfert de charge entre ces deux matériaux qui génère, à l'interface, une région isolante que nous surnommons le "plateau de Mott". Cette thèse couvre de nombreux sujets que l'on peut diviser en deux axes principaux. D'abord les aspects liés à la croissance et à la structure de la bicouche et ensuite les propriétés de transport de l'interface isolante. Dans un premier temps, une interface directe et franche entre ces deux cuprates de dopages opposés est réalisée via une optimisation de la croissance épitaxiale de ces matériaux en bicouche par ablation laser pulsé. La qualité cristalline des meilleurs échantillons obtenus est exceptionnelle, et ce, malgré l'important désaccord de maille entre les deux structures. La structure cristalline est ensuite principalement caractérisée par la diffraction des rayons X. Cette mesure permet d'obtenir des informations pertinentes sur la composition, l'homogénéité et les dimensions caractéristiques des couches minces. Le champ de déformation causé principalement par le désaccord de maille et la présence de dislocations à l'interface est également étudié. À cet effet, le formalisme de séparation des effets de taille et des déformations structurelles de Warren et Averbach est adapté au cas particulier des couches minces. L'accord frappant avec laquelle ce formalisme s'applique à nos résultats témoigne de la qualité des mesures expérimentales et de la netteté de ces structures. Afin d'expliquer la forme du champ de déformation mesuré, un modèle analytique basé sur la présence de dislocations d'interface est développé. Celui-ci nous permet, entre autres, d'extraire les paramètres caractéristiques du champ de déformation. Ces nouveaux outils d'analyse permettront sans doute de tirer davantage d'informations pertinentes de la diffraction des rayons X dans des projets futurs. La mise en évidence de l'existence du plateau de Mott et la caractérisation des propriétés sont menées via des mesures de résistance électrique. Plusieurs obstacles liés à la microfabrication des échantillons doivent d'abord être considérés. Le présent travail permet d'identifier un certain nombre de procédés qui provoquent une dégradation, parfois fatale, des propriétés des bicouches de cuprates. Dans certains cas, des solutions sont fournies ou suggérées. Les causes de ces dégradations sont généralement en lien avec la mobilité des atomes d'oxygène dans ces structures. Le savoir-faire développé ici pourra donc s'appliquer à l'étude des systèmes à base d'oxydes en général. Finalement, des mesures de transport électrique doublées du modèle analytique de la barrière ohmique permettent d'observer l'apparition d'une zone isolante à l'interface entre les cuprates supraconducteurs La1.85Sr0.15CuO4 et Pr1.85Ce0.15CuO4. Les propriétés de transport non linéaires et asymétriques en tension de cette interface indiquent qu'elle conduit principalement par effet tunnel. L'existence de cette barrière isolante est causée par un transfert de charge entre les deux matériaux à la manière d'une jonction p-n semi-conductrice. Par contre, dans ce cas-ci, la barrière isolante est le résultat d'une transition de Mott dans la zone d'appauvrissement ce qui lui vaut l'appellation de plateau de Mott.

This thesis details the fabrication of three different plasmon-polariton based devices: a plasmon-polariton Bragg grating (PPBG) biosensor, an intensity modulator incorporating grating couplers, and optically separated electrical contact, and finally an array of nanoholes in an ultrasmooth Au film. The biosensor involves a 35 nm Au stripe, lithographically stepped in width to produce a Bragg reflector. The waveguide is embedded in symmetric, Cytop claddings 8 µm thick. Channels are etched into the top cladding, exposing the waveguides and allowing for the integration of fluidics. The modulator involves a 20 nm Au pad, overlaid with 80 nm Au diffraction gratings, supported by an ultrathin (~3 nm) SiO2 insulator, on a p-doped Silicon wafer backed by an Al Ohmic contact. Electrical contact pads are separated from the waveguide by a thick dielectric (700 nm PMMA), and 2.5 µm vias in-filled with Au allow for electrical connection between the contact pads and waveguides. The nanohole array is machined by focused ion beam into an ultrasmooth Au film revealed by template stripping. The Au film is stacked on a thick film of Cytop between ~5 µm thick.

The resonant tunneling diode (RTD) is the fastest electron device to-date in terms of its ability to generate continuous-wave terahertz frequency at room temperature, owing to its unique characteristic of negative differential resistance (NDR). In this work, a lattice-matched In0.53Ga0.47As (on InP) is used as the cladding layer, while a highly-compressive strained In0.8Ga0.2As is sandwiched between two tensile-strained pseudomorphic AlAs barriers to form the active double barrier quantum well RTD structure grown by Molecular Beam Epitaxy. The ultimate aim of this work was to integrate an optimised RTD into an oscillator circuit to enable a 100 GHz (W-band) MMIC RTD oscillator. One of the key challenges in this work was to improve the DC performance of the RTD, through extensive material and structural characterisations. Growing nano-scale epitaxial layers require a high degree of controllability with mono-layer precision. The dependencies of the NDR components, such as the peak current density, peak voltage and peak-to-valley current ratio (PVCR) towards variations in structural thickness were studied systematically. Through this work, it is found that the peak current density is strongly affected by monolayer variation in barrier thickness. The effect of quantum well thickness variation towards peak current density is relatively weaker. Interestingly, variation in spacer layer thickness has very little influence towards the magnitude of the peak current density. The fabrication of the RTD using a conventional i-line optical lithography created its own challenge. The process capability to reduce mesa active area down to sub-micrometer level to reduce device’s geometrical capacitance for high frequency, THz applications has been made feasible in this work. The conventional i-line optical lithography was combined with a newly developed tri-layer soft reflow technique using solvent vapour resulted in sub-micrometer RTDs. The DC characterisation of the fabricated RTDs showed excellent device scalability, indicating a robust processing. This novel sub-micron processing technique with high throughput and repeatability is a very promising low cost technique. A collaborative effort between the University of Manchester and Glasgow paved the way towards the realisation of an integrated W-band RTD MMIC oscillator. The circuit-combining topology was designed by the High Frequency Electronics Group in Glasgow while the mask-layout and oscillator fabrication took place in Manchester. An active RTD from sample XMBE#301 with peak current density of 1.4 x 105 A/cm2 and PVCR of 4.5 was integrated into a 100 GHz MMIC oscillator to successfully produce a measured frequency of 109 GHz with an un-optimised 5.5 μW output power at room temperature (mesa area = 4x4 μm2).

abstract: The current push towards integrating new digital fabrication techniques into all parts of daily life has raised concerns about the changing role of the craftsperson in creative making. The goal of this dissertation is to gain insight into how new technologies can be incorporated into creative practices in a way that effectively supports the goals and workflows of practitioners. To do so, I explore three different cases in which 3D printing, a tool by which complex 3D objects are fabricated from digital designs, is used in tandem with traditional creative practices. Each project focuses on a different way to incorporate 3D printed objects, whether it be as a visualization for artists’ processes, a substitute medium for finished artworks, or as a step toward a larger fabrication workflow. Through this research, I discover how the integration of 3D printing affects creative processes, explore how these changes influence how and why practitioners engage in artistic practices, and gain insight into directions for future technological innovations. / Dissertation/Thesis / Doctoral Dissertation Media Arts and Sciences 2020