TY - THES

T1 - Influence of polyimide substrate on electromechanical properties of sputter-deposited Mo and Cu thin films

AU - Haiden, Lukas

N1 - embargoed until null

PY - 2020

Y1 - 2020

N2 - The fabrication of flexible solar panels, foldable displays, different entertainment devices as well as wearable biomedical sensors has become an interesting field of research in recent years. During the production, various electronical components such as thin film transistors, transparent conductors, metal interconnections, etc. are placed on flexible polymer substrates which are supporting the thin metallic films. It is important that the electrical and mechanical properties of the films are maintained over a wide range of different loading conditions. Furthermore, deformation and evolution of cracks are of high importance and crucial for the reliability of any device using thin films. The majority of the conducted research in literature is focused on the properties and behaviour of the metallic thin films while the influence of the substrate material or its thicknesses is often not taken into account. In this thesis, the change of the electromechanical properties of Mo and Cu films due to different polymers as well as different substrate thicknesses was investigated. For this purpose, polyimide from two different producers was used. The substrates were coated with Cu and Mo applying a physical vapour deposition processes namely, direct current magnetron sputtering and high-power impulse magnetron sputtering. Continuous measurements of the electric resistance of the films while straining with and without optical devices like a laser confocal scanning microscope allow to correlate mechanical properties with electrical ones. Furthermore, different properties like the crack onset strain and crack density were determined and the obtained values were put in relation to each other. The morphology and crystal structure were investigated by scanning electron microscopy and X-ray diffraction analysis. The uncoated polyimides were characterized by using differential scanning calorimetry to investigate possible phase changes in the relevant temperature range. Moreover, tensile tests were performed to evaluate their mechanical behaviour. The obtained different electromechanical properties of the Mo and Cu films arise from the fact that the used polyimides reveal different mechanical properties. Further, thicker substrates tend to have a lower increase in the overall electrical resistance but a higher COS. In order to improve the properties of the thin films used in flexible and wearable devices, it is important to know the specifications of the substrates and include them for an optimization of the deposition process.

AB - The fabrication of flexible solar panels, foldable displays, different entertainment devices as well as wearable biomedical sensors has become an interesting field of research in recent years. During the production, various electronical components such as thin film transistors, transparent conductors, metal interconnections, etc. are placed on flexible polymer substrates which are supporting the thin metallic films. It is important that the electrical and mechanical properties of the films are maintained over a wide range of different loading conditions. Furthermore, deformation and evolution of cracks are of high importance and crucial for the reliability of any device using thin films. The majority of the conducted research in literature is focused on the properties and behaviour of the metallic thin films while the influence of the substrate material or its thicknesses is often not taken into account. In this thesis, the change of the electromechanical properties of Mo and Cu films due to different polymers as well as different substrate thicknesses was investigated. For this purpose, polyimide from two different producers was used. The substrates were coated with Cu and Mo applying a physical vapour deposition processes namely, direct current magnetron sputtering and high-power impulse magnetron sputtering. Continuous measurements of the electric resistance of the films while straining with and without optical devices like a laser confocal scanning microscope allow to correlate mechanical properties with electrical ones. Furthermore, different properties like the crack onset strain and crack density were determined and the obtained values were put in relation to each other. The morphology and crystal structure were investigated by scanning electron microscopy and X-ray diffraction analysis. The uncoated polyimides were characterized by using differential scanning calorimetry to investigate possible phase changes in the relevant temperature range. Moreover, tensile tests were performed to evaluate their mechanical behaviour. The obtained different electromechanical properties of the Mo and Cu films arise from the fact that the used polyimides reveal different mechanical properties. Further, thicker substrates tend to have a lower increase in the overall electrical resistance but a higher COS. In order to improve the properties of the thin films used in flexible and wearable devices, it is important to know the specifications of the substrates and include them for an optimization of the deposition process.

M3 - Master's Thesis

ER -