Sputtered titanium nitride films as pseudocapacitive electrode for on chip micro-supercapacitors

Micro-supercapacitor is one of the most promising types of autonomous, miniaturized and compact electrochemical devices currently used in the Internet of Things (smart and self-powered sensors). Micro-supercapacitor is mainly based on advanced thin-film technology to prepare high-performance thin film electrodes. However, the deposition of electroactive film electrode materials on large-scale substrates remains a challenge. In this paper, a bifunctional pseudocapacitive electrode material titanium nitride was deposited on Si substrate by reactive direct current magnetron sputtering. To obtain the TiN film electrode with excellent electrochemical performance, the intra-column porosity of the TiN film was fine-tuned at the nanoscale, the surface stoichiometric ratio of the film was analyzed, and the relationship between the specific surface area and the areal/volume capacitance of the film was explored. The results show that by fine tuning the working pressure in the sputtering process, films with high intra-column porosity can be obtained; the electrochemical properties of TiN films with stoichiometric ratio of 1:1 and over-stoichiometric ratio are better than those of sub-stoichiometric ratio; and the Gwyddion image analysis technique evaluates the specific surface area of the film surface and shows that the areal capacitance of the film increases linearly with the specific surface area of the film. In addition, the areal capacitance retention of TiN films with a thickness of 626 nm is still as high as 91.4% after 10,000 cycles in the K2SO4 electrolyte solution. These results provide direction for the study of other nitrides film electrode materials.