High density supercapacitors with atomic layer deposited SiO2 dielectric as solid state electrolyte

For on-chip supercapacitors used for energy storage, it is required that the capacitance density is supposed to be large enough to enhance the energy storage capacity and the electrolytes can be easily filled in high aspect ratio structures. Regarding these concerns, different thicknesses of SiO2 thin films are prepared on the TaN electrodes using atomic layer deposition technology, and their ability as solid state electrolytes for supercapacitors is investigated. The results show that SiO2 with thicknesses of 5, 7, and 10 nm exhibits significant capacitance double sweep windows, indicating strong charge storage capabilities. For a 10 nm SiO2 film, when the sweep rate is 10 mV/s, the capacitance density is 7.63 μF/cm2, 13 times higher than the one extracted under high-frequency test conditions. After annealing, the capacitance density is decreased to be 1.02 μF/cm2. The secondary ion mass spectroscopy analysis shows that the hydrogen concentration in the 10 nm SiO2 sample is approximately 8.9 × 1020 atoms/cc, indicating that the double-layer capacitance is formed by the free movement of hydrogen protons in SiO2 and their accumulation/desorption on the electrode surface area. After annealing, the hydrogen concentration of the 10 nm SiO2 sample is decreased to 7 × 1020 atoms/cc, resulting in a decrease in the capacitance density. For 1000 cycles of capacitance double sweep on a 10 nm SiO2 sample, the capacitance density is decayed to approximately half of the initial value.