Paper EM-WeA10
Suppression of Metal-Insulator-Metal (MIM) Capacitor Leakage Current in BaSrTiO3 (BST) Dielectrics by Ni Doping : Spectroscopic Studies Changes in Conduction Band Edge Defects States with Ni Doping

Wednesday, October 17, 2007, 4:40 pm, Room 612

A significant reduction of leakage current in MIM capacitors in Ni-doped BST dielectrics is reported. Ni-doping increases the breakdown voltage from ~10-12 V to >35 V, and reduces the leakage current by several orders of magnitude,10²~10³, as compared to un-doped BST. The conduction mechanism is changed from i) tunneling injection plus Poole-Frenkel transport in un-doped BST to ii) Fowler-Nordheim tunneling in the Ni-doped BST. These decreases are explained by a spectroscopic study of changes in conduction band, and band edge defect states. The large changes in breakdown voltage and leakage current between doped and un-doped BST have been correlated with changes in band edge oxygen vacancy defects detected by spectroscopic ellipsometry (SE). The ¥å₂spectrum from the SE measurements on Ni-doped BST is qualitatively different than that from un-doped BST. Changes in conduction band states from 3.5 to 6 eV are assigned to Ni²⁺/Ni³⁺ transitions, and changes in band edge defect state features between 2.5 and 3 eV due to reduction of Ti³⁺bonding at O-atom vacancies. In particular, the defect state difference is attributed to charge transfer between Ni²⁺ states, and Ti⁴⁺band states, as well as Ti³⁺ pre-existing defect states of the BST host. The band edge vacancy defect is ~0.2 eV shallower in Ni-doped BST and this leads to the significant changes in transport and trapping, accounting for reductions in leakage current, and improved resistance to breakdown in the Ni-doped BST. The study demonstrates that addition of transition metal doping atoms with different valence states than Ti in BST, and/or Zr in other insulating perovskites, can have a significant effect on transport by providing a way to reduce/control leakage current and breakdown. These doping effects will be important in transition metal/rare earth atom complex oxides that have been identified for device applications, not only as high-k capacitors or gate dielectrics, but for ferro-electric devices as well.