Bismuth Zinc Niobate Research Articles

Electrophoretic deposition of Bi1.5Zn1.0Nb1.5O7 thick films on metal foils for flexible electronic devices

Cubic bismuth zinc niobate (c-BZN) thick films were fabricated on flexible platinum foils by electrophoretic deposition technique. The X-ray diffraction studies reveal that the films are under tensile stress. The permittivity of the c-BZN thick film sintered at 850 and 950°C, measured at an applied frequency of 1 MHz were 114 and 125, respectively. The corresponding values of dissipation factors were 0.004 and 0.0038. The films were also exhibiting voltage-dependent dielectric properties. The biaxial tensile stress, which is developed as a result of substrate constraints during the sintering, leads to significant change in the relaxation and dielectric characteristics of the films compared to that of ceramics. From this study, it is expected that large tensile stress in c-BZN thick films can bring down the dielectric loss and the variation of the dielectric permittivity with temperature, which will make them attractive, low loss and temperature stable applications.

Pyrochlore structure and dielectric properties of bismuth zinc niobate thin films prepared by RF sputtering

Abstract Bi 1.5 Zn 1.0 Nb 1.5 O 7 (BZN) thin films with thickness from 60 nm to 200 nm were prepared by radio-frequency magnetron sputtering and post-annealed from 550 °C to 650 °C. The x-ray diffraction results indicated that the BZN thin films possessed a cubic pyrochlore phase. The BZN thin films exhibited thickness-independent dielectric properties with dielectric constant of ~180 and low loss tangent less than 1% at 10 kHz as the film thickness decreased to 60 nm. The BZN thin films with thickness of 200 nm and post-annealed at 650 °C had a tunability of 32.7% at a DC bias field of 1.5 MV/cm. The results suggest that the BZN thin films have promising applications on the embedded capacitors, tunable devices and energy storage devices.

RF MEMS Zipping Varactor With High Quality Factor and Very Large Tuning Range

An RF MEMS zipping analog varactor with a high-permittivity bismuth zinc niobate dielectric has been fabricated and characterized. The varactor can be continuously tuned from 10 to 280 fF, with a very large tuning range of 2700%. By use of gold electrodes to ensure a low series resistance, the high quality factors of 317 and 63 at 1 GHz were measured for the minimum and maximum capacitances, respectively. The self-resonance frequency of the varactor is estimated to be 16.6 GHz at the maximum capacitance and 87.6 GHz at the minimum capacitance. With a small device footprint of $540 \times 130~\mu \text{m}^{2}$ , the zipping varactor is suitable for application in portable reconfigurable RF systems.

Bismuth Zinc Niobate Thin Film Multilayer Capacitors with Cu Electrodes Fabricated at Low Temperature by RF Magnetron Sputtering

Thin film multilayer capacitors (MLCs) composed of amorphous Bi1.5Zn1.0Nb1.5O7 (BZN) dielectric layers with Cu internal electrodes were fabricated by radio‐frequency magnetron sputtering at a temperature below 150°C. Both BZN thin films and Cu internal electrodes were deposited in situ through a set of steel shadow masks at room temperature and postannealed at 150°C. The BZN dielectric layers used in the MLCs are amorphous and the thickness for each BZN layer is approximately 220 nm. Metallic Cu layer used as the internal electrode is about 50 nm thick. Auger electron spectroscopy analysis indicates that there are no diffusion between BZN films and Cu electrodes, as well as no oxidation of Cu electrodes during the fabrication process owing to room‐temperature deposition and low‐temperature postannealing (150°C). The thin film MLCs with different number of BZN layers were fabricated. The thin film MLCs with five BZN layers exhibit promising properties with dielectric constant of 72, capacitance density of 1600 nF/cm2, and loss tangent of 5.4% at 10 kHz. These results suggest that the BZN thin film MLCs have potential applications for the embedded PCBs.

Nanocomposite bismuth zinc niobate tantalate for flexible energy storage applications

The development of complex oxides that can be processed at temperatures at and below 350 °C is desirable for their integration onto polymeric substrates, enabling their use in flexible applications. Nanocomposite films consisting of a nanocrystalline fluorite related to delta-bismuth oxide in an amorphous matrix were prepared via chemical solution deposition. These solutions were batched with the composition Bi1.5Zn0.9Nb1.35Ta0.15O6.9. The nanocomposite had a relative permittivity of 50 ± 2 and dielectric losses on the order of 0.03 ± 0.01. For measurement frequencies of 1 kHz and 10 kHz, the nanocomposite demonstrated a breakdown strength of 3.8 MV/cm, and a room-temperature energy storage density of approximately 40.2 ± 1.7 J/cm3. To determine the suitability of the nanocomposite films for use in flexible applications, flexible nanocomposite films underwent repetitive compressive and tensile bending around a minimum bend diameter of 7 mm, which corresponded to a strain of 0.10%. After bending the films 30 000 times, the energy storage density of the films was unchanged, demonstrating that nanocomposite bismuth zinc niobate tantalate films are suitable for flexible energy storage applications.

Pressure-Dependent Etching Mechanism and Induced Dielectric Properties Variation of BZN Thin Films in SF6/Ar Plasma

Reactive ion etching was used to study bismuth zinc niobate (BZN) thin films etching in SF6/Ar plasma as a function of pressure. The etch rate increases as the pressure increases from 1 to 20 mTorr and decreases when the pressure exceeds 20 mTorr. The film surfaces were analyzed to determine the etching mechanism using X-ray photoelectron spectroscopy. Pressure is found to have an effect on etch reaction and non-volatile etch by-products removal through different ion density and energy, thus resulting in varying compositions, element chemical binding states on the film surface. Dielectric properties of the film, modified by SF6/Ar plasma, show an obvious variation with pressure. The permittivity shows a slight decrease in the range of 1–20 mTorr but a sharp decrease at 30 mTorr. Instead, the dielectric loss variation exhibits an opposite trend.

Bismuth pyrochlore thin films for dielectric energy storage

Thin films of cubic pyrochlore bismuth zinc niobate, bismuth zinc tantalate, and bismuth zinc niobate tantalate were fabricated using chemical solution deposition. This family of materials exhibited moderate relative permittivities between 55 ± 2 and 145 ± 5 for bismuth zinc tantalate and bismuth zinc niobate, respectively, and low loss tangents on the order of 0.0008 ± 0.0001. Increases in the concentration of the tantalum end member increased the dielectric breakdown strength. For example, at 10 kHz, the room temperature breakdown strength of bismuth zinc niobate was 5.1 MV/cm, while that of bismuth zinc tantalate was 6.1 MV/cm. This combination of a high breakdown strength and a moderate permittivity led to a high discharged energy storage density for all film compositions. For example, at a measurement frequency of 10 kHz, bismuth zinc niobate exhibited a maximum recoverable energy storage density of 60.8 ± 2.0 J/cm3, while bismuth zinc tantalate exhibited a recoverable energy storage density of 60.7 ± 2.0 J/cm3. Intermediate compositions of bismuth zinc niobate tantalate offered higher energy storage densities; at 10 mol. % tantalum, the maximum recoverable energy storage density was ∼66.9 ± 2.4 J/cm3.

Effect of excess ZnO on structure and dielectric properties of Bi1.5Zn1.0Nb1.5O7 thin films grown at room temperature by RF magnetron sputtering

Bismuth zinc niobate (BZN) thin films with excess Zn contents were deposited from the ceramic targets containing various excess amounts of ZnO (0–20mol%) on Pt/TiO2/SiO2/Si substrate by RF magnetron sputtering at room temperature. As-deposited thin films were post-annealed at a temperature ≤200°C, which is compatible with PCB substrates. The effect of Zn deficiency and Zn excess on the microstructure, dielectric, and electrical properties of BZN thin films was studied. As-deposited and post-annealed BZN thin films at a temperature ≤200°C were amorphous in nature. An appropriate amount of excess zinc improves the dielectric and electrical properties of BZN thin films, while too much excess zinc leads to deteriorate the properties. BZN thin film with 5mol% excess Zn content exhibits the maximum dielectric constant of 64 with a very low loss of 0.6%, measured at 10kHz and the leakage current of less than 1µA at an applied electric field of 200kV/cm.

Structural and dielectric properties of calcium doped bismuth zinc niobate thin films prepared by pulsed laser deposition at room temperature

(Bi1.5Zn0.1Ca0.4)(Zn0.5Nb1.5)O7 (BZNCa) thin films were prepared by pulsed laser deposition on Pt/TiO2/SiO2/Si substrates at room temperature. The as-deposited films and films post-annealed from 100°C to 175°C for 10min in air are all amorphous. The influence of the post-annealing process on structural and electrical properties was investigated. The surface morphology of BZNCa films remains almost same with the annealing temperature. While the dielectric and leakage-current properties of the films are strongly influenced by the annealing temperature. The film deposited at O2 pressure of 4Pa and then post-annealed at 150°C shows the improved dielectric and leakage-current characteristics. The dielectric constant and loss tangent are 67.2 and 0.03at 100kHz, respectively. The leakage current density is less than 1µA/cm2 at an applied bias electric field of 400kV/cm. The results indicate that calcium doped BZN thin films have potential applications for embedded capacitors.

Cubic Pyrochlore Bismuth Zinc Niobate Thin Films for High‐Temperature Dielectric Energy Storage

Thin films of cubic pyrochlore bismuth zinc niobate, a lead‐free dielectric, were fabricated using a solution chemistry based upon the Pechini method. Scanning electron microscopy confirmed that the films are smooth and mostly dense. The films exhibit a dielectric constant of 145 ± 5, a low dielectric loss of 0.00065 ± 0.0001, and a room temperature, 1 kHz maximum field of approximately 4.7 MV/cm. At frequencies of 100 Hz and 10 kHz, the maximum field sustained by the material increased to 5.0 MV/cm and 5.1 MV/cm, although the dielectric loss increased to 0.0065 ± 0.001. At a measurement frequency of 10 kHz, the maximum energy storage density was ~60.8 ± 2.0 J/cm3, while at a measurement frequency of 100 Hz, the maximum energy storage was ~46.7 ± 1.7 J/cm3. As the temperature was increased to 200°C, the breakdown strength of the films decreased, while the loss tangent remained modest. At 200°C and a measurement frequency of 100 Hz, the maximum energy storage density was ~23.1 ± 0.8 J/cm3, and at 10 kHz, the maximum energy storage density was ~27.3 ± 1.0 J/cm3.

The Etching Reaction and Surface Reconstruction of Bismuth Zinc Niobate Thin Film in SF6/Ar Plasma

Reactive ion etching (RIE) of bismuth zinc niobate (BZN) thin films using an SF6/Ar plasma has been studied. An optimum process parameters was obtained according to the highest etch rate of 90nm/min. Under this etching condition, the crystal structural properties and surface morphology of the BZN film before and after etching were characterized using X-ray diffraction (XRD), the film showed a surface reconstruction after etching, a cubic pyrochlore structure orientation transition was observed from preferential (222) to (400), and ZnF2 phases were detected. The film surface was chemically analyzed by X-ray photoelectron spectroscopy (XPS) to investigate the reactive ion etching mechanism. A zinc-rich surface was formed because low-volatile ZnF2 residues were difficult to remove.

Interactions in water–THF binary mixture by contact angle, FTIR and dielectric studies

Contact angle, dielectric and IR studies of aqueous tetrahydrofuran (THF) are carried over the entire concentration range. IR studies indicate the formation of blue-shifted hydrogen bonds between water and THF molecules over the entire concentration region. On addition of small quantities of THF to water, THF molecules enter into the hydrogen bonded water network forming clathrate like complexes. Concentration dependent wetting of aqueous THF over various substrates is also reported. The effect of clathrate formation on the wetting properties of the substrate has also been explored. The clathrate structures formed are seen to influence the wetting properties on moderately hydrophobic substrates like Indium tin Oxide (ITO), Cubic Bismuth Zinc Niobate thin film on sapphire substrate (CBZN), Yttrium-stabilized zirconia (YSZ), Strontium Titanate (STO) and Si wafer. Contact angles decreases with an increase in THF concentration except in the region (0.03≤XTHF≤0.05 and 0.07≤XTHF≤0.09) where clathrate structure appears and hence no change of contact angle is seen.

Enhanced the Dielectric and Tunable Properties of BZNT Thin Films through Adjusting Annealing Process

Bismuth zinc niobate titanium (Bi1.5Zn0.5 Nb0.5Ti1.5O7) (BZNT) thin films were deposited on PtTiSiO2Si substrates by radio frequency (rf) magnetron sputtering. The microstructure, surface morphology, stress, dielectric and tunable properties of thin films were investigated as a function of initial annealing temperature. It’s found that high initial annealing temperature increases the grain size, dielectric constant and tunability of BZNT films simultaneously and decreases the tensile stress in films. The BZNT thin film annealed from 500 °C to 700 °C shows the highest FOM value of 45.67 with the smallest dielectric loss and upper tunability.

Synthesis and Characterization of Cubic Bismuth Zinc Niobate Pyrochlore (Bi<SUB>1.5</SUB>ZnNb<SUB>1.5</SUB>O<SUB>7</SUB>) Nanotubes

Synthesis and Characterization of Cubic Bismuth Zinc Niobate Pyrochlore (Bi<SUB>1.5</SUB>ZnNb<SUB>1.5</SUB>O<SUB>7</SUB>) Nanotubes

Microwave dielectric properties of bismuth zinc niobate thin films deposited on alumina by pulsed laser deposition

Abstract Bi2Zn2/3Nb4/3O7 thin films were prepared on Al2O3 substrates by pulsed laser deposition. The phase compositions and microstructures were characterized by X-ray diffraction and atomic force microscopy. The as-deposited films were all amorphous in nature. All films were crystallized after the post annealing at the temperature range of 700–900 °C for 30 min in air. The texture characteristics change with annealing temperature. A split post dielectric resonator method was used to measure the microwave dielectric performance at the resonant frequencies of 10, 15 and 19 GHz. For the films annealed at 900 °C, the preferential orientation is similar to the monoclinic BZN bulk. The microwave dielectric constants at 10, 15 and 19 GHz are 69.4, 58.9 and 47.9, respectively, which are closer to these of the monoclinic BZN bulk.

A novel antifuse structure based on amorphous bismuth zinc niobate thin films

A novel antifuse structure with amorphous bismuth zinc niobate (a-BZN) dielectrics was proposed. The characteristics of the a-BZN antifuse were investigated. Programming direction of up to down was chosen to rupture the a-BZN antifuse. The breakdown voltage of the a-BZN antifuse was obtained at a magnitude of 6.56 V. A large off-state resistance of more than 1 GΩ for the a-BZN antifuse was demonstrated. The surface micrograph of the ruptured a-BZN antifuses was illustrated. Programming characteristics with the programming time of 0.46 ms and on-state properties with the average resistance value of 26.1 Ω of the a-BZN antifuse were exhibited. The difference of characteristics of the a-BZN antifuse from that of a cubic pyrochlore bismuth zinc niobate (cp-BZN) antifuse and gate oxide antifuse was compared and analyzed.

Effect of Sintering Temperature on Structure and Dielectric Properties of BZN Ceramics

Bismuth zinc niobate [(Bi1.5Zn0.5)(Nb1.5Zn0.5)O7, abbreviated as BZN] ceramics are receiving increasing attention due to their excellent dielectric properties in the microwave frequency range. This work is aimed at improving the fabrication technology of BZN ceramics. BZN ceramic specimens were prepared using the general electronic ceramic technique including milling, calcining, crushing, pressing, and sintering. Different sintering temperatures in the range of 950-1080°C were used to study how sintering temperature affects the structure and dielectric properties of BZN ceramics. The crystallinity and microstructure of the BZN ceramics, which were measured respectively by X-ray diffraction and scanning electron microscopy, were improved with increasing of the sintering temperature. The frequency dependence of the dielectric constant and loss tangent was measured at room temperature from 1 kHz to 1 MHz. The dielectric properties of the specimen sintered at 1050°C were found to be the best, for which the relative permittivity (εr) and the loss tangent (tanδ) are around 146 and 0.005, respectively. It was also foεund that when the sintering temperature was higher than 1000°C, the εrand the tanδ of BZN ceramics sintered at different temperatures were similar. As a result, 1000°C may be an appropriate sintering temperature for BZN ceramics.

Effects of SF6/Ar gas-mixing ratio on the etching behavior and properties of BZN thin films

Bismuth zinc niobate (BZN) thin films were etched as a function of the SF6/Ar gas-mixing ratio in a reactive-ion etching (RIE) system. The etching characteristics of surface etch rate and compositions were investigated. Within the ratio range of choice, the etch rate of BZN films is found to decrease first and then increase as the ratio decreases. The small error bars shown in the line graph present a high reliability of the etch rate data. BZN films surfaces were investigated by X-ray photoelectron spectroscopy (XPS). Metal fluorides were found to remain in the surface, resulting in varying relative atomic percentages with gas-mixing ratio. Zn-rich surfaces were formed for ZnF2 residues were hard to remove. Bi and Nb can be removed easily through chemical reactions because of their high volatility, while BiF and NbF can be still detected using narrow scan spectra, which were thought to be present in the form of a metal-oxy-fluoride (Metal-O-F). Gas-mixing ratio is found to have an effect on etch reaction and the removal of residues through different plasma ratios etch process, therefore, leading to varying compositions and element chemical binding state, and resulting in the AFM surface morphology and dielectric property variation. The minimum value of F atomic concentration is achieved at SF6/Ar ratio of 32/13, while the lower surface roughness and the greater dielectric constant both appear at the ratio of 40/5.

Microwave and optical properties of monoclinic Bi2Zn2/3Nb4/3O7thin films

Bismuth zinc niobate (Bi 2 Zn 2/3 Nb 4/3 O 7 ) thin films were deposited by PLD on fused silica substrates at different oxygen pressures. The structural, microwave dielectric, optical and Raman characteristics of these thin films were systematically studied for both the as-deposited films and films annealed at 600 °C. The microwave dielectric constant at a frequency of 10 GHz of the annealed m-BZN films varied from 56 to 71, whereas the dielectric loss tangent varied from 1.8 × 10 −4 to 3.5 × 10 −4 as a function of deposition pressure. The as-deposited films exhibit refractive index in the range of 2.06–2.15 with an optical absorption edge value between 3.59 and 3.67 eV. The observed Raman scattering in m-BZN thin films was slightly shifted toward the higher frequency which reveals that the local lattice disorder changes whereas the structure remains the same monoclinic in thin film as well as in bulk.

High dielectric tunability in lead niobate pyrochlore films

High throughput physical vapor deposition has been used to grow crystalline PbnNb2O5+n (0.6 < n < 4.6) thin films on a single chip. Relative permittivity (ɛr) and dielectric loss (tan δ) were frequency independent between 100 Hz and 1 MHz and −60 °C–100 °C. Dielectric tunability achieved a maximum in the cubic pyrochlore phase (Pb1.2Nb2O6.2, PN, Pb ≈ 38%) of ∼26% (0.44 MV/cm). In comparison to barium strontium titanate (BST) and bismuth zinc niobate (BZN), PN exhibited attractive tan δ ∼ 0.0009 (0.013–0.005 in BST and 0.008–0.0005 in BZN), comparable or superior ɛr of 419 (450 in BST and 160–220 in BZN) and 26% tunability (∼50% in BST and 3.5% in BZN at equivalent fields). PN is thus considered an ideal candidate for tunable device applications.