Abstract
The (Pb1-x,Srx)TiO3 (PST) material is a kind of modified PbTiO3. It has a small c/a ratio which reduces unfavorable lattice strain so that it possesses an appropriate ferroelectric polarization. The property of PST thin films highly depends on the composition of the Pb/Sr ratio with potential for applications in high frequency tunable devices and non-volatile ferroelectric random access memory (FeRAM). In this dissertation, the structural and electrical properties of PST ferroelectric thin films fabricated by RF magnetron sputtering were investigated.When the PST thin films were deposited on Pt/Ti/SiO2/Si substrates, the c/a ratio of the crystal structure was found to decrease with the increase of Sr content and W doping. The surface morphology, dielectric properties, leakage currents, and ferroelectric properties of PST thin films with various compositions were examined. The PST(x=0.6) films display excellent tunable dielectric properties, which the PST(x=0.2) films present the best ferroelectric properties. The W-doped PST films exhibit remarkable improvement of fatigue endurance because the substitution of W for Ti compensates oxygen vacancies effectively.For the field effect transistor FeRAM (FET-type FeRAM) applications, the metal/ferroelectric/insulator/semiconductor (MFIS) structure with PST thin films as the ferroelectric layer and ZrO2 (or ZrO2/SiON) thin films as the insulating layer were fabricated. The ultra-thin SiON layer is found to suppress the charge injection effectively and is helpful to obtain a larger memory window. The MFIS structure with thicker PST thin films possesses a larger memory window. The occurrence of charge injection is briefly described and discussed by the capacitance-voltage (C-V) property and the conduction mechanism of PST-based MFIS structures.