Low-Dielectric-Loss Barium Strontium Titanate Thin Films with MgO Buffer Layer for Tunable Microwave Devices

The dielectric and microwave properties of Ba_0.6Sr_0.4TiO₃ (BST60) thin films with a MgO buffer layer deposited on Al₂O₃ substrates were investigated. Insertion of the MgO buffer layer is demonstrated to be an effective approach to fabricate low-dielectric-loss BST thin films. x-Ray pattern analysis indicates that the thin films exhibit good crystalline quality with a pure perovskite phase and that insertion of the MgO buffer layer does not change the crystal structure of BST. The nonlinear dielectric properties of the BST films were measured by using an interdigital capacitor (IDC). At room temperature, the tunability of the BST films with a MgO buffer layer was 24.1% at a frequency of 1 MHz with an applied electric field of 80 kV/cm. The dielectric loss of the BST thin films is only 0.005 to 0.007 in the frequency range from 20 Hz to 2 MHz, the same as for BST films prepared on single-crystal MgO substrates. The microwave dielectric properties of the BST thin films were also measured by a vector network analyzer from 50 MHz to 10 GHz.     

Integration of high dielectric Ba0.5Sr0.5TiO3 films into amorphous TaSiN barrier layer structures

The high-k dielectric material (Ba,Sr)TiO₃ has been intensively investigated for possible applications in dynamic random access memory circuits. During the BST deposition process in O₂ ambient, typically at 650°C, the diffusion of oxygen through the bottom electrode into the poly Si plug must be prevented. Amorphous TaSiN films are excellent candidates as oxygen barrier layers. Ba_0.5Sr_0.5TiO₃ (BST) films with thickness of 100 nm were deposited on the electrode structure SiO₂/TaSiN/Pt. The sol–gel method was used to grow the BST films. The barrier effect for oxygen diffusion is studied in TaSiN layers with thickness of 50 nm, which were deposited by a reactive sputter process. X-ray photoemission spectroscopy results confirm that this amorphous material is a suitable barrier against oxygen diffusion at 650°C. The BST films, deposited at 650°C and post-annealed at 650°C show a dielectric constant of 100 at 100 kHz and a dissipation factor of less than 5%.     

钛酸锶钡/铋锌铌多层复合薄膜的制备及性能

采用溶胶一凝胶法在Pt/Ti/SiO2/Si衬底上制备了钛酸锶钡/铋锌铌多层复合薄膜样品.研究了不同退火温度下多层复合薄膜的结构、微观形貌及介电性能.结果表明:在退火温度高于700℃时,所得复合薄膜中会出现立方焦绿石结构的铋锌铌和钙钛矿结构的钛酸锶钡.750℃退火处理得到的多层复合薄膜,表面致密,无裂纹,其相对介电常数...     

Effect of CuO Addition on Microwave Dielectric Properties of 0.80Sm(Mg0.5Ti0.5)O3-0.20Ca0.8Sr0.2TiO3 Ceramics

The effects of CuO addition on phase composition, microstructure, sintering behavior, and microwave dielectric properties of 0.80Sm(Mg_0.5Ti_0.5)O₃-0.20 Ca_0.8Sr_0.2TiO₃(8SMT-2CST) ceramics prepared by a conventional solid-state ceramic route have been studied. CuO addition shows no obvious influence on the phase of the 8SMT-2CST ceramics and all the samples exhibit pure perovskite structure. Appropriate CuO addition can effectively promote sintering and grain growth, and consequently improve the dielectric properties of the ceramics. The sintering temperature of the ceramics decreases by 50°C by adding 1.00 wt.%CuO. Superior microwave dielectric properties with a ε _r of 29.8, Q × f of 85,500 GHz, and τ _f of 2.4 ppm/°C are obtained for 1.00 wt.%CuO doped 8SMT-2CST ceramics sintered at 1500°C, which shows dense and uniform microstructure as well as well-developed grain growth.     

Pentacene thin-film transistors with sol-gel derived amorphous Ba0.6Sr0.4TiO3 gate dielectric

An amorphous Ba_0.6Sr_0.4TiO₃ (BST) film with the thickness of 200 nm was deposited on indium-tin-oxide (ITO)-coated glass substrate through sol-gel route and post-annealing at 500 °C. The dielectric constant of the BST film was determined to be 20.6 at 100 kHz by measuring the Ag/BST/ITO parallel plate capacitor, and no dielectric tunability was observed with the bias voltage varying from −5 to 5 V. The BST film shows a dense and uniform microstructure as well as a smooth surface with the root-mean-square (RMS) roughness of about 1.4 nm. The leakage current density was found to be 3.5 × 10⁻⁸ A/cm² at an applied voltage of −5 V. The transmittance of the BST/ITO/glass structure is more than 70% in the visible region. Pentacene based transistor using the as-prepared BST film as gate insulator exhibits a low threshold voltage of −1.3 V, the saturation field-effect mobility of 0.68 cm²/Vs, and the current on/off ratio of 3.6 × 10⁵. The results indicate that the sol-gel derived BST film is a promising high-k gate dielectric for large-area transparent organic transistor arrays on glass substrate.     

Improving the Magnetic Properties of Li-Zn-Ti Ferrite by Doping with H3BO3-Bi2O3-SiO2-ZnO Glass for LTCC Technology

Li-Zn-Ti ferrite doped with 0.5 wt.% to 16 wt.% H₃BO₃-Bi₂O₃-SiO₂-ZnO (BBSZ) glass was synthesized using a low-temperature ceramic sintering process. Selected parameters of saturation induction (B _S), coercivity (H _C), Curie temperature (T _C), and complex permeability spectra were measured as functions of doping content, and their relationships with ferrite density and microstructure are discussed. It was found that Li-Zn-Ti ferrite can be fired at low temperature (900°C) with BBSZ glass content varying from 0.5 wt.% to 2 wt.%. The real permeability increased from 80 to 190 in the frequency range from 1 MHz to 3 MHz, the saturation induction B _S increased from 105 mT to 150 mT at 1 kHz, whereas the coercivity H _C decreased from 165 A/m to 65 A/m at 1 kHz and the Curie temperature T _C slightly declined from 155°C to 143°C. These results confirm that this new ferrite material could be used in low-temperature cofired ceramic (LTCC) devices.     

Synthesis of Nanocrystalline CaWO4 as Low-Temperature Co-fired Ceramic Material: Processing, Structural and Physical Properties

Nanocrystalline scheelite CaWO₄, a promising material for low-temperature co-fired ceramic (LTCC) applications, has been successfully synthesized through a single-step autoignition combustion route. Structural analysis of the sample was performed by powder x-ray diffraction (XRD), Fourier-transform infrared spectroscopy, and Raman spectroscopy. The XRD analysis revealed that the as-prepared sample was single phase with scheelite tetragonal structure. The basic optical properties and optical constants of the CaWO₄ nanopowder were studied using ultraviolet (UV)-visible absorption spectroscopy, which showed that the material was a wide-bandgap semiconductor with bandgap of 4.7 eV at room temperature. The sample showed poor transmittance in the ultraviolet region but maximum transmission in the visible/near-infrared regions. The photoluminescence spectra recorded at different temperatures showed intense emission in the green region. The particle size estimated from transmission electron microscopy was 23 nm. The feasibility of CaWO₄ for LTCC applications was studied from its sintering behavior. The sample was sintered at a relatively low temperature of 810°C to high density, without using any sintering aid. The surface morphology of the sintered sample was analyzed by scanning electron microscopy. The dielectric constant and loss factor of the sample measured at 5 MHz were found to be 10.50 and 1.56 × 10^?3 at room temperature. The temperature coefficient of the dielectric constant was ?88.71 ppm/°C. The experimental results obtained in this work demonstrate the potential of nano-CaWO₄ as a low-temperature co-fired ceramic as well as an excellent luminescent material.     

Microstructure and Electrical Properties of K0.5Na0.5NbO3-LiSbO3-BiFeO3-x %molZnO Lead-Free Piezoelectric Ceramics

Lead-free piezoelectric ceramics {0.996[(0.95(K_0.5Na_0.5)NbO₃-0.05LiSbO₃]-0.004BiFeO₃}-xmol%ZnO were prepared through a conventional ceramics sintering technique. The effect of ZnO content on structure, microstructure, and piezoelectric properties of KNN-LS-BF ceramics was investigated. The results reveal that ZnO as a sintering aid is very effective in promoting sinterability and electrical properties of the ceramics sintered at a low temperature of 1,020 °C. The ceramics show a single-perovskite structure with predominant tetragonal phase, and coexistence of orthorhombic and tetragonal phases is observed for x = 2.5–3.0. The addition of ZnO causes abnormal grain growth. A dense microstructure is also obtained at x = 2.0 because the relative density reaches up to 94.6 %. The morphotropic phase boundary and dense microstructure lead to significant enhancement of the piezoelectric properties. The ceramic with x = 1.5 exhibits optimum electrical properties as follows: d ₃₃ = 280 pC/N, k _p = 46 %, Q _m = 40.8, P _r = 25 μC/cm², E _c = 1.2 kV/mm, and T _c = 340 °C.     

Dielectric Tunability of DNA Biopolymer Films with Varying Amounts of Hexadecyltrimethylammonium Chloride

Deoxyribonucleic acid (DNA) biopolymer films are fabricated with varying amounts of hexadecyltrimethylammonium chloride (CTMA), which is a surfactant necessary to produce a DNA complex that is soluble in organic solvents. The dielectric constant (κ) of these films at microwave frequencies as a function of applied static electric field (E _DC) is investigated. Results show that the dependence of κ on E _DC, which is referred to as the dielectric tunability, is influenced by the amount of CTMA in the complex. Dielectric tunability is suppressed when the amount of CTMA is insufficient and improved when more CTMA is added. However, excessive amounts of CTMA also result in a very rough film surface that causes shorting problems when used in a capacitive structure. A varactor employing a 1-μm-thick DNA biopolymer film as the dielectric is demonstrated. Under 5 V DC bias, which generates E _DC = 5 V/μm, its capacitance at 15 GHz changes by 0.04 pF. This change corresponds to a relative dielectric tunability of 6.6%. A simple application of this varactor for modulation of the power transmitted through a microwave transmission line is also demonstrated.     

Coplanar Phase Shifters Based on Ferroelectric Thin Films

Barium strontium titanate (Ba_0.6Sr_0.4TiO₃, short for BST) thin films were prepared by RF-magnetron sputtering. The dielectric tunability, loss tangent, remanent polarization (2Pr) and coercive electric field (Ec) of the BST films are respectively 29.5%, 0.013, 2.29 μC/cm² and 22.27 kV/cm at 1 kHz and 20 V. The designed coplanar waveguide (CPW) phase shifter consists of 56 same sections. It is shown that the fabricated lines of electrodes are smooth and the widths at the tip of bottom electrodes are about 5 μm. At the central frequency of 28 GHz and a bias voltage of 20 V, the figure of merit is approximately 13°/dB.     

Effect of the Addition of B2O3 on the Density, Microstructure, Dielectric, Piezoelectric and Ferroelectric Properties of K0.5Na0.5NbO3 Ceramics

Boron oxide (B₂O₃) addition to pre-reacted K_0.5Na_0.5NbO₃ (KNN) powders facilitated swift densification at relatively low sintering temperatures which was believed to be a key to minimize potassium and sodium loss. The base KNN powder was synthesized via solid-state reaction route. The different amounts (0.1–1 wt%) of B₂O₃ were-added, and ceramics were sintered at different temperatures and durations to optimize the amount of B₂O₃ needed to obtain KNN pellets with highest possible density and grain size. The 0.1 wt% B₂O₃-added KNN ceramics sintered at 1,100 °C for 1 h exhibited higher density (97 %). Scanning electron microscopy studies confirmed an increase in average grain size with increasing B₂O₃ content at appropriate temperature of sintering and duration. The B₂O₃-added KNN ceramics exhibited improved dielectric and piezoelectric properties at room temperature. For instance, 0.1 wt% B₂O₃-added KNN ceramic exhibited d ₃₃ value of 116 pC/N which is much higher than that of pure KNN ceramics. Interestingly, all the B₂O₃-added (0.1–1 wt%) KNN ceramics exhibited polarization–electric field (P vs. E) hysteresis loops at room temperature. The remnant polarization (P _r) and coercive field (E _c) values are dependent on the B₂O₃ content and crystallite size.     

Comparison of Microwave Dielectric Properties of Ba0.6Sr0.4TiO3 Thin Films Grown on (100) LaAlO3 and (100) MgO Single-Crystal Substrates

The microwave properties of barium strontium titanate (Ba_0.6Sr_0.4TiO₃) thin films grown on (100) LaAlO₃ (LAO) and (100) MgO single-crystal substrates through the sol–gel technique were investigated. The interdigital capacitor (IDC) technique was used to measure the nonlinear dielectric properties in the frequency range from 1 GHz to 10 GHz. The results show that the Curie temperature, capacitance, and tunability of the films are strongly dependent upon the substrate. The film fabricated on the LaAlO₃ substrate has a higher tunability of 16.77% than that grown on the MgO substrate (～8.38%), measured at 10 GHz with an applied voltage of 35 V. The loss tangent is a linear function of the frequency in the microwave range, and the film grown on the MgO substrate has a lower loss tangent than that grown on the LAO substrate. This work reveals the great potential of Ba_0.6Sr_0.4TiO₃ (BST) films for application in tunable microwave devices.     

Bi_(1.5)Zn_(1.0)Nb_(1.5)O_7/Ba_(0.5)Sr_(0.5)TiO_3复合薄膜介电性能的频率特性研究

采用射频磁控溅射法在蓝宝石基片上制备了Bi1.5Zn1.0Nb1.5O7(BZN)/Ba0.5Sr0.5TiO3(BST)双层复合薄膜,并研究了该薄膜在100 kHz~6 GHz频率范围内的介电性能。研究结果表明,BZN/BST复合薄膜的介电性能具有良好的频率稳定性。该复合薄膜的介电常数在研究的频率范围内基本与频率无关;其介电损耗在频率低于1 GHz时与频率无关,在频率高于1 GHz时随频率的上升而略微增大;薄膜在研究的频率范围内具有稳定的介电调谐率。     

Preparation and Dielectric Characteristics of Semitransparent CoFe2O4–P(VDF-TrFE) Nanocomposite Films

Polymer–ceramic nanocomposites play an important role in embedded capacitors. However, polymer–ceramic dielectrics are limited for commercial applications due to their low transmittance, poor adhesion, and poor thermal stress reliability at high filler loadings. Thus, materials design and processing is critical to prepare films with improved dielectric properties and low filler loading. In this work, we use a spin coating-assisted method to fabricate poly(vinylidene fluoride-co-trifluoroethylene) [P(VDF-TrFE)]–CoFe₂O₄ (CFO) nanocomposite films. Magnetic CFO nanoparticles in the size range of 10 nm to 40 nm were successfully synthesized using a hydrothermal process. The dispersion of the nanoparticles, the dielectric properties, and the transmittance of the nanocomposite films were studied. The dielectric constant of the nanocomposite films increased by about 45% over the frequency range of 100 Hz to 1 MHz, compared with that of pristine P(VDF-TrFE) film. Optical measurements indicated that the transmittance of the films remains above 60% in the visible range, indicating a relatively low content of CFO in the polymer matrix. Our experimental results suggest that spin coating-assisted dispersion may be a promising route to fabricate dielectric polymer–ceramic nanocomposite films of controllable thickness.     

Effect of Mn and Nb Doped BaTiO3 in the Dielectric Properties in the Ba(Mn1/2Nb1/2)xTi1−xO3

Polycrystalline samples of BaTi_1?x (Mn_0.5Nb_0.5) _x O₃ with x = 0.025, 0.05, 0.075, 0.1, 0.125, 0.15, and 0.175 have been synthesized by the high-temperature solid-state reaction technique. The effects of cationic substitution of manganese and niobium for titanium at B sites of the BaTiO₃ perovskite lattice on symmetry and dielectric properties were investigated. X-ray diffraction at room temperature and dielectric permittivity in the temperature range from 85 K to 500 K and frequency range from 100 Hz to 2 × 10⁵ Hz were studied. The evolution from a normal ferroelectric to a relaxor ferroelectric is emphasized. T _C or T _m decreases when both manganese and niobium are introduced into the lattice of BaTiO₃. High dielectric constant of around 9000 at T _C = 280 K was found for Ba Ti_0.925(Mn_0.5Nb_0.5)_0.075O₃ ceramic. A relaxor ferroelectric with ΔT _m = 60 K and $ \varepsilon_{\rm{r}}^{\prime } $ of about 3500 at 10 kHz with T _m = 150 K was found for the BaTi_0.85(Mn_0.5Nb_0.5)_0.15O₃ sample.     

Influence of Li-B-Si Additions on the Sintering and Microwave Dielectric Properties of Ba-Nd-Ti Ceramics

Li₂O-B₂O₃-SiO₂ (LBS) synthesized via a solid-state reaction process was chosen as a novel sintering aid for tungsten-bronze-type Ba₄Nd_9.3Ti₁₈O₅₄ (BNT) ceramic. The effects of LBS additions on the sintering behaviors, microstructures, and microwave dielectric properties of the BNT ceramic have been investigated, indicating that LBS addition obviously lowered the sintering temperature of the BNT ceramic without damaging its microwave dielectric properties. BNT ceramic doped with 3 wt.% and 4 wt.% LBS addition could be well sintered at 975°C and 950°C for 3 h and had excellent properties: ε _r = 65.99, Q × f = 4943 GHz (f = 4.4 GHz), τ _f = 19 ppm/°C, and ε _r = 64.56, Q × f = 4929 GHz (f = 4.3 GHz), τ _f = 11 ppm/°C, respectively.     

Solid-state synthesis of modified (Bi0.5Na0.5)TiO3 piezoelectric nanocrystalline ceramics and evaluating their properties

The piezoelectric nanocrystalline ceramics of (Bi_0.5Na_0.5) TiO₃, 0.94(Bi_0.5Na_0.5) TiO₃–0.06BaTiO₃, 0.82(Bi_0.5Na_0.5) TiO₃–0.18(Bi_0.5K_0.5) TiO₃ and 0.85(Bi_0.5Na_0.5) TiO₃–0.144(Bi_0.5K_0.5)TiO₃–0.006BaTiO₃ (abbreviated as BNT, BNBT6, BNKT18 and BNT–BT–BKT, respectively) have been synthesized by a modified solid state approach using high-energy planetary ball-milling. The crystal structures of ceramics were determined using X-ray diffraction (XRD) method and that the microstructures as well as the morphology of the sintered ceramic specimens were observed using scanning-electron microscopy (SEM). The dielectric coefficient was also calculated based on its relation with a constant capacitance measured by an electrical circuit on the basis of the Wetston–Bridge and the piezoelectric coefficient (d₃₃) measured with a d₃₃-meter. On the calcination of powders the XRD results showed that the perovskite phase was formed perfectly and the crystallite sizes of BNT, BNBT6, BNKT18 and BNT–BT–BKT were estimated at about >100, 55, 36 and 63 nm, respectively. Also, the crystallite sizes of the calcinated BNT powders over the course of 5, 10, 20, 30 and 40 h of ball-milling were estimated at about 86, 82, 72, 53, 81 nm, respectively. Moreover, the results of XRD and SEM analysis of the sintered powders at 750–1150 °C confirmed the positive effect of nanocrystalline formation during ball-milling in decreasing the sintering temperature and increasing the density of the sintered samples. Furthermore, electrical calculations such as dielectric and piezoelectric coefficients showed that the modified BNKT18 nanocrystalline ceramic sintered at 1150 °C was to have the best values of dielectric (ε_r=792 at 1 kHz) and piezoelectric coefficients (d₃₃=85.9 pC/N) in comparison with the other synthesized piezoelectric ceramics.     

Improvement of Thermoelectric Properties in (Bi0.5Sb0.5)2Te3 Films of Nanolayered Pillar Arrays

In this work, it is found that unique pillar arrays with nanolayered structure can favorably influence the carrier and phonon transport properties of films. p-(Bi_0.5Sb_0.5)₂Te₃ pillar array film with (0 1 5) orientation was successfully achieved by a simple ion-beam-assisted technique at deposition temperature of 400°C, owing to the enhanced mobility of deposited atoms for more sufficient growth along the in-plane direction. The pillar diameter was about 250 nm, and the layered nanostructure was clear, with each layer in the pillar array being <30 nm. The properties of the oriented (Bi_0.5Sb_0.5)₂Te₃ pillar array were greatly enhanced in comparison with those of ordinary polycrystalline films synthesized at deposition temperature of 350°C and 250°C. The (Bi_0.5Sb_0.5)₂Te₃ pillar array film with (0 1 5) preferred orientation exhibited a thermoelectric dimensionless figure of merit of ZT = 1.25 at room temperature. The unique pillar array with nanolayered structure is the main reason for the observed improvement in the properties of the (Bi_0.5Sb_0.5)₂Te₃ film.     

溶胶-凝胶法制备硼硅玻璃掺杂BST陶瓷的研究

研究了Si-B-O系玻璃掺杂对钛酸锶钡(BST)陶瓷的相结构和介电性能的影响.实验结果表明,当x(SiO_2)＞10%时,Si-B-O系玻璃掺杂BST陶瓷易出现杂相,即Ba_2TiSi_2O_8相.x(SiO_2)≤10%,Si-B-O系玻璃掺杂BST陶瓷粉体的相结构为立方钙钛矿相结构,其合成温度大于等于600 ℃,不存在第二相. Si-B-O系玻璃掺杂BST陶瓷的烧结温度低于传统工艺.Si-B-O系玻璃掺杂BST陶瓷的显微结构呈细晶结构(晶粒尺寸＜1 μm).随玻璃含量的增加,Si-B-O系玻璃掺杂BST陶瓷介电常数ε降低,介电峰变低,平坦,峰形宽化,介电损耗降低,居里温度TC向低温移动.     

Dielectric Properties and Defect Chemistry of WO3-Doped K0.5Na0.5NbO3 Ceramics

The dielectric properties and conductivity behavior of WO₃-doped K_0.5Na_0.5 NbO₃ ceramics were investigated as a function of temperature (25°C to 600°C) and frequency (40 Hz to 10⁶ Hz). The dielectric loss and direct-current (DC) conductivity of the ceramics depend strongly on the tungsten content. A high-temperature dielectric relaxation near temperature of 500°C was observed and analyzed using the semiempirical complex Cole–Cole equation. The activation energy of the dielectric relaxation was estimated to be ～2 eV and increased with increasing WO₃. The frequency-dependent conductivity can be well described by the universal dielectric response law. The activation energy obtained from the DC conductivity changes from 0.93 eV to 1.49 eV. A possible mechanism for the high-temperature dielectric relaxation and conductivity is proposed based on the activation energy value and defect compensation.