Achieving on chip micro-supercapacitors based on CrN deposited by bipolar magnetron sputtering at glancing angle

The enhancement of the surface area and ordering of mesopores is a key parameter to increase the specific capacitance of electrochemical capacitors (ECs). These parameters can improve the electrolyte accessibility to the active material in order to improve its charge storage. In this work, magnetron sputtering at glancing angle (GLAD) is used in order to enhance the porosity of CrN for use as electrode material in ECs. The GLAD technique consists on tilting the substrate according to the deposition flux allowing the formation of well-separated columns due to a ballistic shadowing effect. Four different tilts of 0°, 45°, 60° and 75° were explored. While the CrN films deposited at 0° or 75° do not show any capacitive behaviour, a high areal capacitance is obtained at 45° or 60° (35.4 mF cm⁻² at a current density of 1.2 mA cm⁻² in 0.5 M H₂SO₄ electrolyte) with a good cycling stability over 10,000 cycles. On chip interdigitated micro-supercapacitors (MSCs) were assembled with a maximum energy density of 2 μWh.cm⁻² (15.3 mWh.cm⁻³) at a power density of 20 μW cm⁻² (0.15 W cm⁻³). The GLAD strategy can be generalised to other materials deposited by physical vapour deposition techniques, for highly porous electrodes, with improved electrochemical energy storage properties.