铁电薄膜的材料系统与功能性质

集成铁电体把铁电材料与集成半导体技术联合起来,以发展出一批新的电子器件.铁电薄膜在其中发挥着非挥发性记忆、热释电、压电、光折变、抗辐射、声学的和/或介电的功能性质.在不同的器件应用中,铁电薄膜的材料体系是不相同的.在非挥发性存贮器(NVRAM)中,PZT薄膜面临着SrBi2Ta2O9(SBT)系列铁电体的强力挑战;Ba1-xSrxTiO3(BST)则可能出现在下一代高密度动态随机存贮器(DRAM)中.金属氧化物电极和/或过渡层可以克服Pt电极面临的一些问题,并有助于铁电薄膜的外延生长.     

SrBi2Ta2O9(SBT)铁电陶瓷的制备及性能

用固相反应法合成了SrBi2Ta2O9(简称SBT)粉体，通过冷等静压成型、无压烧结的方法，制备出SBT铁电陶瓷。采用XRD、SEM、EPMA研究了材料的物相和微观组织结构，用阻抗分析仪测试了材料的介电和铁电性能。     

SrBi_2Nb_2O_9织构陶瓷各向异性的电性能

以熔盐法制备的片状SrBi2Nb2O9晶粒为模板晶粒,固相法制各的SrBi2Nb2O9为基体粉料,采用模板晶粒生长技术和流延法制备了SrBi2Nb2O9织构陶瓷.研究了SrBi2Nb2O9织构陶瓷沿a-b平面方向和c方向的介电、压电及铁电性能,发现SrBi2Nb2O9织构陶瓷的性能呈现出显著的各向异性,其a-b平面方向的介电常数ε33T/ε0达186,tanδ仅有0.003,压电常数d33=13pC/N,剩余极化强度Pr=10.3iμC/cm2,矫顽场强Ec=4.6kV/mm,均明显优于C方向的电性能.     

Pr~(3+)掺杂SrBi_2Ta_2O_9陶瓷的铁电及介电性能研究

以氧化钽为钽源,采用溶胶-凝胶法合成SrBi2Ta2O9(SBT)、Pr0.2Sr0.8Bi2Ta2O9(SPBT)粉体。用X射线衍射技术(XRD)对所制备的SBT、SPBT粉体进行结构表征,并对其介电、铁电性能进行了测试分析。实验结果表明:Pr3+离子掺杂未改变SBT粉体的晶相,但是会使得SBT的介电常数增大,不过随着测试频率的增加介电常数仍然逐渐下降。另外SBT的铁电性能也随着Pr3+的掺杂有了显著的提升。     

SrBi4Ti4O15薄膜的溶胶凝胶制备及其生长行为

以氯化锶、硝酸铋和钛酸丁酯为原料,柠檬酸为络合剂,配制了稳定的SrBi4Ti4O15（SBTi）前驱液.采用层层快速退火工艺,在Pt/Ti/SiO2/Si基片上制备了a轴取向增强的SBTi铁电薄膜,通过场发射扫描电镜、环境扫描电镜及X射线衍射等微观分析手段研究了保温时间和成膜次数对薄膜结晶性、微观结构和生长行为的影响.结果表明：层层快速退火工艺,可有效抑制焦绿石相的形成.随着退火时间的延长,薄膜的结晶性变好;但退火时间延长到30 min以上,薄膜的结晶性变差.由于SBTi晶体生长的各向异性及单层膜厚对晶体沿[119]方向生长的限制,随着涂覆次数的增加,SBTi薄膜（119）峰和（200）峰的强度逐渐增大,而（00l）峰的强度反而略有减少,从而使I（200）/I（119）、I（200）/I（0010）、I（119）/I（0010）逐渐增大.     

高介电氧化钽薄膜制备与介电性能分析

在较低衬底温度下,通过磁控溅射得到的非晶态Ta2O5薄膜,在氧气氛750℃条件下进行化学热退火,得到晶化的Ta2O5薄膜,其相对介电常数为34.3,漏电流密度小于10-7A/cm2.电容量测试时,为了较好地消除高温退火时产生的SiO2的介质层对电容测试值的影响,用不同厚度氧化钽薄膜为介质层做成金属-绝缘体-金属(MIM)结构的电容器,对这些电容器的电容测试数据,进行sigmoidal拟合,得到极限电容,从而计算出Ta2O5薄膜的介电常数.     

SrBi_4Ti_4O_(15)陶瓷薄膜的铁电性能研究

利用溶胶-凝胶法制备了CaxSr1-xBi4Ti4O15铁电陶瓷薄膜,并研究了Ca掺杂量、退火温度以及保温时间对SrBi4Ti4O15陶瓷薄膜铁电性能的影响。研究结果表明,当Ca掺杂含量为0.4%,退火温度为750℃,保温时间为5 min时,样品的铁电性能最好。     

热处理工艺对钙锶铋钛铁电薄膜性能的影响

用溶胶-凝胶法和快速退火技术在带白金电极和钛过渡层的硅片(Pt/Ti/SiO2/Si)上制备了钙锶铋钛(Ca0.4Sr0.6Bi4Ti4O15,CsBT-0.4)铁电薄膜.结果表明:退火温度及保温时间对CSBT-0.4铁电薄膜的微观结构、晶粒取向以及铁电性能的影响较大.x射线衍射谱表明:退火温度为750℃、保温时间为5min,得到的CsBT-0.4铁电薄膜样品的晶粒大小较均匀且致密性好,而且晶粒以a轴取向的球状晶粒为主,剩余极化强度(2Pr)和矫顽场(2Ec)分别为16.2 μC/cm2和130kV/cm.     

Bi5FeTi3O15薄膜室温多铁性及其磁性机理

用溶胶凝胶工艺在Pt/Ti/SiO2/Si基片上沉积了Bi5FeTi3O15(BFTO)薄膜,研究了前驱液浓度和退火升温速率对BFTO薄膜结晶的影响,前驱液浓度低于0.05mol/L时不利于4层层状钙钛矿结构的形成。沉积BFTO薄膜的最佳制备工艺为:前驱液浓度为0.05mol/L和氧气氛中退火速率为4℃/s。室温下,用最佳工艺制得的BFTO薄膜显示出良好的铁电性,在300 kV/cm的外加电场下,样品的剩余极化强度2Pr达到43.4μC/cm2;同时,BFTO薄膜也显示出弱铁磁性。为了研究其磁性来源,分别在氧气氛和氮气氛下对BFTO薄膜样品进行退火,分析其磁性的差异。认为BFTO薄膜室温下的弱铁磁性主要来源于F中心交换作用。     

退火工艺对Pb(Zr_(0.55)Ti_(0.45))O_3铁电薄膜结晶取向的影响

用射频磁控溅射法在Pt(111)/Ti/SiO2/Si上成功的制备了Pb(zr0.55Ti0.45)O3(PZT)铁电薄膜,通过传统退火(CFA)和快速退火(RTA)不同的退火方式,获得了(100)和(111)择优取向的铁电薄膜。对薄膜电学特性的测试表明,薄膜的织构对其电学性能有很大影响,(111)取向的薄膜与(100)取向的薄膜相比,剩余极化Pr和矫顽场Ec较大,但抗疲劳特性却较差。     

Effect of rapid thermal annealing on the structural and electrical properties of TiO2 thin films prepared by plasma enhanced CVD

Titanium oxide thin films were deposited on p-type Si(100), SiO₂/Si, and Pt/Si substrates by plasma enhanced chemical vapor deposition using high purity Ti(O-i-C₃H₇)₄ and oxygen. As-deposited amorphous TiO₂ thin films were treated by rapid thermal annealing (RTA) in oxygen ambient, and the effects of RTA conditions on the structural and electrical properties of TiO₂ films were studied in terms of crystallinity, microstructure, current leakage, and dielectric constant. The dominant crystalline structures after 600 and 800 ‡C annealing were an anatase phase for the TiO₂ film on SiO₂/Si and a rutile phase for the film on a Pt/Si substrate. The dielectric constant of the as-grown and annealed TiO₂ thin films increased depending on the substrate in the order of Si, SiO₂/Si, and Pt/ Si. The SiO₂ thin layer was effective in preventing the formation of titanium silicide at the interface and current leakage of the film. TEM photographs showed an additional growth of SiO_x from oxygen supplied from both SiO₂ and TiO₂ films when the films were annealed at 1000 ‡C in an oxygen ambient. Intensity analysis of Raman peaks also indicated that optimizing the oxygen concentration and the annealing time is critical for growing a TiO₂ film having high dielectric and low current leakage characteristics.     

Solution transformation of SnS into Cu2ZnSnS4xSe4(1-x) for solar water splitting

Cu₂ZnSnS_4xSe_4(1-x) (CZTSSe) has recently attracted much attention for solar water splitting due to its high absorption efficient and tunable bandgap. However, high quality CZTSSe thin films with good quality and adherence with the substrate are mainly based on physical deposition method, such as magnetron sputtering, which is expensive and energy consuming processes. Here, we have developed a novel and low-cost solution fabrication method and CZTSSe electrodes were synthesized at low temperature by hydrothermal treatment of chemical bath deposited SnS films. The quality and phase purity of CZTSSe thin films were greatly improved after annealing process and the effect of SnS thickness to the physical and photoelectrochemical (PEC) properties of CZTSSe thin films were detailedly studied. The fabrication of FTO/CZTSSe/CdS/TiO₂/Pt photocathode improved the PEC properties of CZTSSe thin films greatly and the highest water splitting photocurrents of 7.2 mA/cm⁻² had been achieved under simulated solar illumination. Furthermore, the electrode showed good stability and had a good incident photon-to-current efficiency (IPCE) response in the visible light range.     

The preparation and properties of PZT thin film by sputering method

The ferroelectric PZT thin films were prepared on Pt/Ti/SiO₂/Si substrate by RF sputtering method followed by the rapid thermal annealing. The preparation of the Pt and Ti thin films as bottom electrode, and their influences on the PZT thin films were studied in details. The substrate temperature during sputtering was room temperature; the rapid thermal annealing temperature was 500°C-750°C and the annealing time was 30-70s. The influences of different preparation parameters on the structure and electric properties were studied with X-ray diffraction technique and RT66A Standardized Ferroelectric Test System. The electric properties of the prepared PZT thin film was: P_a=39μc/cm₂, P_r = 9.3 μc/cm², E_c=28KV/mm, ε=300, p=10⁹ω⋅cm.     

Titanium Diffusion into (K0.5Na0.5)NbO3 Thin Films Deposited on Pt/Ti/SiO2/Si Substrates and Corresponding Effects

Lead-free (K_0.5Na_0.5)NbO₃ (KNN) thin films were prepared on Pt/Ti/SiO₂/Si substrates by a sol–gel processing method, and titanium diffusion from the substrates into the KNN films under different thermal treatment conditions were investigated by the secondary ion mass spectroscopy depth profile and X-ray photoelectron spectroscopy surface analysis. Titanium diffusion was evident in all the KNN thin films, which was further aggravated not only by increasing the annealing temperature, but also surprisingly by higher ramping rate attributed to the resulting larger grain boundaries. The pronounced effects of the titanium diffusion and the resulting substitution of Ti⁴⁺ for Nb⁵⁺ with different valence states on the composition, structure, and electrical properties of the KNN thin films are analyzed and discussed. The results showed that the Ti diffusion from the substrate played a crucial role in affecting the structure and electrical properties of the ferroelectric KNN thin films deposited on Pt/Ti/SiO₂/Si substrate.     

In-Plane Polarized 0.7Pb(Mg1/3Nb2/3)O3–0.3PbTiO3 Thin Films

Ferroelectric 0.7Pb(Mg_1/3Nb_2/3)O₃–0.3PbTiO₃ (PMN-PT) thin films were deposited on ZrO₂/SiO₂/silicon substrates using a chemical-solution-deposition method. Using a thin PZT film as a seed layer for the PMN-PT films, phase-pure perovskite PMN-PT could be obtained via rapid thermal annealing at 750°C for 60 s. The electrical properties of in-plane polarized thin films were characterized using interdigitated electrode arrays on the film surface. Ferroelectric hysteresis loops are observed with much larger remanent polarizations (∼24 μC/cm²) than for through-the-thickness polarized PMN-PT thin films (10–12 μC/cm²) deposited on Pt/Ti/Si substrates. For a finger spacing of 20 μm, the piezoelectric voltage sensitivity of in–plane polarized PMN-PT thin films was ∼20 times higher than that of through-the-thickness polarized PMN-PT thin films.     

Textured ferroelectric SbNbO4 thin films deposited by ion-beam sputtering

In this letter, we report on the first synthesis of oriented SbNbO₄ ferroelectric thin films on Pt coated silicon substrates. Textured SbNbO₄ thin films are formed by rapid thermal annealing of films deposited by Ar⁺ ion-beam sputtering at room temperature. The films are characterized by X-ray diffraction spectra. Ferroelectric P-E loops are measured and dielectric properties are studied at low frequency. The effect of Pt electrodes on the formation of ferroelectric SbNbO₄ thin films is discussed.     

铁电薄膜存储器底电极Pt/Ti的制备及性能研究

应用射频磁控溅射方法 ,在Si基片上采用不同的溅射工艺制备了铁电薄膜底电极Pt/Ti,并分析了在不同温度下退火后材料的电导率性能和粘结力性能 ,从理论和实验上分析了不同的溅射工艺和退火处理对底电极性能的影响。     

Effect of PbTiO3 seed layer on the orientation behavior and electrical properties of Bi(Mg1/2Ti1/2)O3–PbTiO3 ferroelectric thin films

High Curie-temperature 0.63Bi(Mg_1/2Ti_1/2)O₃–0.37PbTiO₃ (BMT–PT) films were fabricated on Pt(111)/Ti/SiO₂/Si substrates by the sol–gel spin-coating method. The oriented growth behavior of thin films was controlled by introducing a PT seed layer onto the platinum electrode surface. The effect of the annealing method of the PT seed layer on the orientation behavior and electrical properties of BMT–PT films was investigated. It was found that BMT–PT thin film exhibits higher (100) orientation degree when the PT seed layer was treated by rapid thermal annealing. The dielectric permittivity increases while the remanent polarization and coercive field decrease with increasing the (100) orientation degree. These results were explained according to the relationship between the preferential orientation and the spontaneous polarization directions of the films.     

Thermal treatment effect on the magnetoelectric properties of (Ni0.5Zn0.5)Fe2O4/Pt/Pb(Zr0.3Ti0.7)O3 heterostructured thin films

Magnetoelectric (ME) property modulation in heterostructured (Ni_0.5Zn_0.5)Fe₂O₄/Pt/Pb(Zr_0.3Ti_0.7)O₃ (NZFO/Pt/PZT) thin films on platinized Si substrate by thermal annealing condition variation was studied. In an attempt to prevent interfacial reaction between NZFO and PZT layers during high temperature annealing, thin Pt layer was deposited which can serve as inter-diffusion barrier as well as electrode. The ferroelectric, magnetic, and ME properties of the heterostructured film were noticeably modulated due to microstructural evolution and clamping relaxation developed during thermal annealing process. Room temperature ME voltage coefficient of the heterostructured thin films was enhanced with increasing annealing temperature and reached to 29 mV/cm·Oe when annealed at 650 °C.     

Electrocatalytic activity of Pt nanoparticles deposited on porous TiO2 supports toward methanol oxidation

Porous TiO₂ thin films were prepared on the Si substrate by hydrothermal method, and used as the Pt electrocatalyst support for methanol oxidation study. Well-dispersed Pt nanoparticles with a particle size of 5–7 nm were pulse-electrodeposited on the porous TiO₂ support, which was mainly composed of the anatase phase after an annealing at 600 °C in vacuum. Cyclic voltammetry (CV) and CO stripping measurements showed that the Pt/TiO₂ electrode had a high electrocatalytic activity toward methanol oxidation and an excellent CO tolerance. The excellent electrocatalytic performance of the electrode is ascribed to the synergistic effect of Pt nanoparticles and the porous TiO₂ support on CO oxidation. The strong electronic interaction between Pt and the TiO₂ support may modify CO chemisorption properties on Pt nanoparticles, thereby facilitating CO oxidation on Pt nanoparticles via the bifunctional mechanism and thus improving the electrocatalytic activity of the Pt catalyst toward methanol oxidation.