In recent years, ferroelectric random access memory (FeRAM) has considerable potential as a new memory due to its properties for ideal memory such as random access, high-density integration, fast read and write operation, long endurance, excellent retention and non-volatility with unlimited usage in...
In recent years, ferroelectric random access memory (FeRAM) has considerable potential as a new memory due to its properties for ideal memory such as random access, high-density integration, fast read and write operation, long endurance, excellent retention and non-volatility with unlimited usage in practical. Among the materials used as FeRAM capacitor, Bismuth layer-structured ferroelectrics have received considerable attention as alternative materials to conventional Pb-based ferroelectrics [e.g., PbTiO3, Pb(Zr,Ti)O3. etc.]. Essentially, Compared with SrBi2Ta2O9 (SBT) and its related materials, Bi4Ti3O12 (BTO) is known to show high crystallinity at lower temperatures. However, BTO in its structure contains unstable bi ions, which are easily evaporated during the heating process. The volatility of Bi ions affects the poor ferroelectric and fatigue characteristics of the thin films. Bi3+ ions in the BTO structure can be substituted by trivalent rare-earth ions, such as La3+, Nd3+ and Sm3+, for the improvement of the properties of such a layer-structure. Among them, Bi4-xSmxTi3O12 (BSmT) has been received much attention due to its large ferroelectricity than that of Bi4-xLaxTi3O12 (BLT). Bi3.35Sm0.65Ti3O9 stock solutions were synthesized by sol-gel process. Tris(2,2,6,6-tetramethyl-3,5-heptanedionato) bismuth (III) [Bi(TMHD)3], Tris(2,2,6,6-tetramethyl-3,5-heptanedionato) Samarium (III) [Sm(OC2H5)3], Titanium (IV) i-propoxide [Ti(OC2H5)4] were used as starting materials. Also 2-methoxyethanol was used for solvent and ethylacetoacetate [EAcAc], a kind of β-diketonate ligands was used as a chelating agent to improve solution stability. These solutions were spin-coated onto the Pt/TiOx/SiO2/Si substrates at 3000 rpm for 30 sec and were baked at about 450℃ for 5 minutes. Rapid thermal annealing (RTA) in oxygen ambient at 600℃ for 1 min was used to promote crystallization of BLT thin films. These films were furnace-annealed at various temperatures (600, 640, 680, and 720
In recent years, ferroelectric random access memory (FeRAM) has considerable potential as a new memory due to its properties for ideal memory such as random access, high-density integration, fast read and write operation, long endurance, excellent retention and non-volatility with unlimited usage in practical. Among the materials used as FeRAM capacitor, Bismuth layer-structured ferroelectrics have received considerable attention as alternative materials to conventional Pb-based ferroelectrics [e.g., PbTiO3, Pb(Zr,Ti)O3. etc.]. Essentially, Compared with SrBi2Ta2O9 (SBT) and its related materials, Bi4Ti3O12 (BTO) is known to show high crystallinity at lower temperatures. However, BTO in its structure contains unstable bi ions, which are easily evaporated during the heating process. The volatility of Bi ions affects the poor ferroelectric and fatigue characteristics of the thin films. Bi3+ ions in the BTO structure can be substituted by trivalent rare-earth ions, such as La3+, Nd3+ and Sm3+, for the improvement of the properties of such a layer-structure. Among them, Bi4-xSmxTi3O12 (BSmT) has been received much attention due to its large ferroelectricity than that of Bi4-xLaxTi3O12 (BLT). Bi3.35Sm0.65Ti3O9 stock solutions were synthesized by sol-gel process. Tris(2,2,6,6-tetramethyl-3,5-heptanedionato) bismuth (III) [Bi(TMHD)3], Tris(2,2,6,6-tetramethyl-3,5-heptanedionato) Samarium (III) [Sm(OC2H5)3], Titanium (IV) i-propoxide [Ti(OC2H5)4] were used as starting materials. Also 2-methoxyethanol was used for solvent and ethylacetoacetate [EAcAc], a kind of β-diketonate ligands was used as a chelating agent to improve solution stability. These solutions were spin-coated onto the Pt/TiOx/SiO2/Si substrates at 3000 rpm for 30 sec and were baked at about 450℃ for 5 minutes. Rapid thermal annealing (RTA) in oxygen ambient at 600℃ for 1 min was used to promote crystallization of BLT thin films. These films were furnace-annealed at various temperatures (600, 640, 680, and 720
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