36 research outputs found

    A Review on Mechanics and Mechanical Properties of 2D Materials - Graphene and Beyond

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    Since the first successful synthesis of graphene just over a decade ago, a variety of two-dimensional (2D) materials (e.g., transition metal-dichalcogenides, hexagonal boron-nitride, etc.) have been discovered. Among the many unique and attractive properties of 2D materials, mechanical properties play important roles in manufacturing, integration and performance for their potential applications. Mechanics is indispensable in the study of mechanical properties, both experimentally and theoretically. The coupling between the mechanical and other physical properties (thermal, electronic, optical) is also of great interest in exploring novel applications, where mechanics has to be combined with condensed matter physics to establish a scalable theoretical framework. Moreover, mechanical interactions between 2D materials and various substrate materials are essential for integrated device applications of 2D materials, for which the mechanics of interfaces (adhesion and friction) has to be developed for the 2D materials. Here we review recent theoretical and experimental works related to mechanics and mechanical properties of 2D materials. While graphene is the most studied 2D material to date, we expect continual growth of interest in the mechanics of other 2D materials beyond graphene

    Reliability analysis of foil substrate based integration of silicon chips

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    Flexible electronics has attracted significant attention in the recent past due to the booming wearables market in addition to the ever-increasing interest for faster, thinner and foldable mobile phones. Ultra-thin bare silicon ICs fabricated by thinning down standard ICs to thickness below 50 μm are flexible and therefore they can be integrated on or in polymer foils to create flexible hybrid electronic (FHE) components that could be used to replace rigid standard surface mount device (SMD) components. The fabricated FHE components referred as chip foil packages (CFPs) in this work are ideal candidates for FHE system integration owing to their ability to deliver high performance at low power consumption while being mechanically flexible. However, very limited information is available in the literature regarding the reliability of CFPs under static and dynamic bending. The lack of such vital information is a major obstacle impeding their commercialization. With the aim of addressing this issue, this thesis investigates the static and dynamic bending reliability of CFPs. In this scope, the static bending reliability of CFPs has been investigated in this thesis using flexural bending tests by measuring their fracture strength. Then, Finite Element Method (FEM) simulations have been implemented to calculate the fracture stress of ultra-thin flexible silicon chips where analytical formulas may not be applied. After calculating the fracture stress from FEM simulations, the enhancement in robustness of ultra-thin chips (UTCs) against external load has also been proved and quantified with further experimental investigations. Besides, FEM simulations have also been used to analyse the effect of Young’s Modulus of embedding materials on the robustness of the embedded UTCs. Furthermore, embedding the UTCs in polymer layers has also been experimentally proven to be an effective solution to reduce the influence of thinning and dicing induced damages on the robustness of the embedded UTCs. Traditional interconnection techniques such as wire bonding may not be implemented to interconnect ultra-thin silicon ICs owing to the high mechanical forces involved in the processes that would crack the chips. Therefore, two novel interconnection methods namely (i) flip-chip bonding with Anisotropic Conductive Adhesive (ACA) and (ii) face-up direct metal interconnection have been implemented in this thesis to interconnect ultra-thin silicon ICs to the corresponding interposer patterns on foil substrates. The CFP samples thus fabricated were then used for the dynamic bending reliability investigations. A custom-built test equipment was developed to facilitate the dynamic bending reliability investigations of CFPs. Experimental investigations revealed that the failure of CFPs under dynamic bending was caused mainly by the cracking of the redistribution layer (RDL) interconnecting the chip and the foil. Furthermore, it has also been shown that the CFPs are more vulnerable to repeated compressive bending than to repeated tensile bending. Then, the influence of dimensional factors such as the thickness of the chip as well as the RDL on the dynamic bending reliability of CFPs have also been studied. Upon identifying the plausible cause behind the cracking of the RDL leading to the failure of the CFPs, two methods to improve the dynamic bending reliability of the RDL have been suggested and demonstrated with experimental investigations. The experimental investigations presented in this thesis adds some essential information to the state-of-the-art concerning the static and the dynamic bending reliability of UTCs integrated in polymer foils that are not yet available in the literature and aids to establish in-depth knowledge of mechanical reliability of the components required for manufacturing future FHE systems. The strategies devised to enhance the robustness of UTCs and CFPs could serve as guidelines for fabricating reliable FHE components and systems

    Flexible and Stretchable Electronics

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    Flexible and stretchable electronics are receiving tremendous attention as future electronics due to their flexibility and light weight, especially as applications in wearable electronics. Flexible electronics are usually fabricated on heat sensitive flexible substrates such as plastic, fabric or even paper, while stretchable electronics are usually fabricated from an elastomeric substrate to survive large deformation in their practical application. Therefore, successful fabrication of flexible electronics needs low temperature processable novel materials and a particular processing development because traditional materials and processes are not compatible with flexible/stretchable electronics. Huge technical challenges and opportunities surround these dramatic changes from the perspective of new material design and processing, new fabrication techniques, large deformation mechanics, new application development and so on. Here, we invited talented researchers to join us in this new vital field that holds the potential to reshape our future life, by contributing their words of wisdom from their particular perspective

    Transfer printing based microassembly and colloidal quantum dot film integration

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    Micro / nanoscale manufacturing requires unique approaches to accommodate the immensely different characteristics of the miniscule objects due to their high surface area to volume ratio when compared with macroscale objects. Therefore, surface forces are much more dominating than body forces, which causes the significant difficulty of miniscule object manipulation. Because of this challenge, monolithic microfabrication relying on photolithography has been the primary method to manufacture micro / nanoscale structures and devices in place of microassembly. However, by virtue of the two-dimensional (2D) nature of photolithography, formation of complex 3D shape architectures via monolithic microfabrication is inherently limited, which would otherwise enable improvements in performance and novel functionalities of devices. Furthermore, monolithic microfabrication is compatible only with materials which survive in a wet condition during photolithography. Delicate nanomaterials such as colloidal quantum dots cannot be processed via monolithic microfabrication. In this context, transfer printing has emerged as a method to transfer heterogeneous material pieces from their mother substrates to a foreign substrate utilizing a polymeric stamp in a dry condition. In this thesis, advanced modes of transfer printing are studied and optimized to enable a 3D microassembly called ‘micro-Lego’ and a novel strategy of quantum dot film integration. Micro-Lego involves transfer printing for material piece pick-and-place and thermal joining for irreversible permanent bonding of placed material pieces. A microtip elastomeric stamp is designed to advance transfer printing and thermal joining processes are optimized to ensure subsequent material bonding. The mechanical joining strength between material pieces assembled by micro-Lego are characterized by means of blister tests and the nanoindentation. Moreover, the electrical contact between two conducting materials formed by micro-Lego are examined. Lastly, inspired from the subtractive transfer printing technique, protocols of quantum dot film patterning using polymeric stamps made of a shape memory polymer as well as a photoresist are established for the convenient integration of quantum dots in various geometries and configurations as desired. Transfer printing-based micro / nanoscale manufacturing presented in this thesis opens up new pathways to manufacture not only complex 3D functional micro devices but also high resolution nano devices for unparalleled performance or for an unusual functionality, which are unattainable through monolithic microfabrication

    Flexible sensors—from materials to applications

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    Flexible sensors have the potential to be seamlessly applied to soft and irregularly shaped surfaces such as the human skin or textile fabrics. This benefits conformability dependant applications including smart tattoos, artificial skins and soft robotics. Consequently, materials and structures for innovative flexible sensors, as well as their integration into systems, continue to be in the spotlight of research. This review outlines the current state of flexible sensor technologies and the impact of material developments on this field. Special attention is given to strain, temperature, chemical, light and electropotential sensors, as well as their respective applications

    MME2010 21st Micromechanics and Micro systems Europe Workshop : Abstracts

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    Feature Papers in Electronic Materials Section

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    This book entitled "Feature Papers in Electronic Materials Section" is a collection of selected papers recently published on the journal Materials, focusing on the latest advances in electronic materials and devices in different fields (e.g., power- and high-frequency electronics, optoelectronic devices, detectors, etc.). In the first part of the book, many articles are dedicated to wide band gap semiconductors (e.g., SiC, GaN, Ga2O3, diamond), focusing on the current relevant materials and devices technology issues. The second part of the book is a miscellaneous of other electronics materials for various applications, including two-dimensional materials for optoelectronic and high-frequency devices. Finally, some recent advances in materials and flexible sensors for bioelectronics and medical applications are presented at the end of the book

    3D printing assisted development of bioinspired structure and device for advanced engineering

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    Smart materials with bio-inspired structure and stimuli responsive features can sense the external and internal condition changes, such as temperature, light intensity, pH or ion concentration. Those unique functions have been widely utilized in cutting edge engineering applications, such as flexible sensors, soft robotics and tissue engineering. Meanwhile, conventional manufacturing methods such as moulding, and lithography-based microfabrication still represent the mainstream force in scale up manufacturing. Considerable limitations for these technologies, such as on demand rapid prototyping, the high cost and low-volume production, remain to be overcome. In this PhD project, I explored the advanced manufacturing in facilitating the complex structure, with higher controllability, lower prototyping cost and extended applications (flexible sensors, soft robots, biomedical devices, etc.). The key practice is to utilize the high resolution 3D printing technology to create dedicated bio inspired structures based on functional materials. Combined with advanced micro/nano engineering, we have achieved a variety of techniques/prototypes for future applications, such as optical control, micro-fluidic and bio-medical systems, etc
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