YMnO3 thin films were sputtered on Si (100) substrates under different ambient conditions. After rapid thermal annealing process at 850 °C, the YMnO3 film deposited in Ar ambient had random orientations and the YMnO3 film deposited in Ar+O2 ambient was crystallized with distinct two layers, i.e., c-axis oriented layer in top region and random oriented layer in bottom region. Relations between the microstructure and the electrical properties of Pt/YMnO3/Si capacitor were investigated. Memory window and leakage current depended on the orientation of the YMnO3 thin films and the interfacial microstructure of the YMnO3/Si, respectively

Ir and its conductive oxide, IrO2, are candidates to replace Pt as the electrodes in ferroelectric capacitors (FECAPs) because of improved endurance (since e.g. Pt/PZT/Pt shows strong fatigue) and also because of the oxygen barrier properties of Ir/IrO2 stacks that enable the fabrication of stacked FECAPs on top of contact plugs. Two important issues related to these electrodes are the control of the ferroelectric layer orientation on top of these materials, as well as material stability (e.g. oxidation and possible growth of large IrO2 crystallites).

In this work, we show that IrO2 bottom electrodes affect the crystallization of sol-gel deposited Pb(Zr,Ti)O3 (PZT). While PZT films deposited on (111) Pt show a (111) preferential orientation, IrO2 electrodes nucleate strongly different oriented PZT. Controlling and changing the microstructure of the bottom electrode allows tuning of these PZT orientations and the resulting grain morphology, and, consequently, their FECAP polarization hysteresis properties.

Impurity effects were investigated in (Ba,Sr)TiO3 (BST) systems in order to suppress leakage currents under relatively low oxygen pressure conditions by Pulsed Laser Deposition (PLD). We tried to dope transition metals, such as Mo, Mn, Cr, W and Fe into the BST target and used the targets to fabricate the films. By measuring electrical properties, we found Fe-doping had a significant effect on suppressing leakage current. Subsequently, we changed the amount of Fe doping from 0.1mol% to 6%. As a result, with post annealing, the sample with Fe:4% showed the lowest leakage current among those analyzed. Even without post annealing, the sample with Fe:6% showed the lowest leakage current. As for the dielectric constants, they decreased as the doping increased. At most, a 30% reduction was observed, compared with non-doped BST. XANES (X-ray Absorption Near Edge Structures) results indicated that the valency of the Fe ion was 3+ and located at the B-site of BST.

Bismuth layered structured ferroelectrics (BLSF) thin films with different number of octahedron number (m-number) were prepared by MOCVD and directly crystallized on the substrates. Directly-crystallized SrBi2Ta2O9 (SBT) (m=2) films on a (111) Pt/Ti/SiO2/Si substrate were ascertained to have a strong (103) one-axis orientation by the X-ray reciprocal space mapping and to be hetero-epitaxially grown on the (111) Pt grains by the TEM observation. Moreover, directly crystallized Bi2VO5.5 (m=1) and Bi4Ti3O12 (m=3) films deposited on the same substrate showed (102) and (104) one-axis preferred orientations, respectively. These orientations are basically the equal ones with SBT (103) orientation because the tilting angle of c-axis from the substrate surface is also about 55°. Therefore, the direct crystallization is one of the important key techniques for orientation control of BLSF films. Moreover, the directly crystallized SBT film deposited on a (111) Ir/TiOx/SiO2/Si substrate at 570 °C by ECR-MOCVD exhibited (103) one-axis orientation, which also originated from the local epitaxial growth on (111)-oriented Ir grains. The remanent polarization (2Pr), and the coercive field (Ec) of this film were 16.1 μC/cm2 and 83 kV/cm at an applied electric field of 360kV/cm, respectively. This Pr value is about 88% of the expected value of (103)-oriented SBT film from both the Pr values of the (116) and (001)-oriented epitaxial films and detailed crystal analysis.

The basic mechanism for one transistor memory device has been studied. Ferroelectric material, Pb5Ge3O11 (PGO) was selected for MFOS (M: Metal, F: Ferroelectrics, O: oxide, S: silicon) memory transistor fabrication. Processing of one-transistor memory devices dealt with the following issues: decomposition of ferroelectric materials, the etching damage of ferroelectric materials, the forming gas annealing damage of ferroelectric materials, the selective deposition of ferroelectric materials, the alignment for device making processes. The integration processes for one transistor memory device have been optimized to reduce process-induced damages. The gate dielectric material is (Zr, Hf)O2. Extremely high c-axis oriented Pb5Ge3O11 thin films were successfully deposited on high k gate oxide. Memory transistors having 0.6, 3 and 10μm channel length and 10 μm channel width have been fabricated. The memory windows are around 1 - 2V. The memory windows are almost saturated from operation voltage of 4V. After programming at -5V (on “off” state), the drain current (ID) at VD of 1V and VG of 2.5 V is about 1.15 ×10−10A. After programming at 5 V (on “on” state) the drain current (ID) at VD of 1V and VG of 2.5 V is measured about 6.4 ×10−8 A, which was 2.5 order higher than that of “off” state.

Grazing incidence x-ray diffraction has been employed to perform the depth-profile analysis on SrBi2Ta2O9 (SBT) thin films with different preferential orientations. For the polycrystalline SBT thin film, the change in structural orientation occurs only within the 15-nm-thick top layer, which is associated with the formation of the (200)-predominant SBT thin film prepared by the layer-by-layer annealing process. The inhomogeneity of structural orientation is more significant in the full film thickness for the (200)- predominant SBT thin film. (0010) peak can only be observed for the grazing angle larger than 0.6°. A layer with the highest ratio of I(200)/I(115) is found in the top surface layer (i.e., the latest layer during deposition) of the (200)-predominant SBT thin film.

Extrinsic and intrinsic size effects on the spontaneous polarization of epitaxial ferroelectric films are discussed. The extrinsic effect of electrostatic origin is attributed to the presence of nonferroelectric subsurface layers in the film. Theoretical studies of this depolarizing-field effect are reviewed. It is concluded that, for perovskite ferroelectrics sandwiched between electrodes with a perovskite structure, the depolarizing-field effect on the static properties should be negligible. The extrinsic size effect is also attributed to the thickness dependence of the film in-plane lattice strain S m, which is due to the generation of misfit dislocations in the epitaxy. Variation of the film polarization with the misfit strain S m is described by a nonlinear thermodynamic theory, which allows for the mechanical film/substrate interaction. The intrinsic effect of the film surfaces, which is associated with spatial correlations of the ferroelectric polarization, is simultaneously taken into account via the concept of extrapolation length δ. It is shown that, in films grown on compressive substrates (S m < 0), the strain-induced increase of the mean polarization prevails over the negative intrinsic size effect (δ > 0). As a result, well below the transition temperature, ferroelectricity may be present even in nanometer-thick epitaxial layers. Motivated by this result, we propose the concept of ferroelectric tunnel junction. First results on tunnelling through ultrathin barriers of perovskite ferroelectrics are presented.

Thin films of antimony sulpho iodide (SbSI) were grown on platinized silicon substrates by the pulsed laser deposition method. As grown films were amorphous and annealing at 250 °C for 5 minutes introduced crystallinity in the films. Infrared reflectance measurements were done in the frequency range ∼ 500 – 5000 cm−1 (wavelength ∼ 2–20 μm). The reflectance measurements were taken at temperatures above and below the ferroelectric transition of SbSI ∼ 20° C. The index of refraction for a (121) oriented film was determined to be 2.83 ± 0.35 at a temperature of 25.6 °C, and 2.80 ± 0.35 at a temperature of 9.6 °C. For a (002) oriented film, the index was 3.82 ± 0.48 at a temperature of 26.5 °C, and 3.76 ± 0.48 at a temperature of 8.0 °C. Pyro-optic coefficients of 1.5 × 10−3 °C−1 for the (121) oriented film, and 3.2 × 10−3 °C−1 for the (002) oriented film were obtained. These results are consistent with measurements done in the visible region, and demonstrate the potential of SbSI as an infrared detector material.

Pulsed laser deposition has been used to fabricate thin-film capacitor structures in which the dielectric layer is a superlattice. The properties of two superlattice systems were investigated as a function of superlattice wavelength (δ) – one based on barium strontium titanate and the other on lead-based relaxor electroceramics. In both systems the dielectric constant was significantly enhanced at stacking wavelengths of a few unit cells. However, the dielectric enhancement seen in the barium strontium titanate superlattices was found to be due to Maxwell-Wagner effects, whereas in the relaxor superlattices Maxwell-Wagner behaviour was not evident; rather, the dielectric enhancement was associated with the onset of polar coupling aroundδ ∼ 10nm.

Recently we proposed ferroelectric sodium potassium niobate (Na0.5K0.5NbO3, NKN) thin films to be a candidate for applications in nonvolatile memories and electrically tunable devices [1-5]. In this paper we report on processing and characterization of metal-ferroelectric-insulatorsemiconductor (MFIS) diode structures based on RF-magnetron sputtered NKN films. 0.7 μm thick NKN films have been deposited at 650 °C on the thermally grown 47 nm thick SiO2 layer on Si(001) wafers. Stoichiometric Na0.5K0.5NbO3 ceramic target was sputtered in an O2-Ar atmosphere with a total pressure of 5 mTorr. Grown films were analyzed as deposited as well as after an oxygen annealing at 600 °C for 30 minutes. The NKN films exhibit a strong (001) preferential orientation, which was appreciably improved after the oxygen annealing. A leakage current density of 2.3 nA/cm2 at an electric field of 400 kV/cm, and a memory window of 7.2 V was measured for Au/NKN/SiO2(47nm)/Si(001) diode structures at the programmable voltage of 40 V. I-V measurements were performed in the time domain to distinguish between the relaxation of polarization, “true” leakage current, and the degradation of the resistance in ferroelectric NKN film.

Polycrystalline 0.4 μm thick films of Ag(Ta,Nb)O3 (ATN) were grown on sapphire (Al2O3-0112, r-plane) wafers by pulsed laser deposition technique. 2 and 4 μm gap interdigital capacitors were defined by photolithography on the top of Au/Cr/ATN(0.4μm)/Al2O3 film structures. They exhibit high dielectric performance. In the frequency range of 1 kHz to 1 MHz dielectric permittivity shows frequency dispersion as low as 3.5 %, loss tangent ∼ 0.0035 @ 1 MHz, Kfactor = tunability/tan δ is about 20.2 @ 200 kV/cm, and resistivity as high as 1.8 × 1011 ×cm @ 100 kV/cm. C-V and I-V characteristics recorded in time domain revealed slow Curie-von Schweidler-type relaxation of the polarization. Low frequency dispersion and loss, high tunability and low noise in the biased state promise thin ATN film capacitors for microwave applications.

Bismuth titanate (Bi4Ti3O12; BIT) -based ferroelectric materials are proposed from the view of the “Site-engineering”, where the Bi-site ions are substituted by lanthanoid ions (La3+ and Nd3+) and Ti-site ions by other ions with higher charge valence (V5+). In the present study, influences of vanadium (V) - substitution for (Bi,M)4Ti3O12 thin films [M = lanthanoid] on the ferroelectric properties are evaluated. V-substituted (Bi,M)4Ti3O12 films have been fabricated using a chemical solution deposition (CSD) technique on the (111)Pt/Ti/SiO2/(100)Si substrate. Remnant polarization of (Bi,La)4Ti3O12 and (Bi,Nd)4Ti3O12 films has been improved by the V-substitution independent of the coercive field. The processing temperature of BLT and BNT films could also be lowered by the V-substitution.

We studied the crystallization of sol-gel derived Pb(Zr0.4Ti0.6)O3 [PZT(40/60)] thin films at 400 down to 390°C on Pt/SiO2/Si substrates by combination of diol-based solutions and modified film preparation processes. It was found that PZT films could be crystallized at 390°C and that PZT films crystallized at 400°C had microstructures with perovskite-single-phase columnar grains and good ferroelectric characteristics such as switched polarization (2 Pr) of 20 μC/cm2 and relative permittivity (εr) of 740. Next, we evaluated annealing temperature dependence of PZT(40/60) thin films crystallized at 390 to 435°C. The results indicated that (111)-orientation of perovskite phases became weaker, (100)-orientation of those became stronger, and the perovskite grain size increased with decreasing in annealing temperature.

The Al2O3 thin films were deposited on the Si3N4 (radical- Si3N4) prepared by the direct nitridation of a Si substrate using atomic nitrogen radicals. Because the radical- Si3N4 is highly resistive against the oxidation process, we can completely eliminate the metal phase in Al2O3 that degrades the insulating properties of Al2O3. The 1.3nm thick Al2O3 film was found to have a permittivity of 9.76 in this stacked Al2O3/Si3N4 structure. It was also found that no oxidation took place at the interface of Si3N4 and the Si substrate during the deposition and post-oxidation of the Al2O3 film on the radical-Si3N4/Si substrates. As a result, highly capacitive MIS (Metal-Insulator-Semiconductor) structures were realized using the Al2O3/Si3N4 stacked insulator. The MIS diode with Al2O3/Si3N4 is found to have 105 times less leakage current compared to the diode with Si3N4 insulator film with similar capacitance density. We have shown that the insulating properties of the Al2O3/radical-Si3N4 stack are suitable for the MFIS (Metal-Ferroelectric-Insulator-Semiconductor) transistors.

We present evidence that the microstructure of the metastable fluorite phase Pb2(Zr,Ti)2O6, which forms during the pyrolysis treatment of sol-gel PZT layers by homogeneous nucleation throughout the film, has a larger impact on orientation selection than has previously been realized. Elaborate TEM studies demonstrate that by varying the pyrolysis time, temperature and duration, the crystallinity of the transient fluorite phase can be greatly influenced. Pyrolysis at 350°C leads to the formation of a well crystallized fluorite phase with a cubic structure (Fd3m space group) and a= 10.5-10.6 Å. Rapid crystallization of the transient fluorite phase is attributed to the low oxygen partial pressure conditions, prevailing during burnoff of acetate groups originating from the lead starting compound. A possible connection between the fluorite formation kinetics and orientation selection in the layers is discussed.

Lithium niobate has a wide variety of applications because of its excellent ferroelectric, piezoelectric and electrooptic properties. In this study, epitaxial lithium niobate thin films were deposited on c-sapphire (α-Al2O3) by the low-cost, open-atmosphere Combustion Chemical Vapor Deposition (CCVD) technique developed by MicroCoating Technologies, Inc. It was found that deposition temperature plays a critical role in determining the growth behavior and quality of the lithium niobate thin films. XRD measurements show that the lithium niobate films are epitaxial with two in-plane orientations (twin structure). A surface roughness (root mean square) of about 4 nm was obtained from the deposited film (about 200 nm thick), as measured by optical profilometry.

The growth mechanism of epitaxial BaTiO3 films on vicinal Nb-doped SrTiO3 (SrTiO3:Nb) (001) substrate surfaces was studied in terms of surface morphology, crystalline orientation, microstructure, and film/substrate interface. Well-oriented BaTiO3 thin films were grown on SrTiO3 substrates with well-defined terraces by pulsed laser deposition. The regularly terraced TiO2-terminated surfaces of vicinal SrTiO3:Nb (001) substrates were prepared by a definite chemical and thermal treatment. Under our conditions, BaTiO3 seems to grow with a layer-then-island (Stranski-Krastanov) growth mechanism. In order to investigate the orientation and crystallinity of the BaTiO3 films, x-ray diffraction and high-resolution transmission electron microscopy were performed. Ferroelectricity of the BaTiO3 films was proved by electrical measurements performed on Pt/BaTiO3/SrTiO3:Nb heterostructures.

Thin film capacitor structures of Au / (1−x)Pb(Mg1/3Nb2/3)O3 - xPbTiO3 /(La1/2Sr1/2)CoO3 were fabricated by pulsed laser deposition on single crystal {001} MgO substrates. Films were found to be perovskite dominated and highly {001} oriented. Dielectrically, films displayed relaxorlike features, though maximum permittivity was low compared to single crystal or bulk ceramic (∼1400 at peak @1kHz, for x=0.07, 0.1 & 0.2). A field induced piezoelectric coefficient d33 was measured by piezoresponse atomic force microscopy for specific compositions x =0, × =0.07, and x =0.1 and found to be disappointingly low - indicating poor electric field induced strain. Despite this macroscopic electrostrictive coefficients Q33 were found to be (3.6 ± 0.6) ×10−2C−2m4, (2.6 ± 0.2) ×10−2C−2m4, and (0.9 ± 0.3) ×10−2C−2m4 respectively. Crystallographic electrostrictive coefficients were determined by in-situ x-ray diffraction and found to be (4.9 ± 0.2) ×10−2C−2m4 for PMN-(0.07)PT and (1.9 ± 0.1) ×10−2C−2m4 for PMN-(0.1)PT. Considering that all these Q33 values are of the same order of magnitude as found in single crystal experiments (2.5 – 3.8 ×10−2C−2m4), it is suggested that low out-of-plane strain is entirely a result of reduced polarisability rather than reduced electrostrictive coefficients in thin films relative to bulk ceramic or single crystal. An estimate was also made of the Q13 electrostrictive coefficient for PMN and PMN-(0.07)PT by measuring permittivity as a function of applied in-plane strain. The values obtained were -1.31 ×10−2C−2m4 and -0.46 ×10−2C−2m4 respectively.

a- and b-axis-oriented epitaxial Bi4Ti3O12 films were prepared on (101)TiO2 substrates (rutile) at 600°C by metalorganic chemical vapor deposition (MOCVD). Subsequently, the same films were similarly prepared on (101)-oriented conductive materials with the same rutile structure and similar lattice parameters as TiO2, such as RuO2 and IrO2. Their perfect epitaxial growth was confirmed by several X-ray diffraction measurements. RuO2 and IrO2 were deposited on not only structurally equivalent (101)RuO2//(101)TiO2 and (101)IrO2//(101)TiO2 structures, but were also successfully deposited on the corundum (012)Al2O3 and (110)Al2O3 single crystals by the MOCVD and rf-sputtering method, respectively. A well-saturated P-E hysteresis with a remanent polarization above 20 μC/cm2 was observed for a- and b-axis-oriented Bi4Ti3O12-based materials, (Bi4−xNdx)(Ti3−yVy)O12 (BNTV), that were epitaxially grown on rutile-rutile and rutile-corundum stacking structures. These results should enable broader application of the bismuth layer-structured ferroelectrics.

The crystallization kinetics of SBT and SBT-BTT thin films formed by sol-gel technique on Pt substrate was studied. Phase formation and crystal growth are greatly affected by the film composition and crystallization temperature. Isothermal kinetics analysis was performed on x-ray diffraction (XRD) patterns of the thin films heated in the range 730 to 760° at 10° intervals. Activation energy and Avrami exponent values were determined for the fluorite to Aurivillus phase formation. A reduction of ∼55 kJ/mol in activation is observed for the SBT-BTT system. A comparison has been made and the possible crystallization mechanism is discussed.