Fig. 7
a Charge-discharge curve of the fabricated capacitor with 5 nm of Al2O3 together with the equivalent RC circuit. b Impedance spectrum of the capacitor, which was measured at a dc bias of 0 V with an AC signal of 5 mV over a frequency range from 1 MHz to 1 kHz. c The charging process of the corresponding fabricated capacitor with different voltages. The used pad area is 200 × 200 μm2