Improvement of electrical properties of Sr-modified (Pb,Ca)TiO3 thin films grown by soft chemistry route

Strontium and calcium-modified lead titanate (Pb_0.70Ca_0.15Sr_0.15)TiO₃ soft chemistry-derived thin films were prepared on platinum-coated silicon substrate by spin-coating method. Investigations were made on the structure, surface morphology and electrical properties of the film. The results by XRD and FE-SEM showed that the film exhibits a pure tetragonal perovskite phase and an average grain size of about 50-60 nm, respectively. Electrical measurements of a metal-ferroelectric-metal type capacitor exhibited a stable and switchable electrical polarization in the film. The structure of the Au/PCST/Pt capacitor showed well-saturated hysteresis loops at an applied voltage of 300 kV/cm with remanent polarization and coercive field values of 22 μC/cm² and 100 kV/cm, respectively. At 100 kHz, the dielectric constant and the dielectric loss of the (Pb_0.70Ca_0.15Sr_0.15)TiO₃ thin film with thickness 240 nm were 528 and 0.05, respectively.     

Dependence of functional properties on processing in sol-gel (Pb,La)TiO3 thin films

Pb_0.88La_0.08TiO₃ films were processed on Si-based substrates by a diol-based sol-gel route from solutions with variable content of PbO excess. Crystallisation was performed at heating rates of 10 °C min^-1 and higher than 500 °C min^-1 (rapid heating). The pyroelectric coefficient was measured after poling the samples by two methods: applying a sinusoidal wave and applying a train of square pulses, with the latter showing a higher poling efficiency. The piezoelectric d₃₃ coefficient was determined by double-beam interferometry. Strain vs. field measurements provided evidence of 90° domain orientation in these films. Those crystallised at 10 °C min^-1 showed the highest functional properties (%=1.7᎒^-2 7C cm^-2 K^-1 and d₃₃=57 pm V^-1). This is a consequence of the higher stability of the 90° domains oriented during poling, caused by the lower tensile stress arising during preparation. The voltage responsivity of these films also benefited from the lower permittivity arising from their higher porosity. These films are good candidates for applications in infrared detectors and microelectromechanical devices.     

Improved dielectric properties of (Pb,Ca)TiO3 thin films prepared by metal-organic decomposition method

(Pb,Ca)TiO₃ (PCT) thin films have been deposited on Pt/Ti/SiO₂/Si substrate by metal-organic decomposition (MOD) technique. The film processing parameters such as drying and annealing temperatures have been optimized to obtain good-quality PCT films. Compositional analysis of the film has been studied by X-ray photoelectron spectroscopy (XPS). The effect of the annealing temperature on the crystalline structure, microstructure and electrical properties have been investigated by X-ray diffraction, atomic force microscopy (AFM) and impedance analyzer, respectively. Amorphous PCT films form at 350 °C and crystallize in the perovskite phase following the isothermal annealing at ?650 °C for 3 h in oxygen ambient. Typical tetragonal structure of the PCT film is evidenced from X-ray diffraction pattern. The grain size in the PCT films increases with an increase in annealing temperature. Significant improvement in the dielectric constant value is observed as compared to other reported work on PCT films. The observed dielectric constant and dissipation factor at 100 kHz for 650 °C annealed PCT films are 308 and 0.015, respectively. The correlation of the film microstructural features and electrical behaviors is described.     

化学溶液法制备的Pb(Mg1/3 Nb2/3)O3-PbTiO3薄膜的光学性能

用化学溶液方法在宝石衬底及有LaNiO3缓冲层的Pt/TiO2/SiO2/Si衬底上制备了92%Pb(Mg1/3 Nb2/3)O3-8%PbTiO3(PMNT)薄膜,X射线衍射测试结果表明:在有LaNiO3缓冲层的Pt/TiO2/SiO2/Si衬底上制备的PMNT薄膜几乎是纯钙钛矿相,且薄膜呈现(110)择优取向.通过对Pt/TiO2/SiO2/Si衬底上的PMNT薄膜在2.5-12.6μm波长范围内的红外椭圆偏振光谱测试,并拟合得到了PMNT薄膜在2.5-12.6μm波长范围内的光学常数(n和k),通过对宝石衬底上的PMNT薄膜在200-1100nm波长范围内的可见-紫外透过率测试,并拟合得到了PMNT薄膜在200-1100nm波段的光学常数(n和k)和吸收系数α,进而推导出PMNT薄膜的禁带宽度为4.03eV.     

Absence of relaxor-like ferroelectric phase transition in (Pb,Sr)TiO3 thin films

We have performed dielectric and micro-Raman spectroscopy measurements in the 298–673 K temperature range in polycrystalline Pb_0.50Sr_0.50TiO₃ thin films prepared by a soft chemical method. The phase transition have been investigated by dielectric measurements at various frequencies during the heating cycle. It was found that the temperature corresponding to the peak value of the dielectric constant is frequency-independent, indicating a non-relaxor ferroelectric behavior. However, the dielectric constant versus temperature curves associated with the ferroelectric to paraelectric phase transition showed a broad maximum peak at around 433 K. The observed behavior is explained in terms of a diffuse phase transition. The obtained Raman spectra indicate the presence of a local symmetry disorder, due to a higher strontium concentration in the host lattice. The monitoring of some modes, conducted in the Pb_0.50Sr_0.50TiO₃ thin films, showed that the ferroelectric tetragonal phase undergoes a transition to the paraelectric cubic phase at around 423 K. However, the Raman activity did not disappear, as would be expected from a transition to the cubic paraelectric phase. The strong Raman spectrum observed for this cubic phase is indicative that a diffuse-type phase transition is taking place. This behavior is attributed to distortions of the perovskite structure, allowing the persistence of low-symmetry phase features in cubic phase high above the transition temperature. This result is in contrast to the forbidden first-order Raman spectrum, which would be expected from a cubic paraelectric phase, such as the one observed at high temperature in pure PbTiO₃ perovskite. PACS 78.30.-j; 77.80.Bh; 64.70.Kb; 68.55.-a; 77.22.-a; 77.55.+f     

Dielectric enhancement in pulsed-laser-deposited (Pb,Sr)TiO3/(Pb,La)TiO3 multilayered films

Multilayered (Pb_0.5Sr_0.5)TiO₃(PST)/Pb_0.8La_0.2TiO₃(PLT)/PST and PLT/PST/PLT films were prepared on platinum coated silicon substrates by pulsed laser deposition. Significant enhancement of the dielectric constant over the whole temperature region from 30 °C up to 220 °C has been observed for both multilayers with respect to the identically prepared single-component PST and PLT films. However, larger frequency dispersion of dielectric properties has also been obtained in the multilayers. This effect is attributed to the compositional fluctuation revealed by the atomic interdiffusion in the interface regions of the multilayers. Thermally and electric-field driven space charges at relative low temperature and low electric field were found in the PLT/PST/PLT and PLT films, attributed to the substitution of La³⁺ non-isovalent for Pb²⁺ in these films. PACS 81.15.Fg; 42.70.Mp; 79.60.Jv     

(111)取向(Pb,La)TiO3铁电薄膜中90°纳米带状畴与热释电性能的研究

采用射频磁控溅射技术在Pt/Ti/SiO2/Si(100)衬底上生长了掺镧钛酸铅(PLT)铁电薄膜.用X射线衍射技术(XRD)研究了PLT薄膜结晶性能,结果表明PLT薄膜为(111)择优取向钙钛矿相织构.使用原子力显微镜(AFM)和压电响应力显微镜(PFM)分别观察了PLT薄膜的表面形貌和对应区域的电畴结构.PFM观察显示PLT薄膜中存在90°纳米带状畴,电畴的极化为首尾相接的低能量的排列方式,带状畴的宽度为20-60nm.研究了PLT10铁电薄膜的制备条件与性能之间的关系.发现在优化条件下制备的PLT10铁电薄膜的介电常数εr为365、介电损耗tgδ为0.02,热释电系数γ为2.18×10-8C·(cm2·K)-1,可以满足制备非制冷红外探测器的需要.     

Structural and ferroelectric properties of Pb1-xSrxTiO3 thin films

Strontium-modified lead titanate (PST) thin films with composition Pb_1-xSr_xTiO₃ (0.10<x0.60) were grown on Pt/Ti/SiO₂/Si substrates using a soft chemical process. The crystallization of the PST thin films was achieved by heat treatment at 600 °C. The structural and microstructural modifications in the films were studied using X-ray diffraction (XRD) and atomic force microscopy, respectively. The XRD study shows that the lattice parameters of polycrystalline PST thin films calculated from X-ray data indicate a decrease in lattice tetragonality with the increase in strontium content in these films. This indicates a gradual change from tetragonal to cubic structure. By atomic force microscopy analysis, the average grain size of the thin films was systematically reduced with the increase in Sr content. The dielectric property of the thin films was found to be strongly dependent on the Sr concentration. With 60 at.% Sr content, a ferroelectric to paraelectric phase transition was observed at room temperature. PACS 61.10.Nz; 68.37.Ps; 77.55.+f; 77.84.-s; 81.15.-z     

The dependence of dielectric properties on the thickness of (Ba,Sr)TiO3 thin films

In the dielectric (Ba,Sr)TiO₃ thin films, the correlation between the film thickness and the dielectric properties was investigated. The dielectric properties such as the dielectric constant (ε) and dielectric loss (tan δ) were measured using the capacitor geometry. As the film thickness increased, the dielectric constant also increased due to the reduction of the interfacial dead-layer effect. However, the dielectric loss did not show a monotonous variation with the increasing film thickness. It was found that the dielectric loss correlated well with the non-uniform distribution of local strain, as analyzed by X-ray diffraction, according to the Curie–von Schweidler relaxation law.     

Dielectric and piezoelectric properties of(110) oriented Pb(Zr_(1-x)Ti_x)O_3 thin films

A phenomenological Landau–Devonshire theory is developed to investigate the ferroelectric, dielectric, and piezoelectric properties of(110) oriented Pb(Zr_(1-x)Ti_x)O_3(x = 0.4, 0.5, 0.6, and 0.7) thin films. At room temperature, the tetragonal a_1 phase, the orthorhombic a_2c phase, the triclinic γ_1 phase, and the triclinic γ_2 phase are stable. The appearance of the negative polarization component P_2 in the a_2c phase and the γ_1 phase is attributed to the nonlinear coupling terms in the thermodynamic potential. The γ phase of the Pb(Zr_(1-x)Ti_x)O_3 thin films has better dielectric and piezoelectric properties than the a_2c phase and the a_1 phase. The largest dielectric and piezoelectric coefficients are obtained in the Pb(Zr_(0.5)Ti_(0.5))O_3 thin film. The piezoelectric coefficient of 110–150 pm/V is obtained in the(110) oriented Pb(Zr_(0.5)Ti_(0.5))O_3 thin film, and the Pb(Zr_(0.3)Ti_(0.7))O_3 thin film has the remnant polarization and relative dielectric constant of 50 μC/cm~2 and 100, respectively,which are in agreement with the experimental measurements reported in the literature.     

Pb1－xMnxSe薄膜的光学特性

采用分子束外延的方法在BaF₂(111)衬底上制备出了高质量的Pb_1-xMn_xSe(0≤x≤0.0681)薄膜.X射线衍射结果表明，Pb₁-xMn_xSe薄膜为立方相NaCl型结构，没有观察到MnSe相分离现象，薄膜的取向为平行于衬底(111)晶面.晶格常数随着Mn含量的增加逐渐减小，Mn含量由Vegard公式得到.通 关键词： 1-xMn_xSe外延薄膜')" href="#">Pb_1-xMn_xSe外延薄膜 透射光谱 带隙 折射率     

Improvement of the electrical properties of TiO2-doped Bi5Nb3O15 thin films by the addition of MnO2

The leakage current density of a 1.0 mol% TiO₂-doped Bi₅Nb₃O₁₅ (TB₅N₃) film was high, and the breakdown electric field was low. This could be attributed to the presence of intrinsic oxygen vacancies and free electrons. The electrical properties of the TB₅N₃ film improved upon the addition of MnO₂ because of the formation of extrinsic oxygen vacancies, which caused the number of intrinsic oxygen vacancies to decrease in order to maintain the equilibrium concentration of oxygen vacancies in the film. However, the electric properties degraded when the MnO₂ content exceeded 15.0 mol% because of the formation of interstitial oxygen ions and holes. The dielectric constant (?_r) of the TB₅N₃ film slightly decreased upon the addition of a small amount of MnO₂. The TB₅N₃ film with 15.0 mol% MnO₂, which exhibited a small leakage current density of 2.5 × 10^?11 A/cm² at 0.15 MV/cm and a high breakdown electric field of 0.47 MV/cm, still maintained a large ?_r of 118 with a small loss tangent of 2.0% at 100.0 kHz.     

Preparation of epitaxial compositionally graded (Ba1-xSrx)TiO3 thin films with enhanced dielectric properties

Epitaxial compositionally graded (Ba_1-xSr_x)TiO₃ (BST) (0.0x0.25) thin films were deposited on (100) LaAlO₃ substrates by pulsed laser ablation, the substrates having bottom electrodes made of 100-nm-thick conductive La_0.5Sr_0.5CoO₃ (LSCO). Extensive X-ray diffraction, rocking-curve, and -scan studies indicate that the graded films are (100)-oriented and exhibit good in-plane relationships of [010]_BST//[010]_LAO and [001]_BST//[001]_LAO. For the up-graded films with barium concentration (1-x) increasing across the film thickness in the direction from the film/substrate interface to the film surface, the full width at half maximum of the BST film (200) rocking curve and the surface roughness, examined by atomic force microscopy, were larger than those of the down-graded films with barium concentration decreasing from the film/substrate interface to the film surface. The dielectric properties of the graded films, measured using vertical structures, show that at room temperature, the dielectric constant (_r) and dissipation factor (cos) at 100 kHz were 380 and 0.013 for the up-graded films, and 650 and 0.010 for the down-graded films, respectively. The dielectric behavior was enhanced in the down-graded films, which was attributed to the fact that the pure BaTiO₃ layer in the down-graded BST films not only serves as a bottom layer but also acts as an excellent seeding layer for enhancing subsequent film growth, leading to better film crystallinity and larger grain sizes in the down-graded films. The graded BST films undergo a diffuse phase transition, giving a broad, flat capacitance-versus-temperature profile. With such a graded structure, it is possible to build a dielectric thin-film capacitor having a capacitance which has a low temperature dependence over a broad temperature regime. PACS 77.55.+f; 68.55.Jk; 81.15.Fg     

Optical properties of thin epitaxial Ba0.8Sr0.2TiO3 films

The properties of nanodimensional (Ba_0.8, Sr_0.2)TiO₃ films on single-crystal magnesia substrates are studied. The films are applied by rf sputtering and grow in the layer-by-layer mode. The lattice parameters are measured by the X-ray diffraction method. The transmission of the films with different thicknesses is studied in the wavelength range 190?C1100 nm. When analyzing experimental optical parameters, additional relaxation parameters depicting a final lifetime of the oscillator are used to characterize the refractive index and absorption factor in the dispersion relation. Such an approach allows a more accurate approximation of experimental data.     

Direct characterization of nanoscale domain switching and local piezoelectric loops of (Pb,La)TiO3 thin films by piezoresponse force microscopy

〈111〉 and 〈001〉, 〈100〉 preferentially oriented lanthanum-modified lead titanate thin films have been studied at the nanometre scale by means of piezoresponse force microscopy. The nanoscale domain structures, domain switching, and local piezoelectric loops of the films have been analysed. The imaging of the domain structures after the application of a dc field suggests the existence of 90° and 180° domains within the regions with intermediate contrast. The variation of piezoresponse under an electric field in domains of two types has been discussed. Significant differences have been found between the local piezoelectric loops measured in the films deposited on different substrates. These differences are related to the different textures present in the films. PACS 61.16.Ch; 77.84.Dy; 77.80.Dj     

Microstructures and dielectric properties of compositionally graded (Ba1-xSrx) TiO3 thin films prepared by pulsed laser deposition

Compositionally graded (Ba_1-xSr_x)TiO₃ (BST) (x:0.0∼0.25) thin films were grown on Pt (111)/TiO₂/SiO₂/Si (100) substrates using layer-by-layer pulsed laser deposition in the temperature range 550–650 °C. Both downgraded (Ba/Sr ratio varying from 100/0 at the bottom surface to 75/25 at the top surface) and upgraded (Ba/Sr ratio varying from 75/25 at the bottom surface to 100/0 at the top surface) BST films were prepared. Their microstructures were systematically studied by X-ray diffractometry and scanning electron microscopy. A grain morphology transition from large ‘rosettes’ (>0.30 μm) to small compact grains (70–110 nm) was observed in the downgraded BST films as the deposition temperature was increased from 550 to 650 °C. No such grain morphology transition was detected in the upgraded BST films. Dielectric measurements with metal electrodes revealed an enhanced dielectric behavior in the downgraded films. This enhancement is mainly attributed to the large compressive stress field built up near the interface between the downgraded film and substrate. Furthermore, the BaTiO₃ layer in the downgraded BST films not only serves as a bottom layer but also as an excellent seeding layer for enhancing the crystallization of the subsequent film layers in the downgraded films. Received: 10 December 2001 / Accepted: 12 March 2002 / Published online: 19 July 2002 RID="*" ID="*"Corresponding author. Fax: 86-25/359-5535, E-mail: xhzhu@public1.ptt.js.cn     

Ferroelectric (Na1/2Bi1/2)TiO3 thin films showing photoluminescence properties

Polycrystalline lead-free (Na_1/2Bi_1/2)TiO₃ (NBT) ferroelectric thin films doped with 1 mol% of rare earth (RE) elements are processed on Pt-terminated silicon substrates using a solution deposition method. The thin films that exhibit single-phase perovskite structure show photoluminescence properties with highest intensities in the wavelength range between 700 and 850 nm, depending on RE element. The ferroelectric properties of the pure NBT film (P _r: 20.5 µC cm^?2, E _c: 150 kV cm^?1) are somewhat decreased for the doped films, which is ascribed to decreasing of the number of Bi lone pairs through the substitution of Bi with RE elements in the perovskite lattice.     

Transverse piezoelectric properties of Mn-doped Bi0.5Na0.5TiO3 thin films

Lead-free (Bi_0.5Na_0.5)(Ti_1-xMn_x)O₃ (BNTMn-x; x = 0, 0.0025, 0.0050, 0.0100) thin films were fabricated using a chemical solution deposition method on Pt/TiO₂/SiO₂/Si substrate. The effect of Mn substitution on crystal structures, surface morphologies, and ferroelectric and transverse piezoelectric properties of BNTMn-x thin films was investigated. The 0.5 mol% Mn-doped (Bi_0.5Na_0.5)(Ti_0.995Mn_0.005)O₃ thin film exhibited a well-saturated ferroelectric P-E hysteresis loop at room temperature. A remnant polarization (P_r) of 16 μC/cm² was obtained for the BNTMn-0.0050 film at an applied electric field of 400 kV/cm. In addition, a 1.12-μm-thick BNTMn-0.0050 film was applied as a cantilever. The Pt/BNTMn-0.0050/Pt/TiO₂/SiO₂/Si unimorph cantilever exhibited a high transverse piezoelectric coefficient ($e_{31}^1$) of 2.43 C/m².     

Study on the properties of Pb(Zr,Ti)O3 thin films grown alternately by pulsed laser deposition and sol-gel method

In order to prepare good quality Pb(Zr,Ti)O₃ (PZT) thin films, we consider the method of alternately growing PZT thin films on Pt (111)/Ti/SiO₂/Si (100) substrates by pulsed laser deposition (PLD) and sol-gel. In this work, we conducted comparative experiments on different film preparation methods, and 1.0 um thick PZT film was grown on platinized silicon wafers by an alternate PLD and sol-gel method. The microstructure and electrical properties of the films is analyzed. Through the study of X-ray diffraction, SEM, AFM, PFM, and ferroelectric testing, it is found that the alternating growth of a film by the alternate PLD and sol-gel method has good compactness, excellent ferroelectric properties, and smaller leakage current compared to film prepared by the sol-gel method alone.     

Texture control of Pb(Zr, Ti)O3 thin films with different post-annealing processes

The non-crystalline Pb(Zr, Ti)O₃ thin films sputtered on Pt(1 1 1)/Ti/SiO₂/Si(1 0 0) substrates at room temperature were crystallized by conventional furnace annealing (CFA) and rapid thermal annealing (RTA), respectively. It was found that the RTA process favored the (1 1 1)-preferred orientation in lead zirconate titanate (PZT) thin films while the CFA process favored the (1 0 0)-preferred orientation. The origin of the different orientation selection might be due to the different epitaxial nucleation mechanism. The long heating duration would lead to the aggregation of Pb and the formation of PbO(1 0 0) on film surface; therefore, the nucleation at the PbO(1 0 0)/PZT interface on film surface might lead to the (1 0 0)-preferred orientation. However, the nucleation at the PZT/Pt(1 1 1) electrode interface by RTA process would result in the formation of (1 1 1)-preferred orientation. The RTA-derived (1 1 1)-preferentially oriented PZT thin films exhibited a high remnant polarization of 35 μC/cm².