Characterization in a Wide Frequency Range (40 MHz–67 GHz) of a KTa0.65Nb0.35O3 Thin Film for Tunable Applications

A (100) oriented KTa_0.65Nb_0.35O₃ 400 nm-thin film has been deposited by Pulsed Laser Deposition on MgO substrate. Microwave measurements, performed on InterDigitated Capacitors, show a paraelectric phase at room temperature with a tunability for the devices of 64% under an electric field of 400 kV/cm. Then, using a specific de-embedding method, the complex permittivity of the KTN thin film has been extracted from 40 MHz up to 67 GHz on coplanar waveguides. As promising applications are pointed out at 60 GHz, such as indoor communications, material characterizations are expected in this spectrum.     

Investigations on KTN thin films by XRD,XPS and micro raman spectroscopy

Abstract

The renewed interest in KTa_1?xNb_xO (KTN) mixed perovskite materials, especially in thin films of a high quality, is connected with their remarkable dielectric properties in the dilute compositions. Off-center Nb ions in the highly polarizable KTaO₃ lattice provide a drastic increase in the dielectric peak up to 20 times in comparison with pure KTaO₃ and KNbO₃. This paper reports a continuation of KTN thin films studies with several Nb concentrations in the range of 0 ≤ x ≤ 1 prepared by pulsed laser deposition from segmented KTaO₃, KNbO₃ and KNO₃ targets. The effect of the substrate and symmetry-breaking defects was studied by micro-Raman spectroscopy. An anomalous residual intensity of the forbidden first-order scattering modes in the cubic paraelectric phase of the KTN films was connected with the formation of polar microregions even far above the bulk T_c value. On the whole, the KTN film behavior shows the existence of specific defects enlarging the perovskite unit cell in the film so that the activity of off-center Nb ions increases in producing larger electric dipoles and extending the precursor phase above T_c.     

The Effect of Size, Strain, and Long-Range Interactions on Ferroelectric Phase Transitions in KNbO3KTaO3KNbO3 Superlattices Studied by X-ray, EXAFS, and Dielectric Measurements

Epitaxial, uniformly strained superlattices of ferroelectric KNbO₃ and paraelectric KTaO₃ are studied with respect to their structural and dielectric properties. For dielectric measurements, perfectly lattice-matched conducting KNbO₃Sr(Ru_0.5Sn_0.5)O₃ electrodes are used, and a broad, frequency-dependent maximum is observed in the capacitance-vs-temperature curves. Niobium K-edge glancing-angle EXAFS provides information regarding the crystal structure of KNbO₃ films as thin as two unit cells in superlattices with equal KTaO₃ and KNbO₃ layer thicknesses, showing a clear difference between these thinnest-layer superlattices and films of the KNbO₃K(Ta_0.5Nb_0.5O₃ solid-solution. X-ray diffraction measurements, on the other hand, indicate that these samples exhibit the same transition temperature KNbO₃T_c, indicating the importance of long-range electrostatic interactions. Analysis of the transition temperature for various structures leads to a clear identification of the effect of size and strain on KNbO₃T_c.     

Effect of seed layer on electrical properties of Pb(Zr,Ti)O3 films grown by metalorganic chemical vapor deposition

Abstract

Pb(Zr_xTi_1?x)O₃ (PZT) ferroelectric thin films were prepared by metalorganic chemical vapor deposition (MOCVD) on Pt/Ti/SiO₂/Si substrate. Very thin PZT films, which were deposited at a lower temperature and post-annealed at higher temperature for crystallization, were used as a seed layer. PZT films grown on the seed layer exhibited superior characteristics in the crystalline structure and electrical properties, compared to those deposited without seed layer. Depending on the deposition conditions of PZT seed layer, a wide variation of surface morphology and stoichiometry was found between samples, whereas chemical composition was found to be very similar.     

Formation of a KNbO<Subscript>3</Subscript> single crystal using solvothermally synthesized K<Subscript>2-m</Subscript>Nb<Subscript>2</Subscript>O<Subscript>6-m/2</Subscript> pyrochlore phase

A K_2-mNb₂O_6-m/2 single crystal with a pyrochlore phase formed when the Nb₂O₅?+?x mol% KOH specimens with 0.6?≤?x?≤?1.2 were solvothermally heated at 230 °C for 24 h. They have an octahedral shape with a size of 100 μm, and the composition of this single crystal is close to K_1.3Nb₂O_5.65. The single-crystal KNbO₃ formed when the single-crystal K_2-mNb₂O_6-m/2 was annealed at a temperature between 600 °C and 800 °C with K₂CO₃ powders. When annealing was conducted at 600 °C (or with a small amount of K₂CO₃), the KNbO₃ single crystal has a rhombohedral structure that is stable at low temperatures (< ? 10 °C). The formation of the rhombohedral KNbO₃ structure can be explained by the presence of the K⁺ vacancies in the specimen. The KNbO₃ single crystal with an orthorhombic structure formed when the K_2-mNb₂O_6-m/2 single crystal was annealed at 800 °C with 20 wt% of K₂CO₃.     

Random-Site Cation Ordering and Dielectric Properties of PbMg1/3Nb2/3O3-PbSc1/2Nb1/2O3

(1 ? x)PbMg_1/3Nb_2/3O₃-(x)PbSc_1/2Nb_1/2O₃ (PMN-PSN) solid solution crystals have been grown by the flux method in the whole concentration range. X-ray supercell reflections due to B-cation ordering were observed for as-grown crystals from the 0.1 ≤ x ≤ 0.65 compositional range. Though the ordered domains are rather large (～50 nm) the relaxor-like dielectric behavior is observed for compositions with x < 0.6. The diffusion of the dielectric permittivity maximum in as-grown crystals is the lowest at x = 0.6 and increases towards the end members of solid solution. Such behavior is explained within a Bragg-Williams approach by employing the random layer model. At x ～ 0.6 the excitation energy determined from the Vogel-Fulcher relation exhibits a jump which we regard to changing the kind of the polar regions from PbMg_1/3Nb_2/3O₃ to PbSc_1/2Nb_1/2O₃ related type.     

Epitaxial thin film heterostructures of relaxor ferroelectric Pb(Mg1/3Nb2/3)O3-PbTiO3

Abstract

We have grown stoichiometric pure perovskite phase Pb(Mg_1/3Nb_2/3)O₃-PbTiO₃ (PMN-PT) thin films and PMN-PT/SrRuO₃ heterostructures on miscut (100) SrTiO₃ substrates by pulsed laser deposition. X-ray diffraction θ–2θ scans show that the PMN-PT films are purely c-axis oriented. The off-axis Φ scans show that the heterostructures grow “cube-on-cube” with an in-plane epitaxial arrangement of PMN-PT[100], [010] // SrRuO₃[001] // SrTiO₃[100] and PMN-PT[010], [100] // SrRuO₃[110] // SrTiO₃[010]. The crystalline quality of the films found to be comparable to that of bulk single crystals. The AFM images show that the SrRuO₃ and PMN-PT layers have smooth surfaces with root mean square roughness of 9Å. These epitaxial heterostructures can be used for the fabrication of piezoelectric devices.     

Processing and properties of nanocrystalline Pb(Sc0.5Ta0.5)O3, Pb(Sc0.5nb0.5)O3 and Pb(Mg1/3Nb2/3)O3 films produced by RF-sputtering from ceramic targets

Abstract

Nanocrystalline thin films of different relaxor materials, namely Pb(Sc_0.5Ta_0.5)O₃ (PST), Pb(Sc_0.5Nb_0.5)O₃(PSN), Pb(Mg_1/3Nb_2/3)O₃(PMN) have been produced by RF-sputtering to investigate whether it will affect their dielectric properties if their grain size is reduced to the dimensions known from their nanodomains. The XRD shows that the amorphous film crystallizes in pyrochlore structure at lower temperatures and short times. Annealing at higher temperatures and far longer time intervals leads to an increasing amount of perovskite phase with a grain size in the nanometer range. These results including dielectric measurements will be presented and discussed.     

Pb(Mg1/3Nb2/3)O3 and (1 − x)Pb(Mg1/3Nb2/3)O3 − xPbTiO3 Relaxor Ferroelectric Thick Films: Processing and Electrical Characterization

The lead magnesium niobate [Pb(Mg_1/3Nb_2/3)O₃ or PMN], and its solid solutions with lead titanate (PbTiO₃ or PT), are of great interest because of their high electromechanical properties. At large PMN content, these materials exhibit relaxor characteristics with large electrostrictive strains and a large permittivity, while compositions near the morphotropic phase boundary present very interesting piezoelectric properties. So far, properties of these materials in ceramic, thin film and single-crystal form have been investigated. In this paper, we report on preparation and properties of pyrochlore free PMN and 0.65PMN-0.35PT thick films (thickness = 10 to 20 m). The films were prepared from ethyl cellulose ink by screen printing on alumina substrate. The influence of various parameters, such as powder characteristics, inks formulation and films sintering conditions, on films densification are discussed. The dielectric and electromechanical properties of the films were examined. Relaxor-like behaviour was clearly demonstrated in PMN films. The maximum relative permittivity for PMN film was 10000 (at 0.1 kHz), which is lower than in bulk ceramics (17800 at 0.1 kHz) prepared under the same conditions. For 0.65PMN-0.35PT, the maximum relative permittivity was around 15500 against 24000 in the bulk. Several parameters, which might be responsible for the lower permittivity, are discussed. Poled 0.65PMN-0.35PT thick films exhibit relatively large piezoelectric response (d ₃₃ up to 200 pm/V) and unipolar strains approaching 0.1%, making these films of interest for various actuator and transducer applications.     

Phase Stability of Tungsten-Bronze-Structured KLN Ceramics: Effect of Excess Nb2O5

The effect of excess Nb₂O₅ on the phase stability of tungsten-bronze-structured K₃Li₂Nb₅O₁₅ (KLN) ceramics was studied. Stoichiometric KLN ceramics are not obtained as a single phase and second phases of KNbO₃ and Li₃NbO₄ were observed. Additionally, stoichiometric KLN is difficult to sinter. In Nb-rich compositions, the second phase disappeared and a single KLN phase was obtained. This phase development behavior, that is, the phase stability of the KLN, was analyzed from the viewpoint of the electrostatic potentials of ions. The calculated Madelung energy of the completely filled stoichiometric KLN was unstable, while Nb-rich compositions showed much reduced Madelung energy, indicating that the ions were stabilized electrostatically. Enhanced sinterability in Nb-rich compositions is also discussed.     

Chemical processing and properties of Sr2(Ta,Nb)2O7 thin films

Abstract

The crystallographic orientation, microstructure and electrical properties of Sr₂(Ta, Nb)₂O₇ thin films strongly depended on the composition (Ta:Nb). Post-annealing at 850°C was effective for the improvement of some properties. The thin films with relatively Nb-rich compositions, such as Sr₂(Ta_0.6Nb_0.4)₂O₇ and Sr₂(Ta_0.5Nb_0.5)₂O₇, showed the (0k0) preferred orientation. The Sr₂(Ta_0.5Nb_0.5)₂O₇ thin film had a lamination layer structure after the post-annealing at 850°C for 6 min in oxygen. The characteristic microstructure originated in the crystallographic orientation of (0k0), which is the cleavage plane, and influenced electrical properties. The dielectric constant little change with the composition, however, the P-E hysteresis properties improved with the Nb content.     

Chemical solution processing and properties of tungsten bronze (ba,la)nb2o6 thin films

Abstract

Highly oriented (Ba,La)Nb₂O₆ thin films have been synthesized by a chemical solution deposition method. A homogeneous and stable (Ba_0.75La_0.167)Nb₂O₆ (BLN) precursor solution was prepared by controlling the reaction of metal alkoxides. BLN precursor films crystallized in the tetragonal tungsten bronze phase at 700°C. BLN thin films on MgO(100) and Pt(100)/MgO(100) substrates showed the prominent c-axis preferred orientation. BLN thin films on Pt(100)/MgO(100) exhibited the diffuse phase transition depending upon the frequency.     

Surface acoustic wave properties in 0.955Pb(Zn1/3Nb2/3)O3-0.045PbTiO3 multidomain single crystal poled along [001]c

Surface acoustic wave propagation in a 0.955Pb (Zn_1/3Nb_2/3)O₃-0.045PbTiO₃ multidomain single crystal poled along [001]_c has been analyzed theoretically using Christoffel wave equations. From the measured experimental data, the orientational dependence of surface acoustic wave phase velocities, electromechanical coupling coefficients and power flow angles was calculated. The results showed that surface acoustic wave propagations of 0.955Pb (Zn_1/3Nb_2/3)O₃-0.045PbTiO₃ are poor than 0.93Pb(Zn_1/3Nb_2/3)O₃-0.07PbTiO₃ crystal slightly. However, the 0.955Pb (Zn_1/3Nb_2/3)O₃-0.045PbTiO₃ single crystals have higher rhombohedral-tetragonal phase transition temperature and much stabler electromechanical properties. This may expand applications range of SAW devices.     

Rf Sputtered Na0.5K0.5NbO3 Films on Oxide Substrates as Optical Waveguiding Material

Highly crystalline Na_0.5K_0.5NbO₃ (NKN) thin films of 1–2 μm thickness were deposited by rf-magnetron sputtering of a stoichiometric, ceramic target on single crystal LaAlO₃(001) and Al₂O₃(0112) substrates. X-ray diffraction measurements revealed epitaxial quality of NKN/LaAlO₃ film structures, whereas NKN films on sapphire substrates were found to be preferentially c-axis oriented. A prism-coupling technique was used to characterize optical and waveguiding properties. A bright-line spectrum at λ = 632.8 nm, revealed sharp peaks, corresponding to transverse magnetic (TM) and electric (TE) waveguide propagation modes in NKN/LaAlO₃ and NKN/Al₂O₃ thin films. Using a least mean square fit the refractive index for the films and film thickness were calculated. The extraordinary and ordinary refractive indices were determined to n _e = 2.207 ± 0.002 and n _o = 2.261 ± 0.002, and n _e = 2.216 ± 0.002 and n _o = 2.247 ± 0.002 at λ = 632.8 nm for 2.0 μm thick NKN films on LaAlO₃ and Al₂O₃, respectively. This corresponds to a birefringence Δn = n _e ? n _o = ?0.054 ± 0.003 and Δn = ?0.031 ± 0.003 in the films, where the larger Δn for the NKN/LaAlO₃ structure can be explained by the superior crystalline quality compared to NKN/Al₂O₃. Atomic force microscopy images of the film surfaces revealed rms roughnesses of 2.5 nm and 8.0 nm for 1.0-μm thick NKN/LaAlO₃ and NKN/Al₂O₃ films, respectively. We believe surface scattering is one of the main sources of waveguide losses in the thin films.     

Growth of MgTiO3 thin films by pulsed laser deposition and their electrical properties

Abstract

MgTiO₃ thin films have been grown on various substrates by pulsed laser deposition (PLD) to investigate the application for microwave dielectrics and optical devices. Highly oriented MgTiO₃ thin films were obtained on sapphire (c-plane Al₂O₃). MgTiO₃ thin films deposited on SiO₂/Si and platinized silicon (Pt/Ti/SiO₂/Si) substrates were polycrystalline nature. MgTiO₃thin films grown on sapphire were transparent in the visible and had a sharp absorption edge at 280 nm. These MgTiO₃ thin films had extremely fine feature of surface morphology, i.e., rms roughness of 0.87 nm. Dielectric constant and loss of MgTiO₃ thin films deposited by PLD were about 24 and 1.5% at 1MHz, respectively. These MgTiO₃ thin films also exhibited little dielectric dispersion.     

Solution synthesis of epitaxial films of bismuth containing ferroelectric materials

Abstract

Methoxyethoxide complexes in 2-methoxyethanol were used to produce epitaxial thin films of SrBi₂Nb₂O₉, SrBi₂Ta₂O₉, BaBi₂Nb₂O₉, and BaBi₂Ta₂O₉ on [100] oriented single-crystals of SrTiO₃ and LaAlO₃. Films were prepared by spin coating substrates with alkoxide solutions and firing in air at 850 °C for 20 minutes. With the exception of BaBi₂Ta₂O₉ on LaAlO₃, all of the films were the desired c-axis oriented Aurivillius phase. Out-of-plane orientation was confirmed by θ-2θ scans which showed only [002/] reflections, and in-plane orientation was determined by phi-scans about the [105] plane. Lattice constants and full-width at half-maximum (fwhm) values for both in-plane and out-of-plane reflections are reported.     

Synthesis and characterizations of the (1 − x)Pb(Sc1/2Nb1/2)O3–xPbTiO3 solid solution ceramics

We report a systematic study of the (1???x)Pb(Sc_1/2Nb_1/2)O₃–xPbTiO₃ (PSN–PT) solid solution in the form of ceramics with compositions at or near the morphotropic phase boundary (MPB) region (0.35?≤?x?≤?0.50). The PSN–PT ceramics have been synthesized by an improved two-step wolframite precursor method. The synthetic process has been optimized in terms of calcining and sintering conditions. Both dielectric permittivity measurements and differential scanning calorimetry (DSC) show a clear peak at T _C, at which the transition from the paraelectric to ferroelectric phase takes place. Interestingly, the solid solution of the MPB compositions displays a T _C?>?200 °C, i.e. higher than the T _C of the Pb(Mg_1/3Nb_2/3)O₃–PbTiO₃ and Pb(Zn_1/3Nb_2/3)O₃–PbTiO₃ solid solutions, making the PSN–PT system very promising piezoelectric and ferroelectric materials for high-temperature applications. A dielectric maximum as high as 50,000 is obtained for the 0.65PSN–0.35PT ceramic with losses smaller than 0.05. The values of the remnant polarization and the strain level of the PSN–PT ceramics are comparable to those of the PZT ceramics.     

Epitaxial structure SrBi2Ta2O9<116> /SrTiO3<011> /Ce0.12Zr0.88O2<001> /Si<001> for ferroelectric-gate FET memory

Abstract

Epitaxial thin film growth of SrBi₂Ta₂O₉/SrTiO₃/Ce_0.12Zr_0.88O₂ on Si was studied, and this epitaxial layer structure was applied to fabrication of ferroelectric-gate field effect transistors (FETs). The films were prepared by a pulsed laser deposition technique and epitaxial growth was identified by x-ray diffraction. The devices exhibited excellent electrical performances: Capacitance-voltage characteristic of a metal-ferroelectric-insulator-semiconductor (MFIS) diode showed a retention longer than 10 days and I_d-V_g characteristic of an MFIS-FET showed 1 day retention. It is proved that the crystalline quality of ferroelectric thin films is of great importance to develop integrated devices with high performance.     

Chemical solution technique to prepare perovskite PZT and PLZT thin films and powders

Abstract

PbZr_0.65Ti_0.35O₃ and Pb_0.91La_0.09Zr_0.65Ti_0.35O₃ thin films with thickness of around 100 nm were prepared by the chemical solution deposition technique on Si (100) substrate. Complex metal alkoxide precursors were synthesized by alcoholisis and alcohol exchange reactions starting from metallorganics compounds. NMR spectroscopic techniques, ¹H and ¹³C, and FTIR analysis were used to study the arrangement of the metals and oxygen in the precursor molecules. The films were deposited on Si (100) by spin coating technique and thermal treated by Rapid Thermal Processing for film crystallization. The thermal evolution and structural characterization were performed by DTA-TG/FTIR and by glazing incidence XRD and XRD powder. A PLZT powder with a well-crystallized perovskite structure was obtained at 700°C free of pyrochlore phase whereas the PLZT film exhibits a distorted perovskite structure and residual pyrochlore. The PZT films were less crystallized. The silicon substrate affects the crystal structure of the film. The residual acetylacetonate groups in the precursor of PLZT, would reduce the clustering of Zirconium species.     

Development and Electromechanical Properties of Multimaterial Piezoelectric and Electrostrictive PMN-PT Monomorph Actuators

Monolithic multimaterial monomorphs, comprised of varying ratios of piezoelectric 0.65Pb(Mg_1/3 Nb_2/3)O₃-0.35PbTiO₃ to electrostrictive 0.90Pb(Mg_1/3Nb_2/3)O₃-0.10PbTiO₃, have been co-fired at 1150^∘C. The relative permittivity, displacement, and polarization hysteresis were investigated for varying ratios of piezoelectric to electrostrictive material. The permittivity of the 1:1 multimaterial monomorphs followed the dielectric mixing laws, showing a dielectric constant of 5,500 at room temperature. The P-E hysteresis loop of the 1:1 sample exhibited a maximum and remnant polarization slightly less than the piezoelectric PMN-PT 65/35, but higher than the electrostrictive PMN-PT 90/10. Displacement was found to be higher for the 3:1 monolithic monomorph actuators, reaching 76 μ m at 6 kV/cm. The results indicate that by minimizing the electrostrictive layer thickness the tip displacement can be substantially increased while maintaining a lower hysteresis than that of the purely piezoelectric counterpart.