Electrical behavior of Y-doped Ba<Subscript>0.6</Subscript>Sr<Subscript>0.4</Subscript>TiO<Subscript>3</Subscript> thin films

Ba_0.6Sr_0.4TiO₃ (BST) and 1.5 at% Y-doped Ba_0.6Sr_0.4TiO₃ (Y-BST) thin films have been deposited on single-crystal (100) oriented LaAlO₃ substrates using pulsed-laser deposition technique (PLD), respectively. X-ray diffraction (XRD) scanning revealed that the two kinds of films could be epitaxially grown in pure single-oriented perovskite phases, but Y-BST thin films showed an enhanced crystallization effect. The dielectric properties of the pure and Y-BST thin films were measured at 10 kHz and 300 K with a parallel-plate capacitor configuration. The results revealed that the addition of Y as an acceptor doping is very effective to increase dielectric tunability, and to reduce leakage current of BST thin films. The figure-of-merit (FOM) factor value increases from 17.32 for BST to 25.84 for Y-BST under an applied electric field of 300 kV/cm. The leakage current density of the BST thin films at a negative bias field of 300 kV/cm decreases from 2.45 × 10⁻⁴ A/cm² to 1.55 × 10⁻⁶ A/cm² by Y doping. The obtained results indicated that the Y-doped BST thin film is a promising candidate material for tunable microwave devices.     

Structural and dielectric properties of Bi doped Ba<Subscript>0.6</Subscript>Sr<Subscript>0.4</Subscript>TiO<Subscript>3</Subscript> ceramics

The dielectric properties of 0.1–15% mol bismuth doped Ba_0.6Sr_0.4TiO₃ (BST) ceramics have been investigated systematically. The solubility limit of bismuth is determined as about 10 mol% by means of both X-ray diffraction and scanning electron microscopy, which is further verified by the fact that the lattice constant of the samples above 10 mol% is almost invariable. The temperature dependence of the dielectric permittivity suggest that the ferroelectric behavior transit to relaxor ferroelectric type when impurity concentration reaches 5 mol%, and further to relaxor behavior for samples above 10 mol% Bi content, which is verified by the absence of a hysteresis loop. Thermal expansion results show differences between 5 and 10 mol% doped samples. Dielectric tunability at room temperature decreases with bismuth content increasing. The variation of properties was attributed to the impurity induced polar regions and former long-order structure.     

Low loss and highly tunable (Ba,Sr)(Ti,Mn)O<Subscript>3</Subscript>/(Ba,Sr)TiO<Subscript>3</Subscript> bilayered films for electrically tunable microwave device applications

Ba_0.05Sr_0.95TiO₃ (BST), 5 mol% Mn-doped BST (Mn-BST) and bilayered Mn-BST/BST films with a thickness of about 100 nm were fabricated by using pulsed laser deposition technique on MgO single crystal substrates, and their microwave dielectric properties were comparatively investigated. It was confirmed that all the BST-based films were crystallized in pure single-oriented perovskite phase. There appeared nanosized pores in the BST film; after addition of Mn, however, the film surface morphology became denser while exhibiting an increased roughness, and ultimately, a smooth and dense morphology was achieved by the design of bilayered Mn-BST/BST film. Coherently, the microwave dielectric properties of BST films were enhanced by Mn doping and more significantly enhanced in the bilayered Mn-BST/BST film. As a result, for the bilayered film, a very low loss tangent of 0.017–0.007 and a high dielectric tunability of 70.9% under E?=?36 V/μm were simultaneously obtained at 79 K and L-band frequency (1–2 GHz), thereby resulting in an extremely high commutation quality factor of 14492. The excellent microwave dielectric properties obtained in the Mn-BST/BST bilayered film originate not only from the Mn-doping effect, but are also ascribed to the pre-deposition of BST layer, which serves as a good template for the growth of Mn-BST film.     

Effects of bottom electrodes on dielectric properties of epitaxial 2% Mn doped Ba(Zr<Subscript>0.2</Subscript>Ti<Subscript>0.8</Subscript>)O<Subscript>3</Subscript> thin films

2 mol% Mn doped Ba(Zr_0.2Ti_0.8)O₃ (Mn-BZT) thin films were prepared by pulsed laser deposition (PLD) on single crystal oxide substrates LaAlO₃(001) and MgO(001), with conductive oxide bottom electrodes LaNiO₃ and SrRuO₃, respectively. Both the Mn-BZT films and the bottom electrode films could be c-axial oriented with a cube-on-cube arrangement on the corresponding substrates. The dielectric properties measured with parallel plate capacitor configurations of Au/Mn-BZT/LNO and Au/Mn-BZT/SRO revealed that the Mn-BZT film on LNO bottom electrode exhibited comparatively higher dielectric constant, larger dielectric tunability and lower dielectric loss than that on SRO. It could be mainly attributed to the better epitaxial growth characteristics and mismatch stress of Mn-BZT thin film on LNO, as well as less misfit dislocation and the better morphology of LNO bottom electrode.     

Dielectric properties of Yb<Subscript>2</Subscript>O<Subscript>3</Subscript>-doped barium strontium calcium titanate thick films for microwave device applications

(Ba_0.56Sr_0.34Ca_0.10)TiO₃ (BSCT) thick films doped with 0.1 mol% MnCO₃ and Yb₂O₃ (0.1–0.7 mol%) were fabricated by the screen-printing method on the alumina substrate. The structural and electrical properties as a function of Yb₂O₃ amount were investigated. All BSCT thick films showed the formation of a complete solid solution in a cubic perovskite polycrystalline structure. Average grain size of the specimen doped with 0.7 mol% Yb₂O₃ was about 2.7 μm. The thickness of all BSCT thick films was approximately 50–55 μm. The relative dielectric constant, dielectric loss, and tunability of the BSCT thick films doped with 0.3 mol% Yb₂O₃ were 2,966, 0.7, and 14.3%, respectively.     

Co掺杂对Ba0.6Sr0.4TiO3薄膜介电性能的影响

利用溶胶凝胶工艺在Pt/TiO2/SiO2/Si衬底上制备了Co掺杂量为0～10%(摩尔分数)的(Ba0.6Sr0.4) Ti1-xCoxO3薄膜.研究了薄膜的结构、表面形貌、介电性能与Co掺杂量的关系.薄膜的介电损耗随着Co含量的增加而减少,在摩尔含量10%时达到最小值0.0128.FOM值在摩尔含量为2.5%达到最大值20,它的介电常数、介电损耗和调谐量分别为639.42、0.0218、43.6%.     

Crystallization and electrical properties of Ba<Subscript>0.7</Subscript>Sr<Subscript>0.3</Subscript>TiO<Subscript>3</Subscript> thin films on SrRuO<Subscript>3</Subscript>/Pt hybrid bottom electrode

Ba_0.7Sr_0.3TiO₃ (BST) thin films were deposited on Pt and SrRuO₃(SRO)/Pt hybrid bottom electrodes by radio frequency magnetron sputtering. X-ray analysis indicated that both films were polycrystalline. Dielectric measurements showed that the films on SRO/Pt hybrid bottom electrode had lower dielectric constant and loss than the films on single Pt and the dielectric properties were frequency-independent. The leakage current density of Ba_0.7Sr_0.3TiO₃ thin films on hybrid bottom electrode was also lower. Leakage mechanism investigations showed that the contact between the electrode-film interfaces of thin films on SRO/Pt hybrid bottom electrode was ohmic. Based on the results, the effects of SRO/Pt hybrid bottom electrode on the crystallization and electrical properties of BST thin films were discussed.     

Fabrication of conductive SrRuO<Subscript>3</Subscript> thin film and Ba<Subscript>0.60</Subscript>Sr<Subscript>0.40</Subscript>TiO<Subscript>3</Subscript>/SrRuO<Subscript>3</Subscript> bilayer films on MgO substrate

Conductive SrRuO₃ (SRO) thin films have been grown on (100) MgO substrates by pulsed laser deposition (PLD) technique. Effects of oxygen pressure and deposition temperature on the orientation of SRO thin film were investigated. X-ray diffraction (XRD) θ/2θ patterns and the temperature dependent resistivity measurements indicated that oxygen pressure of 30 Pa and deposition temperature of 700 °C were the optimized deposition parameters. A parallel-plate capacitor structure was prepared with the SRO films deposited under optimized condition as an electrode layer and Ba_0.60Sr_0.40TiO₃ (BST) thin film as the dielectric layer. XRD Φ scans indicated a epitaxial relationship between BST and SRO on MgO substrate. The dielectric constant and loss tangent measured at 10 kHz and 300 K was 427 and 0.099 under 0 V bias, and 215 and 0.062 under 8 V bias, respectively. A tunability of 49.6% has been achieved with DC bias as low as 8 V. The C–V hysteresis curve and the P–E hysteresis loop suggested that the BST films epitaxially grown on SRO/MgO have ferroelectricity at room temperature. The induced ferroelectricity was believed to originate from the compressive strain between the epitaxial BST and SRO thin films. These results show the potential application of the BST/SRO heterostructures in microelectronic devices.     

Microstructure,dielectric and photoluminescence properties of Tm-doped Ba<Subscript>0.8</Subscript>Sr<Subscript>0.2</Subscript>TiO<Subscript>3 </Subscript>thin films fabricated by sol–gel method

Ba_0.8Sr_0.2TiO₃ thin films doped by Tm from 0 to 7 mol% were fabricated by sol–gel method on silicon and Pt/Ti/SiO₂/Si substrates. X-ray diffraction, scanning electron microscopy, and Raman spectroscopy have been used to study variations of crystal structure, surface morphologies, and phase stability of Tm-doped BST films, respectively. The residual stress in BST films on silicon substrates can be reduced by Tm doping, as demonstrated by the blueshift of phonon peaks in Raman spectra. The dielectric measurements were conducted on metal-insulator-metal capacitors at the frequency from 1 kHz to 1 MHz. The grain size and dielectric constant decreased with increasing Tm concentration. While the variation of dielectric loss, tunability and the figure of merit were nonlinear with increasing Tm concentration. In addition, the photoluminescence property of 0.2 mol% Tm-doped BST was also studied. The effect of Tm doping on the microstructure, dielectric and photoluminescence properties were analyzed.     

Enhanced dielectric properties of Mn doped Ba0.6Sr0.4TiO3 thin films fabricated by pulsed laser deposition

Pure and 2 mol% Mn doped Ba_0.6Sr_0.4TiO₃ (BST) thin films have been deposited on La_0.67Sr_0.33MnO₃ (LSMO) coated single-crystal (001) oriented LaAlO₃ substrates using pulsed-laser deposition technique. The bilayer films of BST and LSMO were epitaxially grown in pure single-oriented perovskite phases for both samples, and an enhanced crystallization effect in the BST film was obtained by the addition of Mn, which were confirmed by X-ray diffraction (XRD) and in situ reflective high energy electron diffraction (RHEED) analyses. The dielectric properties of the BST thin films were measured at 100 kHz and 300 K with a parallel-plate capacitor configuration. The results have revealed that an appropriate concentration acceptor doping is very effective to increase dielectric tunability, and to reduce loss tangent and leakage current of BST thin films. The figure-of-merit (FOM) factor value increases from 11 (undoped) to 40 (Mn doped) under an applied electric field of 200 kV/cm. The leakage current density of the BST thin films at a negative bias field of 200 kV/cm decreases from 2.5 × 10^− 4 A/cm² to 1.1 × 10^− 6 A/cm² by Mn doping. Furthermore, a scanning-tip microwave near-field microscope has been employed to study the local microwave dielectric properties of the BST thin films at 2.48 GHz. The Mn doped BST film is more homogeneous, demonstrating its more potential applications in tunable microwave devices.     

Improvement in dielectric and tunable properties of Fe-doped Ba0.6Sr0.4TiO3 thin films grown by pulsed-laser deposition

Fe-doped Ba(0.6)Sr(0.4)TiO3 (BST) thin films were prepared on Pt/Si substrates by the pulsed-laser deposition method. The concentrations of Fe dopants vary from 0.1 mol% to 1.0 mol%. Our results indicate that a certain amount of Fe dopants can decrease the dielectric loss of BST thin films without causing the significant reduction of the tunability. The leakage current of BST thin films also was reduced by the addition of Fe dopants. BST thin films doped with 0.3 mol% Fe ions show a minimum dielectric loss of 0.88% at 10(6) Hz, which is 1.7% for the undoped BST films. Moreover, the 0.3 mol% Fe-doped BST films reveal a maximum figure of merit (FOM) of 51, indicating the improved comprehensive dielectric and tunable properties.     

Preparation and characterization of Mn-doped BaTiO<Subscript>3</Subscript> thin films by magnetron sputtering

Barium titanate (BaTiO₃) thin films doped with Mn (0.1–1.0 at%) were prepared by r.f. magnetron sputtering technique. Oxygen/argon (O₂/Ar) gas ratio is found to influence the sputtering rate of the films. The effects of Mn doping on the structural, microstructural and electrical properties of BaTiO₃ thin films are studied. Mn-doped thin films annealed at high temperatures (700 °C) exhibited cubic perovskite structure. Mn doping is found to reduce the crystallization temperature and inhibit the grain growth in barium titanate thin films. The dielectric constant increases with Mn content and the dielectric loss (tan δ) reveals a minimum value of 0.0054 for 0.5% Mn-doped BaTiO₃ films measured at 1 MHz. The leakage current density decreases with Mn doping and is 10⁻¹¹ A/cm⁻² at 6 kV/cm for 1% Mn-doped thin films.     

Effects of sintering temperature on the properties of Mn/Y codoped Ba<Subscript>0.67</Subscript>Sr<Subscript>0.33</Subscript>TiO<Subscript>3</Subscript> ceramics for tunable application

(Ba_0.67Sr_0.33)_1?3x/2Y _x Ti_1?y/2Mn _y O₃ [BST(Mn + Y), x = 0.006, y = 0.005] ceramics were fabricated by using citrate–nitrate combustion derived powder. Microstructure and dielectric properties of the BST(Mn + Y) ceramic samples were investigated within the sintering temperature ranged from 1220 to 1300 °C. Sintering temperature has a great influence on the microstructure and electrical properties of the ceramic samples. The dielectric properties, ferroelectric properties, and tunability are enhanced by optimizing sintering temperature. The relatively high tunability of 40 % (1.5 kV/mm DC field, 10 kHz) was obtained, and relatively low dielectric loss, <0.0052 (at 10 kHz, 20 °C) was acquired for BST(Mn + Y) samples sintered at 1275 °C for 3 h. Both the low dielectric loss and enhanced tunable properties of BST(Mn + Y) are useful for tunable devices application.     

Low dielectric loss and enhanced tunable properties of Cr-doped barium strontium titanate solid solution

The dielectric response and tunable properties of Cr-doped Ba_0.6Sr_0.4TiO₃ solid solution were investigated. The XRD patterns revealed that all of the doped specimens are cubic perovskite phase, and the SEM micrographs showed that the grain size increases with the increase of Cr content below 0.6 mol%. The dielectric frequency spectra of the doped BST solid solution showed that an additional relaxation of the doped specimens is observed at frequencies above 10 MHz. Both of the tunability and dissipation factor were improved by doping with Cr concentration lower than 1.0 mol% compared with undoped material. The 0.6 mol% Cr-doped specimen reveals a maximum tunability and figure of merit of 23.3% and 518.3, respectively. Extremely low dissipation factor in order of 5 × 10⁻⁴ is found for 0.4–0.6 mol% Cr-doped BST solid solution. The dramatically low dissipation factor of the specimen is explained by the reducing of Cr³⁺ to Cr²⁺ and the acceptor action of Cr³⁺ and Cr²⁺ which neutralized the donor action of oxygen vacancies.     

（Ba0.6Sr0．4）Ti1-xZnxO3薄膜的介电调谐性能

利用溶胶-凝胶法在Pt／TiO2/SiO2/Si衬底上制备了（Ba0．6Sr0．4）Ti1-xZnxO3（BSTZ）薄膜,用X射线衍射和扫描电镜分析测定了BSTZ的微结构和薄膜的表面形貌,研究Zn掺杂量对其介电调谐性能的影响,结果表明,随Zn含量的增加BSTZ物相无明显变化,其介电常数、调谐量先增加后降低,但介电损耗却先降低后增加。在室温1MHz下,1．5m01％Zn掺杂BSTZ薄膜有最大的调谐量54．26％;2．5mol％Zn掺杂BSTZ薄膜有最低的介电损耗0．0148和最大的优值因子30．3。     

Enhanced optical and hydrophilic properties of Si and Cd co-doped TiO<Subscript>2</Subscript> thin films

In this study, preparation of Si and Cd co doped (5 mol% Si and 5–20 mol% Cd) TiO₂ dip-coated thin films on glass substrates via sol–gel process have been investigated. The samples were characterized by X-ray diffraction (XRD) and Scanning electron microscopy analysis after heat treatments. XRD results suggested that adding dopants has a great effect on crystallinity and particle size of TiO₂. Titania rutile phase formation was inhibited by Si⁴⁺ and promoted by Cd²⁺ doping. But the effect of Cd doped appeared at high concentration. Accordingly, the thin films showed various water contact angles. The water contact angles changed from 69.0° to 9.6° by changing the content of Cd doped.     

Chemical solution deposition of CaCu<Subscript>3</Subscript>Ti<Subscript>4</Subscript>O<Subscript>12</Subscript> thin film

CaCu₃Ti₄O₁₂ (CCTO) thin film was successfully deposited on boron doped silica substrate by chemical solution deposition and rapid thermal processing. The phase and microstructure of the deposited films were studied as a function of sintering temperature, employing X-ray diffractometry and scanning electron microscopy. Dielectric properties of the films were measured at room temperature using impedance spectroscopy. Polycrystalline pure phase CCTO thin films with (220) preferential orientation was obtained at a sintering temperature of 750°C. There was a bimodal size distribution of grains. The dielectric constant and loss factor at 1 kHz obtained for a film sintered at 750°C was k ∼ 2000 and tan δ ∼ 0.05.     

Structural,optical and magnetic properties of Cr doped In<Subscript>2</Subscript>O<Subscript>3</Subscript> powders and thin films

The (In_1?xCr_x)₂O₃ powders as well as thin films of x = 0.03, 0.05 and 0.07 were synthesized using a solid state reaction and an electron beam evaporation technique (on glass substrate), respectively. The influence of Cr doping concentration on structural, optical and magnetic properties of the In₂O₃ samples was systematically studied. The X-ray diffraction results confirmed that all the Cr doped In₂O₃ samples exist cubic structure of In₂O₃ without any secondary phases presence. The chemical composition analyses showed that all the Cr doped In₂O₃ compounds were nearly stoichiometric. The X-ray photoelectron spectroscopy analysis of the Cr doped In₂O₃ thin films showed an increase of oxygen vacancies with Cr concentration and the existence of Cr as Cr³⁺ state in the host In₂O₃ lattice. A small blue shift in the optical band gap was observed in the powder compounds, when the dopant concentration increased from x = 0.03 to x = 0.07. In thin films, the band gap found to increase from 3.63 to 3.74 eV, with an increase of Cr concentration. The magnetic measurements show that the undoped In₂O₃ bulk powder sample has the diamagnetic property at room temperature. And a trace of paramagnetism was observed in Cr doped In₂O₃ powders. However (In_1?xCr_x)₂O₃ thin films (x = 0.00, 0.03, 0.05 and 0.07) samples shows soft ferromagnetism. The observed ferromagnetism in thin films are attributed to oxygen vacancies created during film prepared in vacuum conditions. The ferromagnetic exchange interactions are established between metal cations via free electrons trapped in oxygen vacancies (F-centers).     

Photocurrent and Optical Transmission Spectra of Sn- and Pb-Doped (As<Subscript>2</Subscript>S<Subscript>3</Subscript>)<Subscript>0.3</Subscript>(As<Subscript>2</Subscript>Se<Subscript>3</Subscript>)<Subscript>0.7</Subscript> Glass Films

The photocurrent and optical transmission spectra of thin (As₂S₃)_0.3(As₂Se₃)_0.7 glass films doped with Sn and Pb are reported. The strongest photoresponse is offered by the films doped with 0.010– 0.015 at % Sn or Pb. Low doping levels are shown to have a significant effect on the peak-response wavelength and band gap of the films.     

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.