Effect of deposition temperature on dielectric properties of PECVD Ta2O5 thin film

Tantalum oxide film formation by plasma-enhanced chemical vapour deposition (PECVD) using TaCl₅ as a source material was examined. The effects of deposition temperature on the formation, structure and electric properties of the Ta₂O₅ film were investigated for Al/Ta₂O₅/ p-Si (MTS) capacitors. The deposition rate and refractive index increased with increasing deposition temperature. It was found that the structure of Ta₂O₅ deposited by PECVD was amorphous as-deposited. However, crystalline -Ta₂O₅ of hexagonal structure was formed by a 700 °C, 1 h heat treatment in argon. Capacitance and relative dielectric constant of the PECVD Ta₂O₅ were found to be 2.54 fF m^–2 and 23.5, respectively. The PECVD films obtained in this study have higher dielectric constants and remarkably better general film characteristics than those obtained by other deposition methods.     

Charge Properties of a Condenser System Based on the Two‐Layer Dielectric SiO2–Ta2O5

A variant of a combined dielectric for the condensers of very largescale integrated circuits (VLSICs) has been proposed. Its electrophysical and mechanical properties have been analyzed. The influence of the thickness of each of the dielectrics on the effective builtin charge, the permittivity, and the threshold voltage has been considered. Special emphasis has been placed on the residual mechanical stresses in a threelayer dielectric system, namely, the influence of the thickness of a Ta₂O₅ film on the radius of curvature of the Si–SiO₂–Ta₂O₅ system has been analyzed and the dependence of the change in the effective builtin charge in the Ta₂O₅ film on the radius of curvature of the plate has been determined.     

Electrical characteristics of the MOD-derived SrBi2xTa2O9 and SrBi2.4(Ta,Nb)2O9 thin films

Ferroelectric and leakage current characteristics of the MOD-derived SrBi_2xTa₂O₉ (0.8 x 1.6) and SrBi_2.4(Ta_1-yNb_y)₂ O₉ (0 y 1) thin films were investigated. The SBT and SBTN films were fully crystallized to Bi-layered perovskite structure by annealing at 800°C for 1 hour in oxygen atmosphere. The ferroelectric characteristics of the SBT films were optimized at the Bi/Ta mole ratio x of 1.2. The leakage current density of the Bi-excess SBT films decreased remarkably by the post-metallization annealing at 800°C for 10 minutes in oxygen ambient. The ferroelectric characteristics of the SBTN films were optimized with the SBN content y of 0.25. The SrBi_2.4(Ta_0.75Nb_0.25)₂ O₉ film exhibited 2P_r and E_c of 19.04 C/cm² and 24.94 kV/cm at ±5 V, which were superior to 2P_r of 11.3 C/cm² and E_c of 39.6 kV/cm obtained for the SrBi_2.4Ta₂O₉ film after the post-metallization annealing. The MOD-derived SrBi_2.4(Ta_0.75Nb_0.25)₂O₉ film did not exhibit the polarization fatigue after 10¹¹ switching cycles at ±5 V.     

Effects of Ca and Sr substitution on dielectric properties in ceramics

Modification of dielectric characteristics for Ba₃Sm₃Ti₅Ta₅O₃₀ was performed by Ca and Sr substitution for Ba. The temperature coefficient of the dielectric constant () of Ba₃Sm₃Ti₅Ta₅O₃₀ decreased somewhat by Ca substitution, but the dielectric constant () decreased considerably. In the case of Sr substitution, the temperature coefficient could be markedly decreased without considerable decrease of dielectric constant. Ceramics of the two series could obtain dielectric properties of high (> 100) and low loss (10^–3 at 1 MHz).     

Investigation into the growth and electromechanical properties of Pb(Mg1/3Nb2/3)O3 thin films

Pulsed laser deposition (PLD) has been used to fabricate relaxor thin films and thin film capacitors based on the Pb(Mg_1/3Nb_2/3)O₃ system. Best capacitor structures show dielectric constants (_r) of 1000 and losses (tan ) 0.02 at 1 kHz at 300 K. Electromechanical investigations show that tensile longitudinal strains of up to 0.2% can be achieved in these films.     

Microstructure, electrochemical surface and electrocatalytic properties of IrO2+Ta2O5 oxide electrodes

X-ray diffraction (XRD) and scanning electron microscopy (SEM) have been used to characterize physical structure of IrO₂+Ta₂O₅ films over the whole composition range by thermodecomposition of chloride solutions heated at 450°C. Solid solubilization between Ta component and IrO₂ rutile in the mixed films was measured, and three typical surface morphologies of the oxide coatings were observed. The surface electrochemical properties of Ti/IrO₂-Ta₂O₅ electrodes were studied by cyclic voltammetry at varying potential scan rate, and a double-layer electrochemical structure containing the inner and outer layers has been distinguished. The voltammetric charge appears to decline with the decrease of grain size of oxide coatings as a result of the effect of surface tension. However, the coatings of 70% IrO₂+30% Ta₂O₅ with the finest grains still exhibit the highest apparent activity for oxygen evolution evaluated by the anodic current at a constant potential. This result is interpreted by the measurements of open-circuit potential (E _oc) and double-layer capacitance (C _dl) using electrochemical impedance spectroscopy (EIS). Thereby, the reliability of voltammetric charge obtained in double-layer potential region in determining the real electrocatalytic activity for O₂ evolution has been discussed.     

1 : 2 Long-range ordering and defect mechanism of WO3-doped perovskite Ba(Mg1/3Ta2/3)O3

The nature of the B-site cation ordering and the associated defect process necessary to stabilize the ordered domains were investigated using the WO₃-doped BaMg_1/3Ta_2/3O₃ BMT system as a typical example of BaB_1/3B_2/3O₃-type complex perovskites. It was shown that only the 1 : 2 long-range ordering of the B-site cation existed in both undoped and WO₃-doped BMT perovskites. The atomic defect mechanism associated with the stoichiometric 1 : 2 long-range ordering was systematically investigated. It is concluded that the substitution of W⁶⁺ for Ta⁵⁺ in the WO₃-doped BMT enhances the degree of the 1 : 2 long-range ordering and produces the positively charged W _Ta sites with a concomitant generation of tantalum vacancies V_Ta and mobile oxygen vacancies V _O for the ionic charge compensation.     

Effect of Ta2O5 doping on the electrical properties of 0.99SnO2·0.01CoO ceramic

The effect of Ta₂O₅ doping in 0.99SnO₂·0.01CoO on the microstructure and electrical properties of this ceramic were analyzed in this study. The grain size was found to decrease from 6.87 m to 5.68 m when the Ta₂O₅ concentration increased from 0.050 to 0.075 mol%. DC electrical characterization showed a dramatic increase in the current loss and decrease in the non-linear coefficient with the increase of the Ta₂O₅ concentration. The conduction mechanism is by thermionic emission and the potential barriers are of Schottky type, separated by a thin film.     

Origins of conductive losses at microwave frequencies in YBa2Cu3O7?δ/LaAlO3/YBa2Cu3O7?δ trilayers deposited by pulsed laser deposition

Oriented YBa₂Cu₃O_7–/LaAlO₃/YBa₂Cu₃O_7– trilayers were deposited by pulsed laser deposition (PLD) onto 100 MgO and LaAlO₃. Film thicknesses varied from 2000–5000 Å/ layer. A comparision of structure and transport data for the bottom and top superconducting layers indicated a slight decrease in film quality for the top superconducting layer. The critical temperature was lower for the top superconducting layer (90.5 vs. 90 K) and the microwave surface resistance was higher (increasing from 2 to 18 m at 36 GHz, 20 K). The resistivity of the dielectric was estimated to be 10⁶ cm, and the loss tangent of the dielectric film at microwave frequencies had an upper limit of 0.01. Cross-sectional TEM analysis of the trilayer structure showed a high density of threading dislocations in the dielectric layer that appeared to nucleate at steps in the underlying superconducting layer. The threading dislocations may serve as conduction paths in the LaAlO₃ layer.     

Properties of r.f. sputtered cadmium telluride thin films

CdTe thin films were prepared using r.f. magnetron sputtering in an Ar atmosphere. Substrate temperatures in the range 100–320 °C were used. XRD results showed that the films are amorphous below 200 °C while above 200 °C the firms were polycrystalline with cubic structure and grains preferentially oriented along the [1 1 1] crystallographic direction. SEM measurements showed significant enhancement of crystallite size with increase of T _s or with post-preparation annealing above 400 °C. The 5 K photoluminescence spectrum showed a broad (FWHM=80 meV) band with a maximum at 1.538 eV. This band showed significant narrowing after annealing above 400 °C suggesting that it originates from transitions involving grain boundary defects. The refractive index n was determined from the interference pattern of the optical transmission. The results agree with the values of n calculated using the Jensen theory. The absorption coefficient was determined for photon energies hE _g (the energy bandgap) from the optical transmission spectra in the absorption region using the Swanepoel theory. Several direct and indirect allowed optical transitions were identified. It was found that the transitions can be grouped into four main allowed transitions (two direct; E _o, E ₃ and two indirect; E ₁, E ₂) whose energy values vary from one sample to another due the quantum size effect associated with small grain size. The main transitions are: E _o (1.50–1.77 eV) assigned to ₈ valence band (VB)₆ conduction band (CB) transition, E ₁ (1.84–2.05 eV) assigned to L_4,5(VB) _i transition where _i is an impurity level at 1.2 eV above the ₈ (VB), E ₂ (2.37–2.49 eV) assigned to L_4,5 (VB)₆ (CB) transition and E ₃ (2.25–2.55 eV) assigned to ₇ (VB) _i transition. The impurity is attributed to native centers or grain-boundary-related defects.     

Ba4Nd2Ti4Ta6O30 dielectric ceramics modified by Bi substitution for Nd

Modification of dielectric properties for Ba₄Nd₂Ti₄Ta₆O₃₀ ceramic was investigated through Bi partial substitution for Nd. The dielectric constant increased and the dielectric loss decreased with increasing concentration of Bi, and the dielectric constant reached 142, combined with a low dielectric loss of 10^–4 (at 1 MHz) for the composition Ba₄(Nd_0.975Bi_0.025)₂Ti₄Ta₆O₃₀. The temperature coefficient () can be slightly improved.     

Sinterability improvement of Ba(Mg1/3Ta2/3)O3 dielectric ceramics

The sinterability of Ba(Mg_1/3Ta_2/3)O₃ ceramics synthesized by solid-state-reaction methods was investigated. The poor sinterability of the present ceramics was found to be primarily due to the presence of satellite secondary phases of Ba₅Ta₄O₁₅ and Ba₄Ta₂O₉, and the nearly complete densification of Ba(Mg_1/3Ta_2/3)O₃ ceramics was accomplished successfully by controlling the phase constitution of the calcined powders. For this purpose, enhanced ball-milling processes were found to be extremely effective. Moreover, excellent microwave dielectric characteristics (_r = 24.5–24.7, Q = 26 000 at 9.8 GHz, and _f = 1.7 p.p.m. C^–1) were attained in the dense Ba(Mg_1/3Ta_2/3)O₃ ceramics without additives.     

Properties of Va metal-B films prepared by r.f.-sputtering

Ta_100-x B _x alloy films were prepared by r.f.-sputtering in the chemical composition range 45 x 77. Ta_100-x B _x (45 x 58) films consist of the amorphous phase, while the TaB₂ crystal phase was observed in Ta_100-x B _x (66 x 77) films. A remarkable preferred orientation with the (001) plane of TaB₂ parallel to the film surface was observed in Ta₃₄B₆₆. The d.c. electrical conductivity of Ta_100-x B _x (45 x 77) films decreases with increasing boron content in the range 6.7 × 10³ to 1.3 × 10^3–1 cm^–1. The micro-Vickers hardness of Ta_100-x B _x (45 x 77) films was in the range 2200 to 2600 kg mm^–2.     

The dielectic response of K x Al x Ti8−x O16 and K x Mg x/2 Ti8−x/2 O16

Materials of the hollandite structure with the general formulae K_x Al_x Ti_8–x O₁₆ and K_x Mg_x/2 Ti_8–x/2 O₁₆ have been synthesized in the composition range 1.6x2.0 and their dielectric properties have been measured in the temperature range 77 to 800 K and the frequency range 10^–3 to 10⁶ Hz. The observed response shows a whole range of features characteristic for both charge carrier and dipolar polarization processes and these are seen as being associated with the one-dimensional transport in channels in the hollandite structure. At low temperatures the dominant response is the universal dielectric relation in which the loss follows the law x() ^n–1, with the exponent n<1 and equal specifically to approximately 0.7. This is followed at 120 to 180 K by a distinct loss peak superimposed on the above law, and finally at higher temperatures by a region of strong dispersion which is associated with strongly interacting many-body processes between charged carriers restricted by defects to move in limited regions of the channels.     

Transport Properties of Ca1 – x MnO3 – δ + xCeO2(0 < x ≤ 0.15) Mixtures

Data are presented on the temperature-dependent electrical conductivity and thermoelectric power of Ca_{1 – x} MnO_{3 –} + xCeO₂ (0 < x 0.15) mixtures obtained as intermediate products in the synthesis of Ca_{1 – x} Ce _x MnO_{3 –} solid solutions. The electrical properties of the mixtures are shown to be dominated by those of the perovskite-like phase Ca_{1 – x} MnO_{3 –} and to depend on Ca concentration. All of the samples with 0 x 0.15 exhibit n-type conductivity. The charge transport in CaMnO_{3 –} below 930 K is attributable to small-polaron hopping. At higher temperatures, conduction through delocalized states seems to prevail. In the Ca_{1 – x} MnO_{3 –} + xCeO₂ mixtures with 0.05 x 0.15, small-polaron hopping is observed between 160 and 920 K. Below 160 K, the temperature variation of conductivity in the samples with x = 0.1 and 0.15 follows Mott's law.     

Phase Composition of Films Deposited by ZrB2 RF Magnetron Sputtering

X-ray diffraction and electron-microscopic studies demonstrate that the conditions of ZrB₂ rf magnetron sputtering (primarily, the argon pressure) have a significant effect on the thickness, phase composition, and structure of the growing films. The films deposited on silicon substrates at low argon pressures (0.15–0.18 Pa) consist of zirconium diboride and a very thin zirconia layer. At higher argon pressures, from 0.21 to 0.42 Pa, the film thickness is larger, and the film is composed of four layers: ZrB₂/ZrB/ZrO₂/B₂O₃. Increasing the argon pressure to 0.47 Pa, reduces the deposition rate and the thickness of the zirconia layer. The resultant films contain neither ZrB nor B₂O₃. At still higher argon pressures, up to 0.65 Pa, film thickness continues to decrease because of the reduction in the thickness of the ZrB₂ layer. The substrate temperature influences the structural perfection of the growing films. Other sputtering parameters influence the argon pressure and, accordingly, the phase composition of the films. At deposition temperatures of 60–70°C, there are certain orientational relationships between the films and single-crystal substrates. On glass-ceramic substrates, the deposition rate is substantially faster, and the deposits consist of randomly oriented crystallites.     

Copper chemical vapour deposition using copper(I) hexafluoroacetylacetonate trimethylvinylsilane

The effects of the deposition temperature on the microstructure and the electrical resistivity of copper films prepared by chemical vapour deposition (CVD) were studied at the deposition temperatures between 160 C and 330 C. Copper films were prepared on titanium nitride (TiN) substrates in a low-pressure warm-wall reactor using copper(I) hexafluoroacetylacetonate trimethylvinylsilane, Cu (hfac)(TMVS), as the precursor. The activation energy for the deposition was found to be 45.4 kJ mol^–1 at the total pressure of 66.7 Pa. The films deposited at below 200 C, where the deposition is limited by surface reaction, were dense and had low resistivity of approximately 2 cm. Moreover, they exhibited excellent step coverage. However, the films deposited at above 200 C, where the mass transport processes become important, were composed of poorly connected globular grains, resulting in considerably high resistivities and rough surfaces. Effects of the deposition temperature on the grain size and the preferred orientation of the films were also investigated.     

Spectroellipsometric studies of 0.9PbMg1/3Nb2/3O3-0.1PbTiO3 thin films

0.9PbMg_1/3Nb_2/3O₃-0.1PbTiO₃ (PMN-PT) films of different thickness, ranging from 75 to 450 nm, were prepared on La_0.5Sr_0.5MnO₃ (LSMO)-buffered LaAlO₃ (LAO) substrates by pulsed laser deposition (PLD). The structural properties of these films were characterized by X-ray diffraction. The –2 scans indicated that all the films have a pure perovskite phase containing no impurity. The - and -scans confirmed that all the films possess a heteroepitaxial relation of PMN-PT(1 0 0) LSMO(1 0 0) LAO(1 0 0) structure. The surface morphology and cross section of the films were examined by scanning electron microscopy (SEM). Their dielectric constants and the leakage currents were measured by an impedance analyzer and a leakage digital electrometer, respectively. Furthermore, spectroellipsometry (SE) was used to characterize the depth profile, refractive index, and microstructural inhomogeneities, including voids, microroughness of surface, and the electrode/film interface of these films. Based on these studies, the correlation between the electrode/film interface and the electrical properties of the films was discussed. Our results show that the ratio of the electrode/film interface thickness to the film thickness increases as the film thickness decreases. The increase in this ratio results in deterioration of the leakage current and dielectric constant of the films.     

Preparation of YBa2Cu3O7 ? δ Thin Films by the Self-Template Sputtering Method

Using the self-template technique, c-axis-oriented epitaxial YBa₂Cu₃O_{7 –} thin films have been prepared in situ on LaAlO₃ substrate by the d.c. magnetron sputtering method. The properties of thin film dependence on the deposition conditions of the two-step self-template method have been systematically investigated. By optimizing the parameters, high-quality YBCO thin films with T _c0 90 K, T _c 1 K, R _s (77 K, 10 GHz)500 were reproducibly obtained. The best sample grown under optimal conditions gave a low R _s of 330 at 77 K, 10 GHz, which can be used in a microwave field.     

Electrical properties of non c-axis oriented SrBi2(Ta0.95V0.05)2O9 thin films

Pulsed laser deposition technique was used to grow off c-axis oriented SrBi₂(Ta_0.95V_0.05)₂O₉ (SBTV) ferroelectric thin films. X-ray diffraction studies revealed the c-axis suppression in the films grown at lower substrate temperature (350°C) followed by annealing at higher temperatures (650°C). In-plane lattice parameters of the films were decreased with increase in annealing temperature. SBTV films annealed at 750°C exhibited enhanced ferroelectric properties with remanent polarization (2P _r) of 31.5 C/cm² and coercive field (E _c) of 157 kV/cm. The dielectric permmitivity of the films increased with increase in annealing temperature and it was attributed to the grain size dependence. The films annealed at 750°C showed maximum value of dielectric permittivity 172 with a tangential loss of 0.1, at 100 kHz. Higher value of dissipation factor at lower annealing temperature is explained in terms of space charge accumulation at grain boundaries. The leakage current densities of the films follow ohmic behavior at low field regime and space charge limited current dominates at higher fields.