Properties of BaBi 2 Ta 2 O 9 thin films prepared by chemical solution deposition technique for dynamic random-access me
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Properties of BaBi2 Ta2 O9 thin films prepared by chemical solution deposition technique for dynamic random-access memory applications C. R. Foschini and P. C. Joshi Department of Materials Science and Engineering, Virginia Tech, Blacksburg, Virginia 24061-0237
J. A. Varela Instituto de Qu´ımica, Universidade Estadual Paulista – UNESP – Araraquara, SP, Brazil 14801-970
S. B. Desua) Department of Materials Science and Engineering, Virginia Tech, Blacksburg, Virginia 24061-0237 (Received 1 May 1998; accepted 1 December 1998)
We report on the properties of BaBi2 Ta2 O9 (BBT) thin films for dynamic random-access memory (DRAM) and integrated capacitor applications. Crystalline BBT thin films were successfully fabricated by the chemical solution deposition technique on Pt-coated Si substrates at a low annealing temperature of 650 ±C. The films were characterized in terms of structural, dielectric, and insulating properties. The electrical measurements were conducted on PtyBBTyPt capacitors. The typical measured small signal dielectric constant and dissipation factor, at 100 kHz, were 282 and 0.023, respectively, for films annealed at 700 ±C for 60 min. The leakage current density of the films was lower than 1029 Aycm2 at an applied electric field of 300 kVycm. A large storage density of 38.4 fCymm2 was obtained at an applied electric field of 200 kVycm. The high dielectric constant, low dielectric loss and low leakage current density suggest the suitability of BBT thin films as dielectric layer for DRAM and integrated capacitor applications. I. INTRODUCTION
High dielectric constant materials are being explored for the next generation of high-density dynamic randomaccess memory (DRAM) applications because of the physical thickness limit of oxide/nitride based capacitance materials currently being used. The parameters of importance for DRAM applications are dielectric constant and leakage current characteristics. The high dielectric constant materials are desirable, as they will lead to simple capacitor design and charge storage density comparable to conventional dielectrics even at much larger thickness. A low leakage current density is necessary to reduce the refreshing time. Dielectric materials such as Ta2 O5 and Bax Sr12x TiO3 (BST) have been widely investigated for DRAM applications. Ta2 O5 is the most suitable material from a fabrication compatibility point of view; however, it has been unable to match the leakage current characteristics of conventional dielectrics. BST offers the advantage of very high dielectric constant; however, it has to overcome the problems of high leakage current in addition to processing and integration issues. In the present research, we have investigated the properties of BaBi2 Ta2 O9 (BBT) thin films as an alternative dielectric material for DRAM applications. BBT material belongs to the layered-perovskite family and crystallizes in the orthorhombic phase. A high a)
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II. EXPERIMENTAL
Thin films of BaBi2 Ta2
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