Planar Microsupercapacitors Based on Oblique Angle Deposited Highly Porous TiN Thin Films

Microsupercapacitors are gaining increasing interest for energy storage in miniaturized electronic devices. However, the production of porous electrode material with standard microfabrication techniques is a big problem. Here, we report on the oblique angle deposition of highly porous and nanostructured columnar titanium nitride (TiN) films on silicon substrate using magnetron sputtering for high-performance microsupercapacitors. The intercolumnar porosity of the sputtered TiN films can be systematically controlled as a function of the oblique angle alpha achieved by tilting the substrate. The denser morphologies in TiN films deposited at alpha = 0 degrees lead to moderate capacitive behavior in a 1 M Na2SO4 electrolyte solution. Meanwhile, a high areal capacitance of 17.5 mFmiddotcm-2 is obtained for a 60 degrees oblique angle due to high intercolumnar porosity in films, which increases the specific surface area and facilitates easy electrolyte permeation. The electrodes also retain 88.2% of the initial specific capacitance after 10,000 charging/discharging cycles. A planar interdigitated microsupercapacitor has been subsequently fabricated based on an optimized TiN thin film serving as both an efficient electrode and a current collector. TThe device was electrochemically tested using polyvinyl alcohol (PVA)-Na2SO4 hydrogel electrolyte allowing a voltage window of 1.8 V and showed energy densities of 0.46 mu Whmiddotcm-2 while maintaining a high-power density of 703.12 mu Whmiddot cm-2. This work gives insight into the use of oblique angle deposition for obtaining highly porous films of other electrode materials for microsupercapacitor applications with the advantage of using a simple microfabrication process.