Lanthanum-substituted bismuth titanate for use in non-volatile memories

Park, B. H.
Kang, B. S.
Bu, S. D.
Noh, T. W.
Lee, J.
Jo, W.

* Department of Physics and Condensed Matter Research Institute, Seoul National University, Seoul 151-742, Korea
† Department of Materials Engineering, Sung Kyun Kwan University, Suwon 440-746, Korea
‡ LG Corporate Institute of Technology, Seoul 137-140, Korea

Received 23 March; accepted 13 September 1999.

Correspondence and requests for materials should be addressed to T.W.N. (e-mail: [email protected]).

Nature 401(6754):p 682-684, October 14, 1999.

Non-volatile memory devices are so named because they retain information when power is interrupted; thus they are important computer components. In this context, there has been considerable recent interest in developing non-volatile memories that use ferroelectric thin films-'ferroelectric random access memories', or FRAMs-in which information is stored in the polarization state of the ferroelectric material. To realize a practical FRAM, the thin films should satisfy the follwing criteria: compatibility with existing dynamic random access memory technologies, large remnant polarization (P_r) and reliable polarization-cycling characteristics. Early work focused on lead zirconate titanate (PZT) but, when films of this material were grown on metal electrodes, they generally suffered from a reduction of P_r ('fatigue') with polarity switching. Strontium bismuth tantalate (SBT) and related oxides have been proposed to overcome the fatigue problem, but such materials have other shortcomings, such as a high deposition temperature. Here we show that lanthanum-substituted bismuth titanate thin films provide a promising alternative for FRAM applications. The films are fatigue-free on metal electrodes, they can be deposited at temperatures of ∼650°C and their values of P_r are larger than those of the SBT films.