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The PbTiO3/SrTiO3 superlattice thin films with a low volume fraction of PbTiO3 have not attracted much interest because they are thought to exhibit only a paraelectric state. In this study, we focus on a superlattice thin film with thin PbTiO3 (PTO) and thick SrTiO3 (STO) layers, wherein the hidden ferroelectricity in the thin PbTiO3 layer is revealed. Atomic scale imaging analysis and electron energy loss spectroscopy reveal the existence of a disordered ferroelectric polarization state without innate tetragonal distortion in the (6PTO/15STO)5 superlattice. The piezoelectric force microscopy analysis confirms that this disordered ferroelectricity can enhance piezoelectric response. [ABSTRACT FROM AUTHOR]

The displacement performance of piezoelectrically actuated inkjet print head in a bending mode was investigated with the numerical and experimental analysis. The bending actuator membrane with a multi-layered structure, including piezoelectric, elastic and support layers was fabricated by MEMS processing. The displacement of the actuator membrane reaches a maximum at a relative width ratio of PZT to support layer in the range from 0.6 to 0.8, depending on their thickness ratio. The fabricated actuator membrane exhibited its maximum displacement of 0.098 um/V, which agreed well with simulation results, i.e., 0.089 μ m/V. [ABSTRACT FROM AUTHOR]

The electrical conduction properties of 0.2% Cr-doped SrTiO3 thin film in metal-insulator-metal (MIM) structure was investigated by using dc and impedance spectroscopic measurements at room temperature. The dc measurement shows that the electronic conduction is the trap-controlled space-charge-limited current (SCLC) conduction. The impedance study shows that the electrical conduction is bulk-limited conduction. The behavior of the bulk resistance obtained in the equivalent circuit model from the impedance analysis is also consistent with the trap-controlled space-charge-limited conduction with exponential trap distribution. [ABSTRACT FROM AUTHOR]

The resistive switching of 0.2% Cr-doped SrTiO3 (Cr-STO) thin films grown on (La0.5, Sr0.5)CoO3/SrTiO3 (LSCO/STO) substrate have been investigated. The structure in a metal-insulator-metal (MIM) i.e., Pt/Cr-STO/LSCO, shows hysteretic and asymmetric behaviors in current-voltage (I-V) characteristics. The current-voltage characteristics are attributed to the resistive switching of Cr-STO thin films between high resistance state (HRS) and low resistance state (LRS) by applying pulsed or dc bias voltage stress. The current and voltage ramp sweeps in the I-V measurement reveal that threshold current is required to induce the resistive switching from HRS to LRS in the negative voltage region. [ABSTRACT FROM AUTHOR]

Piezoelectrically driven microbridge gas sensors have been fabricated by MEMS process. We have used the resonant frequency change of the microbridge transducer upon mass increase. The sol-gel derived Pb(Zr.0.52,Ti0.48)O3 (PZT) film capacitor as an actuating part was integrated into the thin SiNx bridge structure. The resonant frequency of the microbridge was in the range of 250 kHz to 260 kHz. The microbridge exhibited a mass sensitivity and gravimetric sensitivity factor of ca. 7.27 pg/Hz and 345 cm2/g, respectively. With the PMMA polymer sensing layer, the microbridge showed the gas sensitivity of 1.67 ppm/Hz for ethanol vapor. [ABSTRACT FROM AUTHOR]

Various types of piezoelectrically driven microtransducers which have a similar physical dimension, i.e., microcantilever, microdiaphragm and microbridge, were fabricated by micro electromechanical system (MEMS) technique and are compared on the mass sensing behavior. The diol based sol-gel derived Pb(Zr 0.52 ,Ti 0.48 )O 3 (PZT) thin film capacitors were integrated for the piezoelectric actuation. We have used the resonant frequency change of microtransducer upon mass increase as a sensing mechanism. The resonant frequency of the microtransducer was measured by analysis of electrical signals from microtransducer such as impedance, capacitance, phase and dielectric loss. The fundamental resonant frequencies of the microcantilever, microbridge and microdiaphragm with similar dimension (∼⃒300 μm) were about 26 kHz, 260 kHz and 290 kHz, respectively. The mass sensitivities of bare microtransducers were measured by metallic thin film deposition and analysis of spectral responses from microtransducers. When various microtransducers are compared, the microcantilever exhibited the highest gravimetric sensitivity factor (Δf/Δm×f 0 = 694.4 cm 2 /g), followed by the microbridge and microdiaphragm. However, the microbridge showed the highest mass sensitivity (Δf/Δm = 137.5 Hz/ng) among those transducers. [ABSTRACT FROM AUTHOR]

Various types of piezoelectrically driven microtransducers which have a similar physical dimension, i.e., microcantilever, microdiaphragm and microbridge, were fabricated by micro electromechanical system (MEMS) technique and are compared on the mass sensing behavior. The diol based sol-gel derived Pb(Zr 0.52 ,Ti 0.48 )O 3 (PZT) thin film capacitors were integrated for the piezoelectric actuation. We have used the resonant frequency change of microtransducer upon mass increase as a sensing mechanism. The resonant frequency of the microtransducer was measured by analysis of electrical signals from microtransducer such as impedance, capacitance, phase and dielectric loss. The fundamental resonant frequencies of the microcantilever, microbridge and microdiaphragm with similar dimension (∼⃒ 300 μ m) were about 26 kHz, 260 kHz and 290 kHz, respectively. The mass sensitivities of bare microtransducers were measured by metallic thin film deposition and analysis of spectral responses from microtransducers. When various microtransducers are compared, the microcantilever exhibited the highest gravimetric sensitivity factor (Δ f /Δ m f 0 = 694.4 cm 2 /g), followed by the microbridge and microdiaphragm. However, the microbridge showed the highest mass sensitivity (Δ f /Δ m = 137.5 Hz/ng) among those transducers. [ABSTRACT FROM AUTHOR]

BaTiO 3 /SrTiO 3 superlattices have been deposited onto (La,Sr)CoO 3 /MgO (100) substrate using pulsed laser deposition. As the thickness of BTO/STO superlattice was varied from 100 nm to 10 nm, the dielectric constant decreased, which is know to be the finite size effects. The finite size effect was investigated with structural characteristics such as lattice distortion and volume change. These structural analyses were accomplished by synchrotron X-ray scattering. The anisotropic lattice distortion of the superlattice was significantly influenced by the variation in the thickness. Moreover, the superlattice exhibited the volume change of BTO and STO layers while maintaining the volume of a supercell unchanged, suggesting that the hydrostatic strain (i.e., volume change) as well as the anisotropic lattice distortion exist in the consisting BTO and STO layers. Oxygen vacancy defect, possibly causing the hydrostatic strain, did not affect the dielectric constant of the superlattice significantly, excluding the oxygen nonstoichiometry in thin superlattices from the cause of the finite size effect. The finite size effect observed in BTO/STO superlattices is mainly attributed to the lattice strain (i.e., hydrostatic and anisotropic strains) developed in the superlattices. [ABSTRACT FROM AUTHOR]

We have fabricated piezoelectric microcantilever transducer for a miniaturized gas sensor, to detect environmental gas molecules, i.e., volatile organic compound (VOC). The microcantilever consist of Pb(Zr, Ti)O 3 (PZT) capacitors and SiNx layer as an actuating and a supporting layer respectively. The fundamental resonant frequency of microcantilever was in the range of 17∼⃒29 kHz. To measure the gas sensitivity, the microcantilever surface was coated with polymethylmetacrylate (PMMA), which is known to have sensibility for primary alcohols. The resonant frequency shift of the microcantilever was measured by complex impedance analysis, which only uses electrical signal output from the microcantilever. As the vapor concentration of the alcohol (ethanol or methanol) increased, the resonant frequency of microcantilever was linearly shifted toward the lower frequency range. The gas sensitivity of microcantilever was 0.03 Hz/ppm for methanol vapor. [ABSTRACT FROM AUTHOR]

PbZrO 3 (PZO)/PbTiO 3 (PTO) artificial superlattices have been grown on La 0.5 Sr 0.5 CoO 3 (LSCO) (100)/MgO (100) substrate by pulsed laser deposition with various stacking periods from 1 to 100 unit-cells. The electrical properties of the superlattices were investigated as a function of the stacking period. The dielectric constant and remnant polarization were improved with decreasing the stacking periodicity. The dielectric constant of the superlattice reached 800 at a stacking period of 1unit-cell/1unit-cell (PZO 1 /PTO 1 ), which is larger than that of the single PZT solid solution film grown at a relative high temperature. Moreover, the remnant polarization reached a maximum, 2Pr = 38.7 μ C/cm 2 at 2 unit cell-stacking period. As the total thickness of the superlattices with a 2 unit cell-stacking period (PZO 2 /PTO 2 ) decreased, the corresponding dielectric constant decreased. As long as the dielectric constant is concerned, the finite size effect was observed in the artificial PZO/PTO superlattice with a thickness down to 20 nm. [ABSTRACT FROM AUTHOR]

The BaTiO 3 (BTO) and SrTiO 3 (STO) thin films have been fabricated on (La,Sr)CoO 3 /MgO (100) single crystal substrate by pulsed laser deposition (PLD). The effect of oxygen content in the BTO and STO lattices on their structural characteristics and dielectric properties has been investigated. The variation of the oxygen content was made in BTO and STO thin (10 nm) films by changing oxygen cooling pressure from 10 -3 Torr to 400 Torr. The lattice parameter of STO thin film was sensitive to the variation of the oxygen pressure while that of BTO thin film was not sensitive to the oxygen pressure. The volume of the STO thin film increased with decreasing the oxygen cooling pressure, which is attributed to the volume change caused by oxygen nonstoichiometry (deficiency). The dielectric constant of the STO thin film was insensitive to the oxygen cooling pressure. This result indicates that the dielectric constant of the STO thin film was not influenced by the oxygen deficiency, although the STO thin film was influenced by the oxygen environment and had oxygen deficient nonstoichiometry. Those results suggest that the lattice distortion is the most important factor to influence the dielectric property of specifically STO thin films. On the other hand, the BTO thin film was not susceptible to the change in the oxygen environment, resulting in insensitive lattice parameter and volume as well as the dielectric constant to the oxygen environment. [ABSTRACT FROM AUTHOR]

Multilayered piezoelectric micro-diaphragms have been successfully fabricated by micro-electro-mechanical-system (MEMS) processing. The micro-diaphragms consisted of diol based sol-gel derived Pb(Zr 0.52 Ti 0.48 )O 3 (PZT) capacitor, sputtered Pt electrode, and low temperature oxide(LTO)/SiN x /Si substrate. The PZT film exhibited (111) oriented structure. The dielectric constant and loss of the PZT thin films were 800 and 3% at 100∼⃒ 100 kHz, respectively. The remanent polarization was 20 μ C/cm 2 . The lateral dimension of the PZT film was varied relative to the square-shaped supporting membrane with 300 or 400 μ m length. The relative size (ratio of lateral dimensions) of the PZT film to the supporting membrane was varied from 0.7 to 1.1 to investigate its influence on the system performance. The micro-diaphragm exhibited mechanical displacement from 0.067 to 0.135 μ m at 15 V and had a maximum displacement at a ratio of relative size of 0.8, regardless of the lateral size of the supporting membrane. The fundamental resonant frequency of the micro-diaphragm which has 300 μ m length supporting membrane was in the range of 348 kHz to 365 kHz, depending on the relative size. As the PZT size increased relative to the supporting membrane, the resonant frequency decreased and reached a minimum at the relative size of 0.8. The micro-diaphragm with the supporting membrane (400 μ m length) had a lower resonant frequency, i.e., 251∼⃒270 kHz, but showed a similar behavior to the micro-diaphragm with the supporting membrane (300 μ m length) in relation to the resonant frequencies with the relative size. [ABSTRACT FROM AUTHOR]

PbZrO3 (PZO)/PbTiO3 (PTO) artificial superlattices have been grown on La0.5Sr0.5CoO3 (LSCO) (100)/MgO (100) substrate by pulsed laser deposition (PLD) with various stacking periods from 1 to 100 unit-cells. The ferroelectric properties of the superlattices were investigated by scanning probe microscopy (SPM). We have compared the superlattices to Pb(Zr0.5Ti0.5)O3 (PZT) thin films with respect to topographic features (roughness and grain size) and local polarization behavior. The polarization of PZT and superlattices was evaluated by measuring the surface potential using Kelvin force microscopy (KFM). The roughness and grain size of the superlattices were smaller than that of PZT thin films. The surface potential of superlattice with a 2 unit cell-stacking period (PZO2/PTO2) was as large as 1009 mV compared to PZT thin films with same thickness (i.e., 50 nm). As the total thickness of PZO2/PTO2 decreased, the corresponding surface potential decreased. The polarized domain size of the superlattice was dependent of the applied voltage pulse. The polarized domain as small as 80 nm in 20 nm thick PZO2/PTO2 superlattice was formed by applying 1 s pulse of -1 V. [ABSTRACT FROM AUTHOR]

BaTiO 3 (BTO)/SrTiO 3 (STO) artificial lattices have been deposited on (La,Sr)CoO 3 /MgO (100) substrate by pulsed laser deposition (PLD). Strain manipulation in the oxide artificial lattice was carried out by varying stacking sequence and period of BTO and STO layers with layer-by-layer growth technique. A wide variation of the lattice distortion for both BTO and STO layers has been obtained from this strain manipulation. The dielectric constant of the BTO and STO lattices was sensitively influenced by the lattice distortion. Moreover, it is found that there exist a certain degree of lattice distortion of the strained BTO and STO lattices leading to a maximum value of their own dielectric constant of the BTO and STO lattices. Consequently, an appropriate combination of stacking period and sequence (resulting in a specific lattice distortion) led to the large dielectric constant (1230) and extremely large tunability (94%) in the BTO/STO oxide artificial lattice. [ABSTRACT FROM AUTHOR]

We have fabricated piezoelectrically driven micro-transducer for the application to smart device. Two types of micro-transducers, i.e., micro-cantilever and micro-bridge, have been designed and fabricated. Finite element method (FEM) simulation was performed on the micro-transducer with various length and shapes. Lead zirconate titanate thin film as a piezoelectric layer was incorporated into the micro-transducer. The transducer structure consists of PZT thin layer capacitor, low temperature oxide (LTO) and low stress SiN x layer. Pb(Zr 0.52 Ti 0.48 )O 3 (PZT) films were prepared by diol-based sol-gel process. The PZT films were not damaged by fabrication process and thus maintained their electrical properties in the transducer structure after all the fabrication steps. The dielectric constant and loss of the PZT film in the transducer structure were 870 and 2% respectively. The remanent polarization was 20 μC/cm 2 . The micro-cantilever had a fundamental resonant frequency in the range of 16 to 25 kHz when its length was in the range of 320 μm to 380 μm. Meanwhile, the resonant frequency of the micro-bridge was higher by a factor of 7 than that of the micro-cantilever with a similar dimension. [ABSTRACT FROM AUTHOR]

Artificial superlattice of the ferroelectric BaTiO 3 /SrTiO 3 multilayer thin film has been fabricated by pulsed laser deposition. In this hetero epitaxial BTO/STO layers, each layers have been continuously grown on (La 0.5 ,Sr 0.5 )TiO 3 /MgO(100) with a periodicity ranging from (BTO 1 unit cell /STO 1 unit cell ) 125 to (BTO 125 unit cell /STO 125 unit cell ) 1 . The total thickness of BaTiO 3 /SrTiO 3 superlattice was 100 nm. X-ray diffraction results clearly showed that epitaxial BTO/STO superlattice was formed with a various periodicity. The depth profile in the superlattice showed that there was no serious interdiffusion between BaTiO 3 and SrTiO 3 layer by Auger electron spectroscope(AES). [ABSTRACT FROM AUTHOR]

Epitaxial (Ba 0.5 ,Sr 0.5 )TiO 3 (BST) thin films have been grown on Si substrate with a very thin yttria-stabilized zirconia (YSZ) buffer layer by pulsed-laser deposition. In these BST/YSZ heteroepitaxial structures, the axial relationship was BST[h00]//YSZ[h00]//Si[h00]. Crystallinity of an epitaxial BST films has been investigated using X-ray diffraction study and Φ-scan. The thickness of YSZ buffer layer affects the growth behavior of BST thin films. It is with very thin YSZ buffer layer, under 7 nm thick, that BST thin film is grown epitaxially on Si substrate. [ABSTRACT FROM AUTHOR]

Bi modified YMnO 3 : (Y 0.95 ,Bi 0.05 )MnO 3 (YBM) thin films were deposited on Pt/Ti/SiO 2 /Si (100) substrates by pulsed laser deposition (PLD). The deposition conditions of oxygen partial pressure and cooling atmosphere have influences on the structural and ferroelectric properties of YBM thin films. Addition of Bi in YMnO 3 enhanced crystallization of YMnO 3 thin films. The c-axis oriented YBM thin films have been obtained on Pt at 700 °C, which is lower than the typical deposition temperature of YMnO 3 thin films. YBM thin films deposited in oxygen partial pressure of 100 mTorr were strongly oriented along the c-axis. The hysteresis P-E loop and Capacitance-Frequency (C-F) characteristics of YBM thin films were studied. The dielectric constant and loss was 29 and 0.017 at 1 MHz, respectively. [ABSTRACT FROM AUTHOR]

We report a first-principles study on SrRuO3/SrTiO3 interface in the presence of the oxygen vacancy. While the oxygen vacancy on the side of SrTiO3 significantly lowers the Schottky barrier height, the oxygen vacancy close to the interface or inside the metallic electrode results in a Schottky barrier comparable to that of the clean interface. Based on these results, we propose a model for resistance-switching phenomena in perovskite oxide/metal interfaces where electromigration of the oxygen vacancy plays a key role. Our model provides a consistent explanation of a recent experiment on resistance switching in SrRuO3/Nb:SrTiO3 interface. [ABSTRACT FROM AUTHOR]

We performed first-principles calculation to investigate the effect of epitaxial strain on lattice instabilities and polarization behavior of BaTiO3/SrTiO3 artificial lattice with very short stacking period, i.e., BaTiO3 1 unit cell/SrTiO3 1 unit cell (BTO/STO). The structural analysis of BTO/STO artificial superlattice under in-plane compressive state showed enhanced stability of the tetragonal phase. On the other hand, the stability of monoclinic phase was enhanced when the BTO/STO was in the in-plane tensile state. The phase transition from tetragonal to the monoclinic phase occurs at the misfit strain of -0.25%. As the misfit strain of BTO/STO superlattice increases from -0.25% to -1.5% (in-plane compressive state), the tetragonal superlattice exhibits an increasing polarization along the [001] direction. In the monoclinic phase, the polarization of the superlattice rotates progressively toward [110] direction with increasing the misfit strain, and the magnitude of the polarization simultaneously increases with the rotation. The first-principles study shows that the phase stability and polarization vector is sensitively influenced by the lattice misfit strain. [ABSTRACT FROM AUTHOR]

The dielectric response and optical phonon of hydrostatically and anisotropically strained SrTiO3 lattices were studied using density functional theory. A structural analysis was performed on the strained SrTiO3 lattice. Following the structural analysis, the optical phonon frequency was calculated for a wide range of lattice distortion. The dielectric constant was calculated from the optical phonon frequency and the Börn effective charges. It was found that significant optical phonon softening occurs at a certain degree of lattice distortion and a certain amount of volume change. In other words, the optical phonon frequency decreased and reached a minimum (50 cm-1) at a specific lattice distortion (c/a=0.985) as the SrTiO3 lattice was progressively distorted starting from the unstrained state. The phonon frequency increased as the lattice distortion was further increased. This phonon behavior, i.e., optical phonon softening, leads to a maximum dielectric constant at a certain degree of lattice distortion. The first-principles calculation on the strained SrTiO3 shows that the strain affects the dielectric constant of the strained SrTiO3 through the optical phonon softening (or hardening). [ABSTRACT FROM AUTHOR]