Characteristics of ferroelectric 60/40 PZT films deposited by metallo-organic decomposition technology for memory applications

Abstract

Nearly pin-hole-free ferroelectric films of Pb(Zr_0.6Ti_0.4)O₃ (PZT) with uniform compositions and thicknesses were synthesized using metallo-organic decomposition (MOD) technology. The metallo-organic precursors used for these PZT films were lead diethylhexanoate, (Pb(C₇H₁₅COO)₂), titanium dimethoxy-dineodecanoate (Ti(OCH₃)₂ (C₉ H₁₉ COO)₂), and zirconium tetraethylhexanoate (Zr(C₇H₁₅COO)₄). The film thickness, structural development and electrical properties of these films were characterized using a surface profilometer, X-ray diffraction (XRD) and a standardized RT 66 ferroelectric test system. The effect of the processing conditions on the properties of ferroelectric 60/40 PZT films were investigated. The important processing parameters studied included the substrate history, the spinning speed and time, the film thickness, the pyrolysing temperature and the annealing conditions. The experimental results show that the structural development and electrical properties of these 60/40 PZT films are closely correlated with these processing parameters. The polarization-reversal characteristics and fatigue behaviour, which are important for non-volatile memory applications, were also studied. By optimizing the annealing conditions, a 60/40 PZT film exhibited a dielectric strength of 1 MVcm⁻¹ and a sensed remanent polarization value of 9.3 ΜC cm² after cycling 10¹⁰ times. This demonstrates the excellent potential of PZT films for non-volatile memory applications. The measured dielectric-constant values for these 60/40 PZT films were in the range of 300 to 900, which is about 75 to 220 times larger than that of the currently used dielectric, SiO₂, in dynamic random-access memory (DRAM). This fact suggests that PZT film is an excellent alternative for the new generation, extremely high-density DRAM applications.