Control of crystalline structure and ferroelectric properties of Pb(ZrxTi/sub 1-X/)O3 films by pulsed laser deposition
We have investigated Pb(Zr/sub X/Ti/sub 1-X/)O/sub 3/ (PZT) films on Pt/SiO/sub 2//Si substrates formed by pulsed laser deposition (PLD) and subsequent rapid thermal annealing (RTA) under various growth conditions. X-ray diffraction analysis revealed that preferentially [100]-oriented perovskite PZT films with trigonal structure were formed after RTA from as-deposited films which had consisted of small grains with pyroclore structure. The degree of [100]-orientation of the PZT film increased with the oxygen partial pressure during PLD. The capacitors made from these films showed higher remnant polarization than those from randomly oriented films.
FABRICATION OF FERROELECTRIC PZT THIN FILMS BY LIQUID DELIVERY MOCVD USING NOVEL Zr and Ti PRECURSORS
ABSTRACT Pb(Zr,Ti)O3 (PZT) thin films were deposited by metalorganic chemical vapor deposition (MOCVD) with liquid delivery system. Lead bis(2,2,6,6,-tetramethyl 3,5-heptanedionate) [Pb(thd)2], with two novel mixed ligand precursors Zirconium bis(isopropoxy) bis(1-methoxy-2-methyl-2-propoxy) [Zr(OiPr)2(mmp)2], and Titanium bis(isopropoxy) bis(1-methoxy-2-methyl-2-propoxy) [Ti(OiPr)2(mmp)2] were used in this study. Perovskite PZT films were obtained on (111)Ir/Ti/SiO2/Si substrates at 550°C process temperature with growth rate around 5 nm/min. The deposited PZT films show ferroelectric properties. Remanent polarization was 11.4 μ C/cm2 and coercive field is around 79.9 kV/cm for PZT film of 100 nm thickness.
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.<<ETX>>