An analytical model to predict the depth of sub-surface damage for grinding of brittle materials

This paper proposes an analytical model for predicting grinding-induced sub-surface damage depth in a silicon wafer. The model integrates the dislocation kinetics for crack initiation and fracture mechanics for crack propagation for the first time. Unlike other conventional models, the proposed model considers the effects of strain rate on damage depth and the dynamically changing metastable phase change properties. The model is verified by grinding experiments and a comparison of theoretical and experimental results shows a good quantitative agreement. It is found that increasing grinding speed and decreasing depth of cut cause a higher strain rate so as to enhance material brittleness, which is favorable to achieving low sub-surface damage. These findings will pave a way towards optimizing the grinding parameters and greatly improving the production efficiency of hard and brittle material

Multi-level analysis of atomic layer deposition barrier coatings on additively manufactured plastics for high vacuum applications

While hardware innovations in micro/nano electronics and photonics are heavily patented, the rise of the open-source movement has significantly shifted focus to the importance of obtaining low-cost, functional and easily modifiable research equipment. This thesis provides a foundation of open source development of equipment to aid in the micro/nano electronics and photonics fields. First, the massive acceptance of the open source Arduino microcontroller has aided in the development of control systems with a wide variety of uses. Here it is used for the development of an open-source dual axis gimbal system. This system is used to characterize optoelectronic properties of thin transparent films at varying angles. Conventionally, the ubiquity of vacuum systems in semiconductor fabrication has precluded the development of an open-source development in the “fab” environment and thus has high foundational and operational costs. In order to make vacuum systems and their components cost-effective in a research environment there has been a paradigm shift towards refurbishing and repairing instead of replacing legacy systems. These legacy systems are built, and operate on the principle that the vacuum industry is a small industry, and hence only a small number of sizes and types of parts may be used to reduce costs. The assumption that the vacuum industry is a small industry is no longer valid. The semiconductor industry alone, which is a subset of the vacuum industry, was worth over USD 481b and increasing. Hence,there is a need to not only introduce new methods but also new materials that make up these systems. Additive manufacturing is a low-waste, low-capital cost way to make custom equipment. The most popular materials used in additive manufacturing processes are polymer blends. 3-D printing using Fused Filament Fabrication (FFF) methods has been used to create custom objects for laboratories. However, the use of polymer-based materials is conspicuously absent in the development of vacuum systems, especially those that are used for semiconductor fabrication. There are two major problems identified when polymeric materials are used to make vacuum systems: finding a way to prevent outgassing (which can subsequently lead to contamination), and sealing them so that they can hold a vacuum. This work has demonstrated how an inorganic barrier layer introduced via Atomic Layer Deposition (ALD) can alleviate outgassing to a large extent under high vacuum levels (1E-6 to 1E-7 torr). Recognizing the importance of ALD alumina in back end of the line (BEOL) semiconductor processing, films were deposited on 3-D printed polymer-based substrates with differing constituents. These samples were tested in a bespoke gas analysis chamber for outgassing characterization. Surface and bulk characterization was completed using various tools such as scanning electron microscopy (SEM), energy dispersive x-ray analysis (EDX), x-ray photoelectron spectroscopy (XPS), attenuated total reflectance - Fourier transform infrared spectroscopy (ATR-FTIR) and others. Additionally, spectroscopic ellipsometry (SE) was used to understand how the concept of thickness of a film deposited on a porous polymer-based sample does not correlate directly with its conventional definition. Also, an effort is made to understand the mechanism of ALD alumina deposition on porous plastic surfaces.It was concluded that this deposition is a complex amalgamation of physical and chemical properties of both the polymer and the precursor gases. Finally, recommendations are made for AM materials to be used in vacuum systems

Evaluating subsurface damage in optical glasses

Hard brittle materials (e.g. glasses and ceramics) increasingly appeal to general interests because of their excellent physical, mechanical and chemical properties such as super hardness and strength at extreme temperature and chemical stability. The precision manufacturing of these materials is primarily achieved by grinding and polishing, which generally employs abrasives to wear the materials. With this manufacturing technology, the materials are removed due principally to the fracture of brittle materials, which will leave a cracked layer on the surface of manufactured components, namely subsurface damage (SSD). The subsurface damage affects the strength, performance and lifetime of components. As a result, investigation into the subsurface damage is needed. A host of characterizing techniques have been developed during the past several decades. These techniques based on different mechanisms provide researchers with invaluable information on the subsurface damage in various materials. In this article the typical SSD evaluation techniques are reviewed, which are regularly used in optical workshops or laboratories

Predictive Modeling for Ductile Machining of Brittle Materials

Brittle materials such as silicon, germanium, glass and ceramics are widely used in semiconductor, optical, micro-electronics and various other fields. Traditionally, grinding, polishing and lapping have been employed to achieve high tolerance in surface texture of silicon wafers in semiconductor applications, lenses for optical instruments etc. The conventional machining processes such as single point turning and milling are not conducive to brittle materials as they produce discontinuous chips owing to brittle failure at the shear plane before any tangible plastic flow occurs. In order to improve surface finish on machined brittle materials, ductile regime machining is being extensively studied lately. The process of machining brittle materials where the material is removed by plastic flow, thus leaving a crack free surface is known as ductile-regime machining. Ductile machining of brittle materials can produce surfaces of very high quality comparable with processes such as polishing, lapping etc. The objective of this project is to develop a comprehensive predictive model for ductile machining of brittle materials. The model would predict the critical undeformed chip thickness required to achieve ductile-regime machining. The input to the model includes tool geometry, workpiece material properties and machining process parameters. The fact that the scale of ductile regime machining is very small leads to a number of factors assuming significance which would otherwise be neglected. The effects of tool edge radius, grain size, grain boundaries, crystal orientation etc. are studied so as to make better predictions of forces and hence the critical undeformed chip thickness. The model is validated using a series of experiments with varying materials and cutting conditions. This research would aid in predicting forces and undeformed chip thickness values for micro-machining brittle materials given their material properties and process conditions. The output could be used to machine brittle materials without fracture and hence preserve their surface texture quality. The need for resorting to experimental trial and error is greatly reduced as the critical parameter, namely undeformed chip thickness, is predicted using this approach. This can in turn pave way for brittle materials to be utilized in a variety of applications.Ph.D.Committee Chair: Liang, Steven; Committee Co-Chair: Li, Xiaoping; Committee Member: Garmestani, Hamid; Committee Member: Griffin, Paul; Committee Member: Melkote, Shreyes; Committee Member: Neu, Richar

Effects of Subsurface Damage on the Photoluminescence of Zno

Mechanical Engineerin

Frontiers in Ultra-Precision Machining

Ultra-precision machining is a multi-disciplinary research area that is an important branch of manufacturing technology. It targets achieving ultra-precision form or surface roughness accuracy, forming the backbone and support of today’s innovative technology industries in aerospace, semiconductors, optics, telecommunications, energy, etc. The increasing demand for components with ultra-precision accuracy has stimulated the development of ultra-precision machining technology in recent decades. Accordingly, this Special Issue includes reviews and regular research papers on the frontiers of ultra-precision machining and will serve as a platform for the communication of the latest development and innovations of ultra-precision machining technologies