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 α achieved by tilting the substrate. The denser morphologies in TiN films deposited at α = 0° lead to moderate capacitive behavior in a 1 M Na₂SO₄ electrolyte solution. Meanwhile, a high areal capacitance of 17.5 mF·cm^-2 is obtained for a 60° 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 μWh·cm^-2 while maintaining a high-power density of 703.12 μWh·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.

Influence of the thickness of an antiferromagnetic IrMn layer on the static and dynamic magnetization of weakly coupled CoFeB/IrMn/CoFeB trilayers

The static and dynamic magnetization response of the CoFeB/IrMn/CoFeB trilayer system with varying thickness of the antiferromagnetic (AF) IrMn layer is investigated using magnetization hysteresis (M-H) and ferromagnetic resonance (FMR) measurements. The study shows that the two CoFeB layers are coupled via a long-range dynamic exchange effect through the IrMn layer up to a thickness of 6 nm. It is found that with the increase in IrMn layer thickness a nearly linear enhancement of the effective magnetic damping constant occurs, which is associated with the simultaneous influence of spin pumping and interlayer exchange coupling effects. An extrinsic contribution to the linewidth originating from the two-magnon scattering is also discussed. The AF-induced interfacial damping parameter is derived by studying the evolution of damping with inverse CoFeB thickness. The static magnetic measurements also reveal the interlayer exchange coupling across the IrMn layer both at room temperature and low temperature. The asymmetric hysteresis loop and training effect observed at low temperature is related to the presence of a metastable AF domain state. We show that both the static and dynamic magnetic properties of trilayer films can be adjusted over a wide range by changing the thickness of the IrMn spacer layer.

Orbital moment probed spin orbit coupling effects on anisotropy and damping in CoFeB thin films

Spin orbit coupling based direct correlation between magnetic anisotropy and damping is established in CoFeB thin films on compositional and stress variations.