溶胶-凝胶法制备Sr2Bi4Ti5O18薄膜及其铁电性能研究

采用溶胶-凝胶法,在氧气氛中和层层晶化的工艺条件下,成功地制备了沉积在Pt/Ti/SiO₂/Si(100)衬底上的铁电性能优良的Sr₂Bi₄Ti₅O₁₈ (SBTi)薄膜,并研究了SBTi薄膜的微结构、表面形貌、铁电性能和疲劳特性.研究表明：薄膜具有单一的层状钙钛矿结构，且为随机取向；薄膜表面光滑，无裂纹，厚度约为725nm；铁电性能测试显示较饱和、方形的电滞回线，当外电场强度为275kV/cm时 关键词： 溶胶-凝胶法 铁电薄膜 2Bi₄Ti₅O₁₈')" href="#">Sr₂Bi₄Ti₅O₁₈     

Temperature-dependent ferroelectric and dielectric properties of Bi3.25La0.75Ti3O12 thin films

To investigate temperature-dependent ferroelectric and dielectric properties of ferroelectric films, Bi_3.25La_0.75Ti₃O₁₂ (BLT) thin films were prepared on Pt-coated silicon substrates by pulsed laser deposition. The ferroelectric and dielectric behaviors have been studied in a wide temperature range from 80 K to room temperature. The saturated polarization (P_sat) decreases with decreasing temperature and decreasing electric field, whereas remnant polarization (P_r) shows a more complex temperature dependence. These results, which can be well explained based on a temperature-dependent charged defects-domain wall interaction model, might be helpful for further understanding the domain switching behavior. Based on these results, an alternative way to investigate temperature-dependent ferroelectric fatigue is proposed and experimentally carried out. The measured fatigue rate is found to be linearly dependent on temperature, consistent with the report on Pb(Zr,Ti)O₃ films. Temperature-dependent dielectric measurements of the films further confirm the above explanation.     

Si基Bi4Ti3O12铁电薄膜的制备与特性研究

采用sol-gel工艺, 在分层快速退火的工艺条件下成功地制备了高质量Si基Bi_{4Ti3O12铁电薄膜. 研究了Si基Bi4Ti3O12薄膜的生长行为、铁电性能、C-V特性和疲劳特性. 研究表明: Si基Bi4Ti3O12薄膜具有随退火温度升高沿c轴择优生长的趋势; 退火温度通过影响薄膜的晶粒尺寸、生长取向和薄膜中载流子的浓度来改变Si基Bi关键词： sol-gel法 铁电薄膜 4Ti3O12')" href="#">Bi4Ti3O12 C-V特性}     

SrBi2Ta2O9铁电薄膜微结构及其抗疲劳等铁电特性的研究

在低温Pt/Ti/SiO₂/Si衬底上用脉冲准分子激光沉积技术结合氧气氛下700℃退火获得高质量的SBT薄膜，其择优取向为（008）和（115）．薄膜厚度约为200nm．铁电性能测试显示较饱和的、方形的电滞回线，其剩余极化和矫顽电场分别为10μC/cm²和57kV/cm，在10¹⁰次开关极化后没有显示任何疲劳，在5V直流电压下的漏电流密度约为4×10^-8A/cm²，直流击穿电场约为250kV/cm 关键词：     

Ferroelectric properties of bilayer structured Pb(Zr0.52Ti0.48)O3/SrBi2Ta2O9 (PZT/SBT) thin films on Pt/TiO2/SiO2/Si substrates

Pb(Zr_0.52Ti_0.48)O₃ (PZT) thin films with large remanent polarization and SrBi₂Ta₂O₉ (SBT) thin films with excellent fatigue-resisting characteristic have been widely studied for non-volatile random access memories, respectively. To combine these two advantages_, bilayered Pb(Zr_0.52Ti_0.48)O₃/SrBi₂Ta₂O₉ (PZT/SBT) thin films were fabricated on Pt/TiO₂/SiO₂/Si substrates by chemical solution deposition method. X-ray diffraction patterns revealed that the diffraction peaks of PZT/SBT thin films were completely composed of PZT and SBT, and no other secondary phase was observed. The electrical properties of the bilayered structure PZT/SBT films have been investigated in comparison with pure PZT and SBT films. PZT/SBT bilayered thin films showed larger remanent polarization (2P_r) of 18.37 μC/cm² than pure SBT and less polarization fatigue up to 1 × 10⁹ switching cycles than pure PZT. These results indicated that this bilayered structure of PZT/SBT is a promising material combination for ferroelectric memory applications.     

Ferroelectric properties of neodymium-doped Sr2Bi4Ti5O18 thin film prepared by solgel route

Sr₂Bi₄Ti₅O₁₈ (SBTi) and Nd-modified SBTi (SBNT) thin films were deposited on Pt/Ti/SiO₂/Si (1 0 0) substrates using a sol-gel method. Structure, morphology and electric properties were investigated systematically. These films were randomly oriented and composed of rod-like grains. The remanent polarization (2P_r) and coercive field (E_c) of SBNT films were 30 μC/cm² and 55 kV/cm, respectively. This value of 2P_r was much higher than the reported value of SBTi prepared by pulsed-laser deposition. More importantly, the SBNT films showed high fatigue resistance against continuous switching up to 3×10⁹ cycles and excellent charge-retaining ability up to 3×10⁴ s.     

Effect of pore size on ferroelectric properties of multiferroic BiFeO3 films prepared on porous silicon

The ferroelectric properties of BiFeO₃ (BFO) films spray deposited on porous silicon have been studied. The analysis of XRD and FESEM investigations show that the crystalline strain in the BFO films increases with pore size. The BFO films on porous silicon substrate showed improvement in ferroelectric fatigue behavior, remanent polarization and ferroelectric switching time. A maximum memory window of 5.54 V at 1 MHz and a large remanent polarization (P_r) of 13.1 μC/cm² have been obtained at room temperature. The improvement in the ferroelectric properties of these films has been correlated to the crystalline strain.     

Ti/Pr0.7Ca0.3MnO3/La0.67Sr0.33MnO3/Pt异质结电致电阻效应的改善

采用脉冲激光沉积技术制备了Ti/Pr_0.7Ca_0.3MnO₃/Pt和Ti/Pr_0.7Ca_0.3MnO₃/La_0.67Sr_0.33MnO₃/Pt异质结并研究了La_0.67Sr_0.33MnO₃功能插层对异质结电致电阻特性的影响. 实验结果表明La_0.67Sr_0.33MnO₃功能层的引入有效提高了器件的电阻转变特性,尤其是电阻转变率和疲劳性得到了极大的改善. 对La_0.67Sr_0.33MnO₃插层改善电致电阻转变特性的机理进行了定性的分析. 关键词： 电致电阻效应 电阻转变比率 疲劳特性     

Fatigue behavior of the electric pulse induced reversible resistance change effect in AgLa0.7Ca0.3MnO3Pt sandwich

La_0.7Ca_0.3MnO₃ (LCMO) films were prepared by a chemical solution deposition method on a Pt/Si substrate. Reversible resistance switching by electric pulses is observed in Ag/LCMO/Pt sandwich structures. This R switching behavior shows fatigue with time and applied pulse number. The voltage threshold, the stability and the durability of the reversible R switching are improved by annealing the LCMO films under oxygen atmosphere. PACS 73.40.-c; 75.70.Cn; 81.15.-z     

Interface-related switching behaviors of amorphous Pr0.67Sr0.33MnO3-based memory cells

The resistive switching properties in amorphous Pr0.67Sr0.33MnO3 films deposited by pulsed laser deposition are investigated.Reproducible and bipolar counter-8-shape and 8-shape switching behaviours of Au/Pr0.67Sr0.33MnO3 /F：SnO2 junctions are obtained at room temperature.Dramatically,the coexistence of two switching polarities could be reversibly adjusted by an applied voltage range.The results allocated those two switching types to areas of different defect densities beneath the same electrode.The migration of oxygen vacancies and the trapping effect of electrons under an applied electric field play an important role.An interface-effect-related resistance switching is proposed in an amorphous Pr0.67Sr0.33MnO3-based memory cell.     

Phase compositions and ferroelectric properties of Pb(Zr0.52,Ti0.48)O3 thin films with different highly orientations prepared by a sol-gel route

It is shown that different highly oriented Pb(Zr_0.52,Ti_0.48)O₃ films can be obtained on Pt/Ti/SiO₂/Si substrate using a sol-gel technique. The effects of pyrolysis temperature on the orientation, phase composition and ferroelectric properties of the films are investigated. It is found the ferroelectric hysteresis loops of (1 1 1)-oriented film, (1 1 1) and (1 0 0) mix-oriented film can both be saturated when the external electric field is large enough, whereas the hysteresis loop of (1 0 0)-oriented film is difficult to saturate. The analysis of X-ray diffraction indicated the possibility of different phase composition in different oriented films under large film residual stress. Higher remnant polarization (53 μC/cm²) for (1 0 0)-oriented film can be attributed to its more tetragonal phase composition, which results in that the in-plane domain switching can continuously occur with external electric field increasing.     

Effects of vanadium doping on structure and electrical properties of SrBi4Ti4O15 thin films

The effects of vanadium(V) doping into SrBi₄Ti₄O₁₅ (SBTi) thin films on the structure, ferroelectric, leakage current, dielectric, and fatigue properties have been studied. X-ray diffraction result showed that the crystal structure of the SBTi thin films with and without vanadium is the same. Enhanced ferroelectricity was observed in the V-doped SrBi₄Ti₄O₁₅ (SrBi_4−x/3Ti_4−xV_xO₁₅, SBTiV-x (x = 0.03, 0.06, and 0.09)) thin films compared to the pure SrBi₄Ti₄O₁₅ thin film. The values of remnant polarization (2P_r) and coercive field (2E_c) of the SBTiV-0.09 thin film capacitor were 40.9 μC/cm² and 105.6 kV/cm at an applied electric field of 187.5 kV/cm, respectively. The 2P_r value is over five times larger than that of the pure SBTi thin film capacitor. At 100 kHz, the values of dielectric constant and dielectric loss were 449 and 0.04, and 214 and 0.06 for the SBTiV-0.09 and the pure SBTi thin film capacitors, respectively. The leakage current density of the SBTiV-0.09 thin film capacitor measured at 100 kV/cm was 6.8 × 10⁻⁹ A/cm², which is more than two and a half orders of magnitude lower than that of the pure SBTi thin film capacitor. Furthermore, the SBTiV-0.09 thin film exhibited good fatigue endurance up to 10¹⁰ switching cycles. The improved electrical properties may be related to the reduction of internal defects such as bismuth and oxygen vacancies with changes in the grain size by doping of vanadium into SBTi.     

Stress and its related effects on the fatigue behavior of Bi3.25La0.75Ti3O12 thin films

The effects of external stress cooperated with temperature, measuring frequency and measuring electric field on the fatigue properties of Bi_3.25La_0.75Ti₃O₁₂ thin films are investigated. The fatigue properties can be improved by the external stress (both tensile and compressive). The larger the stress is, the more obvious the improvement is. Meanwhile, the stress-induced improvement is more distinct in the films annealed at a higher temperature. In addition, when measured at a higher frequency or at a larger electric field, the films show better fatigue properties, and the improvement caused by stress is more evident. The experimental results can be explained well by the mechanism in which the charged defects pin the domain walls during electric cycling.     

Switching phenomenon and optical properties of Se85Te10Bi5 films

Se₈₅Te₁₀Bi₅ films of different thicknesses ranging from 126 to 512 nm have been prepared. Energy-dispersive X-ray (EDX) spectroscopy technique showed that films are nearly stoichiometric. X-ray diffraction (XRD) measurements have showed that the Se₈₅Te₁₀Bi₅ films were amorphous. Electrical conduction activation energy (ΔE_σ) for the obtained films is found to be 0.662 eV independent of thickness in the investigated range. Investigation of the current voltage (I-V) characteristics in amorphous Se₈₅Te₁₀Bi₅ films reveals that it is typical for a memory switch. The switching voltage V_th increases with the increase of the thickness and decreases exponentially with temperature in the range from 298 to 383 K. The switching voltage activation energy (ε) calculated from the temperature dependence of V_th is found to be 0.325 eV. The switching phenomenon in amorphous Se₈₅Te₁₀Bi₅ films is explained according to an electrothermal model for the switching process. The optical constants, the refractive index (n) and the absorption index (k) have been determined from transmittance (T) and reflectance (R) of Se₈₅Te₁₀Bi₅ films. Allowed non-direct transitions with an optical energy gap (E_g^opt) of 1.33 eV have been obtained. ΔE_σ is almost half the obtained value of E_g^opt, which suggested band to band conduction as indicated by Davis and Mott.     

2-2型磁电复合薄膜CoFe2O4/Pb(Zr0.53Ti0.47)O3静磁耦合

运用溶胶-凝胶法在Pt/Ti/SiO₂/Si基片上旋涂制备了2-2型CoFe₂O₄/Pb(Zr_0.53Ti_0.47)O₃磁电复合薄膜．制备的磁电薄膜结构为基片/PZT/CFO/PZT*/CFO/PZT,通过改变中间层PZT*溶胶的浓度,改变磁性层间距以及静磁耦合的大小．SEM结果表明,复合薄膜结构致密,呈现出界面清晰平整的多层结构．制备的复合薄膜具有较好的铁电与铁磁性能．实验还研究了静磁耦合对薄膜磁电性能的影响,结果表明,随着复合薄膜磁性层间距的减小,静磁耦合效应的增加,磁电电压系数有逐渐增大的趋势.     

La2/3Ca1/3MnO3薄膜的光致电阻率变化特性

射频磁控溅射法制备了La_2/3Ca_1/3MnO₃纳米薄膜(LCMO).该薄膜发生FM-PM相变的转变点温度为T_c≈308K（近似为电阻峰值温度T_p）；在不同温度下的光电导性质实验表明所制备的LCMO薄膜在连续激光作用时低温段（Tc）表现为光致电阻率增大效应，即ΔR/R＞0，并在R-T曲线拐点附近取得极大值，（ΔR/R）_max=43.5%；当T>T关键词： 钙钛矿薄膜 光响应 电子自旋 小极化子     

Resistive switching effects in CeO2/La0.7(Sr0.1Ca0.9)0.3MnO3/Pt heterostructures prepared by pulse laser deposition method

The heterostructural junctions of CeO₂/La_0.7(Sr_0.1Ca_0.9)_0.3MnO₃/Pt (CeO₂/LSCMO/Pt) were prepared using pulse laser deposition technique. Their resistive switching (RS) behavior was investigated. As compared to the metal/manganite/Pt junction, the CeO₂/LSCMO/Pt device displayed an improved switching characteristic. The RS effects with characteristics of bipolar, threshold, and complementary were realized by adjusting the thicknesses of the CeO₂ layer in the CeO₂/LSCMO/Pt junctions. Under a higher external bias voltage, the threshold and complementary switching modes of the junctions could turn into bipolar switching mode. The switching behavior shows strong dependence on the O₂ partial pressure during the fabrication, indicating that the amount and behavior of the oxygen at the interface play an important role in the determination of the RS behavior. The observed switching behavior is related to the modification of the accumulation/depletion layers as well as the interfacial potential barrier due to the migration of the oxygen vacancies.     

Pico-second photoelectric characteristic in manganite oxide La0.67Ca0.33MnO3 films

Ultrafast photoelectric characteristic has been observed in La_0.67Ca_0.33MnO₃ films on tilted SrTiO₃ substrates. A pico-second (ps) open-circuit photovoltage of the perovskite manganese oxide films has been obtained when the films were irradiated by a 1.064μm laser pulse of 25 ps duration. The rise time and full width at half-maximum of the photovoltage pulse are ～300 ps and ～700 ps, respectively. The photovoltaic sensitivity was as large as ～500 mV/mJ.     

A layer of reduced switchable polarisation in (Pb,La)TiO3 films leading to a thickness dependence of the ferroelectric parameters

Two sets of ferroelectric (Pb,La)TiO₃ thin films have been prepared by a diol-based sol-gel technique by varying the heating rate to the crystallisation temperature of 650°C. Films of increasing thickness were obtained by repeating the solution deposition from 1 to 5 times. The switchable polarisation was evaluated from hysteresis loops and from the integration of the switching current transients during pulse tests, and was found to significantly depend on film thickness. Measurements of the thickness dependence of the reciprocal capacitance and Rutherford backscattering spectrometry results indicate that a layer with different dielectric permittivity, and composition for one set of films, existed next to the bottom electrode. In the one set of films it originated because of interdiffusion between the film and the substrate, while in the other set, it was linked to the tensile stress at the film/substrate interface. These layers had a reduced switchable polarisation, which caused the observed dependence of their properties on thickness.     

Characterization of electrodeposited Bi2S3 thin films by holographic interferometry

Optical non destructive evaluation methods, using lasers as the object illumination source, include holographic interferometry. It is widely used to measure stress, strain, and vibration in engineering structures. Double exposure holographic interferometry (DEHI) technique is used to determine thickness and stress of electrodeposited bismuth trisulphide (Bi₂S₃) thin films for various deposition times. The same is tested for other concentration of the precursors. It is observed that, increase in deposition time, increases thickness of thin film but decreases stress to the substrate. The structural, optical and surface wettability properties of the as deposited films have been studied using X-ray diffraction (XRD), optical absorption and contact angle measurement, respectively. The X-ray diffraction study reveals that the films are polycrystalline with orthorhombic crystal structure. Optical absorption study shows the presence of direct transition with band bap 1.78 eV. The water contact angle measurement shows hydrophobic nature of Bi₂S₃ thin film surface.