Fabrication of precision integrated capacitors

A detailed parametric study on the fabrication of metal-insulator-metal capacitors through the anodization of aluminum in an aqueous ammonium pentaborate octahydrate electrolyte is reported. The dependence of the specific capacitance on anodization voltage (8 V-30 V), time (5 min-60 min), temperature (5 °C-60 °C) and electrolyte concentration (0.01 M-0.05 M) was studied in deionized water and ethylene glycol. A linear increase in capacitance with anodization voltage was found, with the highest capacitance achieved at 473 nF/cm2 in ethylene glycol. Room temperature, long-time anodization time and high electrolyte concentration within the studied range yielded the best quality dielectric films. The leakage current was < 1 nA/cm2 when the dielectric was formed in ethylene glycol. The capacitors fabricated in ethylene glycol satisfy the on-chip capacitors criteria of the International Technology Roadmap for Semiconductor, with quadratic voltage coefficient < 100 ppm/V2.