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Item Open Access Asymmetry of domain forward switching and multilevel relaxation times of domain backswitching in antiferroelectric Pb0.99Nb0.02(Zr0.84Sn0.12Ti0.04)0.98O3 thin films(American Institute of Physics, 2007-04) Jiang, A. Q.; Lin, Y. Y.; Tang, T. A.; Zhang, QiPb0.99Nb0.02(Zr0.84Sn0.12Ti0.04)0.98O3 thin films demonstrate a double hysteresis loop characteristic of antiferroelectric behavior with film thickness at above 150 nm, but only one branch of the loop is present in films that are 90 nm thick. The relaxation time of domain backswitching from ferroelectric into antiferroelectric is multistaged in a range of 100 ns–100 ms, but it is less than 100 ns in the films without Sn and Nb dopants. Electrical modeling of the films composed of elementary regions with inhomogeneities of dielectric constant, conductivity, and polarization embodies the essence of charge injection for the compensation of local backswitching field of domains.Item Open Access Development of residual stress in sol-gel derived Pb(Zr,Ti)O3 films: An experimental study(American Institute of Physics, 2008-04-30T00:00:00Z) Corkovic, Silvana; Zhang, QiResidual stresses develop in the sol-gel-derived ferroelectric thin films during the transformation of the metalorganic gel to the metal oxide upon thermal treatment and due to the thermal and elastic mismatch between the Pb(Zrx,Ti1-x)O3 (PZT) film and the substrate materials during cooling. In this study, residual stresses were determined using the wafer curvature method after the deposition of multilayer PZT film on platinized (100) silicon wafers. A multilayer model for stress analysis was used to calculate the residual stress in PZT films of three different compositions, x=0.4, x=0.52 and x=0.6. Orientation dependent residual stresses were found in compositions containing the tetragonal phase, with x=0.4 and x=0.52. Depending on the fraction of (100) orientated domains low compressive or low tensile stress was found in Pb(Zr0.4Ti0.6)O3 (PZT 40/60). Higher residual stress was found in PZT films consisting of only rhombohedral crystallographic structure (PZT 60/40) while the residual stress in PZT films with morphotropic boundary composition (PZT 52/48) was significantly dependent on the film orientation and the phase composition and could range from 17 MPa to 90 MPa. The effect of the film orientation on residual stress was found to be a function of the anisotropic thermal expansion coefficient of PZT. The contribution of the thermal and elastic properties of materials to the total wafer curvature was investigated and discussed. Finally, the residual stress results calculated with the four layers model were compared to the results calculated using the Stoney equation.Item Open Access Enhanced pyroelectric coefficient of antiferroelectric-ferroelectric bilayer thin films(American Institute of Physics, 2009-12-31T00:00:00Z) Corkovic, Silvana; Zhang, QiIn this study, the pyroelectric coefficient and the figure of merit (FOM) of the ferroelectric PbZr0.3Ti0.7O3 (PZT 30/70) thin films were found to be greatly enhanced by introducing a thin antiferroelectric PbZr0.95Ti0.05O3 (PZT 95/05) layer underneath the ferroelectric film and thus creating a bi-layer structure on platinised silicon substrates. The film properties were investigated as a function of the ferroelectric layer thickness when the thickness of antiferroelectric layer remained unchanged. The highest pyroelectric coefficient of 1 mm thick PZT 30/70 film was 3.18 x10-4 Cm-2K-1. However, the highest pyroelectric coefficient for 1 mm thick bi-layer film was 3.5 x10-4 Cm-2K-1 or 2.5 x10-4 Cm-2K-1 for only 280 nm thick bi-layer film. The enhancement of pyroelectric coefficient suggests switching of antiferroelectric (AF) into ferroelectric (FE) phase during poling and following stabilization of FE phase at room temperature. The reduction of dielectric constant in bi-layer films after poling, compared to pure PZT 30/70, showed a FOM of 2.94 x10-5 Pa-0.5 which is the double of the FOM for pure PZT 30/70 films of similar thickness (1.45 x10-5 Pa-0.5).Item Open Access Fabrication and characterization of red-emitting electroluminescent devices based on thiol-stabilized semiconductor nanocrystals(American Institute of Physics, 2007-01-15T00:00:00Z) Bertoni, Cristina; Gallardo, Diego E.; Dunn, Steve; Gaponik, Nikolai; Eychmüller, AlexanderThiol-capped CdTe nanocrystals were used to fabricate light-emitting diodes, consisting of an emissive nanocrystal multilayer deposited via layer-by-layer, sandwiched between indium-tin-oxide and aluminum electrodes. The emissive and electrical properties of devices with different numbers of nanocrystal layers were studied. The improved structural homogeneity of the nanocrystal multilayer allowed for stable and repeatable current- and electroluminescence-voltage characteristics. These indicate that both current and electroluminescence are electric-field dependent. Devices were operated under ambient conditions and a clear red-light was detected. The best-performing device shows a peak external efficiency of 0.51% and was measured at 0.35mA/cm2 and 3.3V.Item Open Access Giant electrocaloric effect in the thin film relaxor ferroelectric 0.9 PbMg1/3Nb2/3O3–0.1 PbTiO3 near room temperature.(American Institute of Physics, 2006-12) Mischenkoa, A. S.; Zhang, Qi; Whatmore, Roger W.; Scott, J. F.; Mathurb, N. D.We have recently observed a giant electrocaloric effect (12 K in 25 V) in 350 nm sol-gel PbZr0.95Ti0.05O3 films near the ferroelectric Curie temperature of 242oC. Here we demonstrate a giant electrocaloric effect (5 K in 25 V) in 260 nm sol-gel films of the relaxor ferroelectric 0.9 PbMg1/3Nb2/3O3 – 0.1 PbTiO3 near the Curie temperature of 60oC. This reduction in operating temperature widens the potential for applications in novel cooling systems.Item Open Access Growth and high frequency characterization of Mn doped sol-gel Pb xSr1-xTiO3 for frequency agile applications(American Institute of Physics, 2009-06) Fragkiadakis, Charalampos; Luker, Arne; Wright, Robert V.; Floyd, L.; Kirby, Paul B.In pursuit of thin film ferroelectric materials for frequency agile applications that are both easily adapted to large area deposition and also high performance, an investigation has been carried out into sol-gel deposition of 3% Mn doped (Pb0.4Sr0.6)TiO3. Large area capability has been demonstrated by growth of films with good crystallinity and grain structure on 4 in. Si wafers. Metal-insulator-metal capacitors have also been fabricated and development of an improved de-embedding technique that takes parasitic impedances fully into account has enabled accurate extraction of the high frequency dielectric properties of the PbxSr1−xTiO3 films. Practically useful values of ε ∼ 1000, tan δ ∼ 0.03, and tunability ∼ 50% have been obtained in the low gigahertz range (1–5 GHz). Peaks in the dielectric loss due to acoustic resonance have been modeled and tentatively identified as due to an electrostrictive effect with an electromechanical coupling coefficient of ∼ 0.04 at an electric field of 240 kV/cm which is potentially useful for tunable thin film bulk acoustic wave devices.Item Open Access High tunable dielectric response of Pb0.87Ba0.1La0.02 (Zr0.6Sn0.33Ti0.07) O3 thin film(American Institute of Physics, 2010-08-15T00:00:00Z) Correia, T. M.; Zhang, QiThe permittivity maximum of a sol-gel derived Pb0.87Ba0.1La0.02 (Zr0.6Sn0.33Ti0.07) O3 (PBLZST) thin film was observed to appear at Tm=70 ºC rather than at 40 ºC as observed in the bulk ceramics with the same composition. Measurements of permittivity vs. electric field (E) present two maximums at 60 (polarizing) and 25 kVcm-1 (depolarizing), corresponding to antiferroelectric- ferroelectric and ferroelectric-antiferroelectric phase transitions, respectively. Calculations of tunability and Figure-of-Merit (FOM) display a maximum value of 75% at E = 350 kV cm-1 and ~ 141, respectively. These high tunable dielectric responses imply that PBLZST thin films can be an attractive material for tunable device applicationItem Open Access In-plane excitation of thin silicon cantilevers using piezoelectric thin films(American Institute of Physics, 2007-10) Leighton, Glenn J. T.; Kirby, Paul B.; Fox, Colin H. J.This paper deals with the actuation of in-plane and out-of-plane motions of silicon cantilevers, using a single thin film of lead zirconate titanate with a divided electrode configuration. In-plane actuation is demonstrated practically, and excellent agreement is obtained between theoretically predicted and experimentally measured resonant amplitudes, for the fundamental out-of-plane and in-plane modes of vibration of the fabricated test cantilevers.Item Open Access Influence of ferroelectricity on the photoelectric effect of LiNbO3.(American Institute of Physics, 2008-09) Dunn, Steve; Tiwari, DivyaA comparison between the influence of domain dependent photochemical and photoelectric cation reduction on the surface of LiNbO3 is presented. The reduction of the photoelectric threshold for LiNbO3 due to the polar nature of the crystal allows high energy UV irradiation to produce free electrons that can participate in photochemical reduction of silver nitrate on the surface. This is in addition to the previously understood phenomenon of domain directed photophysics, where influences on space charge layer due to the internal dipole of a ferroelectric determine the carrier at the surface. We show that the interaction of photoelectric and domain dependent influences can be observed in LiNbO3 due to the low electron affinity (ca 2eV) and large band bending (0.8eV).Item Open Access Investigation of the electrocaloric effect in a PbMg2/3Nb1/3O3-PbTiO3 relaxor thin film(American Institute of Physics, 2009-05) Correia, T. M.; Young, J. S.; Whatmore, Roger W.; Scott, J. F.; Mathur, N. D.; Zhang, QiPermittivity measurements of a 0.93PMN-0.07PT thin film show a broad maximum near 35 °C, and an anomaly at the depolarizing temperature Td = 18 °C on heating only, suggesting a dipolar glass-relaxor phase transition. No structural phase transition at 18 °C is apparent from ferroelectric hysteresis loops taken on field cooling and field heating. These loops show the thermal hysteresis expected for ferroelectric relaxors, which has not hitherto been experimentally verified in PbMg2/3Nb1/3O3-PbTiO3 thin films. Our data suggest the intriguing possibility of a giant electrocaloric effect (ΔT = 9 K, ΔE = 720 kV cm−1) at and near room temperature.Item Open Access Nanosecond-range imprint and retention characterized from polarization-voltage hysteresis loops in insulating or leaky ferroelectric thin films(American Institute of Physics, 2011-10-03T00:00:00Z) Jiang, A. Q.; Liu, X. B.; Zhang, QiWe transferred ferroelectric domain switching currents under pulses into polarization-voltage (P-V) hysteresis loops. With this transformation, it is possible to derive the remanent polarization and coercive voltage from domain switching currents after the shortest imprint and retention time of 35 ns. After the separation of film leakage current from domain switching current, we measured the P-V hysteresis loop in a semiconducting BiFeO3 leaky thin film, where the apparent coercive field highly reaches 320 kV/cm2, suggestive of a different domain switching mechanism from other insulators. This technique facilitates nanosecond-range measurements of both ferroelectric capacitive and resistive memories.Item Open Access Pyroelectric effect enhancement through product property under open circuit condition(American Institute of Physics, 2009-07) Chang, Harrison Hoon Seok; Huang, ZhaorongAn analytical model for the pyroelectric (PY) effect under open circuit condition and 2-2 connectivity laminates of various pairs of PY and nonpyroelectric (NP)/elastic materials has been developed. It is evident from our analysis that there indeed is a substantial dissimilarity between the PY coefficients and figure of merit for efficiency for various PY-NP pairs under short circuit and open circuit conditions. We believe this implies that there should be a greater distinction made between the PY coefficients under these two electrical conditions than previously thought. The indicators for various PY-NP material pairs that can be utilized to determine their PY coefficient enhancement potential under open circuit condition have been identified. The investigated PY materials are lead zirconate titanate (PZT-5H and PZT-5A), barium titanate, lithium tantalate, lithium niobate, and polyvinylidene fluoride (PVDF), while the NP materials are stainless steel, polytetrafluoroethylene (PTFE or Teflon), chlorinated polyvinyl chloride thermoplastic (CPVC), aluminum, zinc, and Invar 36. Extraordinarily large PY coefficient of 97×10-4 C m-2 K-1 at minimum thickness ratio Rmin is expected for PZT-5H-CPVC pair while PVDF-CPVC could show increase in the secondary PY coefficient of up to 350%. In addition, where the figure of merit for efficiency is concerned, for the same volume of the composite PZT-5A-PTFE pair it reaches 24, a 24-fold increase in efficiency at Rmin. Our analysis techniques should provide a methodological way for appraising the potentials of particular PY material and its 2-2 laminates for applications under open circuit condition such as PY X-ray generation, electron accelerator, and nuclear fusion.Item Open Access Strain behavior of thin film PbZr0.3Ti0.7O3 (30/70) examined through piezoforce microscopy(American Institute of Physics, 2003-11) Dunn, SteveUsing an atomic force microscope (AFM) modified to perform PiezoAFM we have investigated the piezoelectric response of sol-gel thin film lead zirconate titanate (PZT 30/70, PbZr0.3Ti0.7O3) on Pt-Ti/SiO2/Si to a quasi DC electric field. The films were produced by spin coating a PZT 30/70 sol onto a selected substrate and firing at 520ºC. This generated a film that was highly [111] orientated and single phase perovskite. By applying a sinusoidal 2Hz AC waveform between the AFM cantilever and ground we have generated strain-field, or butterfly loops for the PZT film. PiezoAFM butterfly loops show that the localised piezoelectric response for PZT varies depending on the sign of the applied field. The degree of asymmetry in the hysteresis loop has been attributed to charge trapping at the electrode-PZT interface generating a system that can preferentially re-pole in one direction. The charge trapped at the interface has an overwhelming effect on the polarisability of the film. Coercive fields have been calculated from the minimum point of the strain before reversal for the system and are shown to be -30V/μm and +32V/μm in absolute terms and -23V/μm and +39V/μm in terms relative to the charge trapped at the electrode interface. δ33 values obtained for the PZT thin film 2 investigated ranged from 30 to 40pm/V. The maximum strain of the system was shown at applied biases of +/-10V and was 0.3% at a bias of +10V, although at this field the sample was not showing saturated behaviour. By relating the offset of the butterfly loops to the charge density generated by defects at the PZT-electrode interface, calculated to be 0.025Cm-2, an estimate of the number of defects at the interface has been drawn. The concentration of defects at the interface is 1 defect for every 6nm2 of surface, representing 1 defect for every 40 unit cells or 2.5% of unit cells being defected.Item Open Access Substantial pyroelectric effect enhancement in laminated composites(American Institute of Physics, 2008-04) Chang, Harrison Hoon Seok; Huang, ZhaorongA mathematical model has been developed to determine the pyroelectric coefficient (PY coef.) enhancement through secondary pyroelectric effect, utilizing a 2-2 connectivity of the pyroelectric lead zirconate titanate (PZT) and elastic laminate layers. Based on the prediction of this analysis, laminar stainless steel (St) PZT/St structures have been fabricated and more than 100% enhancement in PY coef. has been observed in these structures. Good agreement between the theoretical and experimental results was obtained by taking into account of the stain transfer loss at the St and PZT interface.Item Open Access Theoretical Modelling on the Magnetization by Electric Field Through Product Property.(American Institute of Physics, 2006-12-01T00:00:00Z) Huang, ZhaorongMultilayer composites of piezoelectric and magnetostrictive materials can be designed to exhibit the magnetoelectric (ME) effect. This ME effect can be realised as an electric polarisation induced by a magnetic field (called MEH effect) or a magnetization by an electric field (called MEE effect). Theoretical modelling of the MEE effect for 2-2 connectivity composites has been developed for three different boundary conditions for perfect coupling at the interface. The calculated MEE coefficients using material properties of piezoelectric lead zirconate titanate (PZT) and magnetostrictive Terfenol-D are a few orders of magnitude larger than those of single phase ME materials and the calculated values are compared with experimental results in the literature. Keywords: magnetoelectric, multiferroic, piezoelectric, magnetostrictive, piezomagnetic, laminated composites, modelling.Item Open Access Thin Film Crystal Growth Template Removal: Application to stress reduction in Lead Zirconate Titanate Microstructures(American Institute of Physics, 2007-10) Gkotsis, P.; Kirby, Paul B.; Saharil, F.; Oberhammer, J.; Stemme, G.A key issue for the design and reliability of microdevices is process related; residual stresses in the thin films from which they are composed, especially for sol-gel deposited Pb(Zrx,Ti1-x)O3 ceramics, where use of Pt as a template layer, though essential for the nucleation of the perovskite phase, results in structures with high levels of stress largely fixed by the thermal expansion coefficient mismatch between Pt and Si. Here a technique for the elimination of this stress is presented, involving the use of adhesive wafer bonding and bulk micromachining procedures to remove the Pt layer following the Pb(Zrx,Ti1-x)O3 deposition.Item Open Access Using the surface spontaneous depolarization field of ferroelectrics to direct the assembly of virus particles.(American Institute of Physics, 2004-10) Dunn, Steve; Cullen, David C.; Abad-Garcia, Estefania; Bertoni, Cristina; Carter, Richard C.; Howorth, Dave; Whatmore, Roger W.Tobacco mosaic virus (TMV) particles have been assembled at predetermined locations on the surface of a ferroelectric thin film with the composition PbZr0.3Ti0.7O3. The domain structure, hence the surface depolarization field for the ferroelectric associated with the bending of the ferroelectric band structure, was modified at length scales of around 2 µm. A suspension of TMV particles was deposited onto the surface of the ferroelectric over the region where domain modification had been performed. SPM images (intermittent contact) revealed that the virus particles were attracted to regions of the surface that had either been positively modified or were nominally neutral. Regions of modified negative surface charge effectively repelled the virus particles.