Dielectric Constant Of BST Films Research Articles

The dielectric and flexoelectric properties of Mg2+/K+ doped BST films

BST thin films have been prepared on Pt/Ti/SiO2/Si substrates by spin-coating. Different concentrations of K+ and Mg2+ have been doped in BST thin films by uni-doping and by binary alternate doping to improve the dielectric and flexoelectric properties of the films. At an annealing temperature of 800 °C, the doped thin film crystallizes well, and no heterogeneous phase is formed. The film surface is smooth and dense, and it has no cracks. The dielectric constant of undoped BST film is 262, the dielectric loss is 0.044, and the equivalent piezoelectric constant is 3.077 × 105 μC/N. When the K+ doping concentration is 7 mol%, the dielectric constant of the BST film is 446, the dielectric loss is 0.031, and the equivalent piezoelectric constant is 4.539 × 105 μC/N. When the doping amount of Mg2+ is 5 mol%, the dielectric constant of the film is 401, the dielectric loss is 0.025, and the equivalent piezoelectric constant is 4.165 × 105 μC/N. BST films with Mg2+/K+ alternate doping have better dielectric and flexoelectric properties than uni-doped films. The best doping conditions are 5 mol% Mg2+/7 mol% K+, with a dielectric constant of 479, a dielectric loss of 0.016, and an equivalent piezoelectric constant of 6.137 × 105 μC/N.

Structural and dielectric properties of epitaxial (Ba,Sr)TiO3 films on c-Al2O3 with ultra-thin TiN sacrificial template

Using ultra-thin TiN sacrificial template, the epitaxial (Ba,Sr)TiO3 [BST] films on c-Al2O3 were grown by pulsed laser deposition. TiN epitaxially grew on c-Al2O3 with (111) orientation, which promoted the (111) epitaxial growth of upper BST films. The obtained epitaxial BST films showed significantly larger dielectric constant compared with polycrystalline films directly deposited on c-Al2O3 over the wide temperature range. By inserting the TiN template, the temperature corresponding to maximum dielectric constant of BST films was shifted up by 50 K, which is mainly due to the in-plane tensile strain induced by the difference in thermal expansion coefficients of BST and c-Al2O3.

Thickness dependent ferroelectric properties of BSTO thin films deposited by RF magnetron sputtering

The thickness dependence of ferroelectric permittivity of (Ba, Sr)TiO3 has been investigated. The BST films could be obtained to have a simple cubic perovskite structure, space group Pm3m, and practically c-axis epitaxial structure deposited at 800∘C. Through post-annealing process, we have improved the dielectric properties; dielectric permittivity, dielectric loss, and tunability. The change in dielectric properties before and after annealing is attributed to the change in film strain and the contraction in film lattice. As the thickness of BST films increases from 55 nm to 350 nm, the dielectric constant of BST films increases from about 100 to above 670 due to the reduction of interfacial dead layers with low dielectric constant between films and top electrodes. The dielectric loss of BST thin films decreased as the thickness increases. The existence of interfacial dead layers in a thinner film had a larger effect on the effective dielectric constant than tensile strain between the BST films and MgO substrate.

The role of thermally-induced internal stresses on the tunabilityof textured barium strontium titanate films

The tunability of highly textured thin films of barium strontium titanate (Ba0.5Sr0.5TiO3, BST) is analyzed theoretically using a Landau–Devonshire thermodynamic model. The relative dielectric constant of BST films is determined as functions of the applied external electric field, deposition temperature, and the thermal expansion coefficient of the substrate. Our analysis shows that tunability is highly dependent upon thermally induced strains within the material. Both tension and compression produce deleterious tuning response. However, this effect can be minimized through judicious choices of deposition temperature and appropriate substrate material.

Coplanar Waveguide Using Ferroelectric Thin Oxide Film: Dielectric Constant

Coplanar waveguide (CPW) transmission lines were fabricated on thin ferroelectric Ba1 − xSrxTiO3 films for tunable microwave applications. The growth of the ferroelectric oxide films was accomplished by a pulsed laser deposition with a partial oxygen background. Microwave properties of the CPW phase shifter were measured using a HP 8510C vector network analyzer from 0.045–20 GHz with −40–40 V of dc bias. A large phase shift angle of ∼ 120∘ at 10 GHz was observed from the CPW (gap = 4μm, length = 3 mm) with a 40 V of dc bias change. The dielectric constant of the thin ferroelectric film was extracted from the dimension of the CPW (gap, width, length) and the measured S-parameter by a modified conformal mapping. However, the dielectric constant of the ferroelectric thin film exhibits a gap dependency; dielectric constant (990–830) decreases with increasing gap size (4–19 μm, respectively). By adjusting the filling factors of the film, a ‘constant’ dielectric constant of BST film is found to be 810 ± 5.

Effect of Fe Doping of Thin (Ba,Sr)TiO3 Films on Increase in Dielectric Constant

Barium strontium titanate [(Ba,Sr)TiO3, BST] is an attractive material with a very high dielectric constant. However, the dielectric constant of BST films decreases with film thickness, which has become a serious problem for dynamic random access memory (DRAM) application. We found Fe doping of BST films to be remarkably effective for suppressing the decrease in dielectric constant down to the very thin film regime. As a result, a marked increase in the dielectric constant for thin BST films is achieved. Furthermore, we identify the site where the doped Fe ions are substituted in the crystal by means of electron standing wave method using SrTiO3 single crystal. The result shows that most of the Fe ions are substituted at B sites (Ti sites), which suggests that Fe ions as acceptors compensate donor electrons and reduce band bending. This is thought to be the most likely mechanism of the increase in dielectric constant caused by Fe doping.

Microwave Properties of Tunable Interdigitated Capacitor Fabricated on Ba 0.6 Sr 0.4 TiO 3 Thin Film

Microwave properties of Ba 0.6 Sr 0.4 TiO 3 (BST) thin film have been studied using interdigitated capacitor (IDC) structure in the frequency range from 1 to 10 GHz at room temperature. IDC was fabricated on the c -axis oriented BST film grown by the pulsed laser deposition method. The capacitance of IDC shows high tunability and the quality factor is comparable to the reported values under dc bias voltage from 0 to 40 V. Dielectric constant of BST film was extracted using the conformal-mapping model from the measured data and physical dimensions of capacitors. Calculated dielectric constants depend on the geometric parameter of IDC.

Microwave Properties of Tunable Interdigitated Capacitor Fabricated on Ba 0.6 Sr 0.4 TiO 3 Thin Film

Microwave properties of Ba 0.6 Sr 0.4 TiO 3 (BST) thin film have been studied using interdigitated capacitor (IDC) structure in the frequency range from 1 to 10 GHz at room temperature. IDC was fabricated on the c -axis oriented BST film grown by the pulsed laser deposition method. The capacitance of IDC shows high tunability and the quality factor is comparable to the reported values under dc bias voltage from 0 to 40 V. Dielectric constant of BST film was extracted using the conformal-mapping model from the measured data and physical dimensions of capacitors. Calculated dielectric constants depend on the geometric parameter of IDC.

Dielectric properties of SrTiO3 and BST thin films fabricated using ECR-PEMOCVD

The SrTiO3 Thin films were deposited on Pt/SiO2/Si by ECR-PEMOCVD and their dielectric properties were investigated as a function of composition. The chemical bonding states of elements consisting these films were investigated using X-ray photoelectron spectroscopy (XPS) and Discrete Variational (DV)Xα simulation. The asymmetry of composition dependence on dielectric properties was explained by the XPS data. Further, effectiveness of NH3 carrier gas over Ar to deposit SrTiO3 is discussed in detail. Based on these data, the thickness dependence of dielectric constant of BST films was explained.

Improvement of dielectric properties by inserting oxygen-rich initial layer in Pt/(Ba,Sr)TiO3/Pt structure

Ba0.7Sr0.3TiO3 thin films with thicknesses ranging from 330 Å to 2200 Å were deposited on Pt/SiO2/Si substrates by RF-sputtering. To improve the dielectric constant of BST film, we inserted oxygen-rich layer at the initial stage of BST film deposition, the thickness of which was varied to 60 Å. As the thickness of the initial oxygen-rich layer increased, the dielectric constant of 1100 Å-thick BST films increased rapidly. Based on two assumptions, the thickness of the interfacial layer of the BST film without the oxygen-rich layer was estimated to be less than 70 Å and its dielectric constant to be less than 110. And, it was found that the dielectric constant of the interfacial low dielectric layer increased to 415 when 60 Å-thick initial oxygen-rich layer was inserted.

Microstructure Analysis of Barium Strontium Titanate Thin Film

AbstractMicrostructures of Barium Strontium Titanate (Ba, Sr)TiO3 [BST] thin film play an important role in determining the electrical properties of BST. In particular, it is found that the grain size distribution as a function of deposition conditions correlates with the dielectric constant of BST film. Traditionally, Transmission Electron Microscopy (TEM) provides an accurate method for determining microstructures such as interface structure between BST and electrodes and BST grain size distribution. However, TEM analysis relies heavily upon successful sample preparation, and film adhesion for BST proves to be a difficult problem to overcome for successful sample preparation. With the state of the art Scanning Electron Microscope (SEM) and Atomic Force Microscopy (AFM), useful information can be obtained for BST and electrode microstructures requiring little or no sample preparation. A good correlation among TEM, SEM and AFM techniques is achieved which allows useful information of BST grain size distribution to he obtained via SEM and AFM analyses. Power spectral density (PSD) analysis of contrast enhanced AFM images proves to be an efficient method for estimating BST grain size distribution.

Iridium thin film as a bottom electrode for high dielectric (Ba,Sr)TiO3 capacitors

We propose Ir thin films as new electrode materials for high dielectric BST capacitors. Ir was found to be superior to Pt in a number of aspects such as resistivity, adhesion and surface roughness. The Pt/BST/Ir/SiO2/Si capacitors showed leakage currents as low as Pt/BST/Pt/SiO2/Si ones, but higher capacitance resulted. For endurance properties with +5V unipolar pulse trains, the dielectric constant of BST films on Ir decreased by only 10% below its initial value after switching of 109 cycles while that on Pt degraded by 30% after 108 cycles. Ir bottom electrode effects on BST film properties were well explained by the formation of IrO2 phases on the surface of Ir electrodes.

Microstructural Control of RuO2 Electrode and the Related Properties of (Ba, Sr)TiO3 Thin Films

AbstractEffect of microstructure and surface roughness of oxide electrode on the properties of BST films has been investigated. (Ba, Sr)TiO3 and RuO2 films were deposited by RF magnetron sputtering technique. Surface morphology of RuO2 films were controlled by changing the O2/Ar ratio during deposition. It is found that the grain size and surface roughness of BST films are strongly influenced by RuO2 electrode underneath. When the grain size of RuO2 decreased by reducing either O2/Ar ratio during sputtering or film thickness, BST film resulted in fine grain structure and the leakage current decreased due to the improvement in uniformity of the film. Dielectric constant of BST films, however, was decided from both degree of well defined grains and film continuity related to grain size and surface roughness.