Synthesis and Mechanical Characterization of Metallic Glasses with High Elastic Deformation for Stretchable Encapsulation Films = 스트레쳐블 봉지 재료용 고탄성변형을 가진 비정질 금속의 합성 및 기계적 물성 특성화

다국어 초록 (Multilingual Abstract)

Metallic glasses have been researched expensively due to their remarkable properties such as excellent corrosion resistance, large elastic limit and strength, unique soft magnetic properties, wear resistance etc. One of the most attractive aspect of metallic glasses is impressive suite of mechanical properties. Compared to crystalline material with similar composition, metallic glasses exhibit significantly high elastic limit and tensile strength. On the other hand, they have a lack of tensile ductility that results in sudden and catastrophic failure due to intrinsic properties of atomic arrangement, disordered structure. Considerable work has been aimed at improving the tensile ductility of metallic glasses, and the development of glass-matrix composites with high toughness and tensile ductility is being explored. Two basic techniques are employed to attain high tensile ductility:
introducing a softer secondary phase in the metallic glass matrix to induce generation of local shear banding around the secondary phase and reducing its external dimensions to suppress a propagation of shear bands or occur homogeneous flow instead, leading to enhanced strength and ductility. Since there are limited structural applications for monolithic metallic glass with dimensions of the order of 100 nm, nanolaminates with alternating layers of metallic glass (with dimensions of 100 nm or less) and another material have been suggested as a more practical material. Metallic glass-based nanolaminates with proper interfacial material and optimum layer thickness can exhibit improved strength and ductility by utilizing size-dependent homogeneous flow of metallic glass. In this study, mechanical behavior of nanolaminate with metallic glass and graphene is investigated. Nanolaminate with alternating layers of metallic glass and graphene is fabricated by repeating deposition of metallic glass by sputtering and transfer of chemical vapor deposition-grown graphene. In situ micro-tensile tests reveal that the addition of a very small fraction of graphene in the nanolaminate improve the elastic modulus and yield strength of the nanolaminate, comparing with those of the monolithic metallic glass. The nanolaminate also shows enhanced tensile ductility by homogeneous flow in the metallic glass layers. Using mechanical properties of metallic glass, metallic glass film is investigated for stretchable encapsulation material. Encapsulation is necessary to protect devices vulnerable to moisture and oxygen and as stretchable and wearable devices are developed, stretchability is also required in encapsulation materials. Amorphous structure of metallic glass material is advantageous in encapsulation film since diffusion path of moisture or oxygen vapor is increased comparing to crystalline or organic materials with grain boundary or large size of defects. The ternary metallic glass thin film with high thermal stability is fabricated by co-sputtering process. Electrical Ca test is performed to evaluated diffusion barrier characteristic and reveal metallic glass in the system of CuZr-Ti has water vapor transmission rate of 10 -3 order. Stretchability of ternary metallic glass thin film is evaluated as 4 % through in situ tensile testing and cyclic stretching testing, showing feasibility for stretchable encapsulation material.