CaCu3Ti4O12 thin film capacitors: Evidence of the presence of a Schottky type barrier at the bottom electrode

This study aims to distinguish between the contributions of bottom and top electrodes to the dielectric properties of CaCu₃Ti₄O₁₂ (CCTO) based parallel plate thin film capacitors. For this purpose, Au, Pt, and La_0.9Sr_1.1NiO₄ as electrode materials were compared. Epitaxial and polycrystalline CCTO films were pulsed laser deposited. The nature of electrodes played a major role in altering the dielectric characteristics of the thin films. Existence of one or two Schottky barriers at either or both of the CCTO/electrode interfaces was observed. A careful comparison of the electrical characteristics allowed us to discriminate between the interfaces hosting the Schottky barrier without assuming the conduction type. In return, this knowledge of the Schottky barrier location allowed us to unambiguously establish the carrier's nature. Results point toward n-type carriers in CCTO thin films, in contradiction with previous reports.     

Dielectric oxynitride LaTiOxNy thin films deposited by reactive radio-frequency sputtering

LaTiO_xN_y thin films have been deposited by RF sputtering on (001) Nb-doped SrTiO₃ and (001) MgO single-crystalline substrates at high temperature (T_S = 800 °C) under different nitrogen ratios in the plasma (vol.% N₂ = 0, 25, 71). The band gaps ranged from E_g = 3.30 eV for the epitaxial transparent film containing no nitrogen to E_g = 2.65 eV for the textured coloured film containing a moderate amount of nitrogen. Dielectric characterization in the frequency range [100 Hz-1 MHz], using a metal-insulator-metal structure, has shown a stable permittivity and loss tangent of the epitaxial low-nitrided LaTiO_xN_y film with values of ε′ = 135 and tanδ = 1.2 10^− 2 at 100 kHz (RT).     

The non-ohmic and dielectric behavior evolution of CaCu3Ti4O12 after heat treatments in oxygen-rich atmosphere

CaCu₃Ti₄O₁₂ (CCTO) ceramics pellets were prepared using the solid-state reaction method, and then they were heat-treated at different temperatures in oxygen-rich atmosphere. The effect of heat treatments on the non-ohmic behaviors and dielectric properties were investigated. EDS analysis results indicate that the percent of oxygen at grain boundaries of CCTO ceramics heat-treated in oxygen-rich atmosphere increases markedly with the rise of temperature and approaches saturation state at about 850 °C. The breakdown voltage and nonlinear coefficient also exhibit an increase trend with the rise of temperature. In addition, the calculated results manifest that the height of Schottky potential barrier is closely related to the oxygen content at the grain boundaries. The permittivity and dielectric loss of samples heat-treated present a relatively intense decrease with the rise of temperature. But the permittivity has a behavior just reverse to the non-ohmic characteristics, which can be explained by the Schottky potential barrier theory.     

Electric transport properties of rare earth doped YbxCa1-xMnO3 ceramics (part II: The role of grain boundaries and oxygen vacancies)

A comprehensive overview is provided about the role of bulk conductivity contributions in compounds of the composition Yb_xCa_1-xMnO₃ (0–10 at. % Yb-dopant concentration). For this purpose, in-situ impedance spectroscopy was successfully employed at different temperatures (−100 up to 300 °C) and frequencies (1 Hz–1 MHz). These experiments reveal the main role of grain boundaries as well as electronic and ionic contributions in conductivity. The contribution of different resistance components in electric transport properties were proposed on the base of a double-Schottky-barrier model. Migration of oxygen vacancies and their participation in conductivity were studied and the results are confirmed by observing oxygen released using a ZrO₂ oxygen sensor during dilatometry measurements in a wide range of temperatures.     

Thermal experimental verification on effects of nanoparticles for enhancing electric and dielectric performance of polyvinyl chloride

This paper presents investigation on the enhancement of dielectric constant characterization of polyvinyl chloride (PVC) by organic and inorganic nanoparticles under variant frequencies and thermal conditions. Dielectric spectroscopy has been experiment dielectric properties of polyvinyl chloride at various frequencies (0.01 Hz–1 MHz) and temperatures (20–80 °C); then, it has been specified the effective nanoparticles on dielectric constant performance compared with unfilled base matrix polymer. Therefore, it has been got optimum types and concentrations of nanoparticles that have been used for controlling and enhancing dielectric constant characterization of polyvinyl chloride.     

High permittivity dielectrics for poly(3-alkylthiophene) field-effect transistor devices

In an attempt to disentangle the effects of permittivity and surface energy of the gate insulator (expressed by its dielectric constant k and water contact angle, respectively) on the performance of organic field-effect transistors (FETs), we fabricated top- and bottom-gate FET architectures with poly(3-alkylthiophenes) (P3ATs) of different side-chain lengths, using a range of gate dielectrics. We find that this class of semiconductor, including the short butyl-(C₄-) substituted derivative, is significantly less susceptible to the often detrimental effects that high-k dielectrics can have on the performance of many organic FETs. For bottom gate devices we identify the surface energy of the gate dielectric to predominantly dictate the device mobility.     

The effect of Ca-rich on the electric properties of Ca1+xCu3−xTi4O12 polycrystalline system

Ca_1+xCu_3−xTi₄O₁₂ (x = 0, 0.25, 0.5, 1) ceramics were prepared using the conventional solid-state reaction method. The XRD patterns show that Ca_1+xCu_3−xTi₄O₁₂ compounds are comprised of CaCu₃Ti₄O₁₂ (CCTO) and CaTiO₃ (CTO) phases compared with the traditional CCTO and the content of CTO phase increases with the increase of x. The micrographs demonstrate that the sample for x = 0 has larger grain size 8-10 μm. However, for the samples (x = 0.25, 0.5, 1), the mean grain size decreases markedly with the increase of CTO phase. The measurement for electric properties indicates that the permittivity values decrease with the increase of Ca atoms, but the breakdown electric field E_b and the nonlinear coefficient α values have a behavior reverse to it. The nonlinear coefficient α reaches 28 for x = 1, yet it is only 11.4 for x = 0 in the current range of 1-10 mA. This can be ascribed to the reduction of grain size and the changes in the electric conductivity of main grains and grain boundary with increasing Ca/Cu ratio. Imbalances between Ca and Cu atoms with Ca in excess can favor the non-ohmic properties in detriment to the dielectric property and a suitable Ca/Cu ratio can be selected to adjust the permittivity and I-V nonlinearity, according to different desired device applications.     

Low dielectric constant materials and methods for interlayer dielectric films in ultralarge-scale integrated circuit multilevel interconnections

This paper reviews low dielectric constant materials for interlayer dielectric films in ultralarge-scale integrated circuit (ULSI) multilevel interconnections. The trends of ULSIs in the last decade were briefly described first. Then, the requirements for interlayer dielectric film properties and their formation techniques were explained. They are: (1) a low dielectric constant, (2) a surface planarity, (3) a gap-filling capability, and (4) a low residual stress. In contrast with the requirements, the interlayer dielectric films and related technologies developed in the last decade were reviewed. In the requirements, the low dielectric constant materials are strongly required because the device performance has been limited by signal propagation time and cross-talk in the multilevel interconnections. Furthermore, the low dielectric constant is also required for reduction of power consumption in ULSI operation. Finally, the low dielectric constant materials were summarized, and future trends of the low dielectric constant interlayer dielectric film technologies are discussed.     

Finite element analysis of cracks in piezoelectric materials taking into account the permittivity of the crack medium

In this paper, the influence of the electric boundary conditions on cracks in piezoelectric components shall be studied. Several electric boundary conditions have been proposed in the literature. Here, influence of the permeability of the crack on electric and mechanical fields near the crack tip is considered. Cracks of lower permeability lead to stronger electric singularities. Furthermore, the influence on the stress intensity factors and energy release rate will be discussed. Finally, an experiment with piezoceramic CT specimens, which was performed by Park and Sun, will be evaluated taking into account the permeability of the crack.     

Frequency dependent electrical conductivity and dielectric relaxation behavior in amorphous (90V2O5–10Bi2O3) oxide semiconductors doped with SrTiO3

We report on the experimental results of frequency dependent a.c. conductivity and dielectric constant of SrTiO₃ doped 90V₂O₅–10Bi₂O₃ semiconducting oxide glasses for wide ranges of frequency (500–10⁴ Hz) and temperature (80–400 K). These glasses show very large dielectric constants (10²–10⁴) compared with that of the pure base glass (≈10²) without SrTiO₃ and exhibit Debye-type dielectric relaxation behavior. The increase in dielectric constant is considered to be due to the formation of microcrystals of SrTiO₃ and TiO₂ in the glass matrix. These glasses are n-type semiconductors as observed from the measurements of the thermoelectric power. Unlike many vanadate glasses, Long's overlapping large polaron tunnelling (OLPT) model is found to be most appropriate for fitting the experimental conductivity data, while for the undoped V₂O₅–Bi₂O₃ glasses, correlated barrier hopping conduction mechanism is valid. This is due to the change of glass network structure caused by doping base glass with SrTiO₃. The power law behavior (σ_ac=A(ω^s) with s<1) is, however, followed by both the doped and undoped glassy systems. The model parameters calculated are reasonable and consistent with the change of concentrations (x).