The characteristics of the ultrathin Ta2O5 film capacitors with Ru bottom electrodes have been investigated. Ru films are deposited on n(+)-Si by sputtering in 10% O-2/Ar ambient, for the bottom electrode, and Ta2O5 films are deposited by chemical vapor deposition using Ta(OC2H5)(5) and O-2. By O-2 plasma treatment at 400 degrees C after N-2 thermal treatment at 700 degrees C, excellent properties, are obtained such that the effective SiO2 film thickness is 0.68 nm for 6 nm thick Ta2O5 film and the leakage current is less than 1 x 10(-8) A/cm(2) between the range of -2.1 and +1.8 V. The Ta2O5 film with a Ru bottom electrode is one of the most suitable structures for Gbit dynamic random access memory capacitors.