Ternary composite Si/TiN/MnO₂ taper nanorod array for on-chip supercapacitor

We present a ternary composite Si/TiN/MnO₂ taper nanorod array electrode for large specific capacitance on-chip supercapacitor. The capacitor is based on conformal deposition of pseudo-capacitive MnO₂ nano-layer and TiN current collector nano-layer on a silicon taper nanorod array (Si-TNR) scaffold. The key fabrication processes include cyclic deep reactive ion etch (DRIE) of silicon, atomic layer deposition (ALD) of TiN, as well as solution chemical deposition of MnO₂. Different growth modes of MnO₂ functional layers via electrochemical deposition (ED) and electroless chemical deposition (CD) are investigated in terms of thickness, morphology, and conformality. Optimization of the supercapacitor performance by controlling the loading amount of pseudo-capacitive layer on taper nanorod array scaffold is demonstrated. The electrode design targeting taper nanorod array enables improved and effective mass loading of active material towards high specific capacitance. The obtained Si-TNR/TiN/MnO₂ electrode offers areal specific capacitance of 81.6 mF cm^-2 as evaluated at 5 mV s^-1 scan rate (41.3 mF cm^-2 at 200 mV s^-1), showing ~70 times improvement in areal capacitance compared to that of the Si-TNR/TiN electrode.