Dielectric behavior of Cu–GeO<Subscript>2</Subscript> cermet thin films

Capacitance and dielectric loss measurements were carried out using an Al/Cu–GeO₂/Al sandwich structure for 0 to 10 vol% Cu films, 120–400 nm thick, deposited at 0.4–1.5 nm/s in the frequency and temperature range 1–10⁶ Hz and 90–573 K, respectively. The variation of capacitance and dielectric loss with frequency and temperature follows the Goswami and Goswami model. Capacitance decreases slowly with increasing thickness and also varies with the change in deposition rate of the cermet film.     

Influence of temperature and frequency on electrical properties of electron beam evaporated bromoaluminum phthalocyanine, BrAlPc, thin films

The AC electrical properties of electron beam evaporated Bromoaluminum phthalocyanine (BrAlPc) thin films have been studied in the frequency range 10²–10⁵ Hz and in the temperature range of 303–413 K. The BrAlPc thin films are characterized by field emission scanning electron microscopy (FESEM). The capacitance is found to be sensitive to the frequency and increases with increasing temperature and decreases with increasing frequency. A loss minimum has been observed in the frequency dependence of the dissipation factor. Such behavior is found to be in good qualitative agreement with the model of Goswami and Goswami. The AC conductivity $\sigma \left( \omega \right)$ σ ( ω ) is found to vary as $\omega^{s}$ ω s in the studied frequency range. At frequencies 10–10² Hz, s is less than unity and decreases with increase in temperature indicating a dominant hopping process. At frequency ranges 10²–10⁴ Hz, exponent s lies very close to the unity and is independent of temperature, which shows the quantum mechanical tunneling is dominated conduction mechanism. At higher frequencies 10⁴–10⁵ Hz, s is found to be temperature independent. The temperature dependence of AC conductivity shows a linear increase with the increase in temperature. Moreover, the activation energies of device are determined as a function of frequency.     

Effect of substrate temperature on ac conduction properties of amorphous and polycrystalline GaSe thin films

X-ray diffraction analysis of GaSe thin films used in the present investigation showed that the as-deposited and the one deposited at higher substrate temperature are in amorphous and polycrystalline state, respectively. The alternating current (ac) conduction properties of thermally evaporated films of GaSe were studied ex situ employing symmetric aluminium ohmic electrodes in the frequency range of 120-10⁵ Hz at various temperature regimes. For the film deposited at elevated substrate temperature (573 K) the ac conductivity was found to increase with improvement of its crystalline structure. The ac conductivity (σ_ac) is found to be proportional to (ω^s) where s < 1. The temperature dependence of ac conductivity and the parameter, s, is reasonably well interpreted by the correlated barrier-hopping (CBH) model. The maximum barrier heights W_m calculated from ac conductivity measurements are compared with optical studies of our previous reported work for a-GaSe and poly-GaSe thin films. The distance between the localized centres (R), activation energy (ΔE_σ) and the number of sites per unit energy per unit volume N(E_F) at the Fermi level were evaluated for both a-GaSe and poly-GaSe thin films. Goswami and Goswami model has been invoked to explain the dependence of capacitance on frequency and temperature.     

Conductivity and dielectric properties of silicon nitride thin films prepared by RF magnetron sputtering using nitrogen gas

Silicon nitride is an important material in very-large-scale integration fabrication and processing. Recent work on films prepared by radio frequency magnetron sputtering using nitrogen gas have shown that the relative permittivity is typically 6.3 and that aluminium forms an ohmic contact to this material. Under direct current (DC) bias the films exhibited space-charge-limited conductivity with a bulk trap density of the order of 2×10²⁴ m⁻³. In the present work alternating current electrical measurements were made on identical samples as a function of frequency and temperature. Conductivity appeared to be by hopping at lower temperatures, giving way to a free-band conduction process with activation energy of typically 0.44 eV at higher temperatures. Over a limited range of frequency and temperature the model of Elliott was applicable, and yielded a value of 2.87×10²³ m⁻³ for the density of localised states, in reasonable agreement with our estimate of the trap density from DC measurements. As in the DC measurements capacitance followed a geometric relationship with relative permittivity 6.3, and showed a moderate decrease with increasing frequency and an increase with increasing temperature, tending towards a constant value at high frequencies and low temperatures. The loss tangent showed a minimum in its frequency dependence, which appeared to shift to higher frequencies with increasing temperature. The measurements are consistent with the model of Goswami and Goswami for samples having ohmic contacts, and are typical of results obtained on other insulating thin film structures.     

Nanostructures bilayer ZnO/MgO dielectrics for metal–insulator–metal capacitor applications

Bilayer ZnO/MgO dielectrics for metal–insulator–metal (MIM) capacitor application were successfully deposited using simple chemical technique which is sol–gel spin coating method with different annealing temperatures. Important criteria in determining good dielectric layer have been investigated which include structural, electrical and dielectric properties. Cubic-like grain was observed for films annealed at 400 and 425 °C which enhance the carrier density and polarization that resulted in high k value produced. Bilayer film annealed at 475 °C improved in small surface roughness (17.629 nm), minimum leakage current density (~10^?8 A cm^?2) and high resistivity (3.14 × 10⁵ Ω cm). Dielectric constant, k was varied with frequency and k value was found to be 5.09 at 10 kHz. The results obtained in this study indicated that film annealed at temperature of 475 °C is suitable to be used as dielectrics for MIM capacitor application.     

Ac conductivity and dielectric properties of Ge20Se75In5 films

Amorphous films of Ge₂₀Se₇₅In₅ chalcogenide glass were prepared using a thermal evaporation technique. The chemical composition of the deposited films was examined using energy dispersive X-ray spectroscopy (EDX). The ac conductivity and dielectric properties of the prepared films have been studied as a function of temperature in the range from 300 to 423 K and frequency in the range from 10² to 10⁵ Hz. The experimental results indicate that ac conductivity σ_ac(ω) is proportional to ω^s where s equals 0.902 at room temperature and decreases with increasing temperature. The results obtained are discussed in terms of the correlated barrier hopping (CBH) model. The density of localized states N(E_F) at the Fermi level is found to have values of the order 10¹⁹ eV⁻¹ cm⁻³, which increase with temperature. The dielectric constant ?₁ and dielectric loss ?₂ were found to decrease with increasing frequency and to increase with increasing temperature over the ranges studied. The maximum barrier height W_m was estimated from an analysis of the dielectric loss ?₂ according to Giuntini equation. Its value for the deposited films (0.43 eV) agrees with that proposed by the theory of hopping of charge carrier over a potential barrier as suggested by Elliott for chalcogenide glasses.     

Dielectric and optical properties of ZnS films

A.c. properties of ZnS film capacitors were studied at different temperatures (78 to 380 K) and frequencies (10² to 10⁵ Hz). Dielectric constant was found to be independent of frequency and film thickness (>900 Å). Capacitance, though dependent on temperature and frequency, became constant in a low temperature region for all frequencies. Loss factor, showing a pronounced minimum with frequency, increased with the rise of temperature and tan δ_min shifted to a higher frequency. Breakdown voltages were also measured.A proposed model of an equivalent circuit predicts some characteristic features of the capacitors which have been experimentally verified. Refractive indices of these films were measured for the visible region and the dielectric constant was evaluated for optical frequencies. Effects of substrate temperatures on these films were also studied.     

Effect of strain and grain boundaries on dielectric properties in La0.7Sr0.3MnO3 thin films

High dielectric constant and its dependence on structural strain and grain boundaries (GB) in La_0.7Sr_0.3MnO₃ (LSMO) thin films are reported. X-ray diffraction, magnetization, and magneto-transport measurements of the LSMO films, made by pulsed laser deposition on two different substrates—MgO and SrTiO₃ (STO), were compared to co-relate magnetic properties with dielectric properties. At room temperature, in the ferromagnetic phase of LSMO, a high dielectric constant (6 × 10⁴) was observed up to 100 kHz frequency for the films on MgO, with polycrystalline properties and more high-angle GB related defects, while for the films on STO, with single-crystalline properties but strained unit cells, high dielectric constant (≈10⁴) was observed until 1 MHz frequency. Also, a large dielectric relaxation time with significant broadening from the Debye single-dielectric relaxation model has been observed in samples with higher GB defects. Impedance spectroscopy further shows that large dielectric constant of the single-crystalline, strained LSMO film is intrinsic in nature while that in the polycrystalline films are mainly extrinsic due to higher amount of GBs. The presence of high dielectric constant value until high frequency range rules out the possibility of “apparent giant dielectric constant” arising from the sample-electrode interface. Coexistence of ferromagnetism and high dielectric constant can be very useful for different microelectronic applications.     

Electrical characterization of amorphous germanium dioxide films

Amorphous germanium dioxide (GeO₂) films have been deposited by electron beam evaporation onto different substrates including glass, SnO₂ conducting glass, evaporated gold and n-type silicon in order to examine the electrical behaviour of GeO₂ in metal/insulator/metal (MIM) and metal/insulator/semiconductor (MIS) structures. In MIM structures the as-deposited films are strongly influenced by electrode barriers but heat treatment at 600 K induced ohmic behaviour. The dielectric response of the films in the frequency range 0.1–100 kHz and the temperature range 180–350 K showed that the dielectric constant at 300 K was 9 and was virtually independent of frequency, while the a.c. conductivity follows the relation σ ∞ ω^s, where s is temperature dependent. Good agreement with a classical electronic hopping model is obtained. In MIS structures, GeO₂ on silicon gives rise to heterojunction behaviour at low voltages while, at higher voltages, the d.c. conduction is bulk dominated and exhibits space-charge-limited conduction. The dielectric response of MIS structures is strongly influenced by the depletion capacitance at the interface between GeO₂ and silicon.     

The chemical vapour deposition and characterization of ZrO2 films from organometallic compounds

ZrO₂ films were deposited on silicon substrates by oxygen-assisted decomposition of zirconium-β-diketonates at temperatures of 400–550°C. The deposits, fine-grained nearly stoichiometric monoclinic ZrO₂, were hard and showed strong adherence to the substrate. The films were characterized by transmission electron microscopy, X-ray diffraction and electron microprobe analysis and by measuring their dielectric and optical properties. The index of refraction was found to be 2.18, and the optical energy band gap was found to be 5.16 eV. The dielectric constant at 1 MHz was 17–18, and the dielectric strength varied between 1 × 10⁶ and 2.0 × 10⁶ V cm^?1. Capacitance-voltage measurements at 1 MHz indicated the presence of effective surface states with a concentration in the range (1.0?6.0) × 10¹¹cm^?2 for films deposited at temperatures above 500°C or for films deposited at 400–450°C and annealed at above 750°C. The flat-band voltages were between ?0.6 and + 0.2 V. The films showed satisfactory bias-temperature stability. The current-voltage characteristic followed an I ∝ V² dependence for negative bias and an I ∝ V^2.6 to I ∝ V^3.4 dependence for positive bias.     

γ-Irradiation effect on the trap-hopping conductivity of thin film SiO2-Si3N4 structures

The a.c. properties of r.f. sputtered aluminium fluoride metal-insulator-metal capacitors were measured at different temperatures in the range 103–423 K and at various frequencies between 10² Hz and 10⁶ Hz. The capacitance of the specimens varied slightly with frequency and temperature. Both the capacitance and loss tangent of freshly prepared samples tended to be larger before the first heating cycle was initiated but attained a constant value after three or four heating cycles. The relative permittivity (?_r = 2.8) was found to be smaller than that for thermally evaporated AlF₃ films, indicating that the sputtered films were more highly amorphous.Tha activation energy of the conduction mechanism in the temperature range 103–273 K was found to be 0.0018 eV while that at higher temperatures was 0.068 eV. The plot of tan δ versus frequency showed a minimum with tan δ_min shifting towards higher frequencies as the temperature was increased. The conductance varied as fⁿ where n had the value 0.85 in the low frequency low temperature range and the value 2 in the high frequency high temperature region.The sputtered AlF₃ films showed a lower value of loss tangent and less temperature dependence of permittivity than thermally prepared samples.     

Structural characterization and frequency response of sol–gel derived Bi3/2MgNb3/2O7 thin films

The Bi_3/2MgNb_3/2O₇ (BMN) thin films were prepared via a modified sol–gel process on glass substrates at various post-annealing temperatures. The crystalline structure, morphology and frequency response have been investigated systematically. The X-ray diffraction results indicated that the BMN thin films had different orientations depending on post-annealing temperature. Thin films annealed above 650 °C presented well crystallized cubic pyrochlore structure with (222) orientation, and (400) preferentially oriented were observed when they were annealed below 600 °C. The surface morphology images of the BMN thin films revealed different grain size and grain size distribution, and the average grain size increased from 28.3 to 37.0 nm as the post-annealing temperature increasing. The low frequency dielectric properties of the BMN thin films were closely correlated with the (222) orientation, which was favorable to enhanced dielectric constant and tunability. The high-frequency optical measurements revealed an average transmittance (T _av ) varying between 76.6 and 82.2 % and band gap energy (E _g ) ranging from 3.40 to 3.44 as a function of the temperature and the crystallite size. Thin film annealed at 700 °C possessed the best crystallinity and highest (222) orientation, and showed the best electrical properties, with a dielectric constant of 105 at 1 MHz, dielectric tunability of 25.8 %, and an average optical transmittance of 82.2 % in the visible range (400–800 nm), making it promising for optical/electronic tunable devices applications.     

Synthesis of SiOF nanoporous ultra low-k thin film

In this work, we have investigated the effect of annealing temperature on physical, chemical and electrical properties of Fluorine (F) incorporated porous SiO₂ xerogel low-k films. The SiO₂ xerogel thin films were prepared by sol–gel spin-on method using tetraethylorthosilicate as a source of Si. The hydrofluoric acid was used as a catalyst for the incorporation of F ion in the film matrix. The thickness and refractive index (RI) of the films were observed to be decreasing with increase in annealing temperature with minimum value 156 nm and 1.31 respectively for film annealed at 400 °C. Based on measured RI value, the 34 % porosity and 1.53 gm/cm³ density of the film annealed at 400 °C have been determined. The roughness of the films as a function of annealing temperature measured through AFM was found to be increased from 0.9 to 1.95 nm. The Electrical properties such as dielectric constant and leakage current density were evaluated with capacitance–voltage (C–V) and leakage current density–voltage (J–V) measurements of fabricated Al/SiO₂ xerogel/P–Si metal–insulator-semiconductor (MIS) structure. Film annealed at 400 °C, was observed to be with the lowest dielectric constant value (k = 2) and with the lowest leakage current (3.4 × 10^?8 A/cm²) with high dielectric breakdown.     

2.12 Dielectric dispersion and polarization effects in thin transition metal oxide films

Dielectric properties of thin polycrystalline and amorphous films of NiO, NiO(Li), CoO, CoO(Li), Nb₂O₅ and TiO₂ in the thickness range 0.14–15 ωm were studied as a function of frequency, temperature, applied voltage and dopant concentration in the frequency range 3–10⁸ Hz. These films were prepared either by anodization or thermal oxidation and in some cases by reactive sputtering. Experimental data for the real ?₁ and imaginary ?₂ parts of the dielectric constant, ac conductivity σ(ω) and loss tangent tan δ indicate the existence of several dispersion mechanisms. Cole-Cole plots and the modified Debye relations were used to derive the values for relaxation times at low frequencies. The frequency dependence of σ(ω) in the frequency region 10³–10⁶ Hz where σ(ω)αωⁿ indicates that the dispersion mechanism is due to charge carriers hopping between sites with either correlated or non-correlated potentials. The observed quadratic dependence of σ(ω) on frequency in the frequency region 10⁶–10⁸ Hz is attributed to a Debye type loss resulting from thermally activated hopping. Polarization effects at lower frequencies <10³Hz indicate the existence of Schottky barriers at the metal-insulator interfaces in agreement with Simmons theory of MIM structures.     

Preparation and dielectric properties of Si3N4 thin films

Thin Si₃N₄ films of thickness 50–1500 nm were prepared by a low pressure, room temperature chemical vapour deposition process. The dielectric properties of the layers were studied in the frequency range from 10 Hz to 1 MHz and at temperatures between 77 and 400 K. We observed a σ'(ω, T) = A(T)ω^s(T) dependence with s?1 (where σ' is the real part of the a.c. conductivity). For samples prepared in various ways, A varied between a constant value and a superlinear dependence on temperature. At 77 K, however, σ' for all the samples was found to be approximately the same (about 8 × 10^?12 Ω^?1 cm^?1 at 1 kHz) irrespective of the preparation parameters.     

Orientation-dependent microwave dielectric properties of Ba0.6Sr0.4TiO3 thin films prepared by sol–gel method

Barium strontium titanate (Ba_0.6Sr_0.4TiO₃, BST) thin films have been prepared on the (100) LaAlO₃ single-crystal substrates by sol–gel technique. The X-ray diffraction study indicated that the thin films exhibited (100) preferred orientation and random orientation depending upon the concentration of precursor solution. The nonlinear dielectric properties of the BST films were measured using an interdigital capacitor. The temperature dependence of dielectric constant of the BST thin films was measured at 1 MHz in the temperature range from ?100 to 80 °C. The Curie temperature T _c of the films derived from 0.1, 0.2 and 0.3 M was found to be ?18.5, ?32.5 and ?39.9 °C, respectively. The tunability of BST films with the (100) preferred orientation was 30.74 %, which was much higher than that of thin films with random orientation at the frequency of 10 kHz with an applied electric field of 80 kV/cm. The microwave dielectric properties of the BST thin films were measured by a vector network analyser from 1 to 10 GHz.     

Deposition temperature effect on the electric and dielectric properties of InSbSe3 thin films

Thin films of InSbSe₃ compound were obtained by thermal evaporation on to clean glass substrates maintained at various deposition temperatures from 423 to 593 K. At deposition temperature T_d?473 K, the films have an amorphous structure, while those prepared at T_d>473 K have a polycrystalline structure identified by X-ray diffraction analysis. The DC electrical conductivity of the films increases as T_d increases, whereas activation energy decreases with increasing T_d, which reflects a change in the degree of disorder. AC conductivity was studied as a function of frequency in the range (10²-10⁵ Hz) and as a function of deposition temperature. The dependence of T_d on the frequency exponent s in the conductivity-frequency relation confirmed that the mechanism of AC conductivity is correlated barrier hopping with a single polaron hopping mechanism. The discrepancy between DC and AC activation energies was studied as a function of deposition temperature. The maximum barrier height W_m and the density of defect states N were also determined. Finally, the dependence of dielectric constant and dielectric loss on T_d were studied. A Debye-like relaxation of dielectric behavior was observed for crystalline films and is found to be a thermally activated process. The position of maximum dielectric loss is shifted towards higher temperature with T_d treatment and there by reduces the relaxation time.     

Structural,dielectric, and electrical studies on thermally evaporated CdTe thin films

Sandwich structures of cadmium telluride (CdTe) thin films between Ag electrodes were prepared by thermal evaporation technique at a vacuum of ~2 × 10⁻⁵ torr. Structural characterization of these thin films was performed using X-ray diffraction (XRD) studies. The effect of temperature and frequency on the electrical and dielectric properties of these films was studied in detail and reported in this article. The experimental study indicates that for the CdTe thin film the dielectric constant and dielectric loss increases with temperature and decreases with frequency. However, A.C. conductivity increases both with temperature and frequency. The data of complex impedance measurements over the same range of temperature and frequency are used to describe the relaxation behavior of the CdTe film. Our results indicate that the transport behavior of carriers in CdTe thin films is consistent with the correlated barrier hopping (CBH) model.     

La-graded heterostructures of Pb1−xLaxTiO3 thin films

This work presents the preparation of La-graded heterostructure thin films and their property comparison with those of conventional thin films of similar compositions. La-graded heterostructure films were prepared on platinum substrates using sol–gel technique. These films showed relatively higher values of P_m and P_r (68 and 38 μC/cm², respectively) and excellent dielectric properties with lower loss and higher dielectric constant (K=1900, tanδ=0.035 at 100 kHz). AC electric field dependence of the permittivity at sub-switching fields in terms of Rayleigh law was investigated for both conventional 15 at.% La-doped PbTiO₃ and La-graded heterostructure films. The estimated irreversible domain wall displacement contribution to the total dielectric permittivity was 17% and 9% for conventional and graded heterostructure films, respectively.     

Structural and dielectric properties of parylene-VT4 thin films

58% semi-crystalline thin parylene-VT4 (–H₂C–C₆F₄–CH₂−)_n films, have been investigated by dielectric spectroscopy for temperature and frequency ranges of [−120 to 380 °C] and [0.1–10⁵ Hz] respectively. The study comprises a detailed investigation of the dielectric constant, dielectric loss and AC conductivity of this fluoropolymer. Dielectric behavior of parylene-VT4 is represented by a low dielectric constant with values in the range of 2.05–2.35 while the dielectric losses indicate the presence of two relaxation processes. Maxwell−Wagner−Sillars (MWS) polarization at the amorphous/crystalline interfaces with activation energy of 1.6 eV is due to the oligomer orientation. Electrical conductivity obeys to the well-known Jonscher law. The plateau in the low frequency part of this conductivity is temperature-dependent and follows an Arrhenius behavior with activation energy of 1.17 eV (deep traps) due to the fluorine diffusion. Due to its thermal stability with a high decomposition temperature (around 400 °C under air and 510 °C under nitrogen) and due to its good resistivity at low frequency (10¹⁵–10¹⁷ Ω m⁻¹), parylene-VT4 constitutes a very attractive polymer for microelectronic applications as low k dielectric. Moreover, when parylene-VT4 is subjected to an annealing, the dielectric properties can be still more improved.