Ferroelectric materials for 64 Mb and 256 Mb DRAMs

The authors have studied the feasibility of using ferroelectric materials as the capacitor dielectric in the one-transistor memory cells for 64-Mb and 256-Mb DRAMs. They have performed an intensive literature search and analysis. They discuss the crystal structure of the materials reviewed, their hysteresis curve, temperature dependence of the spontaneous polarization, leakage current, dielectric breakdown, reliability, ageing, and fatigue. The authors examine the charge storage capacity in a 1-T DRAM cell and analyze a number of ferroelectric materials for their potential use as the dielectric in 64-Mb and 256-Mb DRAM capacitors, focusing on projected requirements for the electrical parameters and preferred material characteristics. Of the materials examined, those that appear to hold the greatest promise for 64-Mb and 256-Mb DRAMs are the paraelectric phase compositions of (Pb,La)TiO/sub 3/ (PLT) and (Pb,La)(Zr,Ti)O/sub 3/ (PLZT). Pb(Mg,Nb)O/sub 3/ (PMN) is also attractive because it is paraelectric, but it may not be able to achieve the required charge densities when deposited as a thin film.<
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