Study on the Influence of Grain Boundary of Ferroelectric Thin Films on Elelectrical Properties and Its Application to Memory Devices

点击翻译按钮获取中文摘要

1. Crystalline and electrical properties of polycrystalline Pb(Zr,Ti)O_3 (PZT) thin films on SrRuO_3/SiO_2/Si and epitaxial PZT thin films on SrRuO_3/SrTiO_3 were investigated. Increase in grain size and decrease in current density of polycrystalline PZT films were observed as film thickness increased. Decrease in current density was also observed as film thickness increased for epitaxial PZT films. Polycrystalline PZT films showed stronger thickness dependence of dielectric constant and remanent polarization than that of epitaxial PZT films due to thickness dependence of grain size and grain boundary.2. The Volmer-Waber (V-W) growth mode for PZT thin films grown on Pt/SiO_2/Si by MOCVD, the V-W growth mode for PZT on SrO plane of SrTiO_3, the Stranski-Krastanov (S-K) mode for PZT on TiO_2 plane of SrTiO_3 and the S-K mode for PZT films on SrRuO_3/SrTiO_3 were observed, respectively. From piezoresponse measurements using scanning probe microscopy(SPM), it was found that nano-size PbTiO_3 and PZT islands showed ferroelectricity.3. PZT thin films were successfully obtained at 395 ℃ by two step growth rocess using seeds. Increase in grain size and improvements in crystalline and electrical properties were observed for PZT films by two step growth process.4. Polarization reversal process of PZT thin films was observed by piezoresponse measurements using SPM. Velocity of polarization reversal in in-plane direction and out-of plane direction were measured.5. Planer and three dimensional PZT capacitors with Ir/PZT/Ir/SiO_2/Si structure were successfully fabricated solely by MOCVD only at 400 ℃.6. The 20nm-thick ultra thin PZT films which showed ferroelectricity were successfully obtained on SrRuO_3/SrTiO_3.