Thin film techniques for the fabrication of nano-scale high energy density capacitors

Dielectric thin films of either TiO₂ or BaTiO₃ were sputtered in O₂/Ar plasmas on Si wafers to thicknesses ranging from approximately 25 to 200 nm with patterned Ni or Pt electrodes sputtered in Ar plasmas at thicknesses from about 20 to 250 nm to form nano-capacitors. Statistical design of experiments (DOE) was used to determine the effects of the deposition power, plasma composition, and deposition temperature on the measured electrical properties of the nano-capacitors. Additional tests to determine the effects of the dielectric and electrode thickness on the measured dielectric responses of the devices were also undertaken. Characterization was performed with a combination of direct current (DC) and alternating current (AC) testing methods including AC impedance, coercive field and leakage current versus voltage, scanning electron microscopy, transmission electron microscopy (TEM), x-ray diffraction (XRD), x-ray photoelectron spectroscopy, focused ion beam microscopy, and atomic force microscopy. The dielectric properties were found to depend on complex interactions of the process variables that could be modeled using statistical software. The permittivity was found to range from 100 to 10,000 with losses between 0.013 and 0.570. The resistance at 1 V DC varied from approximately 1.5 to 360 GΩ, and either a ferroelectric or paraelectric hysteretic response was observed for all specimens tested. Chemical analyses showed the films to be oxygen rich, while XRD and TEM data indicated the BaTiO₃ was amorphous. The electrical, chemical, and microstructural properties were found to depend on the sputtering conditions of the BaTiO₃, dielectric thickness, electrode material choice, and the electrode thickness. Collectively, the results indicated that the properties of nanometer thick dielectric and electrode materials have a significant impact on the measured electrical propertie