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Leakage Degradation in BST Dielectric Capacitors with Oxide and Metal Electrodes

  • N. Fukushima (a1), K. Abe (a1), M. Izuha (a1) and T. Kawakubo (a1)

Abstract

Leakage degradation under DC stresses in epitaxially-grown Ba1−xSrxTiO3/SrRuO3 capacitors with various top electrodes was examined. Epitaxial capacitors employed in this study exhibit higher dielectric constant arising from optimized lattice deformation caused by lattice mismatch between Ba1−xSrxTiO3 and SrRuO3; dielectric constant for SrRuO3/30nm thick Bal-xSrxTiO3/SrRuO3 all oxide capacitor was 550, which corresponds SiO2 equivalent thickness of 0.21 nm. In addition, this type of capacitors have interfaces of higher cleanliness between dielectrics and electrodes, which are expected to provide opportunities of more simplified discussions on reliability issues for thin film capacitors. Dielectric breakdown properties and DC stress-induced leakage degradation properties were examined in room temperature and elevated temperatures. Various kinds of leakage degradation were observed and categorized in anode degradation and cathode degradation. The degradation in capacitors with oxide electrodes was markedly suppressed compared to that in capacitors with metal electrodes such as Pt or Ru. This higher degradation resistance yielded longer lifetime in capacitors of this type and the estimated life time at 458K for SrRuOS/ Bal-xSrxTiO3/SrRuO3 capacitor was 3E8 seconds, which exceeds required specification for DRAM application. These differences were discussed on the basis of a supposed degradation mechanism in which oxygen vacancy generation at anode interface is taken into account as well as vacancy accumulation at cathode interface.

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References

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1) Izuha, M. et al., Jpn. J. Appl. Phys., 9B, 208 (1997)
2) Scimizu, T., Solid State Commun., 102, 523 (1997)
3) Al-Sareef, H. N. et al., J. Appl. Phys., 79, 1013 (1996)
4) Kawakubo, T. et al., Technical Digest of Int. Electron Devices Meeting, 1996
5) Sano, K. et al., 39th Electronic Material Conference (Fort Collins, Colorado. 1997)

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