Fabrication And Characterization Of PHT Ferroelectric Thin Films

With the dielectric, piezoelectric, pyroelectric, and ferroelectric properties, ferroelectric thin films are widely used in microelectronics, integrated electronics, micro electrom echanical system(MEMS), optoelectronics, and other important fields. Ferroelectric thin film is one of the most important parts of Non-volatile Random Access Memory(NVRAM). With the rapid development of modern science technology and information processing technology, there are many growing demands for storage density, stability and service life about NVRAM. Although the preparation methods of traditional ferroelectric thin films(PZT, SBT) are very perfect, there still exists some problems in industrial applications, such as ferroelectric fatigue, high growth temperature. It is important to find another high-performance ferroelectric material to improve the performance of NVRAM. Recently, Pb(HfxTi1-x)O3(PHT), a perovskite-type ferroelectric material with large remanent polarization, low coercive field, adjustable composition and good fatigue character, has great potential in NVRAM.In this thesis, the integrated structures of PHT and semiconductor materials(Si, GaN) have been studied. We have carried out the following works: optimaling the growth process of PHT thin film on Pt(111)/TiO2/SiO2/Si substrate, studying the effect of different bottom electrodes and researching the effect of buffer layer of PHT film on Al2O3 substrate, preliminarily, exploring the properties of the integrated PHT and GaN. The results can be conclued as follows:1. The optimal growth of PHT thin film by PLD on Pt(111)/TiO2/SiO2/Si substrate was studied. The intrinsic electric properties of PHT film were tested. It is found that the oxygen pressure and growth temperature have significant effects on the crystal structure, ferroelectric properties and insulation characteristic of PHT film. It can effectively improve the microstructure and electrical properties of PHT film by using low temperature self-buffer layer. It is found that the self-buffered layers deposited at different temperatures have serious influences on the microstructure and electric properties of PHT. Compared with the PHT films directly deposited at a high temperature, the PHT films with an inserted low temperature(300?C) self-buffered layer have significantly enhanced electrical properties of four orders of magnitude lower leakage current density(3.2×10-8 A/cm2 at 150 kV/cm), 1.5 times larger remnant polarization(2Pr=63 μC/cm2), 0.4 times smaller coercive field(2Ec=190 k V/cm), and more excellent fatigue endurance(almost no degradation after 2×1010 switching cycles).2. Then, the effect of inserting the MgO buffer layer on the microstructure of PHT on Al2O3 substrate was studied. Comparing the the microstructure and electrical properties of PHT with different bottom electrodes, it is found that the PHT thin films on SRO electrode, shown a uniform gain size and significantly enhanced ferroelectric properties with larger remnant polarization(2Pr=59.1 μC/cm2) and lower leakage current density(8.5×10-8 A/cm2 at an applied electric field of 150 kV/cm). Finally, the PHT film with MgO buffer layer and SRO bottom electrode was studied.3. The growth of PHT film on GaN substrate was studied. It was succeseeful to achieve PHT(111) epitaxial film on GaN. Inserting MgO buffer layer, the epitaxial relationship of the PHT film growth on GaN is PHT(111)//MgO(111)//GaN(0002), PHT[1-10]//MgO[1-10]GaN[11-20]. The Au/Ni/PHT/GaN(MFS) and Au/Ni/PHT/MgO/GaN(MFIS) integrated structure were prepared and the electric properties of them were explored.