Investigation On The Microstructure And Electrical Properties Of Lead Zirconate Titanate (PbZr_xTi_1-xO₃) Ferroelectric Films Grown By The Renovated Sol-gel Methods

Recently, ferroelectric thin films have attracted much attention for applications in memory devices, such as dynamic random access memories (DRAMs), non-volatile ferroelectric memories (NVFRAMs), piezo micro-actuators, pyroelectric infrared detectors and non-linear optical devices. Among the various ferroelectric materials, lead zirconate titanate (PbZr_xTi_1-xO₃:PZT) thin films have received much attention because of theirs large remnant polarization(P_r), moderate small coercive field(E_c), high curie temperature, high dielectric constant(ε_r) , together with excellent ferroelectric, piezoelectric, and pyroelectric properties. They also have lower processing temperature (<650℃) and can be integrated with semiconductor circuits, therefore they are the most promising materials for NVFRAMs devices. At present, ferroelectric nonvolatile memories have the potential to replace nonvolatile memories such as floating and flash-erasable programmable read-only memories (EEPROMs), because they combine non-volatility and easy programming/erasing, fast read, fast write and unlimited endurance, lower writing voltages and less program energy, etc. It is well known that the electrical properties of memory devices are strongly influenced by the quality of ferroelectric films. The sol-gel film preparation technique offers numerous advantages, including simpleness and low cost, low processing temperature, excellent compositional control, uniform and easy fabrication films over large areas, etc. Generally, many factors including substrates, precursor solutions, seeding layers, pyrolysis and annealing temperature and ambient, heating rate and so on may affect the electrical properties and microstructure of PZT ferroelectric films. Among them the precursors of good quality that is stable, clear and transparent are primary necessity of the fabrication of PZT films with dense, crack free and homogeneous perovskite structure. Therefore, in this thesis, the above factors and various effects of the employed methods were investigated systemically to improve microstructure and ferroelectric properties, enhance remnant polarization P_r, control fatigue, limit leakage current and decrease annealing temperature. The main results and innovative ideas are as follows:(1) The two renovated preparation techniques of sol-gel were first proposed and applied to coat PZT ferroelectric films. The one is the "Precursor-monomer...