bluuebunny/crossref_metadata_2025 huggingface dataset:
High Electron Mobility SiGe/Si Transistor Structures on Sapphire Substrates
Authors: Alterovitz Samuel A. , Mueller Carl H. , Croke Edward T. , Ponchak George E.
Published: April 2011

SiGe/Si n-type modulation doped field effect structures and transistors (n-MODFETs) have been fabricated on r-plane sapphire substrates. The structures were deposited using molecular beam epitaxy, and antimony dopants were incorporated via a delta doping process. Secondary ion mass spectroscopy (SIMS) indicates that the peak antimony concentration was approximately 4×1019 cm−3. The electron mobility was over 1,200 and 13,000 cm2/V-sec at room temperature and 0.25 K, respectively. At these two temperatures, the electron carrier densities were 1.6 and 1.33×1012 cm−2, thus demonstrating that carrier confinement was excellent. Shubnikov-de Haas oscillations were observed at 0.25 K, thus confirming the two-dimensional nature of the carriers. Transistors, with gate lengths varying from 1 micron to 5 microns, were fabricated using these structures and dc characterization was performed at room temperature. The saturated drain current region extended over a wide source-to-drain voltage (VDS) range, with VDS knee voltages of approximately 0.5 V and increased leakage starting at voltages slightly higher than 4 V.
Integration of III-V Optoelectronic Components on Si Platform
Authors: Katsnelson Alex , Tokranov Vadim , Yakimov Michael , Oktyabrsky Serge
Published: April 2011

A method for hybrid integration of III-V optoelectronic components on Si substrate using BCB was demonstrated. The method included bonding, selective wet etching of the GaAs substrate, components separation by wet etching, two-level metallization and lateral oxidation to form optical apertures. Simulations of thermal behavior and mechanical stresses of this integration scheme were performed using finite element analysis, which revealed adequate heat dissipation. Simulations show that this bonding protocol allows reduction of overheating and mechanical stress that enhances the optoelectronic device performance and increases reliability. Electro-luminescence spectrum, I-V and P-T characteristics were measured and compared with a reference homoepitaxial structure and the results of the simulations. Measured thermal impedance was found to be less then two times higher than that for the devices on a host GaAs wafer. Novel method of substrate removal named oxidation lift-off was proposed and demonstrated. This process allows to release a VCSEL structure with epitaxial DBRs and separate individual components on Si, reduces the number of process steps and eventually reduces cost of the fabricated devices. Au/Ge alloy was used for the metal bonding of the test oxidation lift-off structure. Substrate removal, device separation, bonding and formation of the oxide apertures were done within a single processing step.
Site controlled nucleation of ferroelectric crystals: a step towards lithography modulated self-assembly
Authors: Muralt P. , Bühlmann S. , Von Allmen S.
Published: April 2011

An additive technique for the growth of PZT crystallites in the sub-200 nm range on predefined sites is presented. The method is based on nucleation promotion by TiO2 seeds. Epitaxial (111)-oriented Pt on a SrTiO3 single crystal served as substrate. TiO2 seed sites have been defined by an e-beam lithographic process. The initial Pb flux determines whether (100) or (111) crystallites are obtained. Best results have been obtained with PZT(100) yielding one square grain per site with a narrow size distribution (120 to 150 nm). In this case, the seed collected additional PbO adatoms reaching the seed by diffusion. The sidewalls consist mostly of {110} facets. A model in the frame of classical nucleation theory describes well experimental observations. The piezoelectric response and the ferroelectric switching of the structures have been verified.
Preparation and Characterization of Ferroelectric Bi3TiNbO9-Bi4Ti3O12 (m =2–3) Thin Films with Different Superlattice Structures
Authors: Shibuya Akira , Noda Minoru , Okuyama Masanori
Published: April 2011

Natural-superlattice-structured Bi3TiNbO9–Bi4Ti3O12 (m =2–3) (BTN–BIT) films have been grown on Pt/TiO2/SiO2/Si substrates at 400 °C to 550 °C by pulsed laser deposition (PLD) using BTN–BIT (1 mol:1 mol) target, and were post-annealed in O2 for 45 minutes at 750 °C. BTN–BIT films prepared above 500 °C have single phase whose c lattice parameter is estimated to 8.300 nm in consideration of periodicity of lattice structures. This lattice constant is very close to the value (8.316 nm) of that of two unit cells of BTN and one unit cell of BIT, that is 2–1 superlattice structure of BTN–BIT. The BTN–BIT film with 2–1 superlattice structure has large remanent polarization (2Pr = 50 μC/cm2) and large coercive field (2Ec= 350 kV/cm). La-doped BTN–BIT thin film has also large remanent polarization (2Pr = 52 μC/cm2) and relatively small coercive field (2Ec= 220 kV/cm). The La-doped BTN–BIT film is fatigue-free on Pt electrodes up to 1010 switching cycles.
Structural and Electrical Investigations of Ferroelectric Lead Strontium Titanate Thin Films and Ceramics
Authors: Jain M. , Bhattacharya P. , Yuzyuk Yu. I. , Katiyar R. S. , Bhalla A. S.
Published: April 2011

Lead strontium titanate (PbxSr1-xTiO3) (x=0.3–1.0) ceramic targets were prepared by the conventional powder-processing method. Thin films of these compositions were deposited on platinized silicon substrates by pulsed laser deposition technique. X-ray diffraction studies of the ceramic targets showed that the lattice structure changes from tetragonal to cubic phase with the increase of Sr content in PbTiO3. Raman spectroscopic studies of PbxSr1-xTiO3(PST) ceramics and thin films showed that the soft mode decreases to lower frequency and finally disappear at around 60–70 at% Sr content, which confirms the tetragonal to cubic phase transition at room temperature. Dielectric constant measured for PST thin films was in the range of 900–1500 at 1 MHz, with maximum value obtained for PST30 thin film. The loss tangents at room temperature were in the range of 0.07–0.1 for PST thin films with different compositions.
Mist Deposition of Micron-Thick Lead Zirconate Titanate Films
Authors: Losego Mark D. , Trolier-McKinstry Susan
Published: April 2011

A majority of the work published on liquid source misted chemical deposition (LSMCD) has focused on the fabrication of thin ferroelectric films for random access memory (RAM) applications. However, the ability of LSMCD to combine the characteristically good stoichiometry control of a chemical solution deposition process with good film conformality, makes this a desirable technique for other applications, including microactuators and integrated passive components. For these applications, though, LSMCD is limited by its low throughput. This paper describes the feasibility of depositing micron-thick lead zirconate titanate (PZT) films using the LSMCD tool. PZT films of 52/48 composition were deposited on both platinized silicon and platinized alumina substrates. The chamber temperature and the delivery geometry of the LSMCD tool were identified as limiting factors in the rate at which micron-thick samples can be prepared. By switching to a focused nozzle delivery geometry and increasing the chamber temperature from room temperature to 60°C, the total process time for 1 μm thick films can be reduced from 480 min to 90 min. Polarization hysteresis measurements indicated a 75% higher remanent polarization for PZT films deposited on platinized alumina substrates (35 μC/cm2) compared to those deposed on platinized silicon substrates (20 μC/cm2). The polarization loop for the silicon substrate sample was also tilted. These observations are evidence of higher tensile stresses in the PZT films deposited on silicon substrates due to a larger mismatch in the thermal expansion coefficients of the film and the substrate.
The Synthesis and Structure of New Perovskite-type Niobate Processed in Millimeter Wave Field
Authors: Liu Hanxing , Zou Long , Zhou Jian , Yuan Guangjiang , Hua Hua , Luo Dabing , Luo Jirun , Ouyang Shixi
Published: April 2011

In present paper a new niobate materials Ba5LixTixNb10-xO30 were synthesized by doping Li+ in the system BaO- TiO2- Nb2O5 in millimeter wave field. X-ray diffraction (XRD) quantitative and scanning transition spectroscopy (SEM) analysis were employed to study crystal structure and microstructure of reaction products. It was found that pure products could be obtained at temperature 900°, 8 min which is lower comparing with that by conventional method. The XRD data shown the crystal belongs to tetragonal tungsten bronze structure with space group P4bm. The grain size synthesized in millimeter wave field had smaller size, narrower distribution, better sinter-ability, and without hard agglomeration comparing whit that obtaining from conventional synthesis. At lower temperature Ba5LiTiNb9O30 is a tetragonal ferroelectric phase.
Ir Thin Films for PZT Capacitors Prepared by MOCVD Using a New Ir Precursor
Authors: Fujisawa H. , Watari S. , Shimizu M. , Niu H. , Oshima N.
Published: April 2011

Preparation of Ir thin films for PZT capacitors by MOCVD using a new liquid Ir precursor, Ir(EtCp)(CHD) was investigated. Ir thin films with a highly reflecting surface and (111)-orientation were successfully obtained at 230–400 C. When Ir(EtCp)(CHD) was used, shorter incubation time (20min at 230°C and not observed above 240°C) and higher nucleation density (300–400mm-2at 250–300°C) were observed because of its lower decomposition temperature (300°C) than that of previously reported liquid precursor, Ir(EtCp)(COD). Resistivity of 100nm-thick Ir films grown at 250–350°C were less than 20μΩ·cm. PZT capacitors with top and bottom electrodes prepared using Ir(EtCp)(CHD) showed D-E hysteresis loop with Pr of 15μC/cm and Ec of 60kV/cm. No degradation of switching up to 10 switching cycles by bipolar pulses of ±231kV/cm (±3V) and 500kHz.
MOCVD of Ferroelectric Thin Films
Authors: Rice C. E. , Sun S. , Cuchiaro J. D. , Provost L. G. , Tompa G. S.
Published: April 2011

We have examined the growth of a number of important ferroelectric oxides by MOCVD using a rotating disk reactor. Highly uniform and reproducible films over 6” wafers have been routinely achieved. Materials include Lead Zirconate Titanate (PZT, PbZrxTi1-xO3), Lead Lanthanum Zirconate Titanate (PLZT), Strontium Bismuth Tantalate (SBT), CeMnO3 (CMO), and others. Emphasis has been on achieving highly crystalline and oriented films at the lowest deposition temperatures possible, for compatibility with other integrated device materials and processing; and the achievement of optimum ferroelectric and pyroelectric performance. The effects of varying growth parameters, barrier and/or template layers, and post-growth annealing have been studied. The growth process, physical characterization, and ferroelectric film properties will be discussed.
Enhancement of Aurivillius Phase Formation Kinetics in SBT Thin Films using Nanoparticle Seeding
Authors: Sung Yun-Mo , Kwak Woo-Chul , Jung Se-Yon , Hwang Seung-Joon
Published: April 2011

Pt/Ti/SiO2/Si substrates seeded by SBT nanoparticles (∼60–80 nm) were used to enhance the phase formation kinetics of Sr0.7Bi2.4Ta2O9 (SBT) thin films. The volume fractions of Aurivillius phase formation obtained through quantitative x-ray diffraction (Q-XRD) analyses showed highly enhanced kinetics in seeded SBT thin films. The Avrami exponents were determined as ∼1.4 and ∼0.9 for unseeded and seeded SBT films, respectively, which reveals different nucleation modes. By using Arrhenius–type plots the activation energy values for the phase transformation of unseeded and seeded SBT thin films were determined to be ∼264 and ∼168 kJ/mol, respectively. This gives a key reason to the enhanced kinetics in seeded films. Microstructural analyses on unseeded SBT thin films showed formation of randomly oriented needle-like crystals, while those on seeded ones showed formation of domains comprised of directionally grown worm-like crystals.
Residual Stress Effects in Ferroelectric Thin Films
Authors: Berfield T. A. , Sottos N. R. , Ong R. J. , Payne D. A.
Published: April 2011

Recent developments in soft lithographic patterning enable the integration of functional ceramic thin films on a chip, rather than by adding discrete components to the system. As integrated device applications push the characteristic length scale of materials smaller and smaller, surface and interface effects play an important role, producing significant scientific challenges to the characterization of mechanical properties, performance and reliability. In this paper, we investigate the complex roles of microstructure, interface effects and residual stresses on ferroelectric thin film performance. Pb(Zr0.53Ti0.47)O3 films ranging in thickness from 190 nm to 500 nm were deposited by a sequential build up of sol-gel derived thin layers onto platinized Si substrates. Residual stresses in the films after thermal processing were observed and calculated from laser reflectance measurements of wafer curvature. Field-induced displacements were then measured by interferometric methods for films with well-characterized residual stress states. Results indicate significant increases in film performance with a decrease in measured residual tensile stress.
High Pressure Deposition of Epitaxial PZT Thin Films on Sr(Nb)TiO3
Authors: Blanco O. , Heiras J. , Siqueiros J. M. , Martínez E. , Andrade E.
Published: April 2011

Epitaxial thin ferroelectric films of Pb(Zr0.53Ti0.47) (PZT) were successfully grown on Sr(Nb)TiO3(SNTO) single crystal substrates by high-pressure rf sputtering. Pure O2was used as working gas at a pressure above 1 Torr. Deposition temperature was varied from 550°C to 600°C. Under these conditions we were able to deposit films at a rate of 2.7 Å/min. Their crystalline properties, evaluated by Θ/2Θ, ω and φ scans, showed both in-plane and out of plane orientation. Film composition and film-substrate interface characteristics were studied by Rutherford Backscattering Spectroscopy (RBS). For RBS data the composition ratios for the films were calculated having obtained the expected values for a stoichiometric composition. A very thin diffusion layer of Pb at the film-substrate interface was also introduced. However, the deficiency in Pb, which is correlated to the presence of oxygen vacancies, is lower in our films produced at high O2 pressure than those reported for films produced by sputtering at lower pressures. The ferroelectric hysteresis loops measured in the Pt/PZT/SNTO heterostructures show good ferroelectric behavior with remanent polarizations of 12μ Ccm-2and coercive field of 50kVcm-1at 5V. The high-pressured technique representing a useful and capable method capable of obtainingin situepitaxial, fully oxygenated, pyrochlore-free ferroelectric thin film with high quality structural, compositional and dielectric properties, without post deposit treatment.
Liquid injection MOCVD and ALD studies of “single source” Sr-Nb and Sr-Ta precursors
Authors: Potter Richard J. , Marshall Paul A. , Roberts John L. , Jones Anthony C. , Chalker Paul R. , Vehkamäki Marko , Ritala Mikko , Leskelä Markku , Williams Paul A. , Davies Hywel O. , Tobin Neil L. , Smith Lesley M.
Published: April 2011

A range of “single source” Sr-Nb and Sr-Ta heterometal alkoxides precursors are investigated as potential sources for liquid injection MOCVD (metalorganic chemical vapour deposition) and ALD (atomic layer deposition) of SrBi2Ta2O9 (SBT) and SrBi2(TxNb1-x)2O9 (SBTN). These “single source” precursors are designed to alleviate the mis-match between conventional Sr and Ta or Sr and Nb sources. Strontium-tantalate and strontium-niobate thin films were deposited on silicon using the “single source” alkoxide precursors [Sr{Ta(OEt)5(dmae}2] and [Sr{Nb(OEt)5(dmae)}2] (dmae = OCH2CH2NMe2), and the optimum temperatures for deposition of stoichiometric SrTa2O6 and SrNb2O6 were determined. Separate ALD studies of [Sr{Ta(OEt)5(dmae)}2] and [Sr{Ta(OEt)5(mee)}2] (mee = OCH2CH2OMe) for the growth of strontium-tantalate were carried out to assess precursor suitability for this technique. Liquid injection MOCVD of Bi-oxide films using Bi(mmp)3 indicates similar decomposition behaviour to the Sr-Ta and Sr-Nb alkoxides, demonstrating its suitability as a complementary source of Bi for SBT, SBN and SBTN.
Fabrication and Electrical Characterization of Ba(1-x)SrxTiO3 Based Thin Films
Authors: Ngo E. , Nothwang W. D. , Hubbard C. , Cole M. W. , Chang W. , Kirchoffer S. W. , Pond J. M.
Published: April 2011

Over the past several years there has been a tremendous growth and development of thin film deposition technology in the electronics industry. Ferroelectric thin films have been recognized for their unique dielectric properties and appear to be desirable for tunable microwave device applications. Among the most promising candidates for such applications are Ba(1−x)SrxTiO3[BST] and BST-based thin films. In this work pure BST and acceptor doped BST-based thin films were fabricated on (100) MgO substrates via pulsed laser deposition [PLD]. X-ray diffraction (XRD) in conjunction with the atomic force microscope (AFM) were used to analyze the film crystalinity and surface morphology. The dielectric properties were characterized at both 100 kHz and 20 GHz. The MIM capacitor configuration was used to attain the dielectric properties at 100 kHz and the microwave measurements, S11 reflection parameters, were achieved via interdigitated capacitor design with Au/Ag top electrodes. The parallel resistor-capacitor models were used to determine the microwave capacitance and Q factors and the permittivity was calculated using a modified conformal-mapping partial-capacitance method using the dimension of the capacitors. Our results demonstrated that the low frequency and microwave frequency dielectric properties were strongly influenced by the film composition. Specifically, the Mg doping served to lower the dissipation factor, permittivity, and tunability of the BST based films at both frequencies. This work demonstrates that the BST based thin films possessed excellent microstructural, structural, and dielectric properties. The structure-process-property correlations of the pulsed laser deposited BST and acceptor doped BST-based thin films are discussed in detail.
Microwave Properties of Parallel Plate Capacitors based on (Ba,Sr)TiO3 Thin Films Grown on SiO2/Al2O3 Substrates
Authors: Koutsaroff I. P. , Bernacki T. , Zelner M. , Cervin-Lawry A. , Kassam A. , Woo P. , Woodward L. , Patel A.
Published: April 2011

Ba0.7Sr0.3TiO3 (BST) single and quadruple layer capacitors with Pt electrodes were fabricated together on polycrystalline alumina substrates with a SiO2-based multicomponent amorphous buffer layer (SiO2/Al2O3). This paper presents the results of the characterization of these capacitors, to demonstrate their suitability for application as decoupling (high value) capacitors and as components in tunable RF applications (e.g., phase shifters and filters). BST films of different compositions, (Ba0.7Sr0.3)TiO3 and (Ba0.5Sr0.5)TiO3, were grown by metal-organic decomposition (MOD) and RF magnetron reactive sputtering. The capacitance density of 90–140 nm thick BST films was in the range of 20 to 70 fF/μm 2. Parallel plate capacitors with areas from 16 μm2 to 2.25 mm2 were fabricated using photolithography and ion milling techniques. For large capacitors (0.125 to 2.25 mm2), capacitance and tanδ were measured at low frequencies (1 KHz - 1 MHz) using an LCR meter. Smaller capacitors (16 μm2 to 3600 μm2) were additionally characterized in the frequency range of 50 MHz - 20 GHz. In such case, capacitance, tanδ and equivalent series resistance (ESR) were extracted from two port scattering parameters obtained using a vector network analyzer (VNA). The relationship between dielectric loss, tunability and calculated figure of merit vs. BST composition and deposition temperature was outlined. In addition, loss and ESR at high frequencies was investigated. The typical achieved leakage current density of sputtered BST films for 2.25 mm2 capacitors fabricated on SiO2/Al2O3 was 7.3×10-9 A/cm2 at 300 kV/cm (65 fF/μm2), about 2 times lower than for (Ba0.7Sr0.3)TiO3 films deposited by MOD (1.4×10-8 A/cm2 at 300 kV/cm, 34.5 fF/μm2). Furthermore, the tunability of (Ba0.7Sr0.3)TiO3 deposited by both methods on SiO2/Al2O3 was ∼60% at 350 kV/cm.
Synchrotron X-ray Microdiffraction Images of Polarization Switching in Epitaxial PZT Capacitors with Pt and SrRuO3 Top Electrodes
Authors: Do Dal-Hyun , Kim Dong Min , Eom Chang-Beom , Dufresne Eric M. , Isaacs Eric D. , Evans Paul G.
Published: April 2011

The evolution of stored ferroelectric polarization in PZT thin film capacitors was imaged using synchrotron x-ray microdiffraction with a submicron-diameter focused incident x-ray beam. To form the capacitors, an epitaxial Pb(Zr,Ti)O3 (PZT) thin film was deposited on an epitaxially-grown conductive SrRuO3 (SRO) bottom electrode on a SrTiO3 (STO) (001) substrate. Polycrystalline SRO or Pt top electrodes were prepared by sputter deposition through a shadow mask and subsequent annealing. The intensity of x-ray reflections from the PZT film depended on the local ferroelectric polarization. With 10 keV x-rays, regions of opposite polarization differed in intensity by 26% in our PZT capacitor with an SRO top electrode. Devices with SRO electrodes showed just a 25% decrease in the remnant polarization after 107 switching cycles. In devices with Pt top electrodes, however, the switchable polarization decreased a by 70% after only 5×104 cycles.
Polarization Reversal Model and Prediction of Temperature-Dependent Switching of Ferroelectric Capacitors
Authors: Stolichnov Igor , Tagantsev Alexander K. , Setter Nava , Cross Jeffrey S.
Published: April 2011

Temperature dependent performance of ferroelectric non-volatile memories is an important issue, that impacts memory device reliability. In general, the device temperature strongly influences the speed of polarization reversal in ferroelectric capacitors. In particular, the switching speed decreases with the decreasing temperature, which may give rise to incomplete switching. In the present work, the recently proposed Nucleation-Limited Switching model for ferroelectric thin films is extended for description of the temperature dependence of the polarization reversal. The model is shown to be valid for the temperature range important for memory applications. This model enables quantitative prediction of the switching performance of ferroelectric capacitors at different temperatures based upon results obtained at room temperature. The temperature and voltage range where the proposed concept is applicable is discussed in context of limits of validity of the Nucleation-Limited Switching model.
Low Voltage Operation of PZT Ferroelectric Film deposited by Liquid Source MOCVD
Authors: Nishioka Yutaka , Masuda Takeshi , Kajinuma Masahiko , Yamada Takakazu , Uematsu Masaki , Suu Koukou
Published: April 2011

Thin Pb(Zr, Ti)O3 films were grown on a 8-inch Ir(111)/SiO2/Si substrate by a liquid-source MOCVD system. These films showed dependency of ferroelectric properties on several deposition parameters. PZT single phase was obtained at a substrate temperature of 620°C. The film showed (111) preferred orientation and the Pt/Pb1.16(Zr0.45, Ti0.55)Ox(115nm)/Ir capacitors had excellent ferroelectric properties. The switching charge (Qsw) value (at 2V), saturation voltage (V90) and leakage current density (at 1.5V) were 47.4uC/cm2, 1.7V and 7.5E-8A/cm2 respectively. The capacitor made by using an IrOx top electrode had excellent fatigue-free property.
Comparative studies on BaZrxTi1-xO3thin films deposited by Sol-gel and Pulse laser deposition
Authors: Dixit A. , Bhattacharaya P. , Majumder S. B. , Katiyar R. S. , Bhalla A. S.
Published: April 2011

Ferroelectric thin films of BaZrxTi1-xO3(BZT) were deposited on platinum (Pt) and platinized silicon (Pt/Si) substrates by sol-gel and pulse laser deposition technique respectively. The structure and preferred orientation of the films were examined by x-ray diffraction measurements. The phase formation of sol-gel derived BZT films were found to be at high temperature (1100°C) compare to the pulse laser deposited BZT films ∼ 700°C. Polycrystalline films were observed by both techniques. Ferroelectric nature of the films was confirmed by hysteresis and capacitance-voltage characteristics using platinum top electrodes. Dielectric constant as well as loss was found to decrease by increasing Zr contents. Surface morphology predicted smooth crack free surface.
Temperature Dependent Raman Scattering and Dielectric Permittivity Measurements of Pb1−x Srx TiO3 Films
Authors: Naik V. M. , Smith M. , Dai H. , Talagala P. , Naik R. , Auner G. W. , Mantese J.
Published: April 2011

Pb1-x Srx TiO3 (x = 0 to 1.0) films of thickness ∼ 4 μ m have been prepared on sapphire and Pt substrates by metalorganic decomposition (MOD) method. X-ray diffraction results show that the films are polycrystalline with a perovskite tetragonal phase at room temperature for x < 0.5 and a cubic phase for x > 0.5. Room temperature Raman spectra show a systematic variation of lattice vibrational modes with x. The most notable changes in the Raman spectra with x are the decrease in the splitting of A1(3TO) and E(3TO) modes and the disappearance of E(3TO) mode at x ∼ 0.6. Although the x-ray diffraction peaks for films with x > 0.5 show a cubic phase at room temperature, the Raman spectra show the characteristic phonon modes of a tetragonal phase even at x = 0.7. The dielectric permittivity versus temperature measurements for films with x ≤ 0.7 show a broad dielectric anomaly corresponding to a diffuse ferroelectric to paraelectric phase transition. The phase transition temperature (Tc) values are consistently lower than the corresponding bulk ceramic alloys. Furthermore, Tc are also determined by monitoring the temperature dependence of the splitting between E(3TO) and A1(3TO) phonon modes in the Raman spectra of Pb1-x Srx TiO3 films for x ≤ 0.6. There has been good agreement between the two methods.
Highly Efficient Piezoelectric Actuators for Active Vibration Control
Authors: Colla Enrico L. , Suyal Ganesh , Gentil Sandrine , Setter Nava
Published: April 2011

An high performance / inexpensive diskbender actuator was produced by combining efficient design and fabrication methods and a new technique to operate these actuators was developed and tested, which can enhance the displacement and force capabilities by almost a factor of 2 by using the same maximal driving voltage.

The properties of these actuators are intermediate between those of standard bimorphs, used for very large displacements but providing rather small forces, and those of low voltage stack multilayers, which provide quite large forces but are generally heavier, larger and expensive for equivalent displacements. The absence of any external mechanical amplification mechanism and their geometry make these actuators particularly suitable for active vibration damping applications within buildings affected by perturbations of hundreds of μm or for noise control by emission of controlled sound in antiphase. The class of displacement/force, which can be obtained with suitably dimensioned actuators, provides sufficient high motion even for the lower audio frequency region (400–1500 Hz).

In order to lower the driving voltages, multilayer diskbenders were also fabricated with the same technique. The number of layers does not influence the actuator displacement and force properties but the increased capacity of the actuator may require sophisticated driving amplifiers.
50 Years Of Piezoelectric Transformers. Trends In The Technology
Authors: Vázquez Carazo Alfredo
Published: April 2011

The initial concept of a piezoelectric transformer (PT) was proposed by C.A. Rosen, K. Fish, and H.C. Rothenberg and is described in the U.S. Patent 2,830,274, applied for in 1954. Fifty years later, this technology has become one of the most promising alternatives for replacing the magnetic transformers in a wide range of applications. Piezoelectric transformers convert electrical energy into electrical energy by using acoustic energy. These devices are typically manufactured using piezoelectric ceramic materials that vibrate in resonance. With appropriate designs it is possible to step-up and step-down the voltage between the input and output of the piezoelectric transformer, without making use of wires or any magnetic materials.

This technology did not reach commercial success until early the 90s. During this period, several companies, mainly in Japan, decided to introduce PTs for applications requiring small size, high step-up voltages, and low electromagnetic interference (EMI) signature. These PTs were developed based on optimizations of the initial Rosen concept, and thus typically referred to as “Rosen-type PTs”. Today's, PTs are used for backlighting LCD displays in notebook computers, PDAs, and other handheld devices. The PT yearly sales estimate was about over 20 millions in 2000 and industry sources report that production of piezoelectric transformers in Japan is growing steadily at a rate of 10% annually. The reliability achieved in LCD applications and the advances in the related technologies (materials, driving circuitry, housing and manufacturing) have currently spurred enormous interest and confidence in expanding this technology to other fields of application. This, consequently, is expanding the business opportunities for PTs.
Optical Constants of Vanadium Dioxide Films and Design of a Solar Energy Control Window
Authors: Tazawa Masato , Asada Hideo , Xu Gang , Jin Ping , Yoshimura Kazuki
Published: April 2011

We determined the optical constants of a vanadium dioxide (VO2) thermochromic film deposited on glass substrate by ellipsometry in wavelength range from 380 nm to 1700 nm. The optical constants were employed to design the optimal stacked thin film structure for smart windows which control the solar radiation and heat transmission from the viewpoint of high luminous transmission.
Piezoresistive Properties of Ceramic Strain Sensors with Controlled Nanoporosity
Authors: Gregory Otto J. , You Tao
Published: April 2011

A ceramic strain gage based on reactively sputtered indium tin oxide thin films is being developed to monitor the structural integrity of components employed in aerospace propulsion systems that operate at temperatures in excess of 1500°C. When relatively thick indium-tin-oxide (ITO) strain gages were prepared by reactive sputtering in oxygen:argon atmospheres and annealed in nitrogen, an extremely stable piezoresistive response was observed at temperatures as high as 1530°C. SEM and AFM of these sensor surfaces after high temperature exposure revealed a partially sintered microstructure with interconnected nanoporosity. Specifically, the microstructure consisted of a contiguous network of uniform sized ITO particles with well-defined necks between individual particles. When these microstructures were compared to those of relatively thin ITO sensors sputtered in nitrogen:argon:oxygen atmospheres, i.e. ITO films prepared in a nitrogen rich plasma, the average pore size and particle size was estimated to be an order of magnitude smaller than those associate with thick ITO sensors. In the nitrogen sputtered films, enhanced electrical conduction along the surfaces of the contiguous ITO particles resulted in a very stable and large piezoresistive response with a gage factor of 11.4 and a drift rate of 0.0001%/hour at 1560°C. The improved performance realized when the ITO films were processed in nitrogen may be extended to other ITO based sensors including gas sensors and the advantages of films processed in this manner will be discussed.
Simulations of High-Strain Electrostrictive Chlorinated Terpolymers
Authors: Kavarnos George J. , Ramotowski Thomas
Published: April 2011

Chlorinated poly(vinylidene fluoride/trifluoroethylene) terpolymers are remarkable examples of high strain electrostrictive materials. These polymers are synthesized by copolymerizing vinylidene fluoride and trifluoroethylene with small levels of a third chlorinated monomer. The electromechanical responses of these materials are believed to originate from the chlorine atom, which, by its presence in the polymer chains and by virtue of its large van der Waals radius, destroys the long-range crystalline polar macro-domains and transforms the polymer from a normal to a high-strain relaxor ferroelectric. To exploit the strain properties of the terpolymer, it is desirable to understand the structural implications resulting from the presence of the chlorinated monomer. To this end, computations have been performed on model superlattices of terpolymers using quantum-mechanical based force fields. The focus has been on determining the energetics and kinetics of crystallization of the various polymorphs that have been identified by x-ray diffraction and fourier transform infrared spectroscopy. The chlorinated monomer is shown to act as a defect that can be incorporated into the lamellar structures of annealed terpolymer without a high cost in energy. The degree of incorporation of the chlorinated monomer into the crystal lattice is controlled by annealing conditions and ultimately determines the ferroelectric behavior of the terpolymers.
Effect of piezoelectric vibration on electrical properties of YSZ film prepared by MOCVD
Authors: Masumoto Hiroshi , Goto Takashi
Published: April 2011

To improve electric properties of ion-conductors at low temperatures, ion-conducting/piezoelectric multifunctional film was prepared. Yttria-stabilized zirconia (YSZ) film as an ion-conducting film was deposited on a MgO substrate by metal-organic chemical vapor deposition (MOCVD). The significant [100] preferred orientation of cubic-YSZ single-phase film c ontaining 8 mol%Y2O3 was obtained at a deposition temperature of 973 K. The film consisted of fine grains of about 400 nm in diameter and had a columnar structure. It was capable of ionic conduction, as shown by the fact that a semicircle and a spike appeared at high and low frequencies, respectively, in the complex impedance measurement. The obtained YSZ thin film was placed on a multilayer piezoelectric actuator composed of seven sheets of a PZT (lead zirconate titanate) system. The effect of piezoelectric vibration on the electric properties of the ion-conducting film was investigated. The impedance value of the YSZ thin film decreased with increasing amplitude of piezoelectric vibration. The electrical conductivity of the YSZ thin film at 353 K, with an applied vibration frequency of 115 kHz and a voltage of 40 V, was about 2×10-4 Sm-1. The value of this conductivity was 103 times greater than that without vibration. Vibration by the actuator was thus suggested to improve the ionic conduction of the YSZ thin film.
PZT-Driven Micromagnetic Optical Devices
Authors: Takagi H. , Park J. H. , Mizoguchi M. , Nishimura K. , Uchida H. , Lebedev M. , Akedo J. , Inoue M.
Published: April 2011

A magneto-optic spatial light modulator (MOSLM) driven by electric field is presented. Using finite element method simulation, the parameters of the MOSLM are decided including the 1 μm piezoelectric lead zirconate titanate (PZT)-based layer, the 200 nm bottom electrode, and the 8V electrical applied voltage. A flat surface magneto-optical bismuth-substituted iron garnet (Bi:YIG) based film having an array-pixels structure was created by a site-selected epitaxial method on a SGGG-based substrate. In order to avoid high temperature annealing process which may damage the Bi:YIG film, the PZT film was deposited by the aerosol deposition method (ADM) on the Bi:YIG film. By stress field induced by the PZT film to the Bi:YIG film with an external magnetic field, the pixels of the device were successfully switched.
Phase Stability of Single Crystalline Co-Ni-Ga Shape Memory Alloy
Authors: Schlagel Deborah L. , Lograsso Thomas A. , Pecharsky Alexandra. O.
Published: April 2011

Single crystals of Co48Ni22Ga30 have been synthesized using a modified Bridgman method. The ability to solidify and retain single phase B2 austenite was found to depend not only on the starting composition and growth rate, but also the ability to maintain sufficiently high cooling rates to avoid the precipitation of a Co-rich FCC phase during post-solidification cooling. DSC measurements on the single crystal found the Ms, Mf, As, and Af to be 35.7°C, -1.8°C, 34.1°C and 72.2°C, respectively. On subsequent heating the B2 phase was found to partially decompose into the Co-rich phase at temperatures exceeding 380°C. Decomposition of the single phase B2 phase was tracked by microstructural observation, DSC, powder diffraction and low temperature heat capacity measurement. Restoration of the crystal to single phase B2 austenite required annealing of the crystal at temperatures above 1125°C followed by rapid cooling.
High Transition Temperature Shape Memory Alloys for Micro-actuator Systems
Authors: Baldwin Elizabeth , Rabiei Afsaneh
Published: April 2011

A new generation of thin film shape memory alloy (SMA) for MEMS micro-actuator has been developed, in which film structure and chemistry are optimized, for enhanced higher transition temperature, higher strain recovery rate as well as reduced actuation time by improving the heat transfer rates. Thin film TiPdNi was produced using Ion Beam Assisted Deposition (IBAD) technique both by in-situ heat treating during deposition and followed by post processing heat treatment. Films deposited on unheated substrates were found to be highly amorphous with minimal B2 austenite crystallization, while films deposited on heated substrates produced a highly crystallized twinned B19 martensitic structure through the bulk of the film. For films deposited on heated substrates, a 70 nm thick transition layer was found to exist between the bulk film and silicon substrate. Severe delamination and oxidation as a result of post heat treatment on IBAD deposited samples made in-situ heat treatment most suitable for processing thin film SMAs for MEMS applications. The desire to introduce this innovative technology to the field of SMA micro-actuators is based on two primary advantages of IBAD process over existing technology used to apply thin film SMAs. First, the chemical composition and grain size of the applied coating can be precisely controlled over a wide range of values. Second, the SMA can be deposited as thin films ≤ 2 μm thick with smaller grain size, much denser than films applied using sputter deposition technology. The effects of various processing parameters, and post processing heat treatment, on properties of the thin film SMA were studied.
Ionic Polymer-Metal Composites as Smart Materials under Subzero Temperature Conditions
Authors: Paquette Jason W. , Kim Kwang J.
Published: April 2011

This paper presents a description of Ionic Polymer-Metal Composites (IPMCs) as an attractive solution for cold operation actuators. This is because of their capability for actuation with relatively low voltages (1 to 5 V), durability and capability of operating within the subzero regime T < 0 °C. The building block material of IPMCs experiences phase changes within the base polymeric material that results in an alteration of the performance of the material in terms of actuator performance. An experimental apparatus is constructed in order to have a controlled temperature environment in which to analyze the material. The overall temperature within the reservoir, the temperature on the IPMC surface electrodes, the conductivity of the membrane and the blocking force were all measured. The phase changes inherent at these low temperatures are investigated further by means of Differential Scanning Calorimeter to obtain the phase change temperatures and characteristics. The results are presented and interpreted to show that there is definite promise for these low temperature polymeric actuators to operate in practical applications.
Hybrid Actuation in Coupled Ionic / Conducting Polymer Devices
Authors: Bennett Matthew D. , Leo Donald J.
Published: April 2011

Ionic polymer membrane actuators represent a relatively new and exciting entry into the field of smart materials. Several key limitations of these transducers have prevented them from experiencing widespread use, however. For example, the bandwidth of these devices is limited at very low frequencies by characteristic relaxation and at high frequencies by the low elastic modulus of the polymer. In this paper, an overview of the initial results of work with hybrid ionic / conducting polymer actuators is presented. These hybrid actuators are devices that combine the electromechanical coupling of ionic polymer actuators and conducting polymer actuators into one coupled device. Initial results show that these hybrid devices have the potential to offer marked advantages over traditional ionic polymer membrane transducers, including increased stress and strain generation and higher actuation bandwidth. Details of the preparation of these devices and performance metrics are presented and comparisons to baseline materials are made.
In-Situ Characterisation of Photo-actuating and Photo-rheological Polymers
Authors: Sabey Chris J. , Moniruzzaman M. , Fernando Gerard F. , Badcock Rodney A. , Winter Darren , Akhavan Jackie , Kronfli Esam , Bandara A.
Published: April 2011

This paper reports on the design and validation of three in-situ measurement techniques for characterisation of photo-rheological and photo-actuation phenomena. Results from these in-situ techniques are presented and used to investigate isomerisation and recovery effects in azobenzene and spiropyran polymer systems with and without flexible spacer groups.

A new in-situ technique for the measurement of photo-viscosity effects in polymer solutions has been developed using a cone and plate rheometer. The new technique permits simultaneous irradiation of the photo-responsive polymer solutions and continuous measurement of its viscosity in a controlled environment. An additional benefit of the technique is the greatly reduced sample volume compared to traditional capillary viscometers.

Techniques for the in-situ measurement of the photo-actuation effect in polymer systems are discussed, including image analysis and interferometric methods. The effects of environmental factors such as temperature are considered and steps taken to minimise them. The resulting measurement techniques provide an accurate means of measuring the effect of irradiation on the photo-actuating polymers in solution and as solids.

A range of polymers with photo-responsive azobenzene and spiropyran groups in the polymer side chains have been synthesised and evaluated using these three techniques. The photoviscosity and photo-actuation effects under irradiation have been measured in a variety of solvents. The effect of incorporating a flexible spacer group in the side chain of the azobenzene polymers is examined and its effect on the photo-rheology mechanism is discussed.
Preparation and Properties of the Novel Nanocrystal and Polymer Composite Films for Electro-Optic Applications
Authors: Ren Quan , Xu Dong , Chow Yuktak , Chan Hauping , Chu Paklim
Published: April 2011

Novel nanocrystals and polymer composite thin films for the applications of electro-optical devices were prepared. We used PbTiO3 nanocrystals as a nonlinear chromophore (guest) in the NLO polymer system. The transparent polymer polyetherketone (PEK-c) was chosen as the polymer host due to its high glass transition temperature. The PbTiO3 nanocrystals were synthesized successfully by the chemical solution decomposition method. The size of the PbTiO3 nanocrystals was estimated to be 30–40 nm. The weight ratio of PbTiO3 nanocrystals to polymer polyetherketone was 15 %. The composite thin films of PbTiO3 / PEK-c were prepared by spin-coating technique. The films were then electrically poled to induce asymmetry in the material by heating the films to a temperature close to their glass transition and applying an electric field. The refractive indices of the un-poled composite PbTiO3 / PEK-c film were found to be 1.55165 for 633 nm and 1.65352 for 414 nm by using the Metricon prism coupling system. In the poled composite PbTiO3 / PEK-c film sample, the TE- and TM-indices differences were found to be 0.02945 for 633 nm and 0.03915 for 414 nm, showing very good optical anisotropy properties. Dielectric constant ε of the film was determined to be 7.32 at room temperature at 100 KHz using an Impedance Analyzer. The electro-optic coefficient, γ33, of poled PbTiO3 / PEK-c composite film was measured to be 18.34 pm/Vat 633 nm under room temperature by the simple transmission technique. The factor F2 = n7 γ2 /ε, figures of merit, was estimated to be 1546. The relaxation time constant was calculated to be 5836 min.
Novel Actuating System Based on a Composite of Single-Walled Carbon Nanotubes and an Ionomeric Polymer
Authors: Levitsky Igor A. , Kanelos Peter T. , Euler William B.
Published: April 2011

We report the fabrication and characterization of a novel composite material based on single walled carbon nanotubes (SWNT)s and the ionomeric polymer Nafion. SWNTs were airbrushed from a chloroform suspension onto both sides of a Nafion membrane (180 μm) and the electromechanical properties of the composite material were explored. The outer layers of carbon nanotubes acted as electrodes in order to pass electrical current through the system while the mechanical response was monitored. Under this design, the mechanical response could be characterized, with respect to the electrical signal, as a function of: voltage, waveform (AC vs. DC), and frequency (AC). Data was also compiled to gauge the effect of size and thickness of each individual layer of the system. The reference samples (graphite-Nafion and sputtered gold-Nafion) did not exhibit mechanical actuation at the same conditions. An analytical model for current decay was considered that is in agreement with the experimental data. Bi-exponential decay with a long time component was found for bias, which is above the actuating threshold. That was explained in terms of increasing of the water dielectric constant and polymer-SWNT interface area. The possible mechanisms of the actuation in this novel composite are discussed.
Production of high quality single-walled carbon nanotubes in a nano-agglomerated fluidized bed reactor
Authors: Wang Qixiang , Ning Guoqing , Wei Fei , Luo Guohua
Published: April 2011

ABSTRACTS

Single-walled carbon nanotubes (SWNTs) have attracted much attention due to their unique structural, mechanical, chemical, and electrical properties. Catalytic chemical vapor deposition (CCVD) through decomposition of hydrocarbons is one of the most challenging synthesis methods to produce SWNTs in large scale. In this paper, high quality SWNTs prepared in a nano-agglomerated fluidized bed reactor (NAFBR) was reported. The reactor is a vertical quartz tube with the inner diameter of about 50 mm. Catalysts nanoparticles used for the production of SWNTs were prepared with Fe metal nanoparticles carried on the surface of MgO. About 150g catalysts powders were loaded on the gas distribution grid. The reaction temperature was controlled at not less than 1123 K. The carrier gas of argon was used to maintain turbulent fluidization of the catalysts powders in FBR. The hydrogen gas was used to reduce the catalysts and to synergize the growth of SWNTs with methane. The powder products were spherical agglomerates of SWNTs bundles tangling with the catalysts particles. By optimizing the process parameters of CCVD, the products of SWNTs with the diameter about 0.9 ∼ 1.8 nm were prepared, without any multi-walled carbon nanotubes (MWNTs) or amorphous carbon. The microstructure of SWNTs products were characterized by the methods of high resolution transmission electron microscopy (HRTEM), scanning electron microscopy (SEM), Raman spectra, etc. The NAFBR is a commercially viable (effective and continuous production at a low cost) process for the production of SWNTs.