Physical and electrical properties are investigated for (Ba, Sr)TiO3 (BST) films prepared by electron cyclotron resonance (ECR) plasma chemical vapor deposition (CVD) at relatively low temperatures, between 450 °C and 500 °C. The crystallinity of BST, estimated by X-ray diffraction and from the grain size, is greatly improved when the temperature is raised from 450 °C to 500 °C. Also better crystallinity is obtained for films grown at a deposition rate of 1.1 nn/min than at 2.7 nm/min. The mass transport rates of metal organic sources under our deposition conditions are estimated. The BST film composition is precisely controlled using the results of the investigation on mass transport. At near stoichiometric composition, i.e., (Ba+Sr)/Ti=0.97, and Ba/(Ba+Sr)=0.4, the films grown at 500 °C are found to have the largest dielectric constant, measured using flat capacitors with Pt bottom electrodes. A dielectric constant of 160 is obtained for 27 nm thick films grown at 500 °C and at 1.1 nm/min, without post-deposition annealing. These films exhibit the smallest SiO2 equivalent thickness of 0.65 nm and a leakage current density of 4.6x10−7 A/cm2 at plus IV.

Ba(TMHD)2, Sr(TMHD)2 and Ti-isopropoxide were used to fabricate the (SrxTi1 x)O3 and (Ba1 x Srx)TiO3 thin films. The decomposition and degradation characteristics of Ba(TMHD)2 and Sr(TMHD)2 with storage time were analyzed using a differential scanning calorimeter (DSC). The thin films were fabricated on Si(p-type 100) and Pt/SiO2/Si substrates with Ar carrier gas using ECR plasma (or without ECR plasma) assisted MOCVD. Experimental results showed that the ECR oxygen plasma increased the deposition rate, the ratio of Sr/Ti, the dielectric constant and the leakage current density of the film. The dependency of the crystallinity and the electrical properties on the Sr/Ti ratio of films were investigated. However, almost of the films deposited with Ar carrier gas had slightly high dielectric loss and high leakage current density and showed non-uniform compositional depth profiles. NH3 gas was also used to decrease the degradation of the MO-sources. Mass spectra in-situ monitoring of source vapors in ECR-PAMOCVD system were obtained. By introducing NH3 as a carrier gas, a significant improvement was achieved in the volatility and the thermal stability of the precursors, and the vaporization temperatures of the precursors were reduced compared to Ar carrier gas. The uniform compositional depth profile, less hydrogen and carbon content and the good electrical properties of (SrxTi1−x)O3 thin films were obtained with NH3 carrier gas. The (Ba1−xSrx)TiO3 thin film were fabricated to have very fine and uniform microstructure, the dielectric constant of 456, the dielectric loss of 0.0128, the leakage current density of 5.01 × 10−8A/cm2 at 1V and the breakdown field of 3.65MV/cm.

Semiconducting, epitaxial SrTiO3 thin films doped with Eu3+ donors were analyzed using transient photocapacitance spectroscopy to determine the nature of the charge compensating defects. Deep level defects were detected with optical thresholds at Ec - 0.6 eV, Ec - 0.8 eV, and Ec - 2.05 eV. The level at Ec - 0.8 eV was the dominant defect in all of the films examined, with concentrations ranging from 1.6×1015 to 1.2×1017 cm−3 that increased as the square of donor concentration. The level was attributed to the strontium vacancy.

BaxSrl−xTiO3 thin films with varying Sr concentration were prepared on Pt coated Si substrates using methoxypropoxide based alkoxide precursors. Films were crystallized by heat treating at 700°C for 30 minutes in an oxygen atmosphere after deposition of each layer. Film thickness ranged from 230 to 260 nm. No evidence of tetragonality was observed in any of the compositions. Films with higher Sr concentrations had a larger average grain size, larger grain size distribution, and increased (111) orientation on (111) oriented Pt. The highest dielectric constant of ˜400 was found for Ba 0.5Sr0.5TiO3, although no direct correlation could be made between the composition and dielectric properties.

The application of high dielectric (Ba, Sr)TiO3 [BST] thin films for Metal-Insulator- Semiconductor(MIS) capacitors was investigated. BST thin films were deposited on p-Si(100) substrates by the RF magnetron sputtering with temperature range of 500–600 °C. We examined the characteristics of MIS capacitor with various oxygen pressure, substrate temperature and (Ba+Sr)/Ti ratio. The dielectric properties of MIS capacitors consisting of AI/BST/SiO2/Si sandwich structure were measured for various conditions. The charge state densities of the MIS capacitors were determined by high frequency (1 MHz) C-V measurement. Also, current-voltage characteristics of the MIS capacitor were investigated. In order to reduce the leakage current in MIS capacitor, high quality SiO2 layer was grown on bare p-Si substrate by thermal oxidation. By applying SiO2 layer between BST thin films and Si substrate, low leakage current of 10−10 order was observed. Futhermore, the leakage current showed the dependence on the oxygen concentration in plasma gas and the (Ba+Sr)/Ti ratio. Also, the BST MIS structure showed relatively high capacitance even though it is the combination of high-dielectric BST thin films and SiO2 layer. By C-V measurement, the polarity of effective oxide charge changed with the oxygen concentration in plasma gas and (Ba+Sr)/Ti ratio of sputtering target.

Barium-strontium-titanate (BST) films were deposited on platinum-coated ceramic substrates and platinum foil by the aerosol combustion process. A fine mist of metallic precursors in solution was carried into a methane-oxygen flame to produce ceramic particles, which coated the substrate. Both aqueous and purely organic solutions were tested, the latter producing finer powders (less than 100 nm) with high phase purity. Sintering the as-deposited particulate material led to a porous film at all sintering temperatures studied, regardless of the solution used. Cold pressing of the organicsolution- based material prior to heating, without the addition of any binders or solvents, gave a fully dense solid after sintering at 1450°C.

Effect of microstructure and surface roughness of oxide electrode on the properties of BST films has been investigated. (Ba, Sr)TiO3 and RuO2 films were deposited by RF magnetron sputtering technique. Surface morphology of RuO2 films were controlled by changing the O2/Ar ratio during deposition. It is found that the grain size and surface roughness of BST films are strongly influenced by RuO2 electrode underneath. When the grain size of RuO2 decreased by reducing either O2/Ar ratio during sputtering or film thickness, BST film resulted in fine grain structure and the leakage current decreased due to the improvement in uniformity of the film. Dielectric constant of BST films, however, was decided from both degree of well defined grains and film continuity related to grain size and surface roughness.

Thickness dependence of ferroelectric and structural properties of BaTiO3 thin films were investigated. Stoichiometric BaTiO3 thin films were prepared by off-axis rf magnetron sputtering on polycrystalline Pt substrates at 700°C. Film thickness range was 2,100–20,000Å. Room temperature permittivity, frequency dependence of permittivity, and D-E hysteresis loops were measured and lattice parameters were determined as a function of the film thickness. It has been found that these properties had the strong dependence on film thickness, which was mainly due to grain sizes of BaTiO3 thin films. The main cause of thickness dependence of dielectric properties was thought to be crystallinity and stresses of thin films which is resulted from changes in grain sizes.

Ba0.5Sr0.5TiO3 thin films were grown by rf-magnetron sputtering. Pt and RuO2 films were used as bottom electrodes of the Ba0.5Sr0.5TiO3 thin films. Further, a Pt/RuO2 hybrid electrode was adopted as an electrode for the film. Structural properties of the Ba0.5Sr0.5TiO3 thin films were found to be closely related to the type of the bottom electrodes. Dielectric constants of the films on Pt, RuO2, and Pt/RuO2 were measured as 500, 320, and 450 in the range of 100 Hz ˜ 1 MHz, respectively. Leakage current characteristics of the films were also found to be strongly dependent on the type of the electrodes and their microstructures.

Thin films of SrTiO3 (STO) and SrxBa1−xTiO3 (SBT) with x = 0.35, 0.5, 0.9, and prepared by excimer laser deposition on LaAlO3 and MgO were studied. SEM analysis indicates that the surfaces of these films are smooth with isolated pores, except the SBT(x=0.5)/LaAlO3 sample, where a high concentration of large pores was found. X-ray diffraction (XRD) results show well oriented films. External FT-IR reflection studies reveals a band around 500 cm−x, which shows a significant frequency shift with increasing component concentration. Also, this IR-reflectivity band presents no changes between the SBT(x=0.9)/LaALO3 sample annealed at 750°C and the same film annealed at 850°C. On other hand, the STO/LaAlO3 and STO/MgO films show differences in frequency position of this reflectivity band. Raman spectra of the SBT sample with x ≥ 0.35 show broad bands associated with the BaTiO3 (BTO) material. However, all the phonons bands are broader than those in BTO, in particular the band around 309 cm−. Raman results suggest that the spectrum is a consequence of a breakdown in the translational symmetry due to defects. Raman scattering also indicates a similarity between SBT(x=0.9) at 750°C and that at 850°C. Micro-Raman and EDX analysis show that STO/MgO and SBT(x=0.35)/LaAlO3 films are close to the expected stoichiometry, while STO/LaAlO3 and SBT(x=0.9) films present deficiencies of titanium and oxygen.

We have studied the effects of solvents and additives in the precursor solutions on the characteristics of barium strontium titanate (BST) thin films. The solution having two solvents, ie. acetic acid for barium acetate and strontium acetate and 2-methoxyethanol for titanium isopropoxide and also having an additive of ethylene glycol shows good stability and remains homogeneous even after a month of ageing. It produces excellent BST thin film without cracks. Dielectric constant, loss tangent at 10kHz and leakage current density at 3V of the BST(70/30) thin film made from this solution are 339, 0.052 and 13.3μA/cm2, respectively. We have also found that a Ta layer is a better diffusion barrier against Si than a Ti layer and is functional up to 750°C.

review is given, emphasizing electron microscopy, XPS, heavy-ion scattering, and very high frequency (1 MHz) hysteresis data, of the materials characteristics of thin films of SrBi2NbTaO9, SrBi2Ta2O9, and related titanates.

SrBi2Ta2O9(SBT) capacitors were integrated to the structure for a mega-bit nonvolatile memory, and their electrical properties after metallization were investigated. Annealing above 500°C after contact-etching was necessary to obtain good electrical properties. A well saturated hysteresis loop with 2Pr of more than 15μC/cm2 was obtained for the 0.7×0.7μm capacitor. The read-out polarization was very stable in 105 sec after the write-pulse. No fatigue or imprint was observed up to 1011 cycles. These results show suitability of SBT capacitors for a mega-bit non-volatile memory.

Photo-sensitive SrBi2Ta2O9 (SBT) solutions were evaluated and the patterning process flow for SBT films using the solutions was optimized. By adding a soft-bake process before UVirradiation, self-patterned SBT films were successfully prepared from the solutions and the cross sectional shape of the patterned films was improved. The photo-sensitivity of the solutions was estimated to be 900 mJ/cm2. The photo-reaction in the precursor gel film formed from the solution was traced by measuring IR absorption spectra. The obtained films had excellent ferroelectric properties comparable to conventional SBT films.

Highlights and solutions to some of the challenges involved in integrating SrBi2Ta2O9 (SBT) capacitors with Pt electrodes on silicon wafers for non-volatile memory applications are discussed. These include the diffusion of Bi through the Pt bottom electrode during firing, capacitor patterning, and process damage that results from hydrogen containing atmospheres.

Next, studies of the temperature dependence of many of the important electrical properties of SBT are presented. These include the remanent polarization (2Pr), the non-volatile polarization (Pnv), and the coercive field (Ec) all of which are studied as functions of the pulse amplitude; fatigue resistance of 2Pr and Pnv; the retention; the small signal capacitance versus voltage behavior; and the current versus voltage behavior. These studies demonstrate that SBT looks very promising for ferroelectric non-volatile memories over the consumer application range (0 to 70 °C).

For use in ferroelectric memories, the layer structure ferroelectric SrBi2Ta2O9 (SBT) appears to have some stability-related advantages over the more commonly known PZT class of ferroelectrics. Currently we are evaluating the feasibility of integrating this material into a state of the art CMOS memory process. Our primary scientific goal is to identify the intrinsic limitations of SBT which may restrict the engineering applications of films grown by even perfectly optimized processes. To this end we have utilized a wide variety of microanalysis probes to examine polycrystaline SBT films grown under various conditions by both MOD and Flash MOCVD. We have found that X-ray diffraction methods must be supplemented by high resolution X-ray photoelectron spectroscopy (XPS) in order to fully analyze the secondary phases which are commonly incorporated in SBT films. The more complete knowledge of film microstructure that this provides has enabled us to relate phase structure to growth and annealing conditions. XPS has also given us some insight into the initial stages of the growth chemistry of SBT on various Pt surfaces.

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+.

Thin films of Aurivillius-type layered perovskites of Bi4Ti3O12 and SrBi2Ta2O9 have been epitaxially deposited by pulsed laser deposition (PLD) on SrTiO3 single crystal substrates. Bi4 Ti3O12 has been deposited as well on a CeO2JYSZ/Si(100) buffer layer, and on Pt-coated oxidized silicon for electrical measurements. Using a new technique for large area PLD, Bi4Ti3O12 has also been deposited on a whole (100)-oriented 3”- Si wafer. The obtained films have a uniform thickness over a diameter greater than 50 mm, corresponding to an area of about 20 cm2. It is likely that homogeneous deposition on entire wafers of 3-inch in diameter will be accomplished in the near future. The composition, structure, and electrical properties of the films are presented.

The dielectric and ferroelectric properties of pulsed laser deposited strontium barium niobate (SBN) thin films were investigated. The samples were prepared using a Q-switched Nd:YAG laser with a wavelength of 355 nm and a fluence of 8 J cm−2. The oxygen ambient pressure and substrate temperature were set at 50 mTorr and 700 °C, respectively. The measurements of x-ray diffraction show that the films have tungsten-bronze- type structure. Pt/SBN/Pt capacitor structure was made on (111) silicon wafer to perform the ferroelectric and dielectric measurements. From the observations of the P-E loops, the saturation polarization, remanent polarization and coercive field at 25°C are equal to 40.7 μC cm−2, 32.5 μC cm−2 and 3.8 kV cm−1. The shape of the P-E loop becomes slimmer at temperatures above 150 °C, indicating that a ferroelectric-to-paraelectric transition occurs. The dielectric constant and loss tangent of the films at 10 kHz were found to be equal to 240 and 0.4, respectively. The saturation and remanent polarization remain almost unchanged after 109 switching cycles, indicating that pulsed laser deposited SBN films have good fatigue endurance.

Due to its low resistivity and excellent thermal stability, IrO2 has attracted attention as an alternative for electrode material in ferroelectric integrated circuit applications. In this work, IrO2 films deposited using reactive DC magnetron sputtering were studied. Film properties such as resistivity, crystallinity and morphology were examined as a function of deposition condition. Optimum process parameters to obtain high quality IrO2 thin films are suggested.