1,721,015 research outputs found
Ambipolar field-effect transistors based on solution processable blends of thieno[2,3-b]thiophene terthiophene polymer and methanofullerene.
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Additive Manufacture of RF Electronics
Full text linkThis thesis focusses on printable flexible switches for sub 6 GHz operation, their fabrication, improvement, and stability, for 5G and IOT devices. Indium arsenide nanowire field effect transistors were initially thought as a good semiconductor candidate. Their stability was studied under a variety of atmospheres and substantial long term decay was found preventing their use in printed electronics. This was attributed to either oxidation or leeching of the arsenic into the substrate. Fully printed low resistance carbon nanotube FETs are investigated in detail and their stability, speed, and uses discussed. Resistances in devices as low as 25 Ohms are shown to be possible and their challenges are discussed in detail. A novel method for the creation of micron sized gaps using ink-jet printing is developed which relies only on intrinsic properties of ink-jet printing. This simple method is shown to produce gaps as low at 0.7 microns with limited optimisation necessary.Fully printed carbon nanotube electrolyte gated RF switches are developed and the first ever s-parameter measurements of these switches are undertaken. A simple circuit model for their operation is given and insights into the measurement of flexible RF electronics are discussed. Novel circuits containing these switches are made, measured, and their operation and limitations such as switching speed discussed. An ink-jet printed frequency reconfigurable dipole antenna incorporating the switches for IOT is developed and shown to match simulations closely. Ultra wide band antenna horns are investigated and used to measure the ink-jet printed devices used in this work.Paper based electronics are developed using the above technology, and low impedance switches are fabricated for the first time. Issues surrounding paper technology and fabrication are investigated from a RF point of view with the aim of making novel origami circuits
Organic photodiodes as optical sensors.
Full text linkAbstract cannot be made public due to confidential reason
Alkylidene fluorene liquid crystalline semiconducting polymers for organic field effect transistor devices
No full textOrganic electronic devices comprising arrays of organic field effect transistors (OFETs) are expected to create a range of novel applications for which the ability to be fabricated in large areas, on flexible substrates, with nonconventional shapes, and at low cost are key enabling factors. To improve the electrical performance of such devices, new solution processable organic semiconductors are required with high charge carrier mobilities and environmental stability. This work describes the molecular design of a p-type charge transport liquid crystalline polymer, in an attempt to control the factors responsible for both mobility and stability. Molecules were designed that were able to exhibit closely packed, 7 stacked morphologies, which can result in efficient intermolecular charge hopping and hence high mobility. Molecular manipulation of the conjugated pi electron system was required to optimize the HOMO energy level, to both resist oxidation and be able to readily accept holes from a source electrode
Nanowire field-effect transistors for gas sensor applications.
Full text linkSensing BTEX (Benzene, Ethylbenzene, Toluene, Xylene) pollutants is of utmost importance to reduce health risk and ensure public safety. The lack of sensitivity and selectivity of the current gas sensors and the limited number of available technologies in the field of BTEX-sensing raises the demand for the development of high-performance gas sensors for BTEX applications.
The scope of this thesis is the fabrication and characterisation of high-quality field-effect transistors (FETs), with functionalised silicon nanowires (SiNWs), for the selective sensing of benzene vs. other BTEX gases. This research addresses three main challenges in SiNW FET-sensor device development: i) controllable and reproducible assembly of high-quality SiNWs for FET sensor devices using the method of dielectrophoresis (DEP), ii) almost complete elimination of harmful hysteresis effect in the SiNW FET current-voltage characteristics induced by surface states using DMF solvent, iii) selective sensing of benzene with up to ppb range of sensitivity using calix[4]arene-derivatives.
It is experimentally demonstrated that frequency-controlled DEP is a powerful tool for the selection and collection of semiconducting SiNWs with advanced electrical and morphological properties, from a poly-disperse as-synthesised NWs. The DEP assembly method also leads to a controllable and reproducible fabrication of high-quality NW-based FETs. The results highlight the superiority of DEP, performed at high signal frequencies (5-20 MHz) to selectively assemble only high-quality NWs which can respond to such high DEP frequencies. The SiNW FETs, with NWs collected at high DEP frequencies, have high mobility (≈50 cm2 V-1 s-1), low sub-threshold-swing (≈1.26 V/decade), high on-current (up to 3 mA) and high on/off ratio (106-107). The DEP NW selection is also demonstrated using an industrially scalable method, to allow establishing of NW response characteristics to different DEP frequencies in a very short time window of about 60 seconds. The choice of solvent for the dispersion of the SiNW for the DEP process demonstrates a dramatic impact on their surface trap, with DMF solvent acting as a mild oxidising agent on the NW surface shell. This surface state passivation technique resulted in the fabrication of high-quality, hysteresis-free NW FET transducers for sensor applications.
Finally, the proof-of-concept SiNW FET transducer decorated with calix[4]arene-derivative gas receptors exhibits selective detection of benzene vs. other BTEX gases up to 30 ppm concentrations, and up to sub-ppm benzene concentration.
The demonstrated NW-sensors are low power and compact, and therefore can be easily mounted on a mobile device, providing instantaneous determination of hazardous gases in the surrounding atmosphere. The methodologies developed in this thesis, have a high potential to make a breakthrough in low-cost, selective gas sensors, which can be fabricated in line with printed and flexible electronic approaches
Advanced processing and characterisation of printable single crystal electronics.
Full text linkPrintable electronics offer outstanding potential for novel electronic devices that can be lightweight, flexible, transparent, large area and low cost. These next generation electronics will aid the realization of concepts such as smart cities, structural health monitoring of advanced structures, body area networks, remote medical healthcare and the internet of things. Solution processed nanomaterials hold most of the promise as viable building blocks for these future applications.
A robust and reproducible approach has been developed, for high definition one-step patterning of conductive electrodes, using inkjet printing (part A, chapter 4). Controlled electrode spacing and single droplet deposition was achieved by utilising the droplet kinematic stages and overcoming the built in limitations of our experimental setup. Single and multiple silicon nanowire (NW) field effect transistors were realised in a variety of electrode configurations, demonstrating the capabilities of our technique. The controlled realisation of single NW devices enabled the characterisation of semiconducting nanostructures by correlating their electrical response with defects introduced during growth.
In chapter 7 (part B) a low-cost, scalable printing process to fabricate high-quality organic semicon-ducting single crystals (OSSCs) on virtually any substrate using various types of conjugated molecules is demonstrated. By combining the advantages of antisolvent crystallization and solution shearing with spray-printing, one-step single crystal growth of various small semiconducting molecules was realised. In addition, crystal size, shape, and orientation were controlled by the sheer force generated by the im-pact of the droplets from the spray onto the antisolvent’s surface, eliminating the need for pre-deposition patterning.
For enabling large scale manufacturing of printable single crystal electronics, advances towards non-destructive characterisation techniques are required. In chapter 5 (part A), the capabilities of advanced scanning probe microscopy techniques as a non-destructive alternative for evaluating the growth and device integration defects in NW based devices, was explored. Conductive Atomic Force Microscopy (c-AFM) was used for imaging critical electrical characteristics with high spatial resolution.
In chapter 8 (part B), the potentials of polarised Raman spectroscopy (p-Raman) as a non-destructive approach, for characterising the anisotropy in our OSSCs were explored. By using the aforementioned crystals as reference samples, the potential of the technique is demonstrated
Printed Transition Metal Oxide Electrochemical Capacitors for Energy Harvesting Applications
Full text linkWith the rapid development of Internet-of-Things (IoT), it is estimated that a trillion sensors will be needed around the globe by 2023 to connect most things around us. This rapid growth of portable devices is stimulating the development of flexible, wearable, and conformal embedded electronics with the unprecedented need for next-generation energy storage systems fully adaptable to diverse form factors. With such an enormous production demand of electronic devices, the manufacturing technologies used for current silicon microelectronics are prohibitively expensive. In addition, conventional fabrication methods, such as photolithography for electronics and electrode winding/stacking for energy storage systems, struggle as fabrication strategies to produce devices with advanced form factors (\textit{i.e.} three-dimensional, flexible, stretchable, wearable, conformal etc.). Printed electronics have been accepted as one of the ways forward to meet this high demand at a lower cost, but also represent a paradigm shift in greener electronic manufacturing. Additionally, the solution process, and in many cases digital nature of printed electronics, not only enable the rapid transfer of a prototype straight to the manufacturing process but also enable the fabrication of highly versatile and creative multifunctional designs. In this thesis, the fabrication of high-energy-density and high-power-density, nickel-(II) oxide co-planar micro-supercapacitors fabricated through inkjet printing is demonstrated. The developed micro-supercapacitors showed remarkable areal and volumetric specific capacitances of up to 155 mF/cm2 and 705 F/cm3 respectively (at 5 mV/s scan rate), surpassing the state-of-the-art inkjet-printed supercapacitors but also a few of the best micro-supercapacitors known to date. Moreover, the fabrication of supercapacitors on 3D objects through inkjet and water-transfer printing is also demonstrated. Electrochemical studies were performed to investigate the effect of substrate and printing resolution, different types of current collector silver inks, sintering temperatures and carbon residues in electrodes, different types of electrolytes, binders and other organic compounds in electrolytes, and the effect of electrode gaps on the electrochemical response and capacitance of inkjet-printed, co-planar NiO supercapacitors. This work provides a compelling platform to simplify the fabrication process of next-generation supercapacitors, with focus on digital design, scalable manufacturing, and direct integration with printed electronics to enable a variety of design flexibility needed for countless new IoT applications, including wearable health systems
Polymerisable liquid crystalline organic semiconductors and their fabrication in organic field effect transistors
No full textThe performance of the semiconducting component in organic field effect transistors (OFETs) is a key parameter in the advancement of organic electronic devices. New semiconductors are required, which can be solution processed, possess high mobility and current modulation, and are stable in ambient conditions. This work provides the first demonstration of working field effect transistor devices fabricated from novel solution processible, polymerisable, small molecule liquid crystalline semiconductors, referred to as reactive mesogens. The design, synthesis, and performance of these materials in transistor devices are reported. The relationship between liquid crystal molecular structure, its corresponding phase behaviour and electrical performance is examined. Molecular design methodology was employed to control the liquid crystalline morphology, in an attempt to optimise organisation and packing. Alignment of the molecules in large homeotropic domains was achieved through surface treatment techniques, and the highly ordered mesophase was preserved by polymerisation of the reactive end groups, creating a crosslinked network
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