Influence of N2/Ar Flow Ratio on the Microstructure and Electrochemical Capacitive Performance of TiN Thin-Film Electrodes for Micro-Supercapacitors

With the rapid development of the Internet of Things (IoT), micro-energy storage devices face increasing demands for miniaturization, high energy density, and high power density. Owing to their excellent electrical conductivity and mechanical strength, TiN thin films are promising candidates for micro-supercapacitor electrodes. In this work, TiN thin films were prepared by direct current magnetron sputtering under different N2/Ar flow ratios. The effects of the N2/Ar flow ratio on the crystal structure, surface morphology, roughness, and electrochemical capacitive performance of TiN thin films were systematically investigated. The results show that at lower N2/Ar flow ratios, the films consist of a mixture of TiN and Ti2O3 phases, while at higher N2/Ar ratios, single-phase TiN with a preferred orientation along the (220) plane is detected in the obtained films. AFM measurements indicate that the root mean square roughness first increases and then decreases with increases in N2/Ar flow ratios, and it reaches a maximum of around 15.9 nm when the N2/Ar flow ratio is 5:15. XPS results show that the 5:15 sample contains the highest oxygen vacancy concentration, offering it the best conductivity, which is confirmed by four-probe measurements. Electrochemical tests demonstrate that the N2/Ar flow ratio has a significant influence on the specific capacitance of TiN films, with the highest value of 3.29 mF/cm2 achieved at a N2/Ar flow ratio of 5:15, which is likely due to the rough and porous surface and much better conductivity of the as-deposited films. This study provides an important experimental basis for optimizing the performance of TiN thin-film electrodes.