Dielectric Properties Of Thin Films Research Articles

Modeling interdigital electrode structures for the dielectric characterization of electroceramic thin films

A combination of physical and numerical modeling has been used to investigate the use of co-planar interdigital electrode (IDE) structures to characterize the dielectric properties of isotropic electroceramic thin films. A periodic two-dimensional IDE structure was simulated by finite-difference numerical modeling to investigate different electrode geometries and film thicknesses. A semi-empirical equation that enables the dielectric properties of the thin film to be calculated from the measured capacitance has been developed and is shown to be consistent with conformal mapping approaches. This equation is shown to agree better with various calculations over a wider range of parameters than the existing equation of Farnell (IEEE Trans. Son. Ultrson., SU-17(3) (1970) 188). Physical simulations of IDE structures with a limited number of electrode fingers have enabled the approach to be generalized to any IDE structure including the important special case of a two-electrode strip-line.

Electric‐Field‐Induced Rejection‐Wavelength Tuning of Photonic‐Bandgap Composites

Rejection-wavelength tuning is achieved by combining the mechanochromic response of photonic bandgap composites with the intrinsic electroactive properties of dielectric thin films. By straining the composite electrode, the photonic crystal interparticle lattice constant is varied in situ (see Figure). These simple-to-make films may find use in photonic devices that require a compact light-propagation controlling component.

Mechanical stress in thin film microstructures on silicon substrate

Analysis of residual stress in thin films and its influence on silicon microstructures was performed. Deflection behaviour of silicon membranes due to built-in stress in deposited thin films was investigated in the scope of different bilayer structures which are commonly met in microstructures such as piezoresistive pressure sensors. Silicon membranes are usually covered by thin films such as thermal oxide, LPCVD or PECVD nitride, as required by the actual fabrication process. In our case, high compressive stress was determined for stoichiometric LPCVD nitride (1.2 GPa) and PECVD nitride (706 MPa) while for thermal oxide tensile stress of 298 MPa was determined. Furthermore, thin film cantilever and bridge microstructures were designed, fabricated and investigated, showing that by a proper combination of thin films in the stacked layer, residual stress can be reduced to a reasonable amount without compromising the dielectric properties of thin films.

PREPARATION AND DIELECTRIC PROPERTIES OF Ba(ZrxTi1−x)O3 THIN FILMS GROWN BY A SOL-GEL PROCESS

ABSTRACT Barium zirconium titanate Ba(ZrxTi1 - x)O3 (BZT, x = 0.05, 0.15, 0.2, 0.25, 0.3) thin films have been prepared on Pt/Ti/SiO2/Si substrates by sol-gel process. All films crystallized in the perovskite structure with a crack free microstructure. Dielectric properties of thin films have been investigated as a function of frequency and direct current electric field. The results show that thin films current leakage decrease with increasing Zr content. High tunability is obtained in BZT thin films, which imply that BZT thin films are promising materials for tunable microwave applications.

Influence of Anatase–Rutile Phase Transformation on Dielectric Properties of Sol–Gel Derived TiO2 Thin Films

Effects of annealing temperature on the structural and dielectric properties of sol–gel derived TiO2 thin films were systematically investigated. Thin films annealed at various temperatures showed pure or mixed phases of anatase and rutile. As-deposited films started crystallization below 600°C and fully crystallized into the anatase phase at 800°C, followed by transformation to the rutile phase above 850°C. Dielectric properties of thin films with various phases were studied by LCR-meter using the metal–insulator–metal (MIM) structure. Dielectric constants of thin films increased from 40 to 147 as the portion of rutile phase increased from 0 to 95%, while dielectric losses decreased from 0.011 to 0.001. Temperature dependence of dielectric constants of thin films was also investigated. The dielectric properties of TiO2 thin films were discussed in terms of phase constitution, crystallinity, and preferred orientation.

Characterization of Local Dielectric Properties of Superconductor<tex>$rm YBa_2rm Cu_3rm O_7-delta$</tex>Using Evanescent Microwave Microscopy

A near-field evanescent microwave microscope based on a coaxial transmission line resonator with a tungsten tip protruding through an end-wall aperture is used to measure local dielectric properties of thin film YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// in superconducting state below critical temperature T/sub c/=91 K at T=79.4 K and in normal state at room temperature (T=298 K). The dielectric property of the superconductor within the near field of the tip frustrates the electric field and measurably changes the transmission line's resonant frequency. The shift of the resonator's frequency is measured as a function of tip-sample separation and associated change in quality factor (Q) image scans of the thin film is obtained. A quantitative relationship between the real and imaginary parts of the local dielectric constant and the frequency shift using the method of images is established. The comparison between experimental data and theory based on this method is given and discussed for YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// thin film deposited on LaAlO/sub 3/ substrate.

Theoretical study of influence of substrate microdefects on optical properties of dielectric thin films

Based on the theory of inhomogeneous thin films, a model for refractive index of stratified dielectric substrate is firstly put forward. The substrate can be divided into surface layer, subsurface layer and bulk layer in turn. Both the s urface layer and subsurface layer, whose refractive indices obey statistical dis tributions, are equivalent to inhomogeneous thin films. They can be separated in to N1 and N2 sublayers respetively which are regarded as homogenous thin films. Subsequently, theoretical analysis was carried out utili zing the characteristic matrix method of optical thin films. Numerical calculati on for optical properties of single layer dielectric thin films was carried out. The computing results indicate that microdefects in surface layer and subsurfac e layer of the substrate alter the equivalent refractive indices of the thin film and the substrate, which leads to the deviation of pseudo-Brewster angles and assembling reflectance from ideal conditions. Meanwhile, these microdefects change the propagation characteristics in thin film and substrate, as a result t he phase shift of reflection and phase difference deviate from ideal conditions. In addition, this model is also suitable for calculating the influence of micr odefects in the substrate on optical propertied of multilayer dielectric thin fi lms.

Phase Composition and Dielectric Properties of Thin Films Produced by Annealing Sn/Pb/Ti/Si and Pb/Sn/Ti/Si Heterostructures

Sn/Pb/Ti/Si and Pb/Sn/Ti/Si heterostructures were deposited by magnetron sputtering using Ti and Sn solid targets and liquid-phase Pb self-sputtering in the former case and three solid targets in the latter. The heterostructures were then annealed in flowing oxygen at 470–970 K. The major phase in the film produced from the Sn/Pb/Ti/Si heterostructure at 970 K was the Pb(Sn0.55Ti0.45)O3 solid solution with ferroelectric properties. The film prepared from the Pb/Sn/Ti/Si heterostructure consisted of Pb(Sn0.55Ti0.45)O3 and PbTiO3 and exhibited nonlinear dielectric properties. The coercive field and remanent polarization of the films were determined.

Dielectric Properties of BaTiO3 Thin Films Derived from Clear Emulsion of Well-Dispersed Nanosized BaTiO3 Particles

The dielectric properties of thin films with microemulsion (ME)-routed nanocrystalline BaTiO3 particles were investigated in terms of the films' crystallinity and grain size. The ME method provided a clear emulsion of well-dispersed nanocrystalline BaTiO3 particles. BaTiO3 thin films were prepared by direct spin-coating of the clear emulsion on Si/SiO2/Al2O3/Pt substrates. By varying the postannealing temperature from 600°C to 1000°C, BaTiO3 thin films of different grain sizes were prepared. A fine BaTiO3 powder was removed from the clear emulsion by adding ammonia solution to cause flocculation, followed by centrifugation and washing. A transmission electron microscope (TEM) observation revealed that the powder generated many inner voids, but the thin films did not contain inner voids, thus resulting in high crystallinity. The dielectric properties of these films were measured as functions of temperature. Polarization as a function of voltage was measured, and a ferroelectric D-E hysteresis curve was observed in the sample with a mean grain size of 18 nm. The measurement of piezoelectric hysteresis using a scanning probe microscope (SPM) also revealed ferroelectricity in a small area just below the SPM probe. Direct use of the clear emulsion of well-dispersed nanocrystalline BaTiO3 particles in the ME method enables the fabrication of BaTiO3 thin films that consist of nanocrystalline BaTiO3 grains without inner voids, and the films exhibit great dielectric performance.

THz time domain spectroscopy of pulsed laser deposited BaTiO3 thin films

We have measured the dielectric properties of pulsed laser deposited 1.1μm thick BaTiO3 (BTO) thin films on MgO substrate in the MHz and THz frequency region. The properties of two BTO thin films deposited at substrate temperature 790 and 840°C have been studied. X-ray diffraction pattern and AFM measurement of the films shows that the BTO film grown at temperature 840°C has better epitaxial growth and smooth surface compared to the film grown at 790°C. The dielectric properties of thin films have been measured by THz time domain spectroscopy (THz-TDS) in the frequency range from 0.3 to 2.5THz and by interdigital electrode measurement in the region from 10kHz to 10MHz. The BTO thin film deposited at higher temperature has a higher dielectric constant and tunability in the MHz frequency range whereas at THz frequencies the real and imaginary part of the refractive index and dielectric constant of both films show almost similar behavior.

Dielectric properties of ZrTiO4 thin films synthesized by sol-gel method

ZrTiO4 thin films were successfully prepared on Pt/Ti/SiO2/Si(100) substrates by a sol-gel process and gel films were heat-treated at various temperatures. The surface morphology, crystal structure, and dielectric properties of the thin films were investigated. It was possible to obtain ZrTiO4 phase at temperatures above 650 °C for 2 h, which is much lower than the bulk sintering temperature. The microstructure of well-crystallized ZrTiO4 thin films was a fine-grained microstructure less than 70 nm in grain size and the surface morphology was smooth with 22.4 rms roughness. The dielectric constant and loss of ZrTiO4 thin films were 38 and 0.006, respectively, for thin films with 450 nm thickness heat-treated at 900 °C for 2 h.

Comparison of TiO2 and other dielectric coatings for buried‐contact solar cells: a review

AbstractThis paper compares the optical, electronic, physical and chemical properties of dielectric thin films that are commonly used to enhance the performance of bulk silicon photovoltaic devices. The standard buried‐contact (BC) solar cell presents a particularly challenging set of criteria, requiring the dielectric film to act as: (i) an anti‐reflection (AR) coating; (ii) a film compatible with surface passivation; (iii) a mask for an electroless metal plating step; (iv) a diffusion barrier for achieving a selective emitter; (v) a film with excellent chemical resistance; (vi) a stable layer during high‐temperature processing. The dielectric coatings reviewed here include thermally grown silicon dioxide (SiO2), silicon nitride deposited by plasma‐enhanced chemical vapour deposition (a‐SiNx:H) and low‐pressure chemical vapour deposition (Si3N4), silicon oxynitride (SiON), cerium dioxide (CeO2), zinc sulphide (ZnS), and titanium dioxide (TiO2).While TiO2 dielectric coatings exhibit the best optical performance and a simple post‐deposition surface passivation sequence has been developed, they require an additional sacrificial diffusion barrier to survive the heavy groove diffusion step. A‐SiNx:H affords passivation through its high fixed positive charge density and large hydrogen concentration; however, it is difficult to retain these electronic benefits during lengthy high‐temperature processing. Therefore, for the BC solar cell, Si3N4 films would appear to be the best choice of dielectric films common in industrial use. Copyright © 2004 John Wiley & Sons, Ltd.

Dielectric properties of ultrathin films of molecular crystals

Dielectric properties of thin films (TF) of molecular crystals, including the effect of size and the boundary surfaces were analysed using Green's function method. Polarisability of molecules in various film layers and dielectric susceptibility of TF were calculated. A comparison with crystal bulk has shown that dielectric properties of TF are strongly influenced both by the sample dimensions and by the boundary conditions. The frequency dependence of the dielectric susceptibility has also been derived. One obtains the monotonous variation for the frequencies above and below exciton band. However, for the frequencies within the exciton band there appears to be complicated, non-monotonous dependence. The relationship between the dielectric susceptibility and the film width for the same frequency shows a complex, oscillatory behaviour. Furthermore, the amplitude of these oscillations increases with increasing film width, demanding the introduction of a damping factor. Finally, the thickness dependence of dielectric susceptibility was analysed in the Cole–Cole plot.

Structural and Dielectric Properties of ZnO-Doped (Zr 0.8 Sn 0.2 )TiO 4 Films at Radio Frequency

ZnO-doped (Zr 0.8 Sn 0.2 )TiO 4 thin films were prepared by rf magnetron sputtering on n-type Si(100) substrates at different rf power and substrate temperature have been investigated. The surface structural and morphological characteristics analyzed by X-ray diffraction (XRD) and atomic force microscope (AFM) were found to be sensitive to the deposition conditions, such as rf power (300 W-400 W) and substrate temperature (400°C-450°C). The measurement with radio frequency is taken with a vector network analyzer and a ground-signal probe. The dielectric properties of thin film with radio frequency were strongly depended on the quality of the surface microstructure. Besides, the dielectric constants of ZST films were decreased with increasing frequency. For f = 2.5 GHz, the dielectric constant of 28 was obtained at a rf power level of 400 W and substrate temperature of 450°C and it may applied to integrated the communication component such as chip capacitor with Bluetooth or PCS system.

Double modulated differential THz-TDS for thin film dielectric characterization

Terahertz differential time-domain spectroscopy (DTDS) is a new technique that uses pulsed terahertz radiation to characterize the optical properties of thin dielectric films. Characterizing thin films in the GHz to THz range is critical for the development of new technologies in integrated circuitry, photonic systems and micro-electro-mechanical systems. There are potential applications for gene and protein chips. This paper shows how DTDS can be combined with double modulation in the pump-probe system to improve sensitivity by an order of magnitude. An iterative algorithm is presented to estimate the optical properties of a given thin film. The technique is experimentally verified using 1-μm-thick samples of silicon dioxide on silicon.

The measurement of the dielectric and optical properties of nano thin films by THz differential time-domain spectroscopy

As feature sizes of circuits and devices approach 100nm and chip frequencies climb into the upper GHz to THz range, it becomes increasingly important to have a convenient method of characterizing properties of thin dielectric films in the GHz to THz frequency range. THz time-domain spectroscopy provides a non-contact, non-destructive and highly sensitive optical tool to characterize the dielectric and optical properties of micron to nanometer scaled thin films at GHz and THz frequencies. The measurement of the dielectric and the optical properties of nanometer scaled dielectric films is performed using the THz differential time-domain spectroscopy. The real and imaginary parts of the complex dielectric constants and the optical constants of a variety of nano thin films are measured at GHz and THz frequencies.

Doping Effects on the Properties and Microstructure of Intergrowth Bi 4 Ti 3 O 12 -SrBi 4 Ti 4 O 15 Thin Films

Undoped and La-doped intergrowth Bi 4 Ti 3 O 12 -SrBi 4 Ti 4 O 15 thin films were deposited on platinized silicon substrates by a modified metal-organic decomposition (MOD) method. The deposited films were crystallized at about 550-750C in an O 2 atmosphere. The microstructures of the films were investigated using X-ray diffraction and Raman spectroscopy. The ferroelectric and dielectric properties of thin films were measured using an RT66A test system. Compared with the undoped films, when crystallizing under the same temperatures, the XRD patterns of La-doped films present fewer but wider diffraction peaks. Increasing La dopant concentration results in further broadening. However, XRD and Raman spectroscopy studies show that the doping does not lead to a visible distortion of the lattice structure, which implies that La substitutes for either Bi or Sr. The hysteresis measurements show that the doped and undoped thin films have similar coercive field (E c ) and remnant polarization (2P r ). However, the polarization switching time of doped films is much shorter than that of the undoped films irrespective of film thickness. The reversible polarization was found to decrease for BIT-SBTi thin films with thicknesses greater than 210 nm while a maximum reversible polarization was found for La75BIT-SBTI intergrowth films at 280 nm. For a given film thickness, increasing the applied voltages resulted in increased switching times and increased reversible polarization in both cases.

Phonons of clean and metal-modified oxide films: an infrared and HREELS study

Vibrational properties of thin dielectric films may be investigated by infrared spectroscopy and high-resolution electron-energy-loss spectroscopy (HREELS). Infrared absorption by dielectric films occurs near the frequencies of longitudinal optical bulk phonons (Berreman effect); electron energy losses due to Fuchs–Kliewer surface phonons are observed at similar energies. We report a comparative study of the phonon features of an ultra-thin, well-ordered aluminum oxide film on NiAl(1 1 0) by infrared reflection-absorption spectroscopy (IRAS) and HREELS. At least fourteen vibrational modes are identified. While the spectra are similar to those expected from macroscopic dielectric theory, a detailed band assignment will require microscopic lattice dynamical calculations. Metal particles are grown on the alumina film by vapor deposition of palladium, rhodium, iridium, vanadium, and aluminum. Their sizes, as determined by scanning tunneling microscopy (STM), range from few atoms up to several thousand atoms. Infrared spectroscopy serves to study the impact of the admetals on the oxide phonons. Detailed data on the damping, frequency shift, and broadening of the most intense oxide phonon as a function of metal exposure are presented, spanning an exposure range from below 0.01 to several monolayers. Pd induces a red-shift of the phonon mode, while Rh, Ir, V, and Al initially cause a blue-shift. At larger exposures, most metals induce a shift to lower frequencies. Adsorbed CO and ethene give rise to further changes of the phonon spectrum. Possible reasons for the observed behavior are discussed.

Microstructural, dielectric and ferroelectric properties of calcium-modified lead titanate thin films derived by chemical processes

Abstract Ferroelectric Pb 1− x Ca x TiO 3 ( x =0.24) thin films were formed on a Pt/Ti/SiO 2 /Si substrate by the polymeric precursor method using the dip-coating technique for their deposition. Characterization of the films by X-ray diffraction showed a perovskite single phase with a tetragonal structure after annealing at 700°C. Atomic force microscopy (AFM) analyses showed that the film had a smooth and crack-free surface with low surface roughness. In addition, the PCT thin film had a granular structure with an 80 nm grain size. The thickness of the films observed by the scanning electron microscopy (SEM) is 550 nm and there is a good adhesion between the film and substrate. For the electrical measurements metal-ferroelectric-metal of the type capacitors were obtained, where the thin films showed good dielectric and ferroelectric properties. The dielectric constant and dissipation factor at 1 kHz and measured at room temperature were found to be 457 and 0.03, respectively. The remanent polarization and coercive field for the deposited films were P r =17 μC/cm 2 and E c =75 kV/cm, respectively. Moreover, the 550-nm-thick film showed a current density in the order of 10 −8 A/cm 2 at the applied voltage of 2 V. The high values of the thin film's dielectric properties are attributed to its excellent microstructural quality and the chemical homogeneity obtained by the polymeric precursor method.

Comparison of Dielectric Characteristics of Ta2 O 5 Thin Films on RuO2 and Ru Bottom Electrodes

Dielectric properties of thin films with and Ru as the bottom electrodes were investigated. The thin films were reactively sputtered on the bottom electrodes and then annealed in oxygen ambient at for 30 min. Using X-ray diffraction and Auger electron spectrometry, it has been found that the Ru bottom electrode was partially oxidized during annealing, while the electrode remained its structure. However, the annealed exhibited a higher dielectric constant, as well as a smaller leakage current, on the Ru electrode than on the electrode. Accordingly, the Ru bottom electrode is satisfactory for storage capacitors, even in a high temperature, oxidizing environment. The divergent electrical performances of two electrodes are attributed to the different crystallinity of annealed on Ru and © 2001 The Electrochemical Society. All rights reserved.