We fabricated ferroelectric (Pb,La)(Zr,Ti)O3 (PLZT) capacitors with Sn:In2O3 (ITO) or Pt top electrodes and investigated the ferroelectric properties of these PLZT capacitors. The shape of polarization–voltage hysteresis loops was essentially unchanged and the decrease in the remnant polarization of the ITO/PLZT/Pt capacitors was smaller than that of the Pt/PLZT/Pt capacitors after annealing with 3% D2 (in N2) at 200°C and 1 Torr (i.e., FGAD). Time of flight secondary mass spectrometry revealed that the D atoms were incorporated into the PLZT film of the Pt/PLZT/Pt capacitors after 3% D2 annealing, resulting in a decrease in the ferroelectric properties. In comparison, no D ion signal was detected in the PLZT film after FGAD for ITO/PLZT/Pt capacitors.

We fabricated ferroelectric (Pb,La)(Zr,Ti)O3 (PLZT) capacitors with Sn:In2O3 (ITO) top electrodes using chemical solution deposition. Then, the effects of a thin conductive ITO buffer layer between the Pt bottom electrode and PLZT thin film were investigated in combination with top electrode (ITO/PLZT/ITO/Pt). The H2 degradation resistance of ITO/PLZT/ITO/Pt capacitors with a 3- and 28-nm-thick buffer layer was improved to 78 and 85%, respectively, from 60% without a buffer layer. The time-of-flight secondary ion mass spectrometry profiles indicated the intensity of H ion increased after 45 min forming gas (3% H2/balance N2) annealing.

The electronic transport properties of the organic ferroelectric gate field-effect transistors (FeFETs) with the ZnO channel were investigated. The FeFETs with the channel thickness below 100 nm show nonvolatile operation and the on/off ratio of 105. The field-effect mobility decreased with decreasing the channel thickness. From the Hall-effect measurement, it was found that the Hall mobility increases and the carrier concentration decreases after the deposition of the organic ferroelectric gate. From these results, the effect of the ferroelectric polarization on the electronic transport in the FeFETs was discussed.

CaBi4Ti4O15 growth on different Platinum substrates was carried out through a sol-gel method. Higher crystallization temperature and 20% excess Bi decreased pyrochlore contents in the CaBi4Ti4O15 films. Repetition through coating, calcination and crystallization decreased void formation on the surface. C-axis oriented thin film could be grown on sputtered platinum substrates with low Pt (200) orientation. On electroplated Pt substrates, (119) oriented CaBi4Ti4O15 thin film was grown, suggesting surface roughness of Pt substrates is a crucial factor for orientation control of sol-gel derived CaBi4Ti4O15 thin film.

YMnO3, which is one of hexagonal RMnO3 compounds, has antiferromagnetic and ferroelectric properties, simultaneously. Recently, it has been reported that cross-correlation in the magnetic dielectric properties on hexagonal YMnO3 single crystals. However, the cross-correlation in the magnetic-ferroelectric properties has not been understood yet. In this study, we investigated the cross correlation between magnetism and ferroelectricity on YMnO3 epitaxial films with excellent crystallinity. YMnO3 epitaxial films were deposited pulsed laser deposition. The YMnO3 epitaxial films show the dielectric anomalies at around Néel point of the films. It was suggested that the ferroelectric domain switching was suppressed by the magnetic ordering. The relationship between the magnetic structure and the ferroelectric properties are discussed in terms of the temperature dependences of magnetization and dielectric permittivity. Moreover, the ablation plume of YMnO3 was investigated by optical emission spectroscopy. The effect of the ablation conditions on the thin film growth and electrical properties was discussed.

Electrical conduction properties of charge ordering type ferroelectrics YFe2O4 were investigated. YFe2O4 was synthesized in reduced atmosphere at 1200 °C. Oxygen partial pressure of the reduced atmosphere was controlled by the equilibrium state of CO and CO2. YFe2O4 is paramagnetic at room temperature and has Néel temperature around 250K. The Néel temperature was decreased with increasing the amount of oxygen deficiency. Moreover, YFe2O4 showed ohmic conduction from 260 to 100 K. The temperature dependence of the DC conductivity showed an inflection point at the Néel temperature, which indicated the development of charge ordering of Fe2+ and Fe3+ ions. From the complex impedance measurements, the equivalent circuits of YFe2O4 with different oxygen deficiency were determined at various temperatures.

We have been proposing YMnO3 with low remanent polarization and permittivity as a ferroelectric gate transistor, and reported that c-oriented YMnO3 films were obtained on (111)Si with (111) oriented Y2O3 buffer layer. The ferroelectricity was confirmed by pulsed C-V measurement. However, the retention property was not satisfied because of its poor crystallinity. To improve the crystallinity of YMnO3 films, deposition conditions of Pulsed Laser Deposition (PLD) were optimized. The laser power, oxygen pressure and introducing Ozone gas are effective for maintaining the stoichiometry during the deposition. Improvement of the crystallinity of the YMnO3 film makes the retention property better. We also demonstrate the use of epitaxially grown Y2O3 buffer layer to improve the crystallinity of the YMnO3 films.

YbMnO3 (Yb/Mn = 0.96) thin films were prepared on Y2O3(111)/Si(111). Although the sample exhibited ferroelectric type C-V hysteresis, the window width changed depending on the applied bias voltage. Hence, the ferroelectric type hysteresis might include the effect of space charge. To make clear the C-V behavior caused by only ferroelectricity, and to obtain the optimal relationship between ferroelectric and insulator layer thicknesses, the C-V behavior at high frequency was computed for MFIS structure. Relationships between the counter bias voltage applied to the ferroelectric layer and the thickness of dielectric layer were also demonstrated. Compared with the calculated results, experimental C-V characteristics are discussed.

We have been proposing YMnO3 with low remanent polarization and dielectric permittivity as a transistor type FeRAM. Conventional C-V measurements are normally used to evaluate the ferroelectricity of ferroelectric thin films on Si substrates. For ferroelectric thin films with low polarization, however, there are some issues to understand the C-V hysteresis. For example, interfacial polarization and space charge affect the C-V hysteresis. The effect of interfacial polarization on C-V behavior was calculated assuming the connection of ferroelectric and dielectric layers with different resistivity. If a ferroelectric layer with a leakage current of 1×10-6 A/cm2 is connected to the dielectric layer with a leakage current of 1×10-9 A/cm2, a charge density of 10-9 C/cm2 should be generated in the period of 0.2 sec. Space charge should have a longer time constant for accumulating the charge. Pulsed C-V measurement must be effective to avoid these issues. This paper proposes a simple method to evaluate the real component of ferroelectricity in the C-V hysteresis using YMnO3 or ZnO:Li with very low remanent polarization.

We have been proposing the use of RMnO3 (R: rare earth elements) films for metalferroelectric- semiconductor field effect transistor (MFSFET)-type ferroelectric random access memories (Ferroelectric RAMs). This report describes the progress of YMnO3 and YbMnO3 films for FET type FeRAM application. Although highly (0001)-oriented YMnO3 films are easily obtained on a MgO, ZnO/Sapphire, Pt/Sapphire and Pt/Si substrates, it was very hard to obtain the crystalline films directly on Si or on SiO2/Si substrate. A Y-Mn-O buffer layer improved the crystallinity of the YMnO3 films on Si, and we got the C-V curve with ferroelectric hysteresis. The real ferroelectric component responsible for the C-V hysteresis was calculated to be just 8.4 nC/cm2 by pulse measurements. On the other hand, Y2O3 buffer layer drastically improved the dielectric properties. The window width of the C-V hysteresis does not change by changing the sweep rate and measurement frequency.

We propose the application of ZnO:X (X = Li, Mg, N, In, Al, Mn, Gd, Yb etc.) films for a monolithic Optical Integrated Circuit (OIC). Since ZnO exhibits excellent piezoelectric effect and has also electro-optic and nonlinear optic effects and the thin films are easily obtained, it has been studied as one of the important thin film wave guide materials especially for an acoustooptic device[1]. In terms of electro-optic and nonlinear optic effects, however, LiNbO3 or LiTaO3 is superior to ZnO. The most important issue of thin film waveguide using such ferroelectrics is optical losses at the film/substrate interface and the film surface, because the process window to control the surface morphology is very narrow due to their high deposition temperature. Since ZnO can be grown at extremely low temperature, the roughness at the surface and the interface is expected to be minimized. This is the absolute requirement especially for waveguide using a blue or ultraviolet laser. Recently, lasing at the wavelength of ultraviolet, ferroelectric and antiferromagnetic behaviors of ZnO doped with various exotic elements (exotic doping) have been reported. This paper discusses the OIC application of ZnO thin films doped with exotic elements.

The preparation conditions of YMnO3 thin films by the sol-gel method using yttrium alkoxide were optimized to decrease the leakage current of the films. The leakage current of the films was decreased due to the dense microstructure of the films. Moreover, the heat treatment in hydrogen atmosphere and the zirconium doping resulted in a further decrease of the leakage current. The heat treatment in hydrogen atmosphere and the zirconium doping were effective in the decrease of carriers originating in the valence fluctuation of the Mn ions in YMnO3

SrBi2Ta2O9 has attracted great interest for non-volatile memory applications due to its minimal polarization fatigue. This paper describes systematic studies, using pulsed laser deposition, on the effect of deposition conditions on the Bi-Pt reaction and on the potential for low temperature processing. Changing the deposition temperature (Ts) and oxygen gas pressure during deposition can control the Bi content in the films. At a Ts of 600°C, the films have excess Bi and do not fully crystallize to SBT, resulting in poor remnant polarization (Pr). These films consist mostly of the pyrochlore phase, plus a small amount of disordered, c-oriented layered perovskite SBT. By annealing over 750°C, the films show improved Pr, but further Pt - Bi interactions occur. At a Ts of 700°C, the as-deposited films are fully crystallized and show saturated hysteresis loops. However, Bi deficiency through alloying results in reduced remnant polarization (2Pr = 7.0μC/cm2). Films on Ir/Pt show reduced electrode reactions and improved properties.

We have proposed ReMnO3 (Re:rare earth) thin films, as a new candidate for nonvolatile memory devices. In this paper, we try to fabricate (0001) oriented YMnO3 films on (111)MgO, (0001)ZnO:Al/(0001) sapphire and (111)Pt/(111)MgO using rf magnetron sputtering. We succeed in obtaining (0001) epitaxial YMnO3 films on (111) MgO and (0001)ZnO:Al/(0001)sapphire substrate, and polycrystalline films on (111)Pt/(1 11)MgO for the first time. Electrical property of the bottom electrode (ZnO:Al) changes with varying the deposition condition of YMnO3 films. However, we find an optimum deposition condition of ZnO:Al film such that it functions as a bottom electrode even after YMnO3 film deposition. The dielectric properties of the epitaxial and polycrystalline YMnO3 films are almost the same. The YMnO3 films show leaky electrical properties. This may be caused by a change in the valence electron of Mn from 3+.

The Orientation control of (Ca,Sr)CuO2 film has been investigated under various sputtering conditions from the view point of controlling the “self-texture” and epitaxy. The films with (001), (110) and (101) orientations were able to be obtained by changing partial gas pressure during sputtering. These orientations were observed on glass and MgO(100) single crystal substrates. The cohesive energy between the film and the MgO single crystal substrate was calculated to evaluate the change in orientation on glass and MgO substrates.

ZnO film has a tendency to grow parallel to the <0001> axis. Therefore, it is difficult to obtain epitaxial or oriented films with any other orientation. Nevertheless, we obtained excellent epitaxial (1120) ZnO films on R-cut, (0112), sapphire by controlling the self-texture. Epitaxial (1120) ZnO on R-cut sapphire exhibits an anisotropic misfit at the interface. To clarify the growth mechanism, the stress relaxation was calculated by measuring the curvature of the substrate and the lattice spacings. The change in stress calculated by these two methods differs from each other. We discuss this discrepancy in terms of the growth mechanism.

It is argued that epitaxial films of ionically-bonded materials are more easily achieved than of covalently bonded materials. Good epitaxy can be achieved despite relatively large lattice mismatch with respect to the substrate. However, the strong influence of interfacial energy can result in difficulty in controlling the orientation of epitaxial films.

The crystallographic orientation of ionically-bonded LiNbO3 films was therefore studied. Growth orientation could be controlled by paying attention to the bonding between octahedra in the structure, and to the formation of the octahedra containing lithium and niobium ions. Lithium concentration could be increased by increasing the rf power, 02 partial pressure and total gas pressure, and decreasing the substrate temperature during deposition.

The orientation of the film changed from (012) to (100) via (110) by increasing the Li concentration in the film. The (012) and (100) films were epitaxial with respect to the substrate. In particular, the (100) films were of exce lent quality, being single crystalline with smooth surfaces.