Sodium charge storage in ultrathin MnO2 films was studied using cyclic voltammetry (CV) and electrochemical quartz crystal microbalance (EQCM) measurements. The MnO2 films were fabricated by electrochemical oxidation of MnO films grown by atomic layer deposition (ALD). CV analysis confirmed that oxidation of MnO to MnO2 involved two moles of electrons per mole of Mn in the MnO ALD film. Scanning electron microscopy (SEM) images revealed that electrochemical oxidation of MnO led to the formation of MnO2 nanosheets. EQCM measurements suggested that Na+ cations participate in charge storage in MnO2. X-ray photoelectron spectroscopy (XPS) experiments measured sodium in MnO2 after both positive/anodic and negative/cathodic voltage sweeps. The stoichiometry was Na0.25MnO2 after negative/cathodic voltage sweeps. Approximately one-half of the sodium was removed after positive/anodic voltage sweeps. The areal capacitance increased progressively with initial MnO ALD film thickness. This increase in areal capacitance is consistent with bulk charge storage in MnO2 or higher surface area of MnO2 nanosheets resulting from larger MnO ALD film thicknesses. Experiments at varying scan rates indicated that charge storage in MnO2 originates from a combination of capacitive and diffusive processes. Bulk charge storage makes a significant contribution to total charge storage in the thicker MnO2 films.

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Here, silicon oxide was formed in a U-shaped trench of a power metal-oxide semiconductor field-effect transistor device by various processes. One SiO2 formation process was performed in multiple steps to create a low-defect Si-SiO2 interface, where first a thin initial oxide was grown by thermal oxidation followed by the deposition of a much thicker oxide layer by chemical vapor deposition (CVD). In a second novel approach, silicon nitride CVD was combined with radical oxidation to form silicon oxide in a stepwise sequence. The resulting stack of silicon oxide films was then annealed at temperatures between 1000 and 1100 °C. All processes were executed in an industrial environment using 200 mm-diameter (100)-oriented silicon wafers. The goal was to optimize the trade-off between wafer uniformity and conformality of the trenches. The thickness of the resulting silicon oxide films was determined by ellipsometry of the wafer surface and by scanning electron microscopy of the trench cross sections. The insulation properties such as gate leakage and electrical breakdown were characterized by current–voltage profiling. The electrical breakdown was found to be highest for films treated with rapid thermal processing. The films fabricated via the introduced sequential process exhibited a breakdown behavior comparable to films deposited by the common low-pressure CVD technique, while the leakage current at electric fields higher than 5 MV/cm was significantly lower.