Enhanced tunable dielectric properties of Ba0.5Sr0.5TiO3/Bi1.5Zn1.0Nb1.5O7 multilayer thin films by a sol-gel process

Ba_0.5Sr_0.5TiO₃(BST)/Bi_1.5Zn_1.0Nb_1.5O₇(BZN) multilayer thin films were prepared on Pt/Ti/SiO₂/Si substrates by a sol-gel method. The structures and morphologies of BST/BZN multilayer thin films were analyzed by X-ray diffraction (XRD) and field-emission scanning electron microscope. The XRD results showed that the perovskite BST and the cubic pyrochlore BZN phases can be observed in the multilayer thin films annealed at 700 °C and 750 °C. The surface of the multilayer thin films annealed at 750 °C was smooth and crack-free. The BST/BZN multilayer thin films annealed at 750 °C exhibited a medium dielectric constant of around 147, a low loss tangent of 0.0034, and a relative tunability of 12% measured with dc bias field of 580 kV/cm at 10 kHz.     

Structural and electrical characteristics of chemical solution derived (Bi3.2La0.4Nd0.4)Ti3O12 thin films

(Bi_3.2La_0.4Nd_0.4)Ti₃O₁₂ (BLNT) thin films were prepared on Pt/Ti/SiO₂/Si substrates by using chemical solution deposition technique, and the effects of annealing temperatures in the range of 550-750 °C on structure and electrical properties of the thin films were investigated. X-ray diffraction analysis shows that the thin films have a bismuth-layered perovskite structure with preferred (117) orientation. The surface morphology observation by field-emission scanning electron microscopy confirms that films are dense and smooth with uniformly distributed grains. The grain size of the thin films increases with increasing annealing temperature; meanwhile, the structural distortion of the thin films also increases. It was demonstrated that the thin films show good electrical properties. The dielectric constant and dielectric loss are 191 and 0.028, respectively, at 10 kHz for the thin film annealed at 600 °C, and the 2Pr value of the thin film annealed at 700 °C is 20.5 μC/cm² at an electric field of 500 kV/cm.     

Role of La0.5Sr0.5CoO3 template layers on dielectric and electrical properties of pulsed-laser ablated Pb(Nb2/3Mg1/3)O3-PbTiO3 thin films

Relaxor ferroelectric thin films of 0.7Pb(Mg_1/3Nb_2/3)O₃-0.3PbTiO₃ (PMN-PT) deposited on platinized silicon substrates with and without template layers were studied. Perovskite phase (80% by volume) was obtained through proper selection of the processing conditions on bare Pt/Ti/SiO₂/Si substrates. The films were initially grown at 300 °C using pulsed-laser ablation and subsequently annealed in a rapid thermal annealing furnace in the temperature range of 750-850 °C to induce crystallization. Comparison of microstructure of the films annealed at different temperatures showed change in perovskite phase formation and grain size etc. Results from compositional analysis of the films revealed that the films initially possessed high content of lead percentage, which subsequently decreased after annealing at temperature 750-850 °C. Films with highest perovskite content were found to form at 820-840 °C on Pt substrates where the Pb content was near stoichiometric. Further improvement in the formation of perovskite PMN-PT phase was obtained by using buffer layers of La_0.5Sr_0.5CoO₃ (LSCO) on the Pt substrate. This resulted 100% perovskite phase formation in the films deposited at 650 °C. Dielectric studies on the PMN-PT films with LSCO template layers showed high values of relative dielectric constant (3800) with a loss factor (tan δ) of 0.035 at a frequency of 1 kHz at room temperature.     

Influences of post-annealing on structural and electrical properties of Bi1.5Zn1.0Nb1.5O7 thin films prepared by pulsed laser deposition

Bi_1.5Zn_1.0Nb_1.5O₇ (BZN) thin films were prepared on Pt/TiO₂/SiO₂/Si(100) substrates at 650 °C under an oxygen pressure of 10 Pa by using pulsed laser deposition process. The crystallinity, microstructure and electrical properties of BZN thin films were investigated to verify the influences of post-annealing thermal process on them. The X-ray diffractometer (XRD) results indicate that all Bi_1.5Zn_1.0Nb_1.5O₇ thin films without post-annealing process or with post-annealing in situ vacuum chamber and in oxygen ambient exhibit a cubic pyrochlore structure. The improved crystallinity of BZN thin films through post-annealing was confirmed by XRD and scanning electron microscope (SEM) analysis. Dielectric constant and loss tangent of the as-deposited BZN thin films are 160 and 0.002 at 10 kHz, respectively. After annealing, dielectric properties of thin films are significantly improved. Dielectric constant and loss tangent of the in situ annealed films are 181 and 0.0005 at 10 kHz, respectively. But the films post-annealed in O₂ oven show the largest dielectric constant of 202 and the lowest loss tangent of 0.0002, which may attribute to the increase in grain size and the elimination of oxygen vacancies. Compared with the as-deposited BZN thin films, the post-annealed films also show the larger dielectric tunability and the lower leakage current density.     

Deposition and dielectric properties of CaCu3Ti4O12 thin films deposited on Pt/Ti/SiO2/Si substrates using radio frequency magnetron sputtering

Polycrystalline CaCu₃Ti₄O₁₂ thin films were deposited on Pt(111)/Ti/SiO₂/Si substrates using radio frequency magnetron sputtering. The phase formation and the physical quality of the films were crucially dependent on the substrate temperature and oxygen partial pressure. Good quality films were obtained at a substrate temperature of 650 °C and 4.86 Pa total pressure with 1% O₂. The dielectric constant (∼ 5000 at 1 kHz and 400 K) of these films was comparable to those obtained by the other techniques, eventhough, it was much lower than that of the parent polycrystalline ceramics. For a given temperature of measurements, dielectric relaxation frequency in thin film was found to be much lower than that observed in the bulk. Also, activation energy associated with the dielectric relaxation for the thin film (0.5 eV) was found to be much higher than that observed in the bulk ceramic (0.1 eV). Maxwell-Wagner relaxation model was used to explain the dielectric phenomena observed in CaCu₃Ti₄O₁₂ thin films and bulk ceramics.     

Microstructure and electrical properties of Pb(Zr0.52Ti0.48)O3 ferroelectric films on different bottom electrodes

The crystalline quality, dielectric and ferroelectricity of the Pb(Zr_0.52Ti_0.48)O₃ (PZT) films deposited on the LaNiO₃ (LNO), LNO/Pt and Pt bottom electrodes were comparatively analyzed to investigate the possibility for their application. LNO thin films were successfully prepared on Si (100) and Pt(111)/Ti/SiO₂/Si substrates by modified metallorganic decomposition (MOD). The PZT thin films were spin-coated onto the LNO, LNO/Pt and Pt bottom electrodes by sol–gel method. The crystallographic orientation and the microstructure of the resulting LNO films and PZT thin films on the different bottom electrodes were characterized by X-ray diffraction analysis. The dielectric and ferroelectric properties of PZT films on the different bottom electrodes are discussed. The PZT films deposited onto Pt/Ti/SiO₂/Si and LNO/Si substrates show strong (110) and (100) preferred orientation, respectively, while the films deposited onto LNO/Pt/Ti/SiO₂/Si substrates show the peaks of mixed orientations. PZT films on LNO and LNO/Pt bottom electrodes have larger dielectric constant and remnant polarizations compared with those grown on the Pt electrode.     

The effect of Bi1.5Zn0.5Nb0.5Ti1.5O7 cover layer on the dielectric and tunable properties of Ba0.6Sr0.4TiO3/Bi1.5Zn0.5Nb0.5Ti1.5O7 bilayered thin films

Bi_1.5Zn_0.5Nb_0.5Ti_1.5O₇ (BZNT) thin films with different thicknesses as cover layers were deposited on the Ba_0.6Sr_0.4TiO₃ (BST) thin films on the Pt/Ti/SiO₂/Si substrates by radio frequency magnetron sputtering method. The microstructure, surface morphology, dielectric and tunable properties of BST/BZNT heterogeneous bilayered films were investigated as a function of the thickness of BZNT films and the effect of BZNT films on the asymmetric electrical properties of BST/BZNT bilayered films was discussed. It was found that BZNT cover layer significantly improved the leakage current and the dielectric loss, and the dielectric constant and tunability of BST/BZNT bilayered thin films simultaneously decreased with the increasing thickness of BZNT films. The BST/BZNT bilayered thin film with a 50 nm BZNT cover layer gave the largest figure of merit (FOM) of 33.48 with the upper tunability of 55.38%. The asymmetric electrical behavior of BST/BZNT bilayered films is probably related to an internal electric field caused by built-in voltages at Pt/BST and BZNT/Au interfaces.     

Structural, dielectric and ferroelectric properties of multilayer lithium tantalate thin films prepared by sol-gel technique

Multilayer lithium tantalate thin films were deposited on Pt-Si [Si(111)/SiO₂/TiO₂/Pt(111)] substrates by sol-gel process. The films were annealed at different annealing temperatures (300, 450 and 650 °C) for 15 min. The films are polycrystalline at 650 °C and at other annealing conditions below 650 °C the films are in amorphous state. The films were characterized using X-ray diffraction, atomic force microscopy (AFM) and Raman spectroscopy. The AFM of images show the formation of nanograins of uniform size (50 nm) at 650 °C. These polycrystalline films exhibit spontaneous polarization of 1.5 μC/cm² at an application of 100 kV/cm. The dielectric constant of multilayer film is very small (6.4 at 10 kHz) as compared to that of single crystal.     

High dielectric tunability of Ba0.6Sr0.4TiO3 thin film deposited by radio-frequency magnetron sputtering

In microwave tunable devices, one of the major challenges encountered is the simultaneous minimization of the material's dielectric loss and maximization of dielectric tunability. In this work, Ba_0.6Sr_0.4TiO₃ thin film with the thickness of 300 nm was deposited on Pt/SiO₂/Si substrates using radio-frequency magnetron sputtering technique, and its dielectric properties were investigated. Due to the high temperature annealing process at substrate temperature of 600 °C, well-crystallized Ba_0.6Sr_0.4TiO₃ film was deposited. The dielectric constant and dielectric loss of the film at 100 kHz are 300 and 0.033, respectively. Due to the good crystallinity of the Ba_0.6Sr_0.4TiO₃ films deposited by radio-frequency magnetron sputtering, high dielectric tunability up to 38.3% is achieved at a low voltage of 4.5 V.     

Structure evolution and ferroelectric properties of Bi3.4Yb0.6Ti3O12 thin films crystallized under a moderate temperature

Ytterbium-doped Bi₄Ti₃O₁₂ (Bi_3.4Yb_0.6Ti₃O₁₂, BYT) ferroelectric thin films were successfully deposited on Pt(111)/Ti/SiO₂/Si(100) substrates by chemical solution deposition (CSD). X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used to identify the crystal structure, the surface and cross-section morphology of the deposited ferroelectric films. Structure evolution and ferroelectric properties of the as-prepared thin films annealed under different temperatures (600 °C-750 °C) were studied in detail. Additionally, the mechanism concerning the dependence of electrical properties of the BYT ferroelectric thin films on the annealing temperature was discussed.     

Nanograins dependent dielectric constant, tunability, phase transition, impedance spectroscopy and leakage current of (Pb1 − xSrx)TiO3 thin films

Nanostructured (Pb_1 − xSr_x)TiO₃ (PST) (x = 0.1, 0.2 and 0.3) thin films have been prepared by chemical solution deposition process using spin coating technique. The solution as such was deposited on Pt/Ti/SiO₂/Si substrates and annealed at 650 °C/3h. Nanograins dependent dielectric properties of PST films show dielectric constant up to the higher frequency region, low losses, large tunability and phase transition at small temperature. The impedance data has been fitted by Cole-Cole model to study the effect of grain boundaries on the dielectric properties. The current-voltage characteristics have been measured to study leakage current in PST films and described by Poole-Frenkel emission model. It is suggested that the key carrier transport process in PST films is emission of electrons from a trap state near the metal-film interface into a continuum of states associated with each conductive dislocation. The activation energy value for carrier transport in PST films is obtained from temperature-dependent current-voltage characteristics.     

Effect of post-annealing treatment in oxygen on dielectric properties of K0.5Na0.5NbO3 thin films prepared by chemical solution deposition

K_0.5Na_0.5NbO₃ thin films were prepared on Pt/Ti/SiO₂/Si substrates by chemical solution deposition method with different annealing temperatures of 550 °C, 600 °C, 700 °C. The post-annealing treatment was introduced at 550 °C for 3 min in oxygen ambient. It is found that the films were composed of pure provskite phase, and the post-annealing treatment promoted the crystallization and improved the quality of the films, which resulted in the enhancement of the dielectric property of the films. The effect of the post-annealing on the dielectric properties of the films was also discussed.     

Improved dielectric properties of CaCu3Ti4O12 thin films on oxide bottom electrode of La0.5Sr0.5CoO3

We report on the effect of La_0.5Sr_0.5CoO₃ (LSCO) bottom electrode to the dielectric properties of CaCu₃Ti₄O₁₂ (CCTO) thin films grown on Ir/Ti/SiO₂/Si substrates. Compared with the films grown directly on Ir/Ti/SiO₂/Si substrates, the dielectric constant has been increased greatly about 100%, and the dielectric loss decreased to lower than 0.2 in the frequency range of 1-100 kHz. The origin has been discussed in details based on the analysis of the X-ray diffraction and impedance spectra measurements. Results of the impedance spectra suggest that the absence of undesired interfacial layer between Ir/CCTO thin films might be one of the major reasons of the improvement of the dielectric properties when the LSCO was introduced as the bottom electrode.     

Effect of the orientation on the ferroelectric-antiferroelectric behavior of sol-gel deposited (Pb,Nb)(Zr,Sn,Ti)O3 thin films

The (Pb,Nb)(Zr,Sn,Ti)O₃ (PNZST) antiferroelectric thin films were prepared on two different substrates by sol-gel methods. Films derived on the LNO/Pt/Ti/SiO₂/Si substrates showed a strong (100) preferred orientation. The dependence of electrical properties derived on the Pt/Ti/SiO₂/Si and LNO/Pt/Ti/SiO₂/Si substrates have been studied, with the emphasis placed on field-induced phase switching from the antiferroectric to the ferroelectric state. The PNZST thin films deposition on two kinds of substrates show different phase transition behavior and associated properties such as antiferroelectric (AFE) to ferrroelectric (FE) switching field E_AFE-FE, FE to AFE switching field E_FE-AFE and the hysteresis ΔE=E_AFE-FE−E_FE-AFE.     

Effects of substrate temperature on Bi0.8La0.2FeO3 thin films prepared by pulsed laser deposition

Bi_0.8La_0.2FeO₃ thin films on Pt/TiO₂/SiO₂/Si substrates at various substrate temperatures from 500 °C to 750 °C are prepared by pulsed laser deposition, and their microstructures and ferroelectric/magnetic properties are carefully investigated using various techniques. It is observed that the crystallographic orientation and Fe-ion valence state depend significantly on the substrate temperature, which consequently influences considerably on the ferroelectric and magnetic properties of the thin films. A considerable improvement of the ferroelectric and magnetic properties of the thin films can be achieved by optimizing the substrate temperature for deposition.     

Preparation and characterization of Ba1 − xSrxTiO3 thin films deposited on Pt/SiO2/Si by sol-gel method

BST thin films have been investigated as potential candidates for use in frequency agile microwave circuit devices. Stoichiometric (Ba_1 − xSr_x)TiO₃ (BST) thin films have been prepared on Pt/SiO₂/Si substrates using sol-gel method. The BST films were characterized by X-ray fluorescence (XRF) spectroscopy analysis, X-ray diffraction (XRD), scanning electron microscope (SEM) and electrical measurements. The relationships of processing parameters, microstructures, and dielectric properties are discussed. The results show that the films exhibit pure perovskite phase through rapid thermal anneal at 700 °C and their grain sizes are about 20-40 nm. The dielectric constants of BST5, BST10, BST15 and BST20 are 323, 355, 382 and 405, respectively, at 80 kHz.     

Preparation and characterization of highly (1 1 1)-oriented (Pb,La)(Zr,Ti)O3 thin films by sol-gel processing

Lanthanum modified lead zirconate titanate (Pb_0.91La_0.09)(Zr_0.65Ti_0.35)O₃ (PLZT) ferroelectric thin films were grown on Pt/Ti/SiO₂/Si(1 0 0) and fused quartz substrates using a sol-gel method with rapid thermal annealing processing. The results showed that the highly (1 1 1)-oriented pervoskite PLZT thin film growth on Pt/Ti/SiO₂/Si(1 0 0) substrates. The electrical measurements were conducted on PLZT films in metal-ferroelectric-metal capacitor configuration. The PLZT thin films annealed at 600 °C showed well-saturated hysteresis loops with remanent polarization and coercive electric field values were 10.3 μC/cm² and 36 kV/cm, respectively, at an applied field of 300 kV/cm. At 100 kHz, the dielectric constant and dielectric loss of the film are 682 and 0.021, respectively. The PLZT thin film on fused quartz substrate, annealed at 600 °C, exhibited good optical transmittance, the band gap of optical direct transitions is 3.89 eV.     

Structure of post-annealed ferroelectric PbZrxTi1-xO3 and SrBi2Ta2O9 thin films

In order to fabricate good quality ferroelectric thin films, PbZr_xTi_(1-x)O₃ (PZT) and SrBi₂Ta₂O₉ (SBT) films were fabricated on SiO₂/Si(100) substrates and on Pt/Ti/ SiO₂/Si(100) substrates by pulsed laser excimer deposition (PLD). X-ray diffraction, Rutherford backscattering analysis, and atomic force microscopy were used to characterize the structural properties of the samples, which were post-annealed at different temperatures. The results showed that the PZT and SBT films fabricated on Pt/Ti/SiO₂/Si(100) substrates and annealed at 700 °C exhibited optimum properties.     

Preparation,microstructure and dielectric properties of Ba0.5Sr0.5TiO3 thin films grown on Pt/Ti/SiO2/Si substrates by pulsed laser deposition

Barium strontium titanate Ba_0.5Sr_0.5TiO₃ (BST) thin films have been deposited on Pt/Ti/SiO₂/Si substrates by a pulsed laser deposition method. The low-frequency dielectric responses of the BST films, grown at different substrate temperatures (T_s), were measured as functions of frequency in the frequency range from 1 kHz to 1 MHz. With increase of T_s, the grain size of BST thin films became larger and the crystallinity was greatly improved, and then the dielectric permittivity increased, while the dielectric dispersion rose drastically. The origin of the large dielectric relaxation is believed to result from the aggravation of oxygen diffusion at the BST/Pt interface for the BST thin films grown at comparatively higher temperatures. This concept could be further explained by considering the influence of post-annealing in oxygen ambient on the dielectric properties of BST thin films. Our results reveal that the dielectric properties are strongly dependent on the processing conditions and the microstructure of thin films.     

Enhancement on effective piezoelectric coefficient of Bi3.25Eu0.75Ti3O12 ferroelectric thin films under moderate annealing temperature

Bi_3.25Eu_0.75Ti₃O₁₂ (BET) thin films were deposited on Pt/Ti/SiO₂/Si(111) substrates by a metal-organic decomposition method. The effects of annealing temperatures 600-800 °C on microstructure, ferroelectric, dielectric and piezoelectric properties of BET thin films were studied in detail. The spontaneous polarization (87.4 × 10^− 6 C/cm² under 300 kV/cm), remnant polarization (65.7 × 10^− 6 C/cm² under 300 kV/cm), the dielectric constant (992.9 at 100 kHz) and the effective piezoelectric coefficient d₃₃ (67.3 pm/V under 260 kV/cm) of BET thin film annealed at 700 °C are better than those of the others. The mechanisms concerning the dependence of the enhancement d₃₃ are discussed according to the phenomenological equation, and the improved piezoelectric performance could make the BET thin film a promising candidate for piezoelectric thin film devices.