http://hdl.handle.net/10468/3619 2017-10-30T17:59:51Z 2017-10-30T17:59:51Z Lordan, Daniel http://hdl.handle.net/10468/3891 2017-04-26T18:00:53Z 2017-01-01T00:00:00Z

Alternative materials for flexible transparent conductive electrodes Lordan, Daniel This thesis investigates new alternative materials for flexible transparent electrodes: monolayer graphene and micron-scale metal mesh structures. Growth of graphene on copper foils by chemical vapour deposition (CVD) was investigated by commissioning and developing a CVD system in Tyndall. Initial growth runs resulted in poor graphene coverage. Several routes for growth improvement were examined: an acid pre-treatment, substrate geometry and growth pressure. Following this improvement, a continuous growth run was carried out displaying high monolayer graphene coverage. Graphene was transferred to Si/SiO2 (90 nm thermal oxide) and glass substrates using a wet chemical transfer process. This process involves the use of a polymer which acts as a support mechanism. However, polymer residue can have drastic effects on the electrical performance of CVD graphene films. Therefore an alternative method for polymer removal with the use of heated acetone (~ 60 oC) was investigated. Micron-scale platinum mesh structures were fabricated on rigid glass substrates using a range of metal deposition techniques; metal evaporation and lift-off; ALD and dry etching and sputter deposition and dry etching. Square, hexagonal, circular and a new asymmetric pentagonal tiling were utilised as metal meshes. Their performance were investigated along with the metal deposition technique. Evaporation and lift-off provided the most consistent technique in relation to transparency, haze and sheet resistance. Finally, asymmetric pentagonal platinum meshes were fabricated on flexible transparent substrates using metal evaporation and lift-off. All designs were bent around a radius of curvature (in air) of ~ 3.8 mm up to 1,000 bending cycles for both tension and compression and suggested good performance in comparison to literature. All three designs were used as transparent heaters via Joule heating. All heaters demonstrated good thermal characteristics such as low response times and high thermal resistances. Finally, a pentagonal metal mesh was used to de-ice a glass substrate.

2017-01-01T00:00:00Z Sanchez-Soares, Alfonso http://hdl.handle.net/10468/3904 2017-05-02T18:00:54Z 2017-01-01T00:00:00Z

Electronic transport in metallic and semimetallic nanostructures Sanchez-Soares, Alfonso After 50 years of continued efforts in downscaling basic electronic components which comprise integrated circuits (ICs), research into new device designs is critical as fundamental physical limits are being reached preventing further miniaturisation of designs traditionally employed by the semiconductor industry. With feature sizes in commercial ICs approaching 10 nm, new components designs must take into account the atomistic nature of the materials and interfaces which constitute its lower level components. In this work we explore the electronic structure and electronic transport properties of nanostructures based on metals and semimetals for applications in next generation ICs. We study the non-linear resistivity increase observed in copper nanostructures associated with quantum-size and surface effects in order to assess their suitability for sub-10-nm interconnect networks; for applications in logic gates, we present an alternative design to planar CMOS technology based on exploitation of surface and size effects in semimetallic nanostructures.

2017-01-01T00:00:00Z Quan, Zhiheng http://hdl.handle.net/10468/4053 2017-06-06T11:00:52Z 2017-01-01T00:00:00Z

Thin film technology for optoelectronics and their thermal management Quan, Zhiheng Thin-film semiconductor optoelectronics are important for applications from optical communication, solid-state lighting, and wearable electronics to biomedical sensors. It is now possible to separate the micrometer-thick device layers from their native substrates and transfer them onto new platforms to optimize system performance and integration. The understanding of thermal management for such devices is very important in order to control the junction temperature effectively. Here, the laser-lift-off (LLO) technique was theoretically and experimentally studied. The temperature distribution at the III-nitride/sapphire interface induced by absorption of 248-nm KrF excimer energetic laser pulses was simulated to verify the experimental results. A 1.5-m-thick n-type Al0.6Ga0.4N membrane was separated from a c-plane sapphire substrate and then bonded to a Si substrate. The electrical behaviour of Ti/Al/Ti/Au contacts on the N-polar n-Al0.6Ga0.4N membrane was characterized. Furthermore, free-standing semipolar InGaN/GaN light-emitting diodes (LEDs) emitting at 445 nm were first realized by separation from patterned r-plane sapphire substrate using LLO. The LEDs showed a turn-on voltage of 3.6 V and output power of 0.87 mW at 20 mA. Electroluminescence measurements showed stronger emission intensity along the inclined c-direction. The -3 dB bandwidth of the LEDs is in excess of 150 MHz at 20 mA and a back-to-back data transmission rate at 300 Mbps is demonstrated. This indicates that the LEDs can be used for high bandwidth visible light communications. For thermal management of thin-film optoelectronics, a GaAs based laser diode (LD) was investigated. The 2-dimensional temperature distribution of the transfer-bonded LD was simulated; where the power dissipation, the thermal resistance of different cavity lengths and configurations were investigated. This can be utilized to optimize the device design and the choice of carrier substrate for efficient thermal management of thin-film optoelectronics.

2017-01-01T00:00:00Z Mallick, Dhiman http://hdl.handle.net/10468/4072 2017-06-13T11:00:47Z 2017-01-01T00:00:00Z

Wideband vibration energy harvesting using electromagnetic transduction for powering internet of things Mallick, Dhiman The ‘Internet of Things-(IoT)’ envisions a world scattered with physical sensors that collect and transmit data about almost anything and thereby enabling intelligent decision-making for a smart environment. While technological advancements have reduced the power consumption of such devices significantly, the problem of perpetual energy supply beyond the limited capability of batteries is a bottleneck to this vision which is yet to be resolved. This issue has surged the research to investigate the prospect of harvesting the energy out of ambient mechanical vibrations. However, limited applications of conventional resonant devices under most practical environments involving frequency varying inputs, has gushed the research on wideband transducers recently. To facilitate multi-frequency operation at low-frequency regime, design innovations of the Silicon-onInsulator based MEMS suspension systems are performed through multi-modal activation. For continuous bandwidth widening, the benefits of using nonlinear stiffness in the system dynamics are investigated. By topologically varying the spring architectures, dramatically improved operational bandwidth with large power-density is obtained, which is benchmarked using a novel figure-of-merit. However, the fundamental phenomenon of multi-stability limits many nonlinear oscillator based applications including energy harvesting. To address this, an electrical control mechanism is introduced which dramatically improves the energy conversion efficiency over a wide bandwidth in a frequencyamplitude varying environment using only a small energy budget. The underlying effects are independent of the device-scale and the transduction methods, and are explained using a modified Duffing oscillator model. One of the key requirements for fully integrated electromagnetic transducers is the CMOS compatible batch-fabrication of permanent magnets with large energy-product. In the final module of the works, nano-structured CoPtP hard-magnetic material with large coercivity is developed at room-temperature using a current modulated electro-deposition technique. The demagnetization fields of the magnetic structures are minimized through optimized micro-patterns which enable the full integration of high performance electromagnetic energy harvesters.

2017-01-01T00:00:00Z