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Field effect transistors (FETs) using two-dimensional molybdenum disulfide (MoS2) as the channel material has been considered one of the most potential candidates for future complementary metal-oxide-semiconductor technology with low power consumption. However, the understanding of the correlation between the device performance and material properties, particularly for devices with scaling-down channel lengths, is still insufficient. We report in this paper back-gate FETs with chemical-vapor-deposition grown and transferred MoS2 and Zr doped HfO2 ((Hf,Zr)O2, HZO) high-k dielectric gates with channel lengths ranging from 10 to 30 µm with a step of 5 µm. It has been demonstrated that channels with the length to width ratio of 0.2 lead to the most superior performance of the FETs. The MoS2/HZO hybrid FETs show a stable threshold voltage of ∼1.5 V, current on/off ratio of >104, and field effect mobility in excess of 0.38 cm2 V−1 s−1. The impact of the channel lengths on FET performance is analyzed and discussed in depth. A hysteresis loop has been observed in the Ids − Vgs characteristics of the hybrid FETs, which has been further studied and attributed to the charge effect at the interfaces. The HZO films show a relatively weak ferroelectric orthorhombic phase and thus serve mainly as the high-k dielectric gate. Charge trapping in the HZO layer that might induce hysteresis has been discussed. Our results show that MoS2/HZO hybrid FETs possess great potential in future low power and high-speed integrated circuits, and future work will focus on further improvement of the transistor performances using ferroelectric HZO films and the study of devices with even shorter MoS2 channels. [ABSTRACT FROM AUTHOR]

We have used resonance methods to determine the variation of all the independent piezoelectric, elastic, and dielectric material coefficients, as well as the corresponding electromechanical coupling factors, of soft and hard doped piezoelectric lead zirconate titanate (PZT) ceramics with compositions near the morphotropic phase boundary, as a function of temperature ranging between -165 and 195 °C. The material coefficients were obtained by analyzing the fundamental resonance of the impedance or admittance spectra as a function of frequency for several sample resonance geometries. The piezoelectric coefficients d33, -d31, and d15, as well as the dielectric permittivity coefficients [variant_greek_epsilon]11T and [variant_greek_epsilon]33T, generally increased with temperature for both soft and hard PZT samples. However, the elastic compliance coefficients s11E, -s12E, s33E, and s55E exhibited abnormal variations seen as broad peaks over parts of the tested temperature range. Additionally, thermal hystereses were observed in all the studied material coefficients over the temperature cycle. Finally, it was noted that, overall, the material coefficients of soft PZT varied significantly more than those of hard PZT under changing temperature conditions. [ABSTRACT FROM AUTHOR]

Relaxor lead magnesium niobate (PMN)-based materials exhibit complex structures and unusual properties that have been puzzling researchers for decades. In this paper, a new ternary solid solution of Pb(Mg1/3Nb2/3)O3–PbTiO3–Bi(Zn2/3Nb1/3)O3 (PMN–PT–BZN) is prepared in the form of ceramics, and the effects of the incorporation of BZN into the PMN-PT binary system are investigated. The crystal structure favors a pseudocubic symmetry and the relaxor properties are enhanced as the concentration of BZN increases. The relaxor behavior and the related phase transformations are studied by dielectric spectroscopy. A phase diagram mapping out the characteristic temperatures and various states is established. Interestingly, the piezoelectricity of the PMN-PT ceramics is significantly enhanced by the BZN substitution, with an optimal value of d33 reaching 826 pC/N for 0.96[0.7Pb(Mg1/3Nb2/3)O3-0.3PbTiO3]-0.04Bi(Zn2/3Nb1/3)O3. This paper provides a better understanding of the relaxor ferroelectric behavior, and unveils a new relaxor-based ternary system as piezoelectric materials potentially useful for electromechanical transducer applications. [ABSTRACT FROM AUTHOR]

Bi(Zn0.5Ti0.5)O3 (BZT)-modified Pb(Zr1?ξTiξ)O3 (PZT) single crystals have been grown using a top-seeded solution growth technique and characterized by various methods. The crystal structure is found to be rhombohedral by means of X-ray powder diffraction. The composition and homogeneity of the as-grown single crystals are studied by laser ablation inductively coupled plasma mass spectrometry and X-ray photoelectron spectroscopy. The domain structure of a (001)cub platelet is investigated by polarized light microscopy (PLM), which confirms the rhombohedral symmetry. The paraelectric-to-ferroelectric phase transition temperature TC is found to be 313°C with the absence of rhombohedral?tetragonal phase transition. The ferroelectric properties of the ternary crystals are enhanced by the BZT substitution with a remanent polarization of 28 μC/cm2 and a coercive field EC of 22.1 kV/cm. [ABSTRACT FROM PUBLISHER]

Abstract: Pyrochlore Bi1.5Zn1.0Nb1.5O7 (BZN) thin films deposited at 650°C under an oxygen pressure of 10Pa by pulsed laser deposition were characterized as a function of zinc amount. The zinc concentration in the thin films was varied using ceramic targets having 0–40mol% excess zinc contents. The X-ray diffraction measurement shows that thin films have a cubic pyrochlore phase structure and a strong preferential orientation of (111) plane. The dielectric properties are investigated as functions of temperature and frequency. Dielectric constant and loss tangent of the thin films both slightly increase with the increase of Zn amount. The thin film with 40mol% zinc exhibits a dielectric constant of 198 and a loss tangent of 0.004 at 10kHz. The dielectric relaxation behavior has been studied by measuring the temperature dependence of dielectric properties. The characteristic temperatures (T m) move to the high temperature with the increase of Zn and gradually approach that of BZN ceramic. Meanwhile, in a wide frequency and temperature range (1kHz–1MHz, −100–150°C), the dielectric constant of the thin films almost keeps unchanged and shows a negative temperature coefficient. Leakage current density of the thin films with 20mol% zinc is approximately three order magnitude lower than that of films with 0mol% zinc at 400kV/cm. The conduction of BZN thin films is controlled by the Schottky emission mechanism and the space-charge-limited current mechanism. [Copyright &y& Elsevier]

Lead-free ferroelectric (K0.44Na0.52Li0.04)(Nb0.86Ta0.10Sb0.04)O3thin films have been prepared by pulsed laser deposition. The structures, morphologies and electrical properties of the thin films have been investigated as a function of oxygen pressure from 10 Pa to 40 Pa. The oxygen pressure plays an important role on the thin films. The crystallization and [001] preferential orientation of the thin films increase with oxygen pressure. The thin film deposited at 30 Pa exhibits the moderate dielectric constant of 1330 at 1 kHz and a well-defined ferroelectric hysteresis loop with the remnant polarization of 8.45 μC/cm2and the coercive field of 27.1 kV/cm. [ABSTRACT FROM AUTHOR]

Donor-doped PbZr0.52 Ti0.48 O3 ( PZT) films were utilized to study the effect of dopants on the mobility of ferroelectric domain walls. For chemical solution deposited PZT films 2 μm in thickness, doped with 1%-4% Nb or La, the low field dielectric permittivity remained between 1100 and 1300. With increasing Nb concentration, both the reversible and irreversible Rayleigh constants increased from ɛinit and α′ of 1150 and 39 cm/kV, respectively, for undoped PZT films to 1360 and 43 cm/kV for films doped with 2 mol% Nb. La doping increased the irreversible Rayleigh constant but did not strongly affect the reversible Rayleigh parameter. These observations are consistent with softening of the dielectric and electromechanical response with donor doping. [ABSTRACT FROM AUTHOR]

Abstract: Bi2Zn2/3Nb4/3O7 thin films were deposited on Pt/TiO2/SiO2/Si(100) substrates at a room temperature under the oxygen pressure of 1–10Pa by pulsed laser deposition. Bi2Zn2/3Nb4/3O7 thin films were then post-annealed below 200°C in a rapid thermal process furnace in air for 20min. The dielectric and leakage current properties of Bi2Zn2/3Nb4/3O7 thin films are strongly influenced by the oxygen pressure during deposition and the post-annealing temperature. Bi2Zn2/3Nb4/3O7 thin films deposited under 1Pa oxygen pressure and then post-annealed at a temperature of 150°C show uniform surface morphologies. Dielectric constant and loss tangent are 57 and 0.005 at 10kHz, respectively. The high resolution TEM image and the electron diffraction pattern show that nano crystallites exist in the amorphous thin film, which may be the origin of high dielectric constant in the Bi2Zn2/3Nb4/3O7 thin films deposited at low temperatures. Moreover, Bi2Zn2/3Nb4/3O7 thin film exhibits the excellent leakage current characteristics with a high breakdown strength and the leakage current density is approximately 1×10−7 A/cm2 at an applied bias field of 300kV/cm. Bi2Zn2/3Nb4/3O7 thin films are potential materials for embedded capacitor applications. [Copyright &y& Elsevier]

Amorphous Bi1.5Zn1.0Nb1.5O7 (BZN) thin films have been prepared on Pt/TiO2/SiO2/Si(100) substrates by pulsed laser deposition (PLD) process at low temperature. BZN films were deposited at room temperatures under the oxygen pressure from 1 Pa to 30 Pa, and then post-annealed at the temperature below 200°C. XRD analysis indicates that BZN films are still amorphous in nature after the post-annealing. The dielectric constant of amorphous BZN films increases and the dielectric loss decreases after the post-annealing process. The dielectric properties of BZN films are strongly dependent on the oxygen pressure. BZN Thin films deposited at 1 Pa exhibit superior dielectric characteristics. Dielectric constant and loss tangent are 60.2 and 0.006 at 10 kHz, respectively. Leakage current density is less than 1 × 10-7 A/cm2 at 300 kV/cm. [ABSTRACT FROM AUTHOR]

Lead-free ferroelectric (K0.44Na0.52Li0.04)(Nb0.86Ta0.10Sb0.04)O3 (KNN-LT-LS) thin films have been prepared by a pulsed laser deposition process on Pt/Ti/SiO2/Si substrates. Morphologies, structures and electrical properties of KNN-LT-LS thin films have been investigated as a function of deposition temperature from 680°C to 740°C. X-ray diffraction analysis indicates that KNN-LT-LS thin films are a perovskite phase with a preferential (001) orientation. The dielectric constant and loss tangent of KNN-LT-LS films deposited at 740°C are 1450 and 7.2% at 1 kHz, respectively. The P-E hysteresis loops show that the KNN-LT-LS thin films possess improved ferroelectric properties. The remnant polarization and the coercive field of the films are 7.69 μC/cm2 and 40.8 kV/cm, respectively. [ABSTRACT FROM AUTHOR]

SrNbxTi1-xO3 (0.001 ≤ x ≤ 0.01) thin films have been prepared on Pt/TiO2/SiO2/Si (100) substrates by pulsed laser deposition. X-ray diffracttion and scanning electron microscope studies indicate that all the films were well crystallized and homogeneous with a cubic perovskite structure. Dielectric constant increases from 246 at x equals 0.001 to 342 at x equals 0.01, meanwhile, the dielectric tunability also increases. J-E characteristics of the films suggest that ohmic behavior is predominant at low electric field for all the films, but different conduction mechanisms are predominant at high electric field for the films with different x value. [ABSTRACT FROM AUTHOR]

Abstract: Ti-modified thin films of multiferroic 0.72Bi(Fe1 − x Ti x )O3–0.28PbTiO3 (BFPT, x =0 and 0.02) solid solution were prepared by pulsed laser deposition. The BFPT (x =0 and 0.02) films possess a tetragonal structure with highly preferential (001) orientation. The effects of the ionic substitution on the properties of BFPT (x =0 and 0.02) films have been investigated. The leakage current of the BFPT (x =0.02) thin film is significantly reduced, and the dielectric and ferroelectric properties greatly improved by the aliovalent ionic substitution of Ti4+ for Fe3+. The BFPT (x =0.02) thin film exhibits a reasonably high remnant polarization P r with 2P r up to 90μC/cm2 at 312kV/cm and a switchable polarization up to 92μC/cm2 at 417kV/cm. [Copyright &y& Elsevier]

Abstract: Ba0.5Sr0.5TiO3/Bi1.5Zn1.0Nb1.5O7 (BST/BZN) multilayer thin films were prepared on Pt/Al2O3 substrates by sol–gel method. The structure, morphology, and tunable dielectric properties of BST/BZN thin films were investigated. X-ray diffraction results showed that the structure of BST/BZN multilayer thin films was composed of a cubic BZN pyrochlore phase and a cubic BST perovskite phase. The diffraction pattern confirmed that there was no measurable reaction occurred between the BST and BZN layers. The field-emission scanning electron microscope (FESEM) showed that the surface of BST/BZN multilayer thin films was crack-free and compact. The dielectric constant and loss tangent of the BST/BZN multilayer thin films were 106 and 0.011 at 10kHz, respectively. The dielectric tunability was 10% under dc bias field of 355kV/cm at 10kHz. The medium dielectric constant, low loss tangent and tunability of the dielectric constant suggest that BST/BZN multilayer thin films have potential application for tunable microwave device applications. [Copyright &y& Elsevier]

Abstract: PbZr0.52Ti0.48O3 thick films with thickness of 1–6μm have been prepared by a polymer-assisted MOD process. The polymer, poly(vinyl acetate) (PVAc) was introduced into PZT precursor solutions. The grain size increased from 30nm to 100nm with an increase of the additive amount of PVAc. Meanwhile, the grains grew larger (in a range of 100–500nm) and the surface of the films became rougher with increasing film thickness. This promotes the structural relaxation and prevents cracking formation. The critical thickness at which the film begins to crack increases significantly. The dielectric constant and remanent polarization (P r) increased from 1070 to 1490 and from 36.1μC/cm2 to 52.4μC/cm2, respectively, and the coercive field (E c) decreased from 57.3kV/cm to 41.3kV/cm as the film thickness increased from 0.95μm to 6.02μm. PZT thick films prepared in this study are promising materials for MEMS applications. [Copyright &y& Elsevier]

PbZr0.52Ti0.48O3 (PZT) (52/48) thick films with thickness between 1–5 μ m have been prepared by a metallo-organic decomposition process modified by polymer, poly(vinyl acetate) (PVAc). It has been found that PVAc can increase the single-layer thickness of PZT films. The PZT films with a single-layer thickness over 0.3 μ m have been obtained. The crack-free PZT films annealed at 650–700°C for 3 min exhibit a pure perovskite phase and good electrical properties with dielectric constant between 800–1200, dielectric loss less than 5%, remnant polarization around 28 μ C/cm2 and coercive field less than 100 kV/cm. PZT thick films prepared in this study are promising materials for MEMS applications. [ABSTRACT FROM AUTHOR]

Gaussian white noise (GWN), as an intrinsic noise source, can give rise to various firing activities at the rest state before a supercritical or subcritical Hopf bifurcation (supH or subH) in the Chay system without or with external current input, when VK, VC, λn and I are considered as changeable control parameters. These firing activities are closely related to the global bifurcation mechanism of the whole system and the fast/slow dynamical subsystems, and can be tackled by means of bifurcation analysis. GWN can induce some typical bursting phenomena in the stochastic Chay system. Firstly, integer multiple "fold/homoclinic" or "circle/homoclinic" bursting due to GWN, with only one spike per burst, can arise from rest states before both subH and supH (with respect to the parameter VK), and their respective trajectories have the same shape and property. However, less spikes appear and their peaks are lower before supH, comparing with those before subH. Secondly, a "fold/fold" point–point hysteresis loop bursting due to GWN is generated before supH (with respect to the parameter VC) on the upper branch of a "Z"-shaped bifurcation curve between two fold bifurcations of the fast system. Thirdly, at a rest state before subH (with respect to the additional current I) situated on the lower branch of a "S"-shaped bifurcation curve between two fold bifurcations of the fast system, a GWN-induced firing pattern appears and is classified as "Hopf/homoclinic" bursting via "fold/homoclinic" point–point hysteresis loop. GWN-induced firing activities other than bursting can also be observed in the stochastic Chay system. For example, sometimes GWN-induced continuous spiking without any particular shape may arise at a rest state before supH (with respect to the parameter VK) for certain values of parameters. Moreover, under the situation that a stable node and a stable focus coexist before subH (with respect to the parameter I) and the attractive region of the stable node is larger than that of the stable focus, GWN only provoke random subthreshold impulsing oscillation near the stable node. [ABSTRACT FROM AUTHOR]

Abstract: BaTiO3 is a typical ferroelectric material with high relative permittivity and has been used for various applications, such as multilayer ceramic capacitors (MLCCs). With the tendency of miniaturization of MLCCs, the thin films of BaTiO3 have been required. In this work, BaTiO3 thin films have been deposited on Pt-coated Si substrates by RF magnetron sputtering under different deposition conditions. The films deposited at the substrate temperature from 550°C–750°C show a pure tetragonal perovskite structure. The films deposited at 550°C–625 °C exhibit (111) preferential orientation, and change to (110) preferential orientation when deposited above 650°C. The film morphologies vary with working pressure and substrate temperature. The film deposited at 625°C and 4.5Pa has the relative permittivity of 630 and the loss tangent of 2% at 10kHz. [Copyright &y& Elsevier]

Abstract: Bi2Zn2/3Nb4/3O7 thin films were prepared on Al2O3 substrates by pulsed laser deposition. The phase compositions and microstructures were characterized by X-ray diffraction and atomic force microscopy. The as-deposited films were all amorphous in nature. All films were crystallized after the post annealing at the temperature range of 700–900°C for 30min in air. The texture characteristics change with annealing temperature. A split post dielectric resonator method was used to measure the microwave dielectric performance at the resonant frequencies of 10, 15 and 19GHz. For the films annealed at 900°C, the preferential orientation is similar to the monoclinic BZN bulk. The microwave dielectric constants at 10, 15 and 19GHz are 69.4, 58.9 and 47.9, respectively, which are closer to these of the monoclinic BZN bulk. [Copyright &y& Elsevier]

Abstract: To compensate for bismuth loss that occurred during the film deposition process, Bi1.5Zn1.0Nb1.5O7 (BZN) thin films were deposited at room temperature from the ceramic targets containing various excess amounts of bismuth (0–20mol%) on Pt/TiO2/SiO2/Si substrates by using RF magnetron sputtering technique. The effect of bismuth excess content on the microstructure and electrical properties of BZN thin films was studied. The microstructure and chemical states of the thin films were studied by SEM and XPS. EPMA was employed to assess the film stoichiometry. The X-ray diffraction analysis reveals that the BZN thin films exhibit the amorphous structure in nature. An appropriate amount of excess bismuth improves the dielectric and electrical properties of BZN thin films, while too much excess bismuth leads to deterioration of the properties. BZN thin film with 5mol% excess bismuth exhibits a dielectric constant of 61 with a loss of 0.4% at 10kHz and leakage current of 7.26×10−7 A/cm2 at an electric field of 200kV/cm. [Copyright &y& Elsevier]

We have investigated the temporal evolution of the dielectric properties of Jurkat cells, a malignant human T-cell line, after exposure to microsecond and nanosecond pulsed electric fields. Suspensions with a 10% volume fraction of Jurkat cells were exposed to either 8 consecutive 1.1 kV/cm electroporation pulses of 100 μs, or 8 consecutive 20-kV/cm pulses of 300 ns, applied with a repetition rate of about 1 Hz. The dielectric spectrum of the cell suspensions before and after exposure was determined by means of time domain reflectometry dielectric spectroscopy. After correction for electrode polarization, the conductivity and permittivity of the cell membrane was derived by fitting the suspension spectrum to a combination of Maxwell-Wagner mixture model and single-shell cell model. Both exposure regimens lead to an increase in the conductivities of suspending medium and cell membrane indicating that membrane poration had occurred. This was confirmed by membrane integrity markers. Significantly higher membrane conductivities without uptake of membrane integrity marker suggest different pore formation mechanisms. Accordingly, dielectric measurements allow us to assess conformational and possibly induced functional changes of cells after exposure on biologically relevant time scales, and in turn, evaluate and compare the efficacy of chosen pulse parameters. [ABSTRACT FROM AUTHOR]

Ceramics of a new ternary solid solution system, xBi(Zn1/2Ti1/2)O3-yPbTiO3zPbZrO3 (xBZT-yPT-zPZ), with compositions along the solubility limit curve are prepared by solid-state reaction and sintering technique. Two morphotropic phase boundaries (MPBs) separating the orthorhombic and tetragonal (MPBO-T) phases and the tetragonal and rhombohedral (MPBT-R) phases, respectively, are observed with increasing z (0.10 ⩽ x ⩽ 0.21; 0 ⩽ y ⩽ 0.49). It is found that the transition from the ferroelectric to paraelectric phase becomes more diffuse with the addition of BZT into the PZT solid solution. Enhanced dielectric and ferroelectric properties appear at MPBR-T, which exists over a wide composition region (0.45 ⩽ z ⩽ 0.6), as revealed by X-ray diffraction and dielectric measurements. The dielectric constant reaches a maximum value (ε' = 1250) on the tetragonal majority side of the MPB. The highest remnant polarization (Pr = 34.2 μC/cm2) is found in the composition at the center of the MPB, where the rhombohedral and tetragonal phases coexist in almost equal quantities. [ABSTRACT FROM AUTHOR]

This article gives a review of the research done in our lab over the past few years on the characterization of the transverse elongation of polymeric electrostatic actuators induced by Maxwell stress. Dielectric elastomers are known to produce large transverse strains in response to Maxwell stresses and thus provide a useful form of electromechanical actuation. The transverse strain responses of dielectric elastomer based Maxwell stress actuators have been investigated. The mechanical properties of elastomer cannot be fully understood on the basis of linear elastic theories. Models of hyperelasticity that are capable of describing the large deformation of rubber-like polymer materials have been used to interpret our experimental results. Our experimental and FEA studies on elastomer film actuators have helped us to understand how both the geometry and the material properties of the elastomers influence the observed actuation capabilities. Getting a high transverse strain requires not only good material properties, but also optimized actuator/electrode geometry. Some other factors, such as the electrode properties also influence the actuator performance. [ABSTRACT FROM AUTHOR]

Ferroelectric ceramics derived from the solid solution of (1ߝx)PbTiO3-xBiAlO3 (x = 0, 0.05, 0.10, 0.15, and 0.18) have been synthesized by solid-state reactions. A pure perovskite phase is formed for 0 ⩽ x ⩽ 0.15. The tetragonality (c/a) of the solid solution decreases with the increasing amount of BiAlO3. Scanning electron microscopic images reveal a microstructure with a fine grain size of less than 1 μm for the solid solution ceramics (x ⩾ 0.05). Compared with pure PbTiO3 ceramics whose high conductivity and poor densification were harmful to their dielectric performance, the ceramics of (1ߝx) PbTiO3-xBiAlO3 are well-densified (with a relative density of up to 93%) and their dielectric and ferroelectric properties are significantly improved with the addition of BiAlO3, exhibiting reduced dielectric losses, well-developed P-E hysteresis loops (for x = 0.05, 0.10, and 0.15) and a high remnant polarization (Pr) of 64 μC/cm2 (for x = 0.15). [ABSTRACT FROM PUBLISHER]

CH 3 NH 3 PbI x Br 3− x thin films on FTO substrate were synthesized successfully. The crystal structure and optical properties of these films changed with different ratios of I − /Br − ions. The lattice parameters were reduced and the optical absorption edges were blue-shifted with the increasing ratio of Br - ions. The dielectric spectra have revealed that tetragonal CH 3 NH 3 PbI x Br 3 − x films at room temperature not only have a lower symmetry than cubic films, but also provide more electron transition energies. The mechanism is discussed correspondingly. [ABSTRACT FROM AUTHOR]

Abstract: In order to develop multiferroics with large magnetization and polarization, we have prepared a series of (1−x)[0.9BiFeO3–0.1DyFeO3]–xPbTiO3 [BDF–xPT] solid solution ceramics by solid state reaction. X-ray diffraction reveals that, with the increase of PbTiO3 concentration, the solid solution transforms from a rhombohedral to a tetragonal phase with the presence of a morphotropic phase boundary (MPB) region located at 0.28≤x≤0.40 at room temperature, in which the rhombohedral, tetragonal and orthorhombic phases coexist. The temperature dependence of the dielectric permittivity indicates that the Curie temperature decreases with the increasing amount of PbTiO3. Based upon the structural analysis and dielectric characterization, a preliminary phase diagram for the BDF−xPT pseudo-binary system has been proposed. It is found that the ceramics of compositions around the MPB exhibits much better dielectric properties with dielectric constant of the BDF–0.37PT ceramics reaching 459 at 1kHz, confirming the beneficial effects of the MPB on the dielectric performance. [Copyright &y& Elsevier]