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.

Thin films of bismuth-layered perovskites with the generic formula (Bi2O2)2+(An- 1BnO3n+1)2- with an even Aurivillius' parameter n like SrBi2Ta2O9 (n = 2) and BaBi4Ti4O15 (n= 4) and with an odd Aurivillius' parameter like Bi4Ti3O12 (n= 3) and Ba2Bi4Ti5O18 (n=5) have been grown by pulsed laser deposition on epitaxial conducting LaNiO3 electrodes on single crystalline (100) SrTiO3 or on top of epitaxial buffer layers on (100) silicon. The films are shown to grow epitaxially, however, they do not have a single crystallographic orientation but several preferred orientations. The films consist of both c-axis-oriented regions and mixed (110)-, (100)- and (001)-oriented regions. The regions with mixed orientation feature rectangular as well as equiaxed crystalline grains embedded in a c-oriented matrix, protruding out of its smooth surface. Macroscopic as well as microscopic measurements of the ferroelectric properties of regions with pure c-orientation and of regions with mixed orientations showed a clear relationship between their ferroelectric properties and their morphology and crystallographic orientation. In the regions with mixed orientation, the films exhibited saturated ferroelectric hysteresis loops with well-defined remanent polarization Pr and coercive field Ec. The regions having c-axis orientation with a smooth surface morphology, in contrast, exhibited a linear P-E curve with no hysteretic behavior for SrBi2Ta2O9 and BaBi4Ti4O15, and weak ferroelectric behavior for Bi4Ti3O12. These results might have a technological impact due to the relevance of bismuth-layered ferroelectric oxides for the fabrication of non-volatile FeRAM memories.

Current status of fabrication and integration of ferroelectric-gate FET's is reviewed. Novel applications of ferroelectric-gate FET's are first discussed, which include a single-transistor-cell-type digital memory, reconfigurable LSI's, and an analog memory for an artificial neural network. In the neural network application, fabrication and basic operation of a pulse-frequency-modulation-type adaptive-learning neuron circuit are described as well as an SOI (silicon-on-insulator)-type FET array for synaptic connection is proposed.

Then. data retention characteristics of ferroelectric-gate FET's with MFIS (M : metal, F : ferroelectric, I : insulator (buffer layer), S : semiconductor) and MFMIS structures are discussed. It is shown that the important factors to improve the retention characteristics are (1) increase of the buffer layer capacitance, (2) decrease of the leakage current of both the ferroelectric film and buffer layer, and (3) optimization of the area ratio between the MFM and MIS parts in the MFMIS structure. Based on these considerations, MFMIS-FET's were fabricated using a stacked buffer layer of SrTa2O6/SiON; a current on/off ratio larger than 103 was obtained at a retention time of 10 hours.

METS (Metal Ferroelectric Insulator Semiconductor) capacitors were fabricated using CSD (Chemical Solution Deposition). Thin layers of CeO2 were deposited as an insulating buffer layer on Si(100) substrates and SrBi2Ta2O9 (SBT) was used as a ferroelectric layer. Pt electrodes were deposited by evaporation on top of the SBT layer. At constant SBT thickness the thickness of the CeO2 layer was varied to investigate the effects of the change in capacitance ratio between the ferroelectric and the buffer layer. XRD spectra were used to determine the phase of the SBT and the quality of the CeO2 layer. C(V) measurements showed the ferroelectric nature of the SBT. Additional information was provided by TEM and EDX analysis.

Some samples showed a memory window as big as 1.6 Volt at a moderate voltage sweep from −3.5 to +3.5 Volt. Interface state density is approximately 2×1011/cm2 eV and remanent polarization was found to be in the range of 0.3 μC/cm2. These results are already very promising in terms of fabricating a Ferroelectric FET. Some basic considerations with respect to the development of IT memory cells on the basis of this kind of transistor will also be presented.

A ferroelectric Pb5Ge3O11 thin film with a low dielectric constant is proposed for application in one transistor ferroelectric memories. A strong depolarization voltage on the ferroelectric capacitor with MIFSFET structures diminishes the remanent polarization significantly and, therefore, the low dielectric constant becomes very important to widen the memory window. A memory window of 3V was estimated for the MFMOS memory structure with 2000Å ferroelectric Pb5Ge3O11 and a 100Å gate oxide. In the second part of this paper, Pb5Ge3O11 films deposited on Ir/Ti/SiO2/Si substrates, by using MOCVD system, was demonstrated. Germanium ethoxide, Ge(OC2H5)4, and lead bis-tetramethylheptadione, Pb(thd)2, were used as the MOCVD precursors. The film composition, phase formation, microstructure and ferroelectric properties are reported. The c-axis oriented Pb5Ge3O11 thin films prepared by MOCVD and RTP post-annealing showed a square ferroelectric hysteresis loop with Pr of 2.83 μC/cm2 and EC of 49 kV/cm. A low leakage current of 7.5 × 10−7 A/cm2 at 100 kV/cm and low dielectric constant of 41 were also demonstrated.

Niobium-doped lead zircomate titanate (PNZT) thin film dielectric material has been produced on a large scale using a thick-coating sol-gel process. The material has been applied to the fabrication of commercial integrated capacitor array devices. Compared to conventional processes, this low-cost, long-shelf-life procedure had at least a 4-fold processing time enhancement. The specific capacitance of 2500 nF/cm2 and integrated density of over 200 component/cm2 have been demonstrated. The frequency domain capacitance measurement of integrated PNZT capacitors exhibits a frequency-independent behavior up to 2 GHz when a DC bias is applied. Leakage-voltage dependence follows the space-charge-limited-current (SCLC) mechanism. The fabricated integrated capacitor arrays pass the industrial standard of reliability for discrete multilayer capacitors.

In electronic circuits besides active devices a major part of the components are discrete passive components such as capacitors, resistors and inductors. Especially in the telecommunication circuits, miniaturisation is a major issue. To achieve a high degree of miniaturisation of passive components, thin film processes have been applied. A thin film module for high frequency applications has been demonstrated with a three-dimensional integration of a thin film resistor, a thin film X7R capacitor and a thin film NP0 capacitor processed on top of each other.

A coplanar structure is shown to be free of the asymmetrical I-V characteristics normally observed in MIM capacitors with BST inter-electrode dielectric. The low barrier height at the bottom interface is found to be responsible for the asymmetry, which causes increased leakage current and reduced breakdown voltage in one bias polarity. These problems can be eliminated using a coplanar structure, which has been shown elsewhere to have a very low parasitic inductance and a very high resonant frequency. However, these improvements are realized at the cost of a four times reduction of capacitance per unit area.

We have demonstrated the presence of ferroelectric properties in non-oxide (II-VI type semiconductor) ferroelectric thin films, such as (Zn,Cd)Te, (Zn,Cd)Se and (Zn,Cd)S (thickness: 3000–5000 Å). They have shown the ferroelectric hysteresis feature with memory windows of 0.2V, 0.3V and 0.8V, respectively. The materials design for getting the ferroelectric nature is as follows: when the size of the replaced atom is smaller than the host atom, then the substituent atoms can occupy off-centered positions, thus locally induce electric dipoles, thereby leading to ferroelectric behavior. These II-VI wide gap semiconducting ferroelectric films will open the door for new memory devices.

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

BaTiO3-based multilayer capacitors with Ni electrodes are fired at low Po2 to prevent the oxidation of Ni. Amphoteric dopants such as Y, Ho and Dy are used to prevent electrical degradation due to oxygen vacancy migration. This paper describes use of this approach in preparing thin film BaTiO3 capacitors. Tolerance of reducing atmospheres is particularly important in films which are co-processed with resistors such as TaN for integrated resistor-capacitor networks. To assess this approach, films with and without Y-doping were grown in pure N2 atmospheres by pulsed laser deposition from undoped and 0.2wt% Y2O3 doped BaTiO3 targets, respectively. Films were deposited onto Pt/Ti/SiO2/Si substrates using a 5∼10Hz laser repetition rate, an energy density of 4.2J/cm2 and a working pressure of 100mTorr. It was found that polycrystalline perovskite films could be grown at 700°C and that Y-doped films had better crystallinity than the undoped ones. The dielectric constants of films without and with Y-doping are ∼1100 and ∼1300 at lkHz, respectively. The dielectric losses of Y-doped films were lower than for undoped films, possibly because the concentration of mobile charges including oxygen vacancies was decreased. Y-doped films also have a smaller coercive field (25kV/cm) and higher maximum polarization (∼20μC/cm2) than undoped films. The defect chemistry of the system is also discussed.

Pulsed Laser Deposition (PLD) was used to deposit La-doped Pb(Zr,Ti)O3 (PZT) thin films onto NiTi foils. The substrate alloy with composition Ni50Ti50 shows a strong shape memory effect with a transition temperature of about 80°C. This simple bicomponental system could have the potential of an actuator device (NiTi shows a strain up to 5 % during thermal cycling) with an inherent sensorial component (PZT) for the generated elongation. The deposited ceramic films were characterized with respect to their structural properties (XRD) and their ferroelectric behavior (P-E hysteresis). Under certain deposition conditions the growth of pure perovskite PZT on the polycrystalline shape memory alloy was observed. The growth morphology of PZT on NiTi was compared to the one of PZT on single crystalline substrates whereas no distinctive texture of the films on NiTi could be found. The ferroelectric behavior of the PZT films depend on the stage of bending of the film-substrate compound.

In-situ, reactively sputter deposited 300 nm thick Pb(Zrx,Ti1-x)O3 films on Pt/Si based substrates are investigated as a function of composition and texture. (111) PZT is grown on a (111) oriented Pt bottom electrode covered with a very thin TiO2 film. Highly {100} oriented PZT is grown on Pt (111) by means of a 10 nm thick PbTiO3 seed layer. Pronounced deviations from known bulk PZT behavior are observed for the (111) texture. Maximum of d33 and ε are shifted to 40/60 and 45/55 compositions, respectively. (100) textured films exhibit a higher d33. 1.3 μm (100) thick films attain the predicted d33 value of clamped bulk ceramics. Coercive fields and voltage offsets increase strongly with increasing Ti content. In parallel, the as-grown polarization increases. Polarization switching is not possible for x ≤ 0.1. Post-anneals in O2 and hot poling show that oxygen vacancies play an important role in this phenomenon. Ti-rich (100) oriented films exhibit very high and stable pyroelectric and piezoelectric coefficients whithout poling treatments.

The effect of substrate induced constraint and misfit strain on the structure and piezoelectric properties of epitaxial relaxor ferroelectric lead magnesium niobate-lead titanate (PMN-PT) films were investigated. Relaxor PMN-PT epitaxial 100–400 nm thick films with top and bottom oxide electrodes were grown by pulsed laser deposition on (100) LaAlO3 substrates. A systematic decrease in the temperature of the dielectric maximum with increasing film thickness was observed. This is accompanied by an increase in the room temperature relative dielectric constant. The longitudinal piezoelectric coefficient measured using a scanned probe microscope, increases by almost an order of magnitude with increasing film thickness.

Highly {100} and {111} oriented Pb(Mg1/3Nb2/3)O3-PbTiO3 (70/30) films were deposited on Pt(111)-passivated silicon substrates using a modified sol-gel process. In both cases, the degree of preferred orientation did not change with film thickness from 0.56 μm to 1.5 μm. The room temperature dielectric constants for the {100}-oriented films were 2100–2650, while those for the {111} oriented films were 1900–2350. In both cases tan δ was less than 0.03. It was found that the piezoelectric coefficient (d31) of the PMN-PT films increased with increasing film thickness. The d31 coefficient of highly {100} oriented PMN-PT films poled for 5 minutes at 85 kV/cm were found to range from –45 to –86 pC/N assuming a Young's modulus of 35 GPa. Highly {100} oriented PMN-PT films showed larger piezoelectric coefficients than {111} oriented films. Results on aging of the piezoelectric coefficients for the differently oriented films are also presented.

We have grown epitaxial Pb(Mg1/3Nb2/3)O3 (PMN) and (1-x)(Pb(Mg1/3Nb2/3)O3)- x(PbTiO3) (PMN-PT) thin films by metalorganic chemical vapor deposition at 700 - 780°C on (100) SrTiO3 and SrRuO3/SrTiO3 substrates. The zero-bias permittivity and loss measured at room temperature and 10 kHz for 220 nm thick pure PMN films were 900 and 1.5%, respectively. For PMN-PT films, the small-signal permittivity ranged from 1000 to 1500 depending on deposition conditions and Ti content; correspondingly low values for the zero-bias dielectric loss between 1 and 5% were determined for all specimens. For PMN-PT with x of approximately 0.30–0.35, polarization hysteresis with Pr,≈18μC/cm2 was obtained. Initial piezoresponse data are discussed.

Lead magnesium niobate, Pb(Mg1/3Nb2/3)O3, thin films were formed from alkoxide-based solution precursors. To obtain stable and reproducible PMN precursor solution, a special effort has been undertaken to optimize the precursor synthesis. The organic decomposition behavior and crystalline phase development in a dried gel powder are reported. The influence of different seeding layers on the microstructures is shown. Dielectric and electromechanical measurements were carried out. Films show relaxor-like behavior, but with dielectric permittivity which is low (4500 at peak) compared to bulk ceramics and single crystals. Several parameters which might be responsible for this lower permittivity are suggested. Large electric dc bias fields (up to 120 kV/cm) can be applied to the films. This dc field reduces the permittivity, suppresses the frequency dispersion and flattens the permittivity peak. The anomaly associated with the field induced transition into a ferroelectric phase was not observed. Electrostrictive strains versus amplitude of electric field were measured and are discussed.

A systematic investigation of the piezoelectric and dielectric properties of Pb(Zr1-xTix,)O3 (PZT) thin films fabricated by chemical solution deposition was carried out for rhombohedral (x= 0.40), tetragonal (x=0.55) and morphotropic (x=0.47) composition. Each composition was grown with three different crystallographic orientations (textures): “random”, (111) and (100). Nonlinearity (field dependence) of d33 piezoelectric coefficient and dielectric permittivity of the films was studied in detail under subswitching conditions to reveal domain-wall related contributions to the properties. After analyzing for each texture and composition the domain-wall structure, contributions due to domain-wall displacements, and effects of film clamping by the substrate a consistent interpretation of the electro-mechanical properties and nonlinear behavior was proposed. The (100) oriented rhombohedral films show the largest piezoelectric coefficient (intrinsic effect) but limited nonlinearity (domain-wall structure effect) and should therefore be considered as potential candidates for piezoelectric devices.

The effective transverse piezoelectric coefficient was measured on 1 μm thick sol-gel processed Pb(Zr,Ti)O3 (PZT) thin films as a function of texture and composition. Optimal values were obtained with PZT films of {100} texture near the morphotropic phase boundary (53/47). The best value amounted to -12 C/m2

Integration of piezoelectric Pb(Zr,Ti)O3 (PZT) thin films promises to provide silicon-based microelectromechanical systems (MEMS) with added functionality. PZT films with compositions near the tetragonal/rhombohedral morphotropic boundary have been deposited on iridium-coated Si substrates by a thermal chemical vapor deposition (CVD) process using flash vaporized metalorganic precursors. Process variables including (A-site)-to-(B-site) ratios in the precursor mix and deposition times have been surveyed. Stoichiometric, perovskite films with nominal Zr/Ti ratios ranging from 40/60 to 60/40 were obtained. Parallel-plate capacitor structures have been fabricated by depositing Pt top electrodes using e-beam evaporation through shadow masks. Ferroelectric hysteresis loops were measured using a standard ferroelectric tester. Remenant polarization values in the range of 20∼30 μC/cm2 were obtained. For films of 0.5 μm or thicker, piezoelectric hysteresis loops were characterized by dual-beam interferometry. Longitudinal piezoelectric coefficients (d33) of 30∼60 pm/V were observed on the films deposited between 550 and 600°C.