Dielectric Properties Of Thin Films Research Articles

Effect of Al doping and deposition runs on structural and optical properties of In2S3 thin films grown by CBD

β-In2−x Al x S3 thin films have been grown on glass substrate by chemical bath deposition for different value of Al concentration y = (([Al])/([In]))sol (0 ≤ y ≤ 5 at.%). Samples have been characterized using X-ray diffraction, atomic force microscopy and by spectrophotometric measurements. The influence of the increase of y ratio in the structural and optical properties are described and discussed in terms of crystallinity improvement. In order to increase film thickness of β-In2−x Al x S3, we have been realized multi-deposition system. The structural, the surface morphology as well as the optical properties seem to be improved as the film thickness is of about 1200 nm.

Measurements of Microwave Dielectric Properties of (1-x)TiO2-xCaTiO3 and (1-x)TiO2-xSrTiO3 thin Films By The Cavity Perturbation Method

This research studies the measurements of dielectric properties of thin films at microwave frequencies by the cavity perturbation method. The measured frequency is in X-band (8.2–12.4 GHz). The titanium dioxide based (1-x)TiO2-xCaTiO3 and (1-x)TiO2-xSrTiO3 thin films deposited by the RF reactive magnetron sputtering method are adopted for the measurements. It was found that the dielectric constants of the films are increased as the compositions of CaTiO3 or SrTiO3 are increased. The microwave dielectric constants and loss tangents of films are measured. The accuracy of measurements is discussed.

Optical properties of dielectric thin films including quantum dots

Depending on the minimum size of their micro/nanostructure, thin films can exhibit very different behaviors and optical properties. From optical waveguides down to artificial anisotropy, through diffractive optics and photonic crystals, the application changes when decreasing the minimum feature size. Rigorous electromagnetic theory can be used to model most of the components, but, when the size is a few nanometers, quantum theory also has to be used. The materials, including quantum structures, are of particular interest for many applications, in particular for solar cells because of their luminescent and electronic properties. We show that the properties of electrons in periodic and nonperiodic multiple quantum well structures can be easily modeled with a formalism similar to that used for multilayer waveguides. The effects of different parameters, in particular the coupling between wells and well thickness dispersion, on possible discrete energy levels or the energy band of electrons and on electron wave functions are given. When such quantum confinement appears, the spectral absorption and extinction coefficient dispersion with wavelength are modified. The dispersion of the real part of the refractive index can be deduced from the Kramers-Kronig relations. Associated with homogenization theory, this approach gives a new model of the refractive index for thin films including quantum dots. The bandgap of ZnO quantum dots in solution obtained from the absorption spectrum is in good agreement with our calculation.

Effect of biphase on dielectric properties of Bi-doped lead strontium titanate thin films

Pb 0.4Sr 0.6TiO 3 (PST) thin films doped with various concentration of Bi were prepared by a sol–gel method. The phase status, surface morphology and dielectric properties of these thin films were measured by X-ray diffraction (XRD), scanning electron microscopy (SEM) and impedance analyzer, respectively. Results showed that the thin films with the maximum dielectric constant and minimum dielectric loss were obtained for x=0.15. For x<0.15, only pure PST perovskite phase were in the thin films. For 0.2< x<0.4, the PST/Bi 2Ti 2O 7 biphase were obtained. The thin films with pure Bi 2Ti 2O 7 pyrochlore phase were obtained for x=0.67. The biphase thin films had high tunability and high figure of merit (FOM). The FOM of PST/Bi 2Ti 2O 7 biphase thin film was about 6 times higher than that thin films formed with pure perovskite phase or pure pyrochlore phase.

Annealing and Composition Effects of (BaxSr1-x)Ta2O6 Thin Films Fabricated by Sol–Gel Method

The annealing atmosphere effects and composition effects on the electrical properties of five compositions of (BaxSr1-x)Ta2O6 thin films were investigated. O2 atmosphere annealing prevented the diffusion of Ti from the substrates into thin films and thus improved the dielectric properties of thin films. Thin films of all compositions show dielectric constants higher than 60 and loss tangents lower than 1%. Sr substituted for Ba in BaTa2O6 thin films showed a strong influence on the material properties. Among the samples, (Ba0.75Sr0.25)Ta2O6 thin film shows good bias stability, a high dielectric constant of about 65, low loss tangent of about 0.9% and low leakage current of about 10-7 A/cm2, and is regarded as the most promising for application in next-generation miniaturization.

Initial considerations on the relationship between the optical absorption and the thermal conductivity in dielectrics

The absorption of modulated or pulsed light leads to non-radiative processes that generate a photoacoustic (PA) wave. The standard model assumes that the amplitude of the PA wave is proportional to the optical absorption. In previous reports we have demonstrated experimentally and theoretically that from this proportionality: (1) one can obtain quantitative measurements of the optical properties of dielectric thin films and (2) that there may exist a relationship between the amplitude of the PA wave and the thermal conductivity of a given sample. Here we present analytic results that clearly show that the optical absorption and the thermal conductivity are coupled to the amplitude of the PA wave in the modulated regime and that this correlation holds for any type of macroscopic optical and thermal transparency. In particular, the present analysis shows that the product of the optical absorption and the thermal conductivity is related to the PA amplitude via a partition function.

Measurements of dielectric properties of TiO2 thin films at microwave frequencies using an extended cavity perturbation technique

This research provides a simple method to measure the dielectric properties of thin films at microwave frequencies. The cavity perturbation theory is applied to the measurement method. The measured frequency is in X-band (8.2–12.4 GHz). The titanium dioxide thin films are deposited by the RF reactive magnetron sputtering method onto borosilicate glass substrates. The microwave complex permittivity of films is then measured by the extended cavity perturbation technique. It was found the dielectric constants of titanium dioxide thin films strongly depend on the partial pressure of oxygen. The dielectric constant maximized at a value of 95 with 30% O2. This is the first report that confirms the high dielectric constant of TiO2 thin films at microwave frequencies which shows its potential for high-K related microwave devices.

Characterization of microwave dielectric properties of ferroelectric parallel plate varactors

A procedure to accurately evaluate microwave dielectric properties of parallel plate varactors fabricated on a BST thin film deposited by pulsed laser deposition on a platinized silicon substrate is presented. The reliability of the high-frequency properties of dielectric thin films extracted from the measured reflection coefficient S11 is mainly limited by how accurately the parasitic effects are eliminated from the measured data. The parasitic effects were effectively removed on evaluating the thin-film dielectric properties based on the good agreement between the experimental results measured with the parasitic model and the computer simulation data.

Effects of CeO 2 buffer layer thickness on the orientation and dielectric properties of Ba(Zr 0.20Ti 0.80)O 3 thin films

Ba(Zr 0.20Ti 0.80)O 3 (BZT) thin films are deposited on Pt(1 1 1)/Ti/SiO 2/Si(1 0 0) substrates by the sol–gel technique. The thickness of the CeO 2, serving as a buffer layer, is varied from 0 to 20 nm, to study the dependence of the orientation and dielectric properties of the BZT thin films on the buffer layer thickness. The influence of buffer layer thickness on the microstructure of the thin films is also examined. Dielectric properties of the thin films are investigated as a function of temperature and direct current electric field. The results show that the CeO 2 buffer layer strongly influences the orientation, microstructure and the dielectric properties of the films. The BZT thin films with 5 nm thickness CeO 2 buffer layer have the least loss, smallest leakage current and largest figure of merit (FOM).

Effect of Sr–Ruthenate Seed Layer on Dielectric Properties of SrTiO3 Thin Films Prepared by Plasma-Enhanced Atomic Layer Deposition

The effect of a strontium ruthenate seed layer on the dielectric properties of thin films was investigated. The thin films were deposited by plasma-enhanced atomic layer deposition using titanium tetra-isopropoxide and bis(dipivaloylmethanato) strontium as precursors and oxygen as an oxidant. A strontium ruthenate seed layer was formed through the deposition of ultrathin SrO and a postannealing process. The thin films deposited on a seed layer, prepared by deposition of SrO and postannealing prior to deposition, showed considerably enhanced dielectric properties in comparison to films deposited on Ru directly; that was attributed to enhancement of the films’ crystallinites and a reduction of low- interfacial layers. For optimization of seed-layer formation, the dependency of the inserted SrO layer thickness on the dielectric properties of the films was investigated for a SrO thickness range of . The thick thin film on the seed layer formed by deposition of a thick SrO layer and postannealing exhibited a dielectric constant of about 75 [equivalent oxide thickness ], which meets the requirement of dynamic random access memory technology.

Morphology and Composition of Selected High-k Materials and Their Relevance to Dielectric Properties of Thin Films

We discuss some of the issues associated with the relation between the leakage current and the dielectric constant on the one hand, and the crystallographic structure and the chemical composition of the film on the other. Our focus is on dielectrics containing Pr oxides. Starting with the binary , we investigate electronic properties and formation energies of point defects as revealed by ab initio calculations and we attempt to associate this data with the experimental information on the influence of processing on the dielectric quality of the film. We then consider Pr silicates on Si for metal-oxide-semiconductor field effect transistors and on TiN for metal–insulator–metal front-end applications. In the latter case, annealing above about , needed to noticeably increase the effective dielectric constant, causes an increased leakage. Investigating this effect, in particular we discuss the diffusion mechanism for Ti and the influence of Ti on the leakage current, taking into account the stoichiometry dependence of defect formation energies and the position of electron transition states obtained from ab initio data.

A DIELECTRIC PROPERTY ANALYSIS OF FERROELECTRIC THIN FILM USING TERAHERTZ TIME-DOMAIN SPECTROSCOPY

ABSTRACT This paper presents complex dielectric properties of ferroelectric BSTO thin film, deposited on MgO substrate by pulsed laser deposition, in the frequency range of 0.5 ∼ 3.0 THz using terahertz time-domain spectroscopy (THz-TDS). In order to extract complex dielectric properties of the thin film, multiple reflections within the thin film were considered and an error function between the calculated and measured data was introduced. The real part of the dielectric constant of the BSTO thin film was less than 170 and the dielectric loss tangent of the BSTO thin film varied between 0.9 and 3.0. All values of an error function were less than 7 × 10− 4 in the measured frequency ranges. The analysis method using THz-TDS enables us to find out complex dielectric properties of ferroelectric thin film exactly.

Exact Expressions for Some Dielectric Properties of Ferroelectric Thin Films Based on the Tilley–Zeks Model

The extrapolation length adopted in the Tilley–Zeks model of ferroelectric thin films plays a substantial role in governing the dielectric properties of thin films through the boundary conditions. The boundary conditions under an applied field are reexamined. The exact formulas for the transition temperature, the dielectric susceptibility, and the Curie constant are obtained for the Tilley–Zeks model of ferroelectric thin films, where various combinations of the extrapolation length are taken into account. The polarization profiles obtained under the applied field may be considered to approximately represent the soft mode.

Effect of (La0.5Sr0.5)MnO3 and (La0.5Sr0.5)CoO3 Buffer Layer on the Dielectric Properties of BaTiO3 Thin Films Prepared by a Sol-Gel Process

The dielectric properties of BaTiO3 thin films deposited on (La0.5Sr0.5)MnO3 (LSMO) and (La0.5Sr0.5)CoO3 (LSCO), respectively, as buffer layer, were studied. The influence of buffer layer on the phase of the thin films was examined. Dielectric properties of the thin films were investigated as a function of frequency and direct current electric field. These results showed that the buffer layer strongly influenced the structure and the dielectric properties of the films. The BaTiO3 thin films on LSMO buffered Pt/Ti/SiO2/Si substrates have enhanced tunability and lower leakage current.

Effect of seed layers on dielectric properties of Ba(Zr0.3Ti0.7)O3 thin films

The Barium zirconium titanate Ba(Zr0.3Ti0.7)O3 thin films were prepared on Pt/Ti/SiO2/Si substrates with seed layers at the BZT/Pt interface by sol–gel process. Microstructure and structure of thin films were examined. Dielectric properties of thin films with various seed layers thicknesses were investigated as a function of frequency and direct current electric field. The tunability and dielectric constant of BZT thin films increased with increasing seed layer thickness from 0 to 20 nm, while it decreased with a further increase in thickness above 20 nm, meanwhile, the leakage current showed the similar tendency at applied electric field of 250 kV/cm. The optimized seed layer thickness for BZT thin films plays an important role in maintaining the high tunability and low leakage current, which are suitable for microwave device applications.

MODEL FOR INTERFACE EFFECT ON DIELECTRIC NONLINEARITY OF FERROELECTRIC FILMS

ABSTRACT The interface has a crucial influence on the dielectric properties of thin films. A model, including the film thickness and the interfacial layer thickness, for dielectric nonlinearity of ferroelectric films was established. The ferroelectric film and transition layers are modeled by capacitances and resistances, and the Schottky barriers at metal/dielectric interfaces are modeled in terms of diode equivalent circuits. It is found that the increasing tendencies of the remanent polarization, dielectric constant and tunability from model are consistent with those from experiment. The results proved that the above model can describe the interface effect on dielectric nonlinearity of ferroelectric films.

Investigation of Pb–Mg–Nb–O pyrochlore thin films for tunable material

PMN thin films have been investigated as a feasible material for tunable microwave applications. PMN thin films were deposited by RF magnetron sputtering from Pb 6MgNb 6O 22 ceramic target on platinized Si substrates. The crystallinity, thickness, surface morphology, dielectric property, and voltage tunable properties of thin films were investigated by means of X-ray diffraction (XRD), field emission-scanning electron microscopy (FE-SEM), and an impedance analyzer. The influences of sputtering substrate temperature and post-annealing on the tunable dielectric properties of thin films were investigated. Increasing the sputtering substrate temperature and annealing temperature can significantly increase tunability; however, these relations had the limitation that overly annealing temperature degraded the tunability of the thin film. A tunability of 38% at 1100 kV/cm of dc bias field under 1 MHz was achieved for a sample sputtered at 550 °C and annealed at 700 °C.

Effect of rapid thermal annealing on the properties of thin dielectric films of gadolinium, titanium, and erbium oxides on the silicon carbide surface

The effect of rapid thermal annealing on the properties of Ti, Ga, and Er oxide films on silicon carbide are studied by the methods of atomic force microscopy, monochromatic ellipsometry, optical absorption, and photoluminescence. The atomic composition of these films is analyzed as a function of the annealing time. The phase composition of the Ti, Ga, and Er oxide films on silicon carbide is shown to depend on the annealing time.

The influence of distribution of Na+-dopant on the structure and dielectric properties of Ba0.25Sr0.75TiO3 thin film

Na+-doped and compositional graded doped Ba0.25Sr0.75TiO3 thin films were grown on Pt/Ti/SiO2/Si substrates by Sol-Gel technique. The dielectric properties of thin films were investigated as a function of Na+ doping level. It is revealed that with the increase of Na+ concentrations both the dielectric constant and the loss decrease continuously while the leakage current initially decreases (Na+&lt; 2.5mol%) and then increases. The increase of leakage current may be caused by the formation of porous structure which was confirmed by field emission scanning microscopy (FE-SEM). The improvement of overall dielectric properties were achieved by using the compositional graded doping which results in a better microstructure in the film.

Elimination of parasitic effects due to measurement conditions of SrTiO 3 thin films up to 40 GHz

Effective use of electromagnetic simulation software for evaluation of the microwave properties of dielectric thin films was demonstrated. The reliability of the high-frequency dielectric properties extracted from the measured S 11 reflection coefficients with the aid of the electromagnetic simulation software is mainly limited by how accurately the measured parasitics are simulated. The need to correct the parasitic differences between the simulation and measurement was shown by the significant dependence of probe contact position on the obtained dielectric properties. The parasitic differences were represented by series and parallel correction admittances connected to the measured admittance and were effectively eliminated. The high-frequency dielectric properties of a highly crystalline SrTiO 3 (STO) thin film were investigated up to 40 GHz by using the measurement techniques developed. The permittivity (relative dielectric constant) of the STO thin film remained substantially constant at 265 up to 40 GHz, and the dielectric loss value was about 0.03 at 40 GHz.