Defect states responsible for leakage current in ultrathin (physical thickness <10 nm) tantalum pentoxide(Ta2O5)films were measured with a novel zero-bias thermally stimulated current technique. It was found that defect statesA,whose activation energy was estimated to be about 0.2 eV, can be more efficiently suppressed by usingN2Orapid thermal annealing (RTA) instead of usingO2RTA for postdeposition annealing. The leakage current was also smaller for samples withN2ORTA than those withO2RTA for postdeposition annealing. Hence, defect statesAare quite likely to be important in causing leakage current. ©1997 American Institute of Physics.