Dielectric properties of vacuum deposited Samarium Oxide sandwich structures

Samarium oxide films were prepared by vacuum thermal evaporation using tantalum boats. The effect of aging, frequency and annealing on capacitance and tan δ were studied for Al Sm₂O₃ Al capacitor structures. The variation in capacitance with frequency at low frequency region is quite considerable. The existence of oxygen vacancies were confirmed from the thermoluminescence studies of these oxide films. The results were discussed on the basis of oxygen vacancies existing in these films.     

Dielectric and electrical studies on as-grown CeO2 films

Thin film capacitors of CeO₂ were fabricated by thermal evaporation. The dielectric properties of these films were studied in the frequency range 0.05–16 KHz at various temperatures, starting from liquid nitrogen temperature to 390 K. The effect of annealing on capacitance and tan δ were studied for different frequencies. The behaviour was explained on the basis of relief in strain energy. The plot between current density and temperature was drawn, and from the slope of the plot the activation energy was calculated and found to be 0.52 ev. The results were discussed.     

Dielectric and Electrical Properties of InSe Films

The dielectric and electrical properties of sandwiched Al InSe Al structures of different thicknesses are investigated. For all the thicknesses the capacitance and tan δ decrease with increase in frequency. The I-V characteristics of Al-InSe-Al structures have been studied for different thicknesses. These curves exhibit three regions ohmic, non-ohmic and breakdown regions. Optical micrographs of breakdown patterns at different stages have been taken and the results are discussed.     

Electrical properties of Al-CeO2-Al thin film capacitor structures

Cerium Oxide films were prepared by vacuum thermal evaporation from tantalum boat in a conventional vacuum coating unit. Current-voltage characteristics were studied for different film thicknesses. The breakdown voltage (V_B) and dielectric field strength (E_B) were calculated. It is found that the breakdown voltage increases and dielectric field strength decreases as the thickness of the film increases. The applicability of Forlani-Minnaja relation is discussed. Current-voltage characteristics were also drawn at different temperatures and breakdown voltages were calculated. The breakdown voltage decreases as the temperature of the structure increases but the variation is nonlinear. The variation of current density with temperature was studied and the activation energy for the migration of charge carriers was calculated and it is about 0.52 ev. The results were discussed.     

Dielectric Properties of Beta Barium Borate and Potassium Pentaborate Single Crystals

Single crystals of beta barium borate and potassium pentaborate (commonly known as β-BaB₂O₄ or BBO and KB₅O₈. 4 H₂O or KB5) were grown by high and low temperature solution growth methods, respectively. The dielectric constant and loss tangent were determined as a function of temperature. Frequency response of the dielectric constant and tan δ have been studied over a frequency range of 0.1 −100 kHz; it is found that both the dielectric constant and tan δ decrease with increase in frequency for both crystals. The dielectric constant and tan δ are found to increase with increase in temperature for both the crystals. Further, the dielectric constant and tan δ measured on different orientations of the grown crystals reveal the anisotropic nature of the crystals.     

Study of electrical properties in mixed oxide sandwich structures

I—V characteristics of sandwiched Al—(SnO₂ + Sb₂O₃)—Al mixed films have been studied for different thicknesses. The current-voltage curves in general exhibit three regions, ohmie, non-ohmic and breakdown regions. The breakdown voltage increases and the dielectric strength decreases with increase of film thickness. The de breakdown studies have been done and optical photomicrographs of breakdown patterns during different stages of de voltage have been taken and the results are discussed.     

Effect of Electric Field on Dielectric Properties of SnO2 Sb2O3 and their Mixed Thin Films

Thin films of various thicknesses in the MIM structure have been prepared from the the powders of SnO₂, Sb₂O₃ and (SnO₂ + Sb₂O₃) of high purity by the thermal evaporation technique in a vacuum of 10⁻⁵ Torr. Dielectric properties of SnO₂, Sb₂O₃, and their mixed thin films have been studied with ac and dc electric fields and frequency. Capacitance and loss tangent are almost independent on dc voltage upto 1.0 V for SnO₂, 10.0 V for Sb₂O₃ and 2.5 V for mixed films. These capacitors become unstable at 1.0 V for SnO₂ films and 2.5 V for mixed films. For higher film thicknesses the decay in these films starts at higher voltages. Capacitance and loss tangent increases with applied ac voltage in SnO₂, Sb₂O₃, and their mixed films. A comparison of the capacitance values of SnO₂, Sb₂O₃, and their mixed films showed that the capacitance values are less in Sb₂O₃ as compared to SnO₂ films. In mixed films the capacitance is greater than the constituent films. These studies have shown that Sb₂O₃ films are found to be more stable compared to SnO₂ and their mixed films for ac and dc voltages. The results thus obtained on SnO₂, Sb₂O₃, and their films are presented and discussed.     

I–V characteristics and break down studies of Sb2O3 structures

I–V characteristics of sandwiched Al–Sb₂O₃–Al structures have been studied for different thicknesses. The current-voltage curves in general exhibit three regions, ohmic, non ohmic and breakdown regions. The breakdown voltage increases whereas the dielectric strength decreases with increase in Sb₂O₃ film thickness. The electrical breakdown studies have been done for dc and ac voltages and optical photomicrographs of breakdown patterns during different stages of voltage have been taken and the results are explained.     

Dielectric and electrical properties of vacuum-deposited Didymium oxide thin films

Dielectric and electrical properties of sandwich structures of didymium oxide thin films of several thicknesses have been investigated. The variation of capacitance and dielectric dissipation factor (Tan δ) with frequency in these films have been studied. These studies have shown that at room temperature, the capacitance increases with decrease of frequency and the variation is more pronounced at low frequencies. With increase of frequency, the dissipation factor decreases. The increase of capacitance with decrease in frequency has been attributed to the space-charge polarisation and blocking of charge carriers at the electrodes. The effect of thickness on capacitance and Tan δ in these films have been studied. Current-Voltage characteristics (I—V) of sandwiched Al-didymium oxide-Al structures have been studied at room temperature. These characteristics showed that the breakdown voltage increases and the dielectric strength decreases with increase of oxide film thickness. Conductivity (σ) at room temperature have been calculated to understand the mechanism involved in the conduction process. These results indicated that the conduction in these films is due to Schottky barriers. Breakdown patterns obtained in these structures by the application of de voltage applied across the sandwich structures have been observed with the help of Carl-Zeiss, Jena, optical microscope. The photomicrographs of these breakdown patterns indicate that the type of breakdown in these structures may be single-hole breakdown and is proceeded by propagating breakdown.     

Ageing effect on dielectric properties of SnO2, Sb2O3, and their mixed thin films

Thin films of various thicknesses in the form of MIM structures have been prepared from the powders of high purity of SnO₂, Sb₂O₃, and their mixed powders separately by the thermal evaporation technique in a vacuum of 10⁻⁵ Torr. The dielectric properties of these oxide thin films have been studied with ageing time and also with frequency at room temperature. The results obtained have shown that the capacitance and loss tangent of the structures initially fall off rapidly and thereafter they attain a constant value even after ageing the capacitors for about 20 days. The rapid fall of capacitance and loss tangent may be due to the rapid decrease in the density of defects due to ageing time. The results thus obtained on SnO₂, Sb₂O₃, and their mixed thin film capacitors are presented and discussed.     

Dielectric Properties of Tin Oxide Thin Film Capacitors

Thin films of several thicknesses in the form of MIM structures are prepared from the powders of tin oxide (SnO₂) by thermal evaporation technique in a vacuum of 10⁻⁵ Torr. The dielectric properties of tin oxide film capacitors have been studied with temperatures varying from 77 to 400 K and also with frequency. At 77 K the values of capacitance and loss tangent are small for these films. With increasing temperature the values of capacitance and loss tangent increase. The capacitance-temperature plots show peak values of capacitance at 345 K for 1 kHz, 350 K for 2 kHz, 360 K for 5 kHz and 368 K for 10 kHz. These peak values of capacitance can be eliminated by repeated heating and cooling of the structures. The activation energy for the migration of charge carriers is calculated for tin oxide films and is found to be 0.13 eV. The results obtained on the dielectric properties of tin oxide thin films are presented and discussed.     

Effects of oxygen partial pressure during sputtering growth on physical properties of Zn0.93Mn0.07O thin films

We have studied structural, optical, electrical, and magnetic properties of Zn_0.93Mn_0.07O thin films grown by RF magnetron sputtering under ambient gas mixtures of O₂ and Ar. As the oxygen partial pressure increases, the electron concentration systematically decreases and photoluminescence peaks related to oxygen vacancies gradually diminish. These results suggest that oxygen vacancies are majority donors. Smooth surface morphology and electron concentration as low as ∼10¹⁵ cm⁻³ are obtained simultaneously for the film grown in an optimal oxygen partial pressure. This film exhibits ferromagnetism with the Curie temperature of 78 K, while other films grown in higher or lower oxygen partial pressure show paramagnetic behavior down to low temperature. The disappearance of the ferromagnetism can be explained in terms of crystalline quality and surface smoothness rather than electron concentration.     

Crystalline and electrical properties of pulsed laser deposited BST on platinized silicon substrates

In order to produce thin film capacitors with elevated capacitance and breakdown strength, pulsed laser deposition of the ferroelectric material Ba_0.6Sr_0.4TiO₃ (BST) has been made on (1 1 1)Pt/Ti/SiO₂/Si substrates. The films are in situ crystallized at 700 °C, polycrystalline in nature, and exhibit a single perovskite phase. This paper reports on both the effect of the oxygen pressure during heating and deposition, and the influence of different modes of introduction during the deposition stage, on the crystalline and electrical properties of the BST films. Orientation of films depends on the deposition oxygen pressure, with a (1 1 1) preferential orientation obtained when depositing under vacuum. XRD characterization reveals that the out-of-plane parameter of BST films increases when depositions are made under lower oxygen pressure. This phenomenon is related to a higher concentration of vacancies and defects in the films grown under low-pressure environment. However, a local introduction of oxygen on the substrate improves the annihilation of these defects. The crystalline orientation of the films is also highly dependent on the residual oxygen pressure during heating. A high (1 1 1) preferentially oriented BST film is obtained when heating and depositing under 0.1 mbar oxygen pressure. The heating atmosphere is thought to influence the out-diffusion of titanium on the surface of the Pt layer, thus modifying the nucleation and growth of BST films. Aluminum electrodes have been deposited on top of the BST films by dc sputtering to measure electrical capacitances. The calculated dielectric constant of in situ crystallized films deposited under 0.1 mbar oxygen pressure exceeds 500 at 100 kHz under zero dc bias. This high dielectric constant value obtained without post-deposition treatment appears to be of great technological interest.     

Capacitance-voltage characteristics of In0.3Ge2Sb2Te5 thin films

The influence of indium doping on the capacitance variation with temperature and applied bias voltage of Ge₂Sb₂Te₅ is investigated. The capacitance-voltage (C-V) measurements of In_0.3Ge₂Sb₂Te₅ and Ge₂Sb₂Te₅ thin films were performed for a sweep of voltages from −20 to +20 V at different temperatures. The results show different capacitance behavior of In_0.3Ge₂Sb₂Te₅ and Ge₂Sb₂Te₅ films. As the temperature increases the capacitance of the indium-doped sample decreases and becomes negative. The negative capacitance effect might be attributed to a significant increase of the film’s conductivity due to temperature and applied bias voltage. The nonlinearity in the capacitance and conductivity could be related to the nucleation mechanism as the temperature becomes close to the amorphous-crystalline transition temperature.     

Characteristics of Al/p‐Cu0.5Ag0.5InSe2 Polycrystalline Thin Film Schottky Barrier Diodes

Al/p‐Cu_0.5Ag_0.5InSe₂ polycrystalline thin film Schottky barrier diodes have been prepared. The current‐voltage, capacitance‐voltage and photores ponse have been investigated. Various important physical parameters of the sediodes were derived from these measurements.     

Role of oxygen vacancies in the origin of ferromagnetism in Mn‐doped ZnO

The relationship between the oxygen vacancy and ferromagnetism in Mn‐doped ZnO has been studied based on the first‐principles calculations. Three possible charge states of oxygen vacancies, i.e., neutral (V_O⁰), 1+ (V_O¹⁺) and 2+ (V_O²⁺) are considered. Results show that the lattice relaxations around oxygen vacancies are large difference under different charge states. It is found that V_O¹⁺ and V_O²⁺ oxygen vacancies induce ferromagnetism. However, Mn‐doped ZnO system shows ferromagnetism with V_O⁰ oxygen vacancies in hydrogenated environment, the ferromagnetism is attributed to the interstitial H, which forms a bridge bond and mediates d ‐d coupling and stabilizes the ferromagnetic state. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Conduction Studies on Bismuth Selenide Thin Films

Thin films of Bi₂Se₃ have been prepared by vacuum deposition technique onto well cleaned glass and freshly cleaved KBr substrates. The film thicknesses are measured by Tolansky technique. The capacitance and dielectric constant have been measured from 303 K to 383 K in the frequency range of 10 kHz to 10 MHz. The a.c. conductivity s is calculated at different frequencies for various temperatures. The relation s μ wn fits well and the value of n is found to be greater than 1.5 and above at high frequencies suggests that the conduction mechanism in Bi₂Se₃ thin film is hopping. The d.c. conduction studies revealed the non-ohmic type of conduction( Log I versus Log V plot). From the Log I versus F1/2 plot, the field lowering coefficient b is evaluated.     

Isochronal Studies of α‐Si:H Crystallization and the Performance of it's Schottky Barriers

Hydrogenated amorphous silicon films (α‐Si:H) were crystallized employing a metal induced crystalline (MIC) technique. Structural changes during annealing these films at 300 °C for different periods (0‐300 minutes) were obtained by XRD. Al was used as a metal induced crystalline for α‐Si:H produced by ultra high vacuum (UHV) plasma enhanced chemical vapor deposition (PECVD). XRD shows that crystallization of the interacted α‐Si:H film underneath Al initiates at 300 °C for 15 minutes. A complete crystallization was obtained after annealing for 60 minutes. A gold dot was evaporated onto α‐Si:H films, which annealed for different periods to form Schottky barriers. Electrical properties of Au/α‐Si:H were calculated such as the ideality factor, n, barrier height, Φ_B, donor concentration, N_D, and the diffusion voltage, V_d, as a function of the annealing time of α‐Si:H films. All these parameters were carried out through the current voltage characteristics (J‐V) and the capacitance voltage measurements (C‐V). The results were presented a discussed on the basis of XRD performance and the thermionic emission theory.     

Crystal structure and magnetic properties of nanosized Mg(Fe0.8Ga0.2)2O4-δ films on Si substrates

Film samples of nominal Mg(Fe_0.8Ga_0.2)₂O_4-δ composition were obtained on Si(100) substrates by oxygen-ion-beam sputtering of a Mg(Fe_0.8Ga_0.2)₂O_4-δ ceramic target. The film thicknesses were ～200 and ～400 nm. Field dependences of the specific magnetization of ～200-nm films annealed at different temperatures (800–1000°C) have been measured. The crystal structure, surface morphology, and magnetic characteristics of films of different thicknesses (～200 and ～400 nm) are investigated. The reasons for the discrepancy between the specific magnetizations of the films obtained and their ceramic analog are discussed.     

Decrease in dielectric loss of CaCu3Ti4O12 by the addition of TeO2

CaCu₃Ti₄O₁₂ (CCTO) has challenged for the last few years the scientific community due to its large dielectric constant, which is almost temperature and frequency independent, from 100 K to 400 K and from 1 kHz to 1 MHz, respectively. This makes the material desirable for many electronic applications. However, the dissipation factor is very large, with tan δ values, at room temperature and 1 kHz, higher than 0.1.In our work we report how the addition of TeO₂ lowers the dielectric loss and, although there is a decrease of dielectric constant of doped samples relatively to the undoped one, high dielectric constant values are still being reached. The sample of doped CCTO with 1.5% of TeO₂ by weight, presents, at room temperature and 60 kHz, a large dielectric constant, over 3000, and a dissipation factor around 0.09, which represents a decrease on tan δ over 30% relatively to the CCTO undoped sample. Two relaxation processes were identified for all the samples, one at MHz region and the other one at low frequency region (< 1 kHz). DC bias voltage was applied up to 40 V and a strong dc bias influence on the low frequency region was observed both at dielectric and impedance responses of the undoped sample, which was much weaker than the dc bias effects on the 4% Te doped sample.Dielectric measurements will be discussed and correlated with the samples' microstructure, supported on internal barrier layer capacitance (IBLC) and surface barrier layer capacitance (SBLC) models.