Lead zirconate titanate (PZT) films are promising for acoustic micro-devices applications because of their extremely high electromechanical coupling coefficients and excellent piezoelectric response. Thicker PZT films are crucial for these acoustic applications. A hybrid sol-gel technology has been developed as a new approach to realize simple and cost-effective fabrication of high quality PZT thick films. In this paper, PZT53/47 thick films with a thickness of 5–50 μm are successfully deposited on Pt-coated silicon wafer by using the hybrid sol-gel technology. The obtained PZT thick films are dense, crack-free, and have a nano-sized microstructure. The processing parameters of this technology have been evaluated. The microstructure of the film has been observed using field-emission scanning electron microscopy and the crystallization process has been monitored by the X-ray diffraction. The thick films thus made are good candidates for fabrication of piezoelectric diaphragm which will be an essential element of microspeaker and microphone arrays.

In this work we present the structural, and vibrational properties of ferroelectric Pb1-xSrxTiO3 (PST). Thin films of PST were prepared by using sol-gel technique for various compositions with x values ranging from 0.0–1.0. Respective compositions were also prepared in ceramic and powder forms using sol-gel and solid-state reaction methods. X-ray diffraction was used for the structural characterization of these materials. Raman spectroscopy was utilized to study the phases and lattice vibrational modes, especially the soft mode in PST compositions. The temperature dependence of the soft mode frequency for different PST compositions revealed that the phase transition temperatures increased with increasing Pb contents in PST system. Ferroelectric properties of the films were correlated with the substitution-induced changes in the material.

Polarization-graded ferroelectrics and their electrically active counterparts, graded ferroelectric devices (GFDs) and transpacitors has been achieved in a number ways, including a variation in the composition of the material, or impressing a temperature gradients across the structure. In this article, we report how these same devices can be formed from homogeneous ferroelectric films of lead strontium titanate by imposing stress gradients on the materials normal to their electrode surfaces. A qualitative description of asymmetric hysteresis behavior based on a modified Landau potential is provided.

The dielectric response of BaBi2Nb2O9 (BBN) thin films has been studied as a function of frequency over a wide range of temperatures. Both dielectric constant and loss tangent of BBN thin films showed a ‘power law’ dependence with frequency, which was analyzed using the Jonscher's universal dielectric response model. Theoretical fits were utilized to compare the experimental results and also to estimate the value of temperature dependence parameters such as n(T) and a(T) used in the Jonscher's model. The room temperature dielectric constant (ε') of the BBN thin films was 214 with a loss tangent (tanδ) of 0.04 at a frequency of 100 kHz. The films exhibited the second order dielectric phase transition from ferroelectric to paraelectric state at a temperature of 220 °C. The nature of phase transition was confirmed from the temperature dependence of dielectric constant and sponteneous polarization,respectively. The calculated Currie constant for BBN thin films was 4 × 105°C.

We have studied the nature of the covalent bond between Pb 6s, 6p and O 2p orbitals in perovskites based on first-principles calculations. We conclude that the Pb 6p - O 2p covalent bond, not a bond involving Pb 6s, is crucial for the large ferroelectric effect in PbTiO3. The Pb 6s states behave like a shallow core level. To examine the effect of a Pb atom at the A site in the perovskite-type structure, we compared several calculated properties of PbTiO3 and BaTiO3 - the electric polarization, piezoelectric stress tensor and Young's modulus. The piezoelectric stress tensor e33 was calculated through Berry phase theory. BaTiO3 was found to have a larger e33 value than PbTiO3. In the case of BaTiO3, the response of Ti-O(2) to c-axis distortion is larger than in PbTiO3. We found that PbTiO3 is softer than BaTiO3 because of the cooperation of both Ti-O(2) and Pb-O(1) covalent bonds. We also found that the ferroelectric state is much softer than the paraelectric state. We propose that in the structural phase transition the system with the lower symmetry avoids ion repulsion through the additional degree of freedom available from atom displacement.

A 32 Mbit chain FeRAM™ stack with 0.20μm minimum feature size was etched with two subsequent lithography/RIE steps: in mask step 1 the platinum/SRO (strontium ruthenium oxide) top electrode and the PZT (lead zirconate titanate) layer, in mask step 2 the bottom electrode together with the Ir/IrO2 diffusion barrier were etched. The stack was etched with various chlorine based chemistries. High temperature etching processes were applied to suppress residues by the formation of volatile etching byproducts resulting in a highly anisotropic etching profile and low redeposition.

Profile angles of 75° for step 1 and 80° for step 2 could be achieved. For the thin SRO-layer a separate etching recipe was developed to avoid surface roughening caused by micromasking. The influence of etching temperature and different gas chemistries on the etching behavior was evaluated. Reliable end point detection and good uniformity of the individual etching processes were obtained, both being crucial for the application of a multi-step recipe. The ferroelectric properties of the capacitor were confirmed by hysteresis measurements. This demonstrates that the ferroelectric properties were conserved during RIE etch processes at high temperature.

(BaxSr1-x)TiO3 thin films were deposited on Pt electrodes in a planetary multi-wafer MOCVD reactor combined with a liquid delivery system. The nucleation behavior and the size of the stable nuclei were investigated by different SPM techniques and by XPS. Characteristic differences were observed between deposition temperatures of 565°C and 655°C, i.e. a homogeneous nucleation of small BST grains on the larger Pt grains (100 − 200 nm in-plane size) at low temperatures and a dominating nucleation at the grain boundaries at high temperatures. Further film growth was investigated for nominal film thickness between 5 and 100 nm and details of the grain structure are revealed by HRTEM, e.g., randomly oriented grains (typical in-plane size 10–20nm) with a high density of twins at 565°C and (100)-oriented defect free grains of slightly increased size at 655°C. As the electrical properties like permittivity and also leakage current depend on film thickness the final discussions of the electrical properties are based on thickness series and evaluated within the phenomenological dead layer model.

Thin film capacitor structures of Pb(Mg1/3Nb2/3)O3 (PMN) - PbTiO3 (PT) were fabricated using pulsed laser deposition (PLD) on MgO{100} substrates using (La1/2,Sr1/2)CoO3 (LSCO) as a lower electrode. Crystallographic and dielectric characterisation confirmed perovskite relaxor-like behaviour. Measurements of the electrostrictive coefficients by in-situ X-ray diffraction, piezo-response atomic force microscopy and three point bending experiments showed both Q11 and Q13 to be comparable to accepted values for single crystals. However, for a given field, the electric field-induced strain in the thin films was much less than that of single crystal. This was clearly intimately linked to poor thin film polarisability. Previous work had shown sol-gel PMN-PT films to have significantly greater permittivities than PLD films, and a TEM investigation was undertaken to see if functional differences could be related to differences in microstructure, and hence if the functional and electromechanical properties of PLD films could be improved by attempting to replicate sol-gel microstructures.

Seed layers of (TiO2)x(PbO)y for the growth Pb(Z,Ti)O3 (PZT) thin films have been studied as a function of thickness and composition. The seed layers have been deposited by reactive in-situ sputter deposition at 530°C from two metal targets in a dynamic sputtering mode. The compositional variation was achieved by varying the relative fluxes. The PZT process was run with a limited lead excess resulting in pyrochlore nucleation on bare Pt electrodes. When the electrode was covered with a dense seed layer, perovskite was obtained everywhere. Ti rich seed layers yielded (111)-textured PZT even for very thin seed layers. Pb rich seed layers nucleated as PbTiO3{100} and gave rise to (100)-textured PZT. In an intermediate zone, the major perovskite orientations (100), (110) and (111) have been found together with pyrochlore for a small seed layer thickness. In this zone, the seed layer nucleates in islands leaving bare Pt spots. The intermediate region is a transition region between (111) seeds and (100) seeds. The latter exhibit diverging critical sizes at a given critical flux ratio, leading to large nuclei and bare Pt. Small perovskite(111) seed grains in the 10 to 100 nm range are found at equal lead oxide and titania flux.

Domain wall velocity and nucleation rate in 250nm-thick epitaxial Pb(Zr,Ti)O3 thin films were studied by piezoresponse scanning force microscopy (PFM). Domain growth observed after applying switching pulses shorter than the switching time can be described using the Ishibashi theory. At a pulse voltage of +5V, experimental results indicated that new nucleation occurred during the switching period, which corresponded to the Category I in the Ishibashi theory. Switching time, domain wall velocity and nucleation rate at +5V can be obtained as 70ns, 8.3m/s and 43μs-1 μm-2, respectively. As compared with experimental results reported in BaTiO3 single crystals, domain wall velocity was much smaller but nucleation rate was much larger than those in single crystals.

Ferroelectric random access memory is one of the most promising candidates of non-volatile memories and has already been commercialized. However there still exist some problems to be solved on the ferroelectric materials. We succeeded in solving these problems by forming solid solutions between Bi2SiO5 and conventional ferroelectric materials such as Bi4Ti3O12, SrBi2Ta2O9 and Pb(Zr,Ti)O3. It was found that Bi2SiO5 enhanced crystallization of the ferroelectric materials and finally formed solid solutions with them. As a result, the crystallization temperature of the films decreased by 150 to 200 °C, and the ferroelectric and leakage current characteristics did not degrade even in an ultra-thin film of 13 nm in thickness. On the other hand, it was also found that the ferroelectric and insulating characteristics of the BSO-added films were dramatically improved by annealing in high-pressure oxygen up to 9.9 atms.[1] Three-orders-of-magnitude improvement of the leakage current density was observed in BSO-added BLT films after annealing at 9.9 atms, while pronounced increase of the saturation polarization was observed in BSO-added SBT and PZT films. From cross-sectional TEM (Transmission electron microscopy) observation, origin of the improved characteristics was speculated to be the structural change of the films.[2]

Polarization graded ferroelectrics exhibit unconventional electrical properties that are not usually observed from homogenous ferroelectrics. Systematic spatial variations in the polarization in a ferroelectric material can be achieved by composition, temperature, and stress gradients; resulting in the displacement of the polarization vs. electric field hysteresis curve along the polarization axis. In this paper, this unusual phenomenon of hysteresis offset has been examined in BaTiO3 and BaxSr1-xTiO3 material systems using a Landau-Ginzburg phenomenological model for the first time. It is shown that the spatial non-uniformities can give rise to non-uniformities in polarization with corresponding spatial variations. This non-uniform polarization results in asymmetrical hysteresis with “up” or “down” charge offsets which are strongly dependent upon the magnitude and direction of the temperature, composition and stress gradients for three graded ferroelectrics.

A scanning nonlinear dielectric microscope (SNDM) probe, called theε311 -type probe, and a system to measure the ferroelectric polarization component parallel to the surface using rotating electric field have been developed. This is achieved by measuring the ferroelectric material's nonlinear dielectric constant ε311 instead of ε333, which is measured in conventional SNDM. Experimental result shows that we can successfully determine polarization component parallel to the surface. The SNDM system can measure polarization at any angle from the surface normal which is often of interest.

Sputter deposited barium strontium titanate (BST) based thin film capacitors have been developed for use in GHz LSI decoupling applications. The fabricated 1.60×1.85 mm2 BST chip decoupling capacitors with Pt electrodes and 150 μm bump pitch, have a capacitance density of 1.2 μF/cm2, low equivalent series inductance of 15 pH, and a low equivalent series resistance of 0.02 Ω. The impedance of the chip capacitors at 1 GHz is over 1000 times lower than conventional multilayered ceramic capacitors. Fundamental electrical and reliability properties of Pt/BST/Pt thin film capacitor structures were also investigated. Capacitors with 200 nm thick BST thin films deposited at 500 °C by RF magnetron sputtering achieved a C/A of 1.8 μF/cm2, leakage current density < 10-9 A/cm2 at 2 volts, and a breakdown field > 2.5 MV/cm at 20 °C. A fit of the failure data to a Weibull distribution indicated at least two different physical mechanisms causing capacitor failure. The primary failure mechanism for 1.5 volt operation was due to resistance degradation without catastrophic capacitor failure. At higher applied voltages, catastrophic capacitor failure occurred with the breakdown event characterized by a thermal runway process. The physical mechanisms contributing to capacitor failure are interpreted to be due to ionic migration and charge injection, and the contribution of these mechanisms to the degradation process could be partially resolved by bi-polar voltage pulse stressing. The projected mean time to failure for 1.5 volt operation is extrapolated to be in excess of 104 years at 75 °C and 126 years at 125 °C. The results indicate that sputter deposited BST thin film capacitors are promising for future GHz LSI decoupling applications.

Based on the direct piezoelectric effect, the measurement of piezoelectric module d33 was conducted to examine the self-poling effect in sol-gel derived Pb(Zr1-xTix)O3 (PZT) thin films. It is observed that as-prepared PZT thin films have piezoelectric responses being dependent upon the film thickness and composition. The higher d33 of 26 pC/N is achieved for ∼0.4 μm thick PZT thin films with Zr/Ti ratio of 53/47. The d33 value decreases with increasing the film thickness for as-prepared PZT thin films, however, increases for the same film after external poling. The origin of the self-poling effect was briefly discussed based on the formation of an internal bias field in PZT thin films.

We report on the growth of Ba(Ti1-xZrx)O3 thin films on Pt(111) / TiO2 / SiO2 / Si substrates by means of metal-organic chemical vapor deposition (MOCVD) using liquid precursors. The MOCVD system consists of an AIXTRON AIX-200 horizontal reactor with a TriJet® vaporizer. In the multi-source injection system the different single element precursor solutions were introduced separately in a pulse mode. The focus of our investigations lies on the correlation between processing conditions, growth rate, and film properties, namely stoichiometry, crystal structure, and surface morphology. Dense, polycrystalline Ba(Ti0.63Zr0.37)O3 films were successfully grown on platinum coated silicon substrates at temperatures around 630°C.

DC electric field induced dielectric properties of 0.7Pb(Mg1/3Nb2/3)O3-0.3PbTiO3 (PMN-PT) thin films were studied as a function of frequency at different temperatures. It was observed that the dielectric constant (ε) and dissipation factor (tanδ) were decreased in presence of bias field. The temperature of dielectric maxima was found to increase with increasing bias level. The low temperature (<Tm) frequency dispersion of dielectric permittivity was suppressed with the application of dc bias. After a certain bias voltage the relaxor property of films was disappeared i.e. the films exhibited normal ferroelectric behavior. Since the absence of long range interaction among the nanopolar clusters in PMN and its family is believed to be the origin of relaxor behavior, disappearance of relaxor nature in PMN-PT (70/30) films could be attributed to manifestation of long-range order at higher bias voltage. This was observed in the temperature dependence of dielectric constant i.e. the films neither exhibited any frequency dispersion in the temperature of dielectric maximum (Tm) nor showed any diffused phase transition. The relaxor property of PMN-PT thin films was studied in terms of diffused phase transition together with frequency dispersion of the temperature of dielectric maximum (Tm). Vogel-Fulcher relation was used to analyze the frequency dependence of temperature of dielectric maximum.

Effects on ferroelectric and piezoelectric properties of top-electrode diameter variance from 80 to 8 μm were investigated using an AFM probing system connected with a ferroelectric test system with bipolar and unipolar signals at 5 Hz. The Pt and 1.2-μm-thick PZT layers were etched off to prepare Pt top electrode etched samples or Pt/PZT stack etched samples. In the case of bipolar measurement, the top electrode diameter did not affect ferroelectric properties, while the maximum displacement of the butterfly-shaped hysteresis curve, related with piezoelectric response, increased with decreasing top-electrode diameter. On the other hand, the longitudinal piezoelectric constant, AFM d33, calculated from the strain curve slope at 5 Hz, +5 V, increased with decreasing top-electrode diameter. The average value of the Pt/PZT stack-etched AFM d33 almost equals that of Pt-etched AFM d33. Average AFM d33 of the 8-μm-diameter Pt-etched and Pt/PZT stack-etched samples are 129 and 135 pm/V, respectively.

The phase transition of non ferroelectric pyrochlore to ferroelectric perovskite in CaBi4Ti4O15 thin films depended on matching of the atomic arrangements in platinum bottom electrodes to the Ca-Bi-Ti-O thin films. CaBi4Ti4O15 thin films crystallized on (200)-oriented platinum at 650°C showed c-axis orientation. In contrast, thin films randomly crystallized on highly crystalline (111)-oriented platinum at the same temperature contained pyrochlore phase and showed P-V hysteresis loops. The ferroelectric properties improved with the degrees of (h00) orientation.

The leakage and dielectric properties of a thickness series (90–480 nm) of {100} fiber-textured MOCVD (Ba0.75Sr0.25)Ti1+yO3+z (BST) thin films on Pt/SiO2/Si were investigated. The temperature and voltage dependence of the permittivity were consistent with previous observations, where thinner films demonstrated a suppressed temperature and electric field response that transitioned to a more bulk-like response with increasing film thickness. The current-voltage characteristics showed two distinct regimes. At low fields the current displayed weak field dependence and a monotonic increase with increasing temperature. In contrast, positive temperature coefficient of resistance (PTCR) was observed in the high-field leakage current behavior. The PTCR behavior was more pronounced for thicker BST films. Factors contributing to the observed PTCR effect are outlined and contrasted with the description for bulk BaTiO3 ceramics.