Dynamics of ferroelastic domains in ferroelectric thin films

Dynamics of domain interfaces in a broad range of functional thin-film materials is an area of great current interest. In ferroelectric thin films, a significantly enhanced piezoelectric response should be observed if non-180 degrees domain walls were to switch under electric field excitation. However, in continuous thin films they are clamped by the substrate, and therefore their contribution to the piezoelectric response is limited. In this paper we show that when the ferroelectric layer is patterned into discrete islands using a focused ion beam, the clamping effect is significantly reduced, thereby facilitating the movement of ferroelastic walls. Piezo-response scanning force microscopy images of such islands in PbZr0.2Ti0.8O3 thin films clearly point out that the 90 degrees domain walls can move. Capacitors 1 microm2 show a doubling of the remanent polarization at voltages higher than approximately 15 V, associated with 90 degrees domain switching, coupled with a d33 piezoelectric coefficient of approximately 250 pm V-1 at remanence, which is approximately three times the predicted value of 87 pm V-1 for a single domain single crystal.     

Modeling of ferroelectric domains in thin films and superlattices

We have developed the set of numerical (finite-element) and analytical tools that are based on the self-consistent solution of the electrostatic equations coupled with material Ginzburg–Landau equations with an objective to model the profile of domain textures in the entire temperature region. We calculated the evolution of principal parameters of domain texture: modulation vector, distribution of polarization, renormalization of critical temperature etc. In contrast to the Kittel approximation we conclude that the profile of polarization across domains in nanometric ferroelectric thin films is highly nonuniform.     

Electron energy in exoelectronic emission from a ferroelectric

An analysis is made of the change in the potential in the plane of a grid electrode on the surface of a ferroelectric caused by exoelectronic emission under the influence of a pulsed electric field. The potential is calculated by means of integral equations from electrostatics. An estimate is made of the possible initial energies of electrons leaving the surface of the ferroelectric. Pis’ma Zh. Tekh. Fiz. 24, 54–57 (July 26, 1998)     

Electron emission characterization of diamond thin films grown from a solid carbon source

Diamond films of various morphologies and compositions have been deposited on silicon substrates by a plasma-enhanced chemical transport (PECT) process from a solid carbon source. Electron emission efficiency of these diamond films is related to their morphology and composition. The electric field required to excite emission in a boron-doped polycrystalline diamond film ranged between 20 to 50 MV m⁻¹. In an undoped conducting nanocrystalline diamond composite film, the field was as low as 5–11 MV m⁻¹. The cold field electron emission of these films is confirmed from the Fowler-Nordhelm plots of the data. Enhancement of electron emission by band-bending and by the nanocrystalline microstructure are discussed. New diamond emitters made of nanocrystalline boron-doped diamond composite are proposed.     

An application of polarized domains in ferroelectric thin films using scanning probe microscope

The feasibility of utilizing PZT films as future data storage media was investigated using a modified AFM. Applying voltages between a conductive AFM tip and the PZT films causes the switching of ferroelectric domains. The domains are observed using an EFM imaging technique. The experimental results and calculations revealed that the electrostatic force generated between the polarized area and the tip is a main contributor for the imaging of the polarized domains. The written features on ferroelectric films were less than 100 nm in diameter, implying the possibility of realizing data storage devices with ultra-high area density. The disappearance of the polarized images without any applied voltage was observed, which is a drawback in this application of PZT thin films.     

Sol-Gel法制备PLZT系铁电薄膜

介绍了Sol-Gel法,并对近年来Sol-Gel法制备PLZT系铁电薄膜材料的有关研究进行了分析和总结,详细介绍了Sol-Gel法制备PLZT系铁电薄膜材料的各种原料及工艺流程。     

Nanoscale observation of the distribution of the polarization orientation of ferroelectric domains in lithium niobate thin films

In this paper, an Atomic Force Microscope (AFM) in the so-called piezoresponse mode is used to image the ferroelectric domains in radio frequency sputtered lithium niobate (LiNbO₃) thin films. It is shown that ferroelectric domains are clearly detectable and most of the time confined in the grains. The vertical and the lateral motion of the vibration of the tip in response to the applied alternating voltage is recorded in order to reconstruct a cartography of the orientation of the ferroelectric domains, allowing us to observe the distribution of the orientation of the polarization in the polycrystalline film and providing additional information about the direction of the polarization, although it is not a fully 3D cartography. From Piezoresponse Force Microscopy images, it is clear that the dispersion of the orientation of the polarization vector in the studied LiNbO₃ sample is very high. It is shown that the AFM quasi-3D mapping of the distribution of orientation in the material provides a valuable information and may help understanding the fundamental phenomena which govern the growth of the material.     

Structural distortion and enhanced ferroelectric properties of Tb and Cr co-doped BiFeO3 thin films

BiFeO₃ and Bi_0.92Tb_0.08Fe_1?xCr_xO₃ (BTFCO) thin films were successfully prepared on SnO₂: F (FTO)/glass substrates by a chemical solution deposition technique. The influences of Tb and Cr co-doping on the structure, the leakage current, charge defects, the dielectric and the ferroelectric properties of the BTFCO thin films were investigated systematically. X-ray diffraction and Raman spectra results clearly reveal the structural distortion in the co-doped thin films. The X-ray photoelectron spectroscopy measurements show the absence of Fe²⁺ ions indicating the suppression of oxygen vacancies due to Tb and Cr co-doping. The electrical conduction mechanism of the BTFCO thin film is dominated by the Ohmic conduction in the low resistance state and trap-controlled space charged limited current in the high resistance state. With 8 %Tb and 1 %Cr co-doping, the film exhibits the superior ferroelectric (2P _r  = 105 μC/cm²) and dielectric properties. All the results show the film is very promising in the practical application.     

Electron emission from metal-CdS-insulator-metal and metal-insulator-CdS-metal thin film devices

Electron emission in vacuum from thin film devices of the metal-CdS-insulator-metal or metal-insulator-CdS-metal types has been observed. Typical thicknesses of the layers involved are 10,000 Å for the CdS and 2,000 Å for the insulator. The emitted current is of the order of 1–10 micro A while the current circulating through the device is of the order of 1–10 mA. Electron emission comes from certain localized spots of the device active area (total area is 0.2 cm²). The results are explained in terms of the filamentary conduction model.     

Processing dependences of microstructure of ferroelectric thin films

Ferroelectric thin film has been widely investigated in detail in recent years. The ferroelectric properties of thin films are obviously dependent on the microstructure of the film, which is influenced by some processing parameters for preparing the films, including precursor solution chemistry, nature of substrate, film thickness, and condition of heat treatment etc. In this paper, these processing dependences of the films are reviewed.     

SO1-Gel法硅基PZT铁电薄膜研究

介绍了以硝酸锆、醋本以铅和钛酸四丁酯为原料用溶胶－凝胶（sol-gel）方法在硅衬底上制备Pb（Zr0.53Ti0.47)O3(PZT)铁电膜的工艺流程。对铁电薄膜的表面形貌、晶化程度、界面状态等性质进行了分析,结果表明硅基PZT薄膜形成了良好的钙伏矿结构,并在此基础上实现了制备PZT铁电薄膜的低温改进工艺。     

Flexoelectric rotation of polarization in ferroelectric thin films

Strain engineering enables modification of the properties of thin films using the stress from the substrates on which they are grown. Strain may be relaxed, however, and this can also modify the properties thanks to the coupling between strain gradient and polarization known as flexoelectricity. Here we have studied the strain distribution inside epitaxial films of the archetypal ferroelectric PbTiO(3), where the mismatch with the substrate is relaxed through the formation of domains (twins). Synchrotron X-ray diffraction and high-resolution scanning transmission electron microscopy reveal an intricate strain distribution, with gradients in both the vertical and, unexpectedly, the horizontal direction. These gradients generate a horizontal flexoelectricity that forces the spontaneous polarization to rotate away from the normal. Polar rotations are a characteristic of compositionally engineered morphotropic phase boundary ferroelectrics with high piezoelectricity; flexoelectricity provides an alternative route for generating such rotations in standard ferroelectrics using purely physical means.     

铁电薄膜退火方法的研究

以锆钛酸铅薄膜（PZT）为例，分析了国内外铁电薄膜退火的各种方法。针对解决铁电薄膜基底高温生长工艺与硅集成电路承受温度较低的不兼容及器件性质劣化的难题，分别对普通炉子退火、快速热退火及激光退火进行了详细的分析比较。激光低温退火技术有望成功地在未来应用PZT铁电薄膜制作组件时，增加其制备工艺设计的弹性和可行性。     

Field electron emission from flat metal cathodes covered by thin polymer films

We have studied the physical properties of a new class of field electron emitters representing metal cathodes covered by thin polymer films based on a soluble imide-siloxane copolymer. Polymer coating leads to an increase in the emission current and provides for a quite stable field electron emission of flat polished molybdenum and niobium cathodes.     

组分梯度铁电薄膜的研究进展

与均匀组分铁电薄膜相比,组分梯度铁电薄膜有很多优异的性能,其介电性能显著提高,从而有效改善了微波调谐器件的性能。上、下梯度铁电薄膜的性能也不相同,但目前尚无研究者从实验上证明其产生差异的原因。另外,组分梯度铁电薄膜的电滞回线的极化偏移仍然是一个比较有争议的问题。因此,研究组分梯度铁电薄膜在实际应用和完善理论研究方面均具有重要意义。综述了近年来对组分梯度铁电薄膜的研究进展并提出了研究中需要解决的问题。     

铁电薄膜电疲劳研究进展

铁电薄膜在交变电场下发生电疲劳现象是影响其商业应用的主要障碍，也是目前国内外研究的热点。本文从铁电薄膜电疲劳的影响因素、疲劳机理和消除疲劳的措施出发综述了近年来国内外在铁电薄膜电疲劳研究方面取得的进展。     

Structure transition and enhanced ferroelectric properties of (Mn, Cr) co-doped BiFeO3 thin films

Pure BiFeO₃ (BFO) and (Mn, Cr) co-doped BiFe_0.96?yMn_0.04Cr_yO₃ thin films were prepared on FTO/glass (SnO₂:F) substrates by using a sol–gel method. The effects of (Mn, Cr) co-doped on the microstructure and electric properties of the BiFeO₃ thin films were studied. The result indicates that the co-doped BiFe_0.94Mn_0.04Cr_0.02O₃ (BFMCO) thin film has a structure transition and better ferroelectric properties compared with the pure BFO thin film. The Rietveld refined XRD patterns of BFO and BFMCO thin films conform the trigonal (R3c:H) and the biphasic (R3c:H + R3m:R) structure, respectively. The co-existence of two phases and the mixed valences of Cr^3+/6+ and Mn^2+/3+, which apparently improves the electric properties of the (Mn, Cr) co-doped BFMCO thin films. The remnant polarization (P _r) of the BFMCO thin film was 93.58 μC/cm² at 1 kHz in the applied electric field of 636 kV/cm. At an applied electric field of 100 kV/cm, the leakage current density of (Mn, Cr) co-doped BFMCO thin film is 6.2 × 10^?6 A/cm². It is about three orders much lower than that of the BFO thin film (1.43 × 10^?3 A/cm²).     

Sol-Gel法制备PZT铁电薄膜新进展

从底电极的选择、过渡层的引入、外延膜的生长、取代阳离子的改性四个方面介绍了Sol-Gel法制备PZT铁电薄膜的研究进展,简述了PZT的Sol-Gel机理研究现状和引起PZT铁电薄膜极化疲劳的原因,分析了Sol-Gel法制备PZT铁电薄膜研究中存在的问题,并提出展望。     

金属有机化学气相沉积制备铁电薄膜材料研究进展

铁电薄膜是一类重要的功能材料,是近年来高新技术研究的前沿和热点之一.金属有机化学气相沉积(MOCVD)是制备铁电薄膜的一种重要方法.综述了金属有机化学气相沉积法制备铁电薄膜的历史、原理、工艺参数、特点和采用此方法制备出的某些材料的铁电性能.