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Applications of ferroelectrics, 2006. isaf '06. 15th ieee international symposium on the

Date July 30 2006-Aug. 3 2006

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  • Impedance Spectroscopy of Mn-Doped BiFeO3-PbTiO3 Ceramics

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    BiFeO3-PbTiO3-based materials have the potential to be used as high temperature piezoelectrics and are candidate multiferroic materials. Two drawbacks are the significant conductivity and the apparently low mobility of ferroelastic domain walls. Both may be influenced by aliovalent doping. Here we have investigated a number of B-site dopants, including manganese, plus B-site non-stoichiometry (i.e. Fe/Ti ratio) to determine their role in the conduction mechanism. Dense ceramics of 0.7BiFeO3-0.3PbTiO3 were prepared by conventional preparation techniques incorporating the above dopants or stoichiometric adjustments. DC resistivity measurements were carried out as a function of field. AC impedance spectroscopy from 1 mHz to 20 MHz was also employed to determine the extent of heterogeneity in the transport and displacement properties. The results are interpreted in terms of the conventional models of oxygen vacancy and Fe2+:Fe3+ hopping conduction. View full abstract»

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  • Synthesis, Structure and Properties of Pulsed Laser Deposited BiFeO3-PbTiO3 Thin Films

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    Bismuth ferrite lead titanate (BFPT) films of composition xBiFeO3 - (1-x)PbTiO3, with x from 0 to 1, have been deposited on platinised silicon substrates employing pulsed laser deposition under various temperatures and oxygen pressures. Dense, high quality films were deposited at 530°C with 150 mTorr oxygen pressure. The crystal structure and orientation of the films has been studied by powder x-ray diffraction. The film surface morphology and cross sections were studied on a FEGSEM. The films exhibit significant crystallographic texture across the solid solution range, and appear to exhibit a tetragonal and monoclinic phase mixture across the range. The c/a ratio of the tetragonal phase undergoes a maximum for a composition around x = 0.7corresponding to the bulk morphotropic phase boundary composition, and is 1.137. However, the presence of the monoclinic phase is not observed in the bulk laser targets. View full abstract»

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  • Fabrication and Characterization of ZnO Films for Biological Sensor Application of FPW Device

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    Flexural plate wave (FPW) device has great potential for biological sensor application due to 1) isolation of its electric circuit from the medium being investigated, 2) low acoustic energy loss in liquid medium, and 3) simpler oscillator circuit design. Since FPW device can be fabricated onto silicon-based substrates by micromachining technology, it offers batch processing for economic sensor fabrication. In this study, ZnO was chosen as a piezoelectric material due to non-toxicity, and chemical and thermal stability for biological sensor application. RF magnetron sputtering and chemical solution deposition (CSD) were investigated for achieving strong c-axis orientation of ZnO films required to launch the acoustic wave in the device. Process parameters such as gas ratio, substrate types, and temperature, were varied for sputtering, and heat treatment and substrate types for CSD. Results showed that process parameters have a strong influence on the preferred orientation and microstructure of ZnO films. Uniform and dense microstructures of ZnO films were obtained by both fabrication methods. CSD method showed, however, stronger dependence of the preferred orientation on substrate types while less dependence on the substrates for sputtering due to energetic sputtered species. Mechanism for ZnO thin film growth will be discussed. FPW devices have been successfully integrated onto 4 inch Si-wafer with 22 different interdigitated electrodes. Optimized device demonstrates the capability to detect biological quantity of 446.13 cm2/gram of sensitivity. View full abstract»

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  • Sol-gel derived lead-free piezoelectric Bi1/2Na1/2TiO3 thin film for MEMS applications

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    Bi1/2Na1/2TiO3 (abreviated as BNT) is considered as a promising lead-free piezoelectric material for sensor and actuator applications. In this study, we demonstrate an improved sol-gel process using rapid thermal annealing (RTA). Our results indicate that thermal annealing in an oxygen atmosphere after each layer of coating is effective in promoting crystallization of the BNT film at a low temperature of 650°C. The resulting film is dense and well crystallized in the perovskite phase. The piezoelectric properties of the sol-gel derived BNT films are characterized with the help of a laser interferometer. The BNT based film is expected to be a new and promising candidate for lead-free piezoelectric MEMS applications. View full abstract»

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  • High Strain and Piezoelectric Characteristics of Textured Bi0.5(Na0.85K0.15)0.5TiO3 Ceramics

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    The anisotropy of polarization and strain behavior in textured Bi0.5(Na0.85K0.15)0.5TiO3 ceramics are investigated for lead-free piezoelectric ceramics actuators. The textured Bi0.5(Na0.85K0.15)0.5TiO3 ceramics are fabricated by reactive templated grain growth (RTGG) using plate-like Bi4Ti3O12 particles. RTGG[//] (sliced parallel to the casting direction) and RTGG[//] (sliced perpendicularly to the casting direction) specimens show preferred orientation to ≪001≫pc and ≪IIO≫pc, respectively. RTGG[//] specimen has relatively high piezoelectric coefficient of (d33)~335 pm/V and electric field induced strain levels of 0.067% at 20 kV/cm. This values were 86% higher than those of RTGG[¿] specimen. ≪00l≫pc textured polycrystalline BNKT ceramics, prepared by RTGG, are a strong candidate for lead-free piezoelectric materials of actuators. View full abstract»

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  • Development of Lead-Free PTC Thermistor Materials

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    The electric properties of bismuth- and sodium-modified barium titanate, Ba1-x(Bi1/2Na1/2)x TiO3 (BBNT) were studied as a lead-free PTC (positive temperature coefficient of resistivity) thermistor material usable over 130°C. Two semiconductorization processes and their electric properties are described. Lanthanum(La)-doped BBNT ceramics sintered in air still show dielectric behaviors, but Nb-doped ones have a low resistivity ¿RT on the order of 103¿cm at room temperature and show a PTC behaviors. Sintering under low O2 atmosphere produces BBNT ceramics with less than 102 ¿cm compared to those prepared in air. A trial PTC heater constructed using the BBNT semiconducting ceramics demonstrates a comparable performance of those made of the Pb-contained PTC ones. Our current research shows the BBNT ceramics with a switching temperature Ts around 210°C by increasing the (Bi1/2Na1/2) content x of the ceramics. View full abstract»

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  • Growth of Silver Lithium Niobate Single Crystals and Their Piezoelectric Properties

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    Silver lithium niobate (Ag0.9Li0.1Nb0.3, ALN10) single crystals were grown by a slow cooling method without flux under oxygen flow. By optimizing growth conditions, the ALN10 crystals with sizes of ca. 30 mm cube were successfully grown. Its crystal symmetry was investigated by high energy X-ray diffraction, and the space group at 24°C was assigned to the ferroelectric Pc21b orthorhombic symmetry. The ALN10 crystals were oriented along the [010]o and the [110]o directions, and their piezoelectric properties were measured using the 31 resonators. View full abstract»

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  • Lead-Free Piezoelectric Ceramics vs. PZT?

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    Investigations in the development of lead-free piezoelectric ceramics have recently claimed properties comparable to that of PZT-based materials. In this work, the dielectric and piezoelectric properties of the various systems were contrasted in relation to their respective Curie temperatures. Though comparable with respect to TC, enhanced properties reported in the K,NaNbO3 family are the result of increased polarizability associated with the Torthor-tetragonal polymorphic phase transition being compositionally shifted downward and not from a morphotropic phase boundary (MPB) as widely reported. As expected, the properties are strongly temperature dependent unlike that observed for MPB systems. Analogous to PZT, enhanced properties are noted for MPB compositions in the Na, BiTiO3-BaTiO3 and the ternary system with K,BiTiO3, but offer properties significantly lower than that of PZTs. The consequence of a ferroelectric to antiferroelectric transition well below TC further limits their usefulness. View full abstract»

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  • Piezoelectric Micromachined Ultrasonic Transducers based on PZT films

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    Piezoelectric micro machined ultrasonic transducers (pMUT) are piezoelectric laminated plates operating at flexural modes. The pMUT's fabricated in this work contained a 4 ¿m thick lead zirconate titanate (PZT) thin film deposited by a sol-gel technique, and exhibiting a permittivity of ¿r= 1200, and an effective transverse piezoelectric coefficient e31,f of 12 C/m2. A further optimization of the sol-gel process yielded larger grain diameters and consequently improved properties: ¿r=1600, e31,f of 16 C/m2. A design and micromachining concpet for easy scaling in frequency has been developed. The electromechanical coupling coefficient (k2) and the quality factor (Q) of rectangular clamped elements (with former PZT process) were measured as k2=4.4% and Q=145 in air for a low frequency transducer (@240 kHz). The 16.9 MHz transducer yielded values of Q=25 and k2=3% in air. The effect of DC bias voltage on frequency and k2 has been studied. View full abstract»

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  • Relaxor Ferroelectric 0.2PZN-0.8PZT(53/47) Thick Films Fabricated Using a MOD Process

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    Crack free peroviskite 0.2PZN-0.8PZT (53/47)) thick films up to 6.8 ¿m were prepared by a metallic-organic decomposition (MOD) process on platinum coated titanium (Pt/Ti) foil substrates by a dipping coating technique. The thick film exhibits a pure perovskite phase structure with dense and uniform microstructure. The dielectric, ferroelectric and piezoelectric properties of the thick film have been examined and discussed. A perfect ferroelectric P-E loop was observed. The efficient piezoelectric coefficient d33,f of the film was estimated by a standard Berlincourt type meter. The measured d33,f value of the 0.2PZN-0.8PZT (53/47)) thick film is about 177 pC/N; it is larger than that of the PZT (53/47) thick film examined in the same condition, 98 pC/N. This 0.2PZN-0.8PZT(53/47) thick film promises a good application in the microelectronic devices. View full abstract»

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  • PZT Films on Wafers and Fibers for MEMS Application

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    A single PZT metallic target has been utilized to deposit lead zirconate titanate (PZT) films by DC pulsed magnetron sputtering on Ti/Pt(111)/Ti coated Si wafer and on Au coated glass fibers. Multicrystalline PZT films were obtained after post treatment by conventional (CA) and rapid thermal annealing (RTA) at 650°C in air and vacuum. The influences of both post-annealing treatments on the film properties were evaluated. Conventional annealed films showed a different texture orientation than RTA annealed films. It has been observed that conventional annealed films show higher remanent polarization and lesser coercive field than RTA annealed films. PZT films were also successfully deposited on Au coated glass fibers. Coated fibers were post annealed by RTA@600°C to obtain a PZT structure. Surface morphology of the films showed that the CA annealed films have denser grains and less crack formations than RTA annealed films. Coated fibers show a dense and crack free structure. View full abstract»

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  • A Micro Ultrasonic Scalpel Using Hydrothermal PZT Thin Film

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    A transducer for a micro ultrasonic scalpel has been fabricated. The micro ultrasonic scalpel can be used with an endoscope for a non-abdominal operation or micro surgery, for example, through a microscope. The ultrasonic transducer was 9.8 mm long and 2.7 mm wide and has stepped horn to amplify vibration velocity; tip of the horn is 0.6 mm wide. The scalpel vibrated in longitudinal mode at about 278 kHz resonance frequency. The piezoelectric material was lead zirconate titanate (PZT) that was deposited by the hydrothermal method. This is because the hydrothermal deposition film transducer has superior performance in vibration velocity. The vibration velocity at the tip of the horn in longitudinal direction was 4.0 m/s with 40 Vp-p driving voltage in both side electrodes. To demonstrate a beneficial effect of the scalpel, a cutting test that the transducer was stuck into pork fat was carried out. Efficient cutting performance was demonstrated using the transducer sized for an endoscope. View full abstract»

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  • Cross-Sectional Imaging of Polarization Reversal in Ferroelectric Films

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    Polarization reversal in Pb(Zr,Ti)O3 ferroelectric films was followed by a novel technique of cross-sectional piezoelectric force microscopy (PFM). Instead of the traditional scanning of the top surface of ferroelectric thin films, the domain structure across the cross section is visualized. The probing AC electric field is applied to the capacitor structure between top and bottom electrodes resulting in a homogenous field throughout the film while the Atomic Force Microscope (AFM) tip is only used to sense the piezoelectric vibration. In the cases of the studied (111)-oriented tetragonal and rhombohedral PZT films, the sequence of imaged domain configurations taken at increasing poling voltages puts forward a sideways growth of oblique domains. Additionally, the considered domain growth model could explain the gradual variation of the piezoelectric response amplitude, which is commonly observed in planar PFM images. The cross-sectional PFM setup looks promising for gaining new insights into reversal mechanisms and may be used as a tool for studying phenomena of switching deterioration in ferroelectric film devices. View full abstract»

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  • Nanodomain Manipulation for Ferroelectric Data Storage with High Recording Density, Fast Domain Switching and Low Bit Error Rate

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    Recording density, domain switching time and bit error rate were evaluated using a data storage system based on scanning nonlinear dielectric microscopy. Congruent lithium tantalate single crystals with the thickness less than 50 nm were used as recording media. Local domain switching was carried out by applying voltage pulse on the recording media using a conductive cantilever. Close-packed domain dot arrays were written on the recording media. As a result of optimizing the writing pulse conditions, the dot array with the areal recording density of 10.1 Tbit/inch2 was successfully written. Subsequently, the thickness of recording media was reduced in order to improve the domain switching property, which determines the upper limit of data transfer rate. A nanodomain dot was formed by applying a 500-ps pulse on the 18-nm-thick recording medium. Actual information data were recorded for bit error tests. There were no bit errors in approximately ten-thousand-bit data under the areal recording density of 258 Gbit/inch2. It means bit error rate was less than 1×10-4. Additionally it was also confirmed that actual information data was recorded at the areal recording density of 0.98 Tbit/inch2 with a few bit errors. View full abstract»

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  • Spatial Resolution and Measurement Accuracy of Dielectric Microscope Using Non-contact State Microwave Probe

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    The dielectric measurement for microscopic area of multi-layer ceramics capacitor was carried out by microwave microscope using non-contact microwave probe. The phase of incidence microwave for sample was fixed to ¿2 in order to realize accurate measurement of sample. The spatial resolution for dielectric measurement was increased based on Kirchhoff's diffraction theory with decreasing coaxial cable and probe diameter. From reflection intensity mapping, the dielectric permittivity distribution in microscopic area at GHz order was measured for cross section of multi-layer ceramics capacitor at room temperature. The spatial resolution was experimentally estimated to be about 10¿m from mapping of cross section view of dielectric and inner electrode layers in multi layer ceramics capacitor. View full abstract»

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  • Application of Acoustical Activity in Lithium Niobate Crystals for Control of Light Intensity

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    New technology is offered for measuring and control of light intensity. In the proposed method the phenomenon of acoustical activity and Bragg light diffraction on hypersonic waves in ferroelectric crystal LiNbO3 is used. Control of light intensity can be realized by transference of crystal or by modification of generator frequency by which the transverse acoustic wave is excited. The change of light intensity is provided electronically, fluently and with high accuracy. Using previously the standard calibration, it is possible to measure and change the light intensity to the necessary value. View full abstract»

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  • Domains Inversion in LiNbO3 Using Electron Beam Irradiation for Phononic Crystals

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    We report here, the study of domain inversion in lithium niobate (z-cut) by electron beam irradiation without any static bias associated to wet etching, in view of the fabrication of phononic crystals. The inverted domains are revealed by HF-etching taking advantage of the large difference in etching rate between z+ and z-faces. A pertinent choice of irradiation conditions such as accelerating voltage, probe current and injected dose, (parameters of interest for the geometry and size of the obtained domains), was determined and optimized. Two dimensional structures at the micrometer scale were then realized on z-cut LiNbO3. We demonstrate the achievement of 8¿m diameter hexagons, with a very large depth close to 30¿m, which depends on the etching time. The obtained structures were characterized before etching by optical microscopy to visualize the inverted domains, and after etching by field emission scanning electron microscopy. These characterisations pointed out the high occupancy rate of obtained structures. Numerical simulations of the realized phononic structure band gap show a frequency band gap around 200MHz. View full abstract»

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  • Ferroelectric Relaxor Terpolymers: Properties and Potential Applications

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    Ferroelectric materials are intrinsically multifunctional and have found a broad range of applications. A new class of semicrystalline terpolymers comprising vinylidene fluoride (VDF), trifluoroethylene (TrFE), and 1,1-chlorofluoroethylene (CFE), were prepared at the Institut Franco-Allem and de Recherches in Saint-Louis (ISL) via a suspension polymerization process. Relevant studies and results show that this class of electroactive polymers offers unique properties in comparison with other ferroelectric polymers. The terpolymer exhibits high electrostrictive strain (≫7%) with relatively high modulus (≫0.3GPa). It has been also observed that the large electrostrictive strain is nearly constant in the temperature range from 20 °C to 80 °C. These terpolymers are strong candidates for new devices. Example of the motion and of the performance of terpolymer in a unimorph configuration is presented._The high room temperature relative dielectric constant ( 50), which is the highest among all the known polymers), high induced polarization (0.05 C/m2), and high electric breakdown field (≫400 MV/m) lead to very high volume efficiency for the electric energy storage operated under high voltage (10 J/cm3). View full abstract»

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  • Piezoelectric Micromachined Ultrasonic Transducers Based on P(VDF-TrFE) Copolymer Thin Films

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    Representing a new approach to ultrasound generation and detection, study on piezoelectric micromachined ultrasonic transducers (pMUTs) has been a growing research area in recent years. Intensive research work has been directed on the deposition of lead zirconate titanate (PZT) films on silicon substrates for their excellent piezoelectric coefficients and electromechanical coupling coefficients. However, the high processing temperature required for PZT crystallization results in a low device yield and also makes it difficult to integrate with control circuits. In this paper, a fabrication technology of pMUTs based on piezoelectric P(VDF-TrFE) 70/30 copolymer films has been adopted, with the maximum processing temperature not exceeding 140°C allowing for post-IC compatibility. The entire processing procedures are simple and low cost, as compared with those of capacitive micromachined ultrasonic transducers (cMUTs) and ceramic-based pMUTs. The applications of the fabricated pMUTs as airborne ultrasonic transducers and transducer arrays have been demonstrated. Reasonably good device performances and high device yield have been achieved. View full abstract»

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  • Electrical characteristics of organic ferroelectric FET integrated with Si using P(VDF-TrFE) copolymer films for nonvolatile memory devices

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    The feasibility of nonvolatile memory (NvRAM) structure with nondestructive readout (NDRO) capability based on Si-MOSFET integrated with a ferroelectric polyvinylidene fluoride trifluoroethylene copolymer (P(VDF-TrFE)) as a gate along with SiO2 buffer has been demonstrated. Measurement of channel current IDS shows no saturation due to uniform ferroelectric field across gate channel. Modulation of channel conductance is attributed to sensitively switchable polarization field. Remarkable switching drain current ratio of ≫105 times with ON/OFF operations were obtained. Memory window is obtained to show the polarization field regulating threshold voltages of the integrated organic polymer FET. View full abstract»

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  • Embedded FeRAM Challenges in the 65-nm Technology Node and Beyond

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    To embedded ferroelectric random access memories in the 65-nm CMOS and beyond, three-dimensional structure and low-temperature formation have been developed. View full abstract»

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  • Ferroelectric Gate on AlGaN/GaN Heterostructures

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    A PZT, Pb(Zr,Ti)O3 (40:60), ferroelectric layer has been successfully deposited onto a Al0.3Ga0.7N/GaN heterostructure with a 2DEG, two dimensional electron gas. Due to the chemical and temperature stability of AlGaN/GaN it was possible to implement the concept of field-effect transistor with ferroelectric gate. The high temperature perocessing conditions for PZT were optimised in order to grow highly textured (111) PZT on the heterostructure without destroying the 2DEG. However, it was imperative to measure the transport properties in the 2DEG before and after the PZT deposition process in order to detect any degradation of the 2DEG due to diffusion. Hall measurements also enabled the observation of the partial depletion of electrons in the 2DEG, confirming the functionality of the ferroelectric gate. This depletion was due to a change of the spontaneous polarisation in the PZT layer when poled with a negatively biased voltage. These results are encouraging for the use of PZT as a ferroelectric gate on AlGaN/GaN heterostructures and may open new possibilities for semiconductor heterostructure nano-patteming by polarisation domain engineering. View full abstract»

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  • Atomic Layer Deposition of Pb(Zr,Ti)Ox, Thin Films by a Combination of Binary Atomic Layer Deposition Processes

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    After an evaluation of Zr precursor, quatemary Pb(Zr,Ti)Ox [PZT] films were prepared by a combination of binary atomic layer deposition (ALD) processes. ZrOx films were deposited on Pt/TiOx/SiOx/Si substrates using liquid injection ALD. Zr(C11H19O2)4 [Zr(DPM)4] dissolved in ethylcyclohexane (ECH) with a concentration of 0.1 M and water were used as precursor and oxidant, respectively. According to the Arrhenius plot for the deposition rate of ZrOx films at various deposition temperatures, the Zr precursor appeared to start marked thermal decomposition at a deposition temperature of 360ï¿¿C. Below this thermal decomposition temperature, a saturated deposition rate of ZrOx films against input of Zr precursor was confirmed. The saturated deposition rate was about 5-6ï¿¿10-12 mol/cm2ï¿¿cycle at a deposition temperature of 300ï¿¿C. Subsequently, binary ALD processes of TiOx and PbO films, whose self-regulated growth mode has been already confirmed, were combined with the ZrOx process into multi-precursor ALD of PZT films. Ti(OC3H7)2(C11H19O2)2 [Ti(Oi-Pr)2(DPM)2] and Pb(C11H19O2)2 [Pb(DPM)2] dissolved in ECH with a concentration of 0.1 M were used for PZT film preparation as well as Zr(DPM)4. Unit sequences described as 1ï¿¿(Pb-O) - 2ï¿¿(Ti-O) - nï¿¿(Zr-O) were repeated to deposit PZT films at 240ï¿¿C. In the PZT process, the deposition rates of all cations were higher than those in their binary processes. The Pb/(Zr+Ti) and Zr/(Zr+Ti) ratio was adjusted by repeating the number of Zr-O cycles in a sequence. As-deposited PZT films were amorphous. Crystalline PZT films were obtained after annealing at 650ï¿¿C, and the PZT crystal showed a preferred (- 100)/(001) orientation. View full abstract»

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  • Nonlinear Dielectric Properties of (Ba0.60, Sr0.40)TiO3 Thin Films with Anisotropic Epitaxy

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    Nonlinear dielectric response of (Ba0.60 Sr0.40)TiO3 epitaxial films on ≪100≫ and ≪110≫-oriented NdGaO3 substrates were investigated as a function of film thickness. The second, fourth and sixth order permittivities were determined at 10 GHz and at room temperature from which the so-called critical field for maximum tunability was computed using a thermodynamic formalism recently developed by the authors along the principal residual misfit strain directions. It is shown that the critical field is anisotropic in the plane of the film and its magnitudes are governed by the film thickness. View full abstract»

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  • Electrocaloric Effect In Relaxor Ferroelectric Ceramics and Single Crystals

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    In the last two decades, the electrocaloric (EC) effect which is associated to the temperature (¿) dependence of the macroscopic polarization P(E,¿) under electric field E has been spasmodically studied in ferroelectric materials in order to find an alternative to the classical refrigeration devices using freon. Basically, large electrocaloric temperature variation ¿¿ originates from electric field-induced phase transition at the Curie temperature, but temperature changes of the sample are difficult to measure and depend on the experimental conditions. In this paper, the EC effect has been quantified directly and precisely by measuring the thermal energy exchanged under isothermal conditions using a modified Differential Scanning Calorimetry (DSC) apparatus. The DSC technique allowed comparing the EC properties in the vicinity of ferroelectric- paraelectric phase transition in both high-dielectric-constant pyroelectric ceramics and single crystals of the same formulation. It is showed that although having a much higher pyroelectric coefficient, single crystals exhibit very close ECE compared to ceramics. Indeed, the ECE is around 0.2J/g for an electric field step of 2.5kV/mm for both crystals and ceramics, but the pyroelectric coefficient of ≪111≫ single crystal is found to be around 1300 pC.m-2. K-1 where it is limited to 750 pC.m-2.K-1 for ceramic. This observation is discussed in the paper. View full abstract»

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