Nobuyasu Mizutani

HRTEM investigation of the 90° domain structure and ferroelectric properties of multi-layered PZT thin films

Multi-layered epitaxial Pb(Zrx,Ti1-x)O3 (PZT) films with x = 0.2-0.5 were deposited on La0.5Sr0.5CoO3-x (LSCO)/(001)STO and LSCO/CeO2/YSZ/(001)Si substrates with buffer layers. We investigated using HRTEM and XRD how the 90° domain structure and the P-E hysteresis character depend on the difference in the thermal expansion coefficient by changing the Zr/Ti composition and the substrate. XTEM analysis showed that large 90° domains 8-30 nm in width penetrate the columnar grain and the PZT layer in the PZT stacked film Zr/Ti=20/80,30/70,40/60. On the other hand, close-packed small 90° domains 4-5 nm in width were present in epitaxial columnar grains in the PZT50/50 stacked film. The P-E hysteresis loops of PZT20/80 stacked films deposited on STO and Si substrates show a remanent polarization of 2Pr = 136 and 80 µC/cm2, respectively. On the other hand, those of PZT50/50 stacked films deposited on STO and Si substrates show a polarization of 2Pr = 125 and 36 µC/cm2, respectively. Thus, the P-E hysteresis loop of PZT50/50 exhibits remarkable differences in 2Pr values between the substrates.

Role of Ultra Thin SiOx Layer on Epitaxial YSZ/SiOx/Si Thin Film

The role of an ultra thin SiOx layer for epitaxial growth of a YSZ (Y 2 O 3 stabilized ZrO 2 ) thin film on a (001)Si substrate through the SiOx layer was investigated by high resolution transmission electron microscope (HRTEM), in-situ heating transmission electron microscope and nano-beam diffraction (NBD) methods. It is found that a trace of epitaxial crystallinity remains in an ultra thin SiOx layer within 2 nm from SiOx/Si interface. According to this result, a YSZ layer could epitaxially grow only on an ultra thin 1-2 nm SiOx layer. It is also found that an ultra thin SiOx layer has another effect to relax the crystallization strain at a YSZ/Si interface. These results indicate that an ultra thin SiOx layer plays two important roles: (a) an ultra thin SiOx layer formed just above the Si surface serves as a medium for the epitaxial growth of a YSZ layer, and (b) even in an ultra thin SiOx is able to relax the crystallization strain of YSZ layer at YSZ/Si interface. These are the critical points of the epitaxial growth of YSZ/SiOx/(001)Si thin film together with a role of an oxygen source reported previously.

Hrteminvestigation of 90° Domain Configureuration and P-E Hysteresis Loop of Epitaxial PZT Multilayered Thin Films

Multi-layered epitaxial Pb(Zr x ,Ti 1-x )O 3 (PZT) films of x=0.2–0.5 were deposited on La 0.5 Sr 0.5 CoO 3-x (LSCO)/ (001)STO and LSCO/CeO 2 /YSZ/(001)Si substrates with buffer layers. It was investigated how the 90° domain structure and the P-E hysteresis character depend on the difference of the thermal expansion coefficient by changing the Zr/Ti composition and the substrates, using HRTEM and XRD methods. XTEM analysis showed that usual lamella configuration of 90° domains of 8–30nm in width penetrated the columnar grain and the PZT layer in the PZT stacked film of Zr/Ti=20/80, 30/70, 40/60. On the other hand, the close-packed 90° domains of 4–5nm in width existed in a epitaxial columnar grain in the PZT50/50 stacked film. The P-E hysteresis loops of PZT20/80 stacked films deposited on STO and Si substrates show the remanent polarization of 2Pr=136μC/cm 2 , 2Pr=80μC/cm 2 , respectively. On the other hands, those of PZT50/50 stacked films deposited on STO and Si substrates show the polarization of 2Pr=125μC/cm 2 , 2Pr=36μC/cm 2 , respectively. Thus, the P-E hysteresis loop of PZT50/50 has remarkable difference of 2Pr between the substrates.

Role of Ultra Thin SiOx Layer on Epitaxial YSZ/SiOx/Si Thin Film as Multi Functional Buffer Layer by Nano-Probe and In-Situ TEM Investigation

The role of an ultra thin SiOx layer for epitaxial growth of a YSZ (Y stabilized ZrO 2 ) thin film on a (001) Si substrate through the SiOx layer was investigated by high resolution transmission electron microscope (HRTEM), in-situ heating transmission electron microscope and nano-beam diffraction (NBD) methods. It is found that a trace of epitaxial crystallinity remains in an ultra thin SiOx layer within 2nm from SiOx/Si interface. According to this result, a YSZ layer could epitaxially grow only on an ultra thin 1-2nm SiOx layer. It is also found that an ultra thin SiOx layer has another effect to relax the crystallization strain at a YSZ/Si interface. These results indicate that an ultra thin SiOx layer plays two important roles: (a) an ultra thin SiOx layer formed just above the Si surface serves as a medium for the epitaxial growth of a YSZ layer, and (b) even in an ultra thin SiOx is able to relax the crystallization strain of YSZ layer at YSZ/Si interface. These are the critical points of the epitaxial growth of YSZ/SiOx/(001) Si thin film together with a role of an oxygen source reported previously.

Effect of thickness on the dielectric properties of Pb(Mg/sub 1/3/Nb/sub 2/3/)O/sub 3/ (PMN) thin film prepared by sol-gel method

The dependence of thickness on the dielectric and ferroelectric characteristics were examined for a Pb(Mg/sub 1/3/Nb/sub 2/3/)O/sub 3/ (PMN) thin film prepared by the sol-gel method. The films had stoichiometric composition and epitaxially grown on (100)Pt//(100)MgO substrate. The dielectric constant was decreased with the decrease of thickness, however, the frequency dispersion of the dielectric constant which is characteristic for the relaxor was observed. P-E hysteresis was also observed for the PMN thin film, however, the remanent polarization was much smaller than the value reported for PMN bulk ceramics. These facts imply that the size-effect is also observed for relaxor ferroelectrics.