| Summary: | 博士 === 逢甲大學 === 材料科學與工程學系 === 104 === High power impulse magnetron sputtering (HIPIMS) has been attracted much attention as a next generation power source owing to its remarkable plasma characteristics such as high density, high ionization, and high ionic energy, which enables to deposit high quality and dense films with high adhesion on flexible substrates. Nevertheless, there is a wide discrepancy between HIPIMS and conventional sputtering in terms of plasma fundamental properties, voltage-current response of target, film microstructure, and features under metallic and reactive modes. To understand the pending issue aforementioned, in this thesis the constant voltage HIPIMS power was employed to prepare silver, titanium, copper and brass films, respectively on flexible substrates. By introducing optical emission spectrometry (OES) and residual gas analysis (RGA), the plasma behaviors under metallic and reactive modes, voltage-current response, and microstructure of the films were investigated. The HIPIMS deposition technique as revealed here are expected for application on flexible substrates.
Experimental results show that the self-sputtering can be achieved using all those metallic targets under metallic mode. This is evidenced by the Jp-VD dependency (which possibly can have four discharge stages) and metal ion concentration determined by OES. Accordingly, pure copper and brass plasma achieve only self-sputtering stage (the third stage). On the other hand, pure silver and titanium targets can achieve the discharge stage of loss of magnetron confinement (the fourth stage).
Under metallic mode, the films prepared by HIPIMS exhibit high crystallity with their substrate temperature barely reached 40 C. However, the deposition rate was slightly lower than that of direct current magnetron sputtering (DSMS). The silver and brass films on PET textile perform high color fastness of washing and rubbing, indicating a high film adhesion of the coating. Accordingly, the films remain antibacterial ability after washing test for 20 times. In addition, the mechanical strength of the coated PET textile was greater than that of the bare textile, which demonstrates that HIPIMS process brings no damage to the substrate.
Under reactive mode, by the results of OES and RGA, target poisoning was found for pure titanium target using HIPIMS and DCMS power source with O2 flow rate of 12.4 and 20.0 sccm, respectively, which apparently the target poisoning took place at lower O2 concentration for HIPIMS process than DCMS. The formation of transient oxide layer over the target surface causes the decrease in sputtering rate, which resulted in the decrease of the Ti emission species, and evidenced by the increase in O2 pressure by RGA measurement. On the other hand, the Jp dependence on O2 flow rate for titanium reactive sputtering using HIPIMS was more sensitive than that using DCMS, as O2 flow was increased. This can be attributed to self-sputtering which leads to ion induced electron emission (ISEE) owing to resputtering of Ti ions on the target. As to the titanium oxide films obtained by using HIPIMS reactive sputtering, the crystal structure was found to depend on O2 flow. With increasing O2 flow rate, the structure and the associated film composition changed from featureless substiometrical Ti2O film to coarse columnar -TiO, and eventually to fine-grained R-TiO2. The accompanied target current increase (i.e., power increase) can have its effect on the temperature rising to the substrate. Even that, the substrate temperature reached ultimately 100 C. The optical band gap increased from 0.0 to 3.2 eV, which depends on the phase and composition of the obtained coatings. The electrical properties show a similar trend. When at a O2/Ar ratio of 0.139, the film exhibited the highest carrier mobility (3.1 cm2/V) and the lowest electrical resistance (2.2 10-5 cm).
In conclusion, the enhanced ion species emitted from the self-sputtering mechanism in HIPIMS plasma enable the low-temperature deposition with high film quality, which is useful for flexible electronics applications.
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