BZN Films Research Articles

Effect of precursor pH value on the structure and electrical properties of Bi1.5Zn1.0Nb1.5O7 thin films

Bi1.5Zn1.0Nb1.5O7 (BZN) thin films are synthesized on a FTO (Fluorine -doped SnO2 transparent conductive glass) substrate by an improved sol-gel method. The pH of the precursor is controlled by citric acid and ammonia, and the effect of pH on the crystal structure and electrical properties of the BZN films is studied. When the precursor pH is 5, the relative intensity of the diffraction peak of BZN films is the highest, the FWHM is the narrowest, and the crystallization degree is the highest, compared to those of BZN films synthesized from precursors at other pH, the crystallization energy offset of the element binding energy of the thin films is the smallest and the phase difference of the binding energy is the closest to the theoretical value, and the films have excellent electrical properties with permittivity of 120, loss tangent of 0.003, tunability of 14.8%, breakdown voltage of 0.43 MV/cm and energy storage density of 9.82 × 10−2 J/cm3.

Effect of in-plane ordering on dielectric properties of highly {111}-oriented bismuth–zinc–niobate thin films

Bi 1.5-x Zn 0.92-y Nb 1.5 O 6.92-δ (BZN) thin films were grown by pulsed laser deposition on two different Pt-covered substrates, namely textured {111}Pt/TiO 2 /SiO 2 /(100)Si substrate (Pt/Si) and epitaxial {111}Pt/R-plane sapphire substrate (Pt/sapphire). In both cases, the BZN films present {111} and {100} out-of-plane orientations, in relative ratios of 65/35 on Pt/Si, and 80/20 on Pt/sapphire, respectively. The film grown on Pt/Si is textured, while the film deposited on Pt/sapphire presents epitaxial-like relationships with the substrate, for both out-of-plane orientations. Dielectric measurements were performed on both types of thin films, using Pt/BZN/Pt planar capacitor structures. The BZN/Pt/sapphire film presents higher dielectric constant (245 at 100 kHz) and higher tunability (12 % at 600 kV/cm) than the BZN/Pt/Si film (200; 6 %), while the dielectric losses values are nearly the same (~ 0.05).

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.

Effect of excess Bi2O3 on structure and performance of ZnO-based thin film transistors

High-performance ZnO-based thin film transistors (ZnO-TFTs) were fabricated by radio frequency magnetic sputtering using Bi1.5Zn1.0Nb1.5O7 (BZN) films as the gate dielectrics. BZN films with excess Bi2O3 were compared to traditional BZN films to investigate the effects on ZnO-TFT performance. The results showed that excess Bi2O3 (5 mol. %) can significantly reduce leakage currents and increase dielectric constants in BZN gate dielectrics. The excess Bi2O3 in these films served to compensate for the bismuth loss that typically occurs in BZN films during the deposition process, leading to improved electrical characteristics. At an applied electric field of 250 kV/cm, the leakage current density for the BZN film with excess Bi2O3 was approximately 2 orders of magnitude lower than that of the BZN film without excess Bi2O3. Moreover, the BZN film with 5 mol. % excess Bi2O3 exhibited high capacitance density (233 nF/cm2) and a high dielectric constant (65). The electrical performances of ZnO-TFTs were remarkably enhanced by using BZN films with excess Bi2O3 as the gate insulator, with demonstrated field-effect mobility of 0.25 cm2/Vs, on/off ratio of 1 × 105, and low threshold voltage of 2.3 V.

Structure, composition and microwave dielectric properties of bismuth zinc niobate pyrochlore thin films

(Bi1.5Zn0.5)(Zn0.5Nb1.5)O7 (BZN) pyrochlore thin films were deposited onto both Pt/TiO2/SiO2/Si and polycrystalline alumina substrates using pulsed laser deposition technique and then post-annealed using rapid thermal processing. The deposition temperature varies from 300 °C to 600 °C, and all the BZN films showed cubic pyrochlore structure after annealing at 650 °C for 30 min in air. The influence of the substrate associated with crystal structure is significant in the as-deposited films and disappears after post-annealing. The dielectric properties as a function of frequency up to the microwave frequency in both films were measured by LCR meter and split-post dielectric resonator technique. It is found that the BZN film deposited at 400 °C and post-annealed at 650 °C shows excellent dielectric properties with low loss in the microwave frequency range. This result indicates that the BZN thin film is a potential microwave material.

Strain-Stable Nonlinear Dielectric Responses in Pyrochlore Bismuth Zinc Niobate Thin Films

The effect of film strain on the dielectric responses of pyrochlore Bi–Zn–Nb–O (BZN) thin films was investigated in (111)-oriented BZN thin films grown on various substrates. The bias-field dependence of dielectric constant revealed that both the linear and nonlinear electric susceptibilities of BZN thin films are stable against the film strain, unlike conventional tunable materials, such as (Ba,Sr)TiO3. The difference in dielectric nonlinearity between BZN and BST films is discussed on the basis of the phenomenological theory. The strain stability of linear and nonlinear dielectric responses of BZN is available for practical thin-film tunable applications.

Thickness-ratio-dependent dielectric properties of Bi1.5Zn1.0Nb1.5O7/Ba0.5Sr0.5TiO3 bilayered thin films

Abstract Bi1.5Zn1.0Nb1.5O7 (BZN)/Ba0.5Sr0.5TiO3 (BST) thin films were prepared on Pt/Ti-coated sapphire substrates by radio frequency magnetron sputtering. The specific relationship between the dielectric properties and the thickness ratio of the BZN thickness to the BST thickness was investigated. The presence of BZN films effectively reduced the dielectric loss of the thin films. The thickness-ratio-dependent dielectric constant and dielectric loss behaviors were in good accordance with the simulation results based on the series connection theory. The optimum thickness ratio was determined to be around 0.5, exhibiting a maximum commutation quality factor of about 16,000. The built-in electric field at the region near the BZN–BST interface may be responsible for the asymmetric characteristic of the electric-field-dependent dielectric properties of the BZN/BST thin films.

Effects of A-Site Occupancy of Bismuth Ions on the Dielectric Tunable Properties of Pyrochlore Bismuth Zinc Niobate Films

The A-site composition dependence of cubic pyrochlore Bi–Zn–Nb–O (BZN) thin films of dielectric tunable properties was investigated. (111)-textured BZN films with a wide range of Bi/Nb ratios (0.62–1.26) were fabricated by metal organic chemical vapor deposition. Raman spectral analysis revealed that by changing the Bi/Nb ratio in BZN films, the Bi concentration of the A-site mainly varied. Dielectric constant and dielectric tunability were found to increase with increasing Bi ion occupancy of the A site. These experimental findings suggest that the Bi occupancy of A site is an important factor for designing Bi based pyrochlore dielectric tunable materials.

Structures and Dielectric Properties of Bi1.5Zn1.0Nb1.5O7 Thin Films Prepared by Pulsed Laser Deposition at Low Temperature

Amorphous Bi1.5Zn1.0Nb1.5O7 (BZN) thin films have been prepared on Pt/TiO2/SiO2/Si(100) substrates by pulsed laser deposition (PLD) process at low temperature. BZN films were deposited at room temperatures under the oxygen pressure from 1 Pa to 30 Pa, and then post-annealed at the temperature below 200°C. XRD analysis indicates that BZN films are still amorphous in nature after the post-annealing. The dielectric constant of amorphous BZN films increases and the dielectric loss decreases after the post-annealing process. The dielectric properties of BZN films are strongly dependent on the oxygen pressure. BZN Thin films deposited at 1 Pa exhibit superior dielectric characteristics. Dielectric constant and loss tangent are 60.2 and 0.006 at 10 kHz, respectively. Leakage current density is less than 1 × 10−7 A/cm2 at 300 kV/cm.

Effect of oxygen pressure on structure and properties of Bi 1.5Zn 1.0Nb 1.5O 7 pyrochlore thin films prepared by pulsed laser deposition

The Bi 2O 3–ZnO–Nb 2O 5 (BZN) cubic pyrochlore thin films were prepared on Pt/TiO 2/SiO 2/Si(1 0 0) substrates by using pulsed laser deposition process. The oxygen pressure was varied in the range of 5–50 Pa to investigate its effect on the structure and dielectric properties of BZN thin films. It is found that oxygen pressure during deposition plays an important role on structure and other properties of BZN films. The BZN films deposited at temperature of 650 °C and at O 2 pressure of 5 Pa have an amorphous BZN and Nb 2O 5 phases but exhibits a cubic pyrochlore structure with a preferential (2 2 2) orientation when the oxygen pressure increases to 10 Pa. Dielectric constant and loss tangent of the films deposited at 10 Pa are 185 and 0.0008 at 10 kHz, respectively. The dielectric tunability is about 10% at a dc bias field of 0.9 MV/cm.

Flexible Dielectric Bi1.5Zn1.0Nb1.5O7 Thin Films on a Cu‐Polyimide Foil

Flexible thin films of Bi1.5Zn1.0Nb1.5O7 (BZN) were deposited on a Cu/polyimide (PI) foil by aerosol deposition at room temperature. The BZN film thickness was in the range of 1.2–17.9 μm. Highly dense and nanocrystalline films were obtained without any heat treatment. The dielectric constant and loss of the film at 100 kHz were over 150 and 0.04, respectively. Furthermore, the as‐deposited film showed markedly low leakage current densities of <10−9 A/cm2 at 3.0 V. These reasonably high dielectric properties were due to the nanocrystallinity of the films. The results confirm the significant potential of the BZN films as passive components in flexible printed circuit board applications.

Fabrication and Characterization of ITO/BZN Thin Film Transistors

ITO channel thin film transistors (TFTs) with a Bi1.5Zn1.0Nb1.5O7 (BZN) gate insulator have been fabricated and their electrical properties have been characterized. We first fabricated BZN films by using the sputtering technique and we showed that the film could induce a charge denisty as large as 6.6 µC/cm 2 . Next, we fabricated an ITO-channel TFT by using BZN as a gate insulator. Good electrical performance were demonstrated with an on/o current ratio of 10 8 and a subthreshold voltage swing of 280 mV/decade.

High-permittivity and low-loss dielectric tunable pyrochlore thin films deposited by radio frequency magnetron sputtering from a lead zinc niobate target

Since Bi 2O 3–ZnO–Nb 2O 5 (BZN) pyrochlore thin films have been introduced as a tunable dielectric, the substitution of Bi with Pb could be a reasonable choice. The PbO–ZnO–Nb 2O 5 (PZN) cubic pyrochlore thin films were produced by radio frequency sputtering, and their dielectric properties, in terms of tunability, were measured. Up to 33.4% of tunability and comparable K factors with BZN films were obtained. The effects of film crystallization, along with substrate heating and post-annealing on the dielectric properties, were similar to those of BZN. However, strong texturing developed in the PbO–ZnO–Nb 2O 5 (PZN) films deposited at a high substrate temperature, which caused degradation of the loss tangent and K factor.

The Structural and Electrical Properties of Bismuth-based Pyrochlore Thin Films for embedded Capacitor Applications

【[ $Bi_{1.5}Zn_{1.0}Nb_{1.5}O_7$ ] (BZN), $Bi_2Mg_{2/3}Nb_{4/3}O_7$ (BMN), and $Bi_2Cu_{2/3}Nb_{4/3}O_7$ (BCN) pyrochlore thin films were prepared on $Cu/Ti/SiO_2/Si$ substrates by pulsed laser deposition and the micro-structural and electrical properties were characterized for embedded capacitor applications. The BZN, BMN, and BCN films deposited at $25\;^{\circ}C$ and $150\;^{\circ}C$ , respectively show smooth surface morphologies and dielectric constants of about $39\;{\sim}\;58$ . The high dielectric loss of the films deposited at $150\;^{\circ}C$ compared with films deposited at $25\;^{\circ}C$ was attributed to the defects existing at interface between the films and copper electrode by an oxidation of copper bottom electrode. The leakage current densities and breakdown voltages in 200 nm thick-BMN and BZN films deposited at $150\;^{\circ}C$ are approximately $2.5\;{\times}\;10^{-8}\;A/cm^2$ at 3 V and above 10 V, respectively. Both BZN and BMN films are considered to be suitable materials for embedded capacitor applications.】

Room temperature fabricated ZnO thin film transistor using high-K Bi1.5Zn1.0Nb1.5O7 gate insulator prepared by sputtering

In this letter, we report on dielectric and leakage current characteristics of room temperature deposited Bi1.5Zn1.0Nb1.5O7 (BZN) films on the basis of crystallographic structure and suitability of BZN gate insulators as key building blocks in the fabrication of low voltage operating ZnO based thin-film transistors (TFTs). The BZN films exhibited a high dielectric constant (∼51) and good leakage current characteristics (∼10−7A∕cm2) at an applied voltage of 5V. All room temperature processed ZnO based TFTs using BZN gate insulator exhibited field effect mobility of 1.13cm2∕Vs and low voltage device performance less than 4V.

Bismuth-zinc-niobate embedded capacitors grown at room temperature for printed circuit board applications

We fabricated metal-insulator-metal (MIM) thin film capacitors with Bi1.5Zn1.0Nb1.5O7 (BZN) dielectric films. The BZN films were deposited at room temperatures by pulsed laser deposition and annealed below 200°C which is compatible with the used polymer-based substrates. The dielectric constant of BZN films increases from 2 to 70, when they are annealed at 150°C, but still in amorphous phase. We found that a considerable portion of Bi metallic phase still remains in the as-deposited film. They turn into oxides upon annealing at >120°C, causing the dramatic change of the dielectric properties. Amorphous BZN thin films exhibit superior dielectric characteristics, capacitance density of 150nF∕cm2, and leakage current less than 1μA∕cm2 at 5V. The MIM capacitors using amorphous BZN thin films will be a promising candidate for the PCB-embedded capacitors.

Distributed phase shifter with pyrochlore bismuth zinc niobate thin films

A monolithic Ku-band phase shifter employing voltage tunable Bi/sub 1.5/Zn/sub 1.0/Nb/sub 1.5/O/sub 7/ (BZN) thin film parallel plate capacitors is reported. BZN films were deposited by radio frequency magnetron sputtering on single-crystal sapphire substrates. A nine-section distributed coplanar waveguide loaded-line phase-shifter structure was designed. A differential phase shift of 175/spl deg/ was achieved with a maximum insertion loss of 3.5 dB at 15 GHz, giving a figure of merit /spl sim/50/spl deg//dB. To the best of our knowledge, this is the first demonstration of a monolithic tunable microwave circuit using BZN thin films.

Laser deposition and dielectric properties of cubic pyrochlore bismuth zinc niobate thin films

The Bi1.5ZnNb1.5O7 (BZN) thin films with cubic pyrochlore structure were prepared on Pt∕SiO2∕Si substrates by pulsed laser deposition from a stoichiometric target. The crystallinity, surface morphology, and dielectric properties of BZN thin films at different substrate temperatures were investigated. It was found that the BZN films had a pure cubic pyrochlore structure when deposited at 550–650°C and the strong (222) texture at 650°C. The cubic BZN thin films deposited at 600°C had a dielectric loss lower than 0.004 and maximum voltage tunability of 6% with an applied bias field of 0.5MV∕cm under 100kHz.

Low-temperature crystallized pyrochlore bismuth zinc niobate thin films by excimer laser annealing

The crystallization temperature of Bi1.5Zn0.5Nb1.5O6.5 (BZN) films was reduced by a combination of conventional heating and irradiation with a pulsed KrF excimer laser. Both the energy density and substrate temperature affect the properties of laser-annealed BZN films. It was found that the crystallinity and dielectric properties improved after a postannealing at 400°C for 2h in an oxygen atmosphere. BZN films crystallized with an energy density of 27mJ∕cm2 at a substrate temperature of 400°C with postannealing showed dielectric properties comparable to those of rapid thermal annealed BZN films. Laser crystallization at substrate temperatures ⩽400°C makes integration with polymeric substrates possible.

Microwave dielectric properties of tunable capacitors employing bismuth zinc niobate thin films

Parallel plate capacitors employing Bi1.5Zn1.0Nb1.5O7 (BZN) thin films with the pyrochlore structure were fabricated on platinized sapphire substrates. The total device quality factor and capacitance were analyzed in the microwave frequency range (up to 20 GHz) by measuring reflection coefficients with a vector network analyzer. The parasitics due to the probe pads were extracted from the measurements. The total device quality factor, which included losses from the dielectric and the electrodes, was more than 200 up to 20 GHz for devices with an area of 100μm2. Based on the frequency dependence of the impedance, series losses of unknown origin appear to dominate the device quality factor at higher frequencies. No significant dispersion in the device capacitance, as would be associated with a dielectric relaxation of BZN, was measured. The large electric field tunability of the permittivity of BZN films and the high device quality factors make these films attractive for voltage controlled microwave devices.