Innovative device designs were used to fabricate low leakage ferroelectric BaTiO3 (BTO) thin film capacitors. BTO thin films with thicknesses ranging from 220 nm to 265 nm were deposited using reactive r.f. magnetron sputtering. A highly stable and conductive metallic oxide, RuO2, was used as the bottom electrode of the capacitors on SiO2/Si substrates. Layers of BTO deposited at low temperature were amorphous and those deposited at high temperature above 600 degrees C were polycrystalline. Microcrystallization of amorphous BTO took place at a thermal treatment temperature of above 600 degrees C. Capacitors with a bilayer configuration of polycrystalline layers on microcrystalline layers showed a capacitance per unit area of around 2.4 x 10(5) pF cm(-2) and a leakage current density of (8.5 +/- 0.5) x 10(-8) A cm(-2) at a field intensity of 2 x 10(5) V cm(-1). A capacitance per unit area of around 1.4 x 10(5) pF cm(-2) and a leakage current density of around 10(-10) A cm(-2) at a field intensity of 2 x 10(5) V cm(-1) were achieved on the capacitors with a nanolayer configuration of amorphous layers on a number of stacked cycles of polycrystalline layers on microcrystalline layers.