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.     

Size reduction in crystal grains in LiNb0.5Ta0.5O3 thin films by controlling nucleation density during thermal plasma spray chemical vapor deposition

Two approaches were applied to thermal plasma spray chemical vapor deposition (TPS CVD) in order to reduce crystal grain size or/and surface roughness of LiNb_0.5Ta_0.5O₃ thin films while retaining the advantages of this method, such as high deposition rate. The first method consists of a two-step deposition, where the nucleation density is controlled in the first step and the film with high crystallinity is deposited in the second step. The surface roughness and grain size could be reduced from 1 nm to 7.7 nm, and from 200-350 nm to 120-180 nm, respectively. In the second approach, employing a one-step TPS CVD process, the conventional precursor was substituted by a double-alkoxide precursor and grain size in the deposited films could be reduced to 50-80 nm. Both approaches adopted in this work permitted to reduce the optical propagation loss.     

Impedance spectroscopy and relaxation phenomena of (Na,K) excess Na0.5K0.5NbO3 thin films grown by chemical solution deposition

Na_0.5K_0.5NbO₃ (NKN) and 10 mol% (Na,K) excess Na_0.5K_0.5NbO₃ (NKN10) thin films on Pt/Ti/SiO₂/Si substrate were prepared by chemical solution deposition. Crystallization of NKN10 thin films was confirmed by X-ray diffraction. The (Na,K) excess Na_0.5K_0.5NbO₃ thin film shows a ferroelectric P-E hysteresis loop. Dielectric properties and impedance spectroscopy of thin films were investigated in the frequency range from 0.1 Hz to 100 kHz and the temperature range of 25 ~ 500 °C. By analyzing the complex impedance relaxation with Cole-Cole plots, we found impedance relaxations for the thin film. The contribution of electrical conduction is discussed in relation to grain, grain boundary, and interface effects.     

Epitaxial growth and thermoelectric properties of TiNiSn and Zr0.5Hf0.5NiSn thin films

Due to their exceptional thermoelectric properties Half-Heusler alloys like MNiSn (M = Ti,Zr,Hf) have moved into focus. The growth of single crystalline thin film TiNiSn and Zr_0.5Hf_0.5NiSn by dc magnetron sputtering is reported. Seebeck and resistivity measurements were performed and their dependence on epitaxial quality is shown. Seebeck coefficient, specific resistivity and power factor for Zr_0.5Hf_0.5NiSn at room temperature were measured to be 63 μV K^− 1, 14.1 μΩ m and 0.28 mW K^− 2 m^− 1, respectively. Multilayers of TiNiSn and Zr_0.5Hf_0.5NiSn are promising candidates to increase the thermoelectric figure-of-merit by decreasing thermal conductivity perpendicular to the interfaces. The epitaxial growth of multilayers containing TiNiSn and Zr_0.5Hf_0.5NiSn is demonstrated by measuring satellite peaks in the X-ray diffraction pattern originating from the additional symmetry perpendicular to the film surface.     

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

Bi_1.5Zn_1.0Nb_1.5O₇ (BZN)/Ba_0.5Sr_0.5TiO₃ (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.     

Optical characterization of BaSm2Ti4O12 thin films by spectroscopic ellipsometry

We performed spectroscopic ellipsometric measurement to characterize BaSm₂Ti₄O₁₂ (BST) thin films grown on Pt/Ti/SiO₂/c-Si substrate by rf magnetron sputtering. The six BST films were prepared at various deposition temperatures and thermal annealing times. The resulting refractive indices and extinction coefficients of the BST films show only slight change by the deposition temperature but a significant change after thermal annealing, implying the importance of the post annealing process. The increase of the refractive index can be understood by the higher density of the BST films caused by the crystallization after annealing process.     

溅射工艺参数对Ba0.5Sr0.5TiO3薄膜沉积速率和介电性能的影响

铁电/介电BST(BaxSr1-xTiO3)薄膜在微电子学、集成光学和光电子学等新技术领域有广泛的应用前景.用射频磁控溅射方法制备了厚约700 nm的Ba0.5Sr0.5TiO3薄膜,采用Al/BST/ITO结构研究了溅射功率、溅射气压、O2/(Ar O2)比和基片温度对上述BST薄膜沉积速率和介电性能的影响,并根据这些结果分析了较优的工艺条件,同时用XRD、XPS和SEM研究了薄膜的晶相、组成和显微结构.     

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.     

V-doping effects on ferroelectric properties of K0.5Bi4.5Ti4O15 thin films

V-doped K_0.5Bi_4.5Ti₄O₁₅ (K_0.5Bi_{4.5 − x/3}Ti_4 − xV_xO₁₅, KBTiV-x, x = 0.00, 0.01, 0.03, and 0.05) thin films were prepared on a Pt(111)/Ti/SiO₂/Si(100) substrate by a chemical solution deposition method. The thin films were annealed by using a rapid thermal annealing process at 750 °C for 3 min in an oxygen atmosphere. Among them, KBTiV-0.03 thin film exhibited the most outstanding electrical properties. The value of remnant polarization (2P_r) was 75 μC/cm² at an applied electric field of 366 kV/cm. The leakage current density of the thin film capacitor was 5.01 × 10⁻⁸ at 100 kV/cm, which is approximately one order of magnitude lower than that of pure K_0.5Bi_4.5Ti₄O₁₅ thin film capacitor. We found that V doping is an effective method for improving the ferroelectric properties of K_0.5Bi_4.5Ti₄O₁₅ thin film.     

Frequency and temperature dependence of dielectric and electrical properties of radio-frequency sputtered lead-free K0.48Na0.52NbO3 thin films

Lead-free K_0.48Na_0.52NbO₃ (KNN) ferroelectric thin films were prepared using the radio-frequency magnetron sputtering method. The crystallized KNN phase was confirmed using X-ray diffraction. The KNN thin film exhibited a well-saturated ferroelectric polarization-electric field hysteresis loop with high remanent polarization. The dielectric and electrical properties of the KNN thin film were investigated over a wide range of frequencies from 10 Hz to 1 MHz, and over a wide range of temperatures from 25 °C to 500 °C. The complex impedance relaxations are shown in an impedance Cole-Cole plot. With increasing temperature, the AC conductivity increased, which obeys the power law, σ(ω) = σ₀ + Aω^s. The activation energy for the conduction process is calculated to be 0.57 eV from the slope of the AC conductivity at the low frequency.     

Variations of microstructures and electrical properties of Bi4Ti3O12/SrTiO3/(La0.5, Sr0.5)CoO3/MgO epitaxial thin films by annealing

Epitaxial thin films of a heterostructure with Bi₄Ti₃O₁₂(BIT)/SrTiO₃(ST) were successfully grown with a bottom electrode consisting of La_0.5Sr_0.5CoO₃(LSCO) on MgO(001) substrates using pulsed laser deposition. The grown BIT and ST (001) planes were parallel to the growth surface with the orientation relationship of BIT <110>//ST <010>. In the as-deposited film, the BIT (001) plane appeared to expand to relieve a lattice mismatch with the ST (001) plane. However, annealing for 20-40 min induced the BIT (001) plane to contract horizontally with its c-axis expanding, which was associated with a local perturbation in the layer stacking of the BIT structure. This structural distortion was reduced in the film annealed for 1 h, with restoration of the periodicity of the layer stacking. Correspondingly, the dielectric constant of the as-deposited film was increased from 292 to 411 by annealing for 1 h. In parallel, the film was paraelectric but became more ferroelectric, with the remanent polarization and the coercive field changing from 0.1 μC/cm² and 14 kV/cm to 1.7 μC/cm² and 69 kV/cm, respectively.     

Influence of annealing treatments for ZnO-doped Zr0.8Sn0.2TiO4 thin films by RF magnetron sputtering

Zirconium tin titanium oxide doped 1 wt.% ZnO thin films on n-type Si substrate were deposited by rf magnetron sputtering at a fixed rf power of 300 W, a substrate temperature of 450 °C, a deposition pressure of 5 mTorr and an Ar/O₂ ratio of 100/0 with various annealing temperatures and annealing times. Electrical properties and microstructures of 1 wt.% ZnO-doped (Zr_0.8Sn_0.2)TiO₄ thin films prepared by rf magnetron sputtering on n-type Si(100) substrates at different annealing temperatures (500 °C-700 °C) and annealing times (2 h-6 h) have been investigated. The structural and morphological characteristics analyzed by X-ray diffraction (XRD) and atomic force microscope (AFM) were sensitive to the treatment conditions such as annealing temperature and annealing time. At an annealing temperature of 600 °C and an annealing time of 6 h, the ZnO-doped (Zr_0.8Sn_0.2)TiO₄ thin films possess a dielectric constant of 46 (at f = 10 MHz), a dissipation factor of 0.059 (at f = 10 MHz), and a low leakage current density of 3.8 × 10^− 9 A/cm² at an electrical field of 1 kV/cm.     

Improved dielectric properties of chemical solution derived Pb0.5Sr0.5TiO3 thin films by a layer-by-layer annealing method

Pb_0.5Sr_0.5TiO₃ thin films were prepared on Pt/TiO₂/SiO₂/Si and LaNiO₃ (LNO)/Si substrates by using chemical solution deposition technique, and a layer-by-layer annealing method was used in an attempt to improve the dielectric properties of the thin films. The structure, dielectric, and ferroelectric properties of the thin films were investigated. Improved dielectric properties of the thin films were clearly confirmed: the dielectric constant and dielectric loss for the films on Pt/TiO₂/SiO₂/Si substrates annealed at 650 °C were 1064 and 0.027, respectively, at 1 kHz, with a dielectric tunability of more than 50%; similarly, the films prepared on LNO/Si substrates, showed a high dielectric constant of 1280 and a low dielectric loss of 0.023, at 1 kHz. P-E hysteresis loop measurements indicated that the remanent polarization and coercive field for the films on Pt/TiO₂/SiO₂/Si substrates annealed at 650 °C were 15.7 μC/cm² and 51 kV/cm, respectively.     

Dependence of Zr content on electrical properties of Bi3.15Nd0.85Ti3-xZrxO12 thin films synthesized by chemical solution deposition (CSD)

The Bi_3.15Nd_0.85Ti_3-xZr_xO₁₂ (BNTZ) thin films with Zr content (x = 0, 0.05, 0. 1, 0.15, and 0.2) were prepared on Pt/Ti/SiO₂/Si (100) substrates by chemical solution deposition (CSD) technique. The crystal structures of BNTZ films were analyzed by X-ray diffraction (XRD). The effects of Zr contents on the ferroelectric, dielectric properties, and leakage current of BNTZ films were thoroughly investigated. The XRD results demonstrated that all the films possessed a single phase bismuth-layered structure and exhibited the highly preferred (117) orientation. Among these films, the film with Zr content x = 0.1 held the maximum remanent polarization (2P_r) of 50.21 μC/cm² and a low coercive field (2E_c) of 210 kV/cm.     

Enhanced ferroelectric properties of Fe-doped BaTiO3 thin film deposited on LaNiO3/Si substrate by sol–gel technique

The ferroelectric thin films of Fe-doped BaTiO₃ and undoped BaTiO₃ were prepared on LaNiO₃ coating Si substrates by sol–gel technique. It was found that a small amount of Fe dopant could significantly enhance the ferroelectric properties of the BaTiO₃ thin film. The remnant polarization of Fe-doped BaTiO₃ thin film at room temperature reached to 14.9 μC/cm². The loss tangent, compared to the undoped BaTiO₃ film, was increased with frequency increasing and the dielectric constant was decreased. The possible mechanism of enhanced ferroelectric properties of Fe-doped BaTiO₃ thin film was discussed. The results show the potential role of Fe dopant in improving the ferroelectric properties of BaTiO₃ thin film.     

Highly a-oriented SrBi2Ta2O9 thin film on (111) Pt/TiO2/SiO2/Si substrate by eclipse pulsed laser deposition

A highly a-oriented SrBi₂Ta₂O₉ thin film with a polycrystalline structure was deposited on a preferentially oriented (111) Pt/TiO₂/SiO₂/Si substrate by eclipse pulsed laser deposition (PLD) method. The SrBi₂Ta₂O₉ thin film exhibited flat and smooth surface with the surface roughness of about 0.5 nm resulting from reducing particulates generated by on-axis PLD. The SrBi₂Ta₂O₉ thin film showed a good ferroelectric property with the high remanent polarization of 12 μC/cm² and the low coercive electric field of 140 kV/cm. For the highly a-oriented SBT thin film, domain switching and reading were performed by Kelvin probe force microscope (KFM). The KFM data indicate a good ferroelectric property of the highly a-oriented SrBi₂Ta₂O₉ thin film with high KFM signals that reflect ferroelectric polarizations.     

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.     

Properties of La-substituted Na0.5Bi4.5Ti4O15 ferroelectric thin films

Ferroelectric Na_0.5La_0.5Bi₄Ti₄O₁₅ (NaLaBTi) thin films were prepared by a chemical solution deposition method. The NaLaBTi thin films annealed at 750 °C under oxygen atmosphere were randomly oriented polycrystalline. Electrical properties of the NaLaBTi thin films were compared to Na_0.5Bi_4.5Ti₄O₁₅ thin films and better properties were observed in the NaLaBTi thin films. Remnant polarization (2P_r) and coercive electric field (2E_c) were 43 µC/cm² and 204 kV/cm at an applied electric field of 478 kV/cm, respectively. Leakage current density was 1.95 × 10^− 6 A/cm² at 100 kV/cm. Dielectric constant and dielectric loss were 805 and 0.05 at 1 kHz, respectively. Switchable polarization was suppressed by 15% after 1.44 × 10¹⁰ switching cycles.     

Effect of bottom electrodes on dielectric properties of high frequency Ba0.5Sr0.5TiO3 parallel plate varactor

Three types of Ba_0.5Sr_0.5TiO₃ (BST) thin film parallel plate varactor with different bottom electrodes were fabricated. The bottom electrodes of three types of varactor were perovskite conducting oxide La_0.7Sr_0.3MnO₃ (LSMO), Pt and Au, respectively. Dielectric properties of the BST thin films were characterized in the frequency range from 10 MHz to 15 GHz. The microstructure of the BST thin films was investigated by X-ray diffraction and scanning electron microscope. The microstructural analysis shows that the BST thin films grown on LSMO and Pt bottom electrodes are polycrystalline textured with columnar grains. Dielectric measurement indicates that the BST thin film grown on LSMO bottom electrode has a maximum dielectric constant and a little higher loss tangent.     

Microstructural study of YBa2Cu3O7/SrTiO3/YBa2Cu3O7 heteroepitaxial trilayer films grown on (100) SrTiO3 substrates

Detailed transmission electron microscopic study has been carried out on heteroepitaxial YBa₂Cu₃O₇/SrTiO₃/YBa₂Cu₃O₇ trilayer thin films grown on (100)SrTiO₃ substrates prepared by DC and RF magnetron sputtering. The microstructural results showed the existence of somea-axis-oriented YBCO grains 20–90 nm wide in thec-axis-oriented YBCO matrix. Some of thea-axis grains in the lower YBCO thin film layer have protruded into the above SrTiO₃ layer, which may cause short circuit between the two YBCO superconducting layers. This is unsuitable for the application of trilayer thin films for microelectronic devices. The defects on the surface of the substrates would also influence the growth quality of the YBCO thin films.