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Wireless Surface Acoustic Wave (SAW) devices were fabricated and tested using planar Lithium Niobate (LiNbO₃) as substrate. The working frequencies were in the 180 MHz and 360 MHz range. Using a network analyser, the devices were interrogated with a wireless range of more than 2 metres. Trials with Electron Beam Lithography (EBL) to fabricate SAW devices working in the 2450 MHz with a calculated feature size of 350 nm are discussed. Charging problems became evident as LiNbO₃ is a strong piezoelectric and pyroelectric material. Various attempts were undertaken to neutralise the charging problems. Further investigation revealed that sputtered Zinc Oxide (ZnO) is a suitable material for attaching SAW devices on irregularly shaped material. DC sputtering was used and several parameters have been optimised to achieve the desired piezoelectric effect. ZnO was sputtered using a magnetron sputtering system with a 75 mm Zn target and a DC sputter power of 250 Watts. Several trials were performed and an optimised material has been prepared under the following conditions: 9 sccm of Oxygen and 6 sccm of Argon were introduced during the process which resulted in a process pressure of 1.2x10⁻² mbar. The coatings have been characterised using Rutherford Backscattering, X-ray diffraction, SEM imaging, and Atomic force microscopy. SAW devices were fabricated and tested on 600 nm thick sputtered ZnO on a Si substrate with a working frequency of 430 MHz. The phase velocity has been calculated as 4300m/s. Non-planar samples have been coated with 500 nm of sputtered ZnO and SAW structures have been fabricated on using EBL. The design frequency is 2450 MHz, with a calculated feature size of 1 µm. The surface roughness however prevented a successful lift-off. AFM imaging confirmed a surface roughness in the order of 20 nm. Ways to improve manufacturability on these samples have been identified.

Within recent years, numerous fields of engineering, like mechanics, optics and electronics, have been influenced and revolutionised by the technique of microand nano-structuring. For example, special optical elements for beam shaping, surface structures for the reduction of friction or modern "lab on chip" devices have been produced. Within this thesis a universal system has been developed facilitating the production of such structured surfaces with dimensions down to 500 nm. This system is not only capable of structuring surfaces by means of lithographic processes; it further allows the inspection of surfaces by scanning their topography. To realise such a system, two different technologies have been evaluated: Scanning Near-field Optical Lithography (SNOL), a very sophisticated technique which uses a thin fibre tip to expose a photo resist-covered surface, and confocal scanning technology. Here, the confocal scanning is accomplished using an adapted optical component, the optical pickup unit (OPU), from a gaming console, which turned out to be the most suitable and cost-efficient solution for the realisation of this system. Several test series have been carried out during this work, to verify the performance of the confocal system, both to structure photo resist surfaces and to characterise unknown surfaces. This present work will show the ability of the developed system to produce structures down to the sub-micron range and to characterise unknown surfaces with sub- micron precision. Various patterns have been written into photo resistcoated substrates to structure their surface. Beginning with diffractive optical elements (DOE) for beam shaping, followed by Dammann gratings for twodimensional beam shaping and optical gratings for light guidance as well as producing technical surfaces imitating the properties of sharkskin or simple micromechanical structures, the developed confocal system has shown itself to be flexible and widely-applicable. IV During the development of the confocal system, a strong need for a beam profiling system analysing the light beam diverging from the OPU, was recognised. Due to the fact that no commercially available system was capable of characterising beam sizes within the range of the diffraction limit, a novel method for beam profiling was invented. This method makes use of the fibre tips already applied within the SNOL system, producing tomographical scans of the beam spot.

The objective of this thesis is to successfully design, fabricate, and characterize an optimum metal-insulator-metal diode that can be used as a fast switching diode in various applications such as solar energy conversion. The improvements of this type of diode will result in rectification of a wider spectrum of AC signals to usable electricity. In this project, several proposed designs of MIM diodes were successfully fabricated and characterized. Pt-Al2O3-Al metal-insulator-metal diode was fabricated to have high asymmetry in I-V curve. Additionally, in an attempt to study the effect of material properties on MIM diode???s performance, four different combinations of MIIIIM diode were compared and discussed. Many processes were involved in the fabrication of these diodes such as E-beam evaporation, photolithography, reactive ion etching RIE, and Atomic Layer Deposition (ALD) technique. The fabricated tunneling diodes are intended to operate in the GHz regime and can also operate at higher frequencies (THz) by changing and scaling the dimensions. In addition to MIM diode work, this project attempted to engineer the contrast curve of polystyrene as a negative resist used for E-beam lithography using multi layer resist stack. If the resist stack has a very high contrast and its sensitivity differs between the various layers, it can be ideal for the fabrication of multi-level zone-plate/Fresnel lens.

Ubiquitous concerns in device fabrication are nanoscale positioning and the integration of complex combinations of diverse materials, many of which are extremely fragile. Frequently the completed device requires one or more of the constituent materials to be synthesized under suboptimal conditions, thus compromising the performance of the final structure. We have developed a platform to fabricate multi-component electrode cross-bar structures, where each material can be synthesized under its own ideal conditions. Furthermore, surface treatments and procedures that may otherwise be incompatible can be performed without concern of damage to the other constituent materials. We demonstrate our approach by fabricating an all carbon cross-bar electrode structure comprised of a graphene-graphite heterojunction. Initially, a graphene field effect transistor is fabricated using electron beam and optical lithography. The top graphite electrode is sculpted from a bulk piece of highly oriented pyrolytic graphite with the aid of a focused ion beam (FIB) and integrated micromanipulator system. This requires real-time shaping, cutting, accurate positioning (circa 100 nm precision) and wiring of the graphite top electrode. Electron transport characteristics of each electrode component and the final heterostructure have been measured. We show that this process is effective for the production of micron and submicron-scale multi-layer device structures including other materials such as gold. This fabrication scheme could be extended to produce novel structures such as mechanical resonators, and provide a foundation for combining fragile materials that have otherwise been incompatible with traditional fabrication techniques. / Graduate

Thesis (Ph. D.)--Virginia Polytechnic Institute and State University, 1990. / Vita. Abstract. Includes bibliographical references (leaves 198-208). Also available via the Internet.