Deposition and characterization of thin ferroelectric lead lanthanum zirconate titanate (PLZT) films on sapphire for spatial light modulators applications

Ferroelectric lead lanthanum zirconate titanate (PLZT) films are deposited on R-plane sapphire using RF triode magnetron sputtering. Perovskite PLZT films with the desired composition (9/65/35) are obtained using compensated deposition techniques around 500 degrees C and postdeposition annealing at 650 degrees C. The deposited films exhibit good optical and electrooptical properties. The room temperature dielectric constant of the films was 1800 at 10 kHz. The refractive index of the films was in the range of 2.2-2.5. The films showed a quadratic electrooptic effect with R=0.6 x10(-16) m(2)/V(2). The development of PLZT on silicon-on-sapphire smart spatial light modulators using these films is also explored.     

On the preparation of PLZT thin films grown by pulsed laser deposition

Polycrystalline PLZT thin films have been grown onto glass slides substrate, from a sintered stoichiometric 9/65/35 commercial target, by using a Nd:YAG laser (1064 nm, 7 ns, 10 Hz). The substrate temperature and oxygen pressure were varied during the deposition, as was the post-deposition annealing temperature in order to achieve stoichiometric films with a perovskite structure and with a composition near the ratio 9/65/35. Perovskite PLZT is formed around the substrate temperature of 500°C and oxygen pressure of ∼0.5 mbar after annealing at 580°C during 90 min. The pyrochlore structure, on the other hand, is always formed in the films during the deposition. However, this structure disappear for annealing temperatures above 550°C, for the films grown at oxygen pressure in the range 0.5–1 mbar and temperature deposition above 450°C. The degree of crystallinity and the structure present in the films is correlated with the deposition conditions. The influence of post-deposition annealing conditions on the formation of perovskite PLZT structure and optical transparency of the films is also discussed.     

纳米结构PZT铁电膜的制备及其表征

采用溶胶-凝胶(sol-gel)自旋涂敷法在硅基氧化铝纳米有序孔膜版介质上(膜版孔径尺寸20～100nm,内生长金属纳米线作为底电极一部分)制备Pb(Zr0.53Ti0.47)O3(PZT)纳米结构铁电膜,并对其介电、铁电性能及微结构进行了表征。介电测量结果表明,厚度25nm的PZT铁电膜,其介电常数在低频区域(频率104Hz)从860迅速下降到100,然后保持在100左右,直至测量频率升高到106Hz。低频区域的介电常数迅速下降是由空间电荷极化所致,它与薄膜和电极之间聚集的界面空间电荷密切相关,尤其是在薄膜与Au纳米线的弯曲界面处。介电损耗在4000Hz附近出现峰值,它来源于空间电荷的共振吸收效应。电滞回线测量结果表明,厚度为100nm的PZT铁电膜,其剩余极化强度为50μC/cm2,矫顽场强为500kV/cm。剖面透射电镜(TEM)像表明PZT纳米铁电膜与底电极(金属纳米线)直接相接触,它们之间的界面呈现一定程度的弯曲。在PZT纳米铁电薄膜后退火处理后,发现部分Au金属纳米线顶端出现分枝展宽现象;而改用Pt纳米线后可有效抑制这种现象。为兼顾氧化铝纳米有序孔膜版内的金属纳米线有序分布及PZT纳米膜的结晶度,选择合适的退火温度是制备工艺中的关键因素。     

Microcrystalline silicon thin films for optical applications

Microcrystalline hydrogenated silicon thin films, deposited by the cyclic CVD method, were used for the production of bidimensional detectors. The optical detectors use a standard TCO/μc-p-i-n Si:H configuration as active device and two lateral ohmic contacts. Based on the lateral photovoltaic effect developed in the p-i-n structure under local illumination, we propose to develop a new sensing method for the recognition of a light pattern projected onto a p-i-n optical sensor. It was used strong spatially fixed light spots to simulate an image and a weak chopped light scanning-beam to make its recognition. The induced ac component of the lateral photovoltage was found to be dependent on the image position and intensity. A small signal circuit analysis and simulation is presented. Applications for image detection are discussed.     

Growth of perovskite PZT and PLZT thin films

This paper reports preliminary results on the fabrication of perovskite PZT and PLZT thin films using a sputtering technique. For glass, quartz and sapphire substrates, it was necessary to raise the substrate temperature above 550 ° C to achieve perovskite tetragonal structures of interest. Growth at temperatures below 550 ° C yielded a major pyrochlore structure phase. Excess of PbO in the target was also required to maintain stoichiometry in these films.     

Electrical and optical properties of PLZT thin films on ITO coated glass by sol-gel processing

Sol-gel processed PLZT thin films were fabricated on ITO-coated glass substrates with RTA (rapid thermal annealing). The electrical and optical properties such as hysteresis curves, dielectric constant, dielectric loss and optical transmittance of thin films were investigated. The PLZT thin films were crystallized to the perovskite structure by RTA at 750°C for 5 min. As the La percentage was increased, the dielectric constant increased, and that of 9/65/35 PLZT thin film was 1750. The coercive field and remnant polarization decreased with La increase from 33.82 kV/cm to 14.71 kV/cm and from 39.26 C/cm² to 9.57 C/cm² respectively. As the Zr percentage increased at 2% La, the coercive field decreased from 52.94 kV/cm to 30 kV/cm, but the remnant polarization increased from 22.74 C/cm² to 50.75 C/cm², and the dielectric constant had a maximum value of 1269 at 2/55/45 composition. The optical transmittance was increased as La percentage increased but was decreased as the annealing temperature increased.     

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.     

The role of drying-control chemical additives on the preparation of sol-gel derived PLZT thin films

Films of Pb _x/100La _x/100(Zr _y/100Ti _z/100)_1–x/400O₃ with x=8, y=65 and z=35 (PLZT(8/65/35)) with a single perovskite structural phase were successfully prepared by using drying-control chemical additives in sol-gel processing followed by rapid thermal annealing at 600 °C for only 1 min on Si(Pt) substrates. The roles of the drying-control chemical additives ethylene glycol and formamide in the gel preparation were studied. The hysteresis loop of PLZT(8/65/35) thin film was measured. The remanent polarization and coercive field were found to be about 1.3 C cm^–2 and 15 kVcm^–1, respectively.     

Electrical properties of sol-gel processed PLZT thin films

Sol-gel processed lanthanum-modified lead zirconate titanate (PLZT) thin films consisting of two different perovskite phase contents were fabricated on indium tin oxide coated Corning 7059 glass substrates with two different heating schedules: direct insertion at 650° C for 30 min and at 500° C for 2h. Optical transmittance spectra, polarization versus electric field curves, relative dielectric constant versus frequency and capacitance versus d.c. bias voltage curves of the samples were investigated. The samples showed a good transparency of over 70% and interference oscillation. A thin film consisting of mainly perovskite phase showed a slim loop hysteresis in the polarization versus electric field curve and in the capacitance versus d.c. bias voltage curve, indicating the presence of ferroelectric domains, but a film consisting of mainly pyrochlore phase did not. The dielectric constant and loss factor of the thin film consisting of mainly perovskite phase were about 90 and about 0.2, respectively, at relatively low frequency and showed dispersion of the dipolar polarization of permanent dipole moment in the ferroelectric perovskite phase in the frequency range between 10 kHz and 1 MHz.     

Review Composite and multilayer ferroelectric thin films: processing, properties and applications

This paper reviews recent developments in processing, properties and applications of composite and multilayer ferroelectric thin films. Methods such as physical vapor deposition, chemical vapor deposition and sol-gel, for the processing of composite and multilayer ferroelectric films are described. Among the techniques reviewed for the fabrication of multilayer ferroelectric films, molecular beam epitaxy and atomic layer metal-organic chemical vapor deposition are the most suitable techniques for the deposition of superlattices with atomically sharp interface. As an efficient and quick way, pulsed-laser deposition has been widely used for the preparation of ferroelectric multilayers and heterostructures. Superior dielectric properties have been reported for sol-gel-derived micrometer-thick ceramic/ceramic composite ferroelectric films. Properties of multilayer ferroelectric films vary as a function of periodicity, which can be exploited for the development of various electronic devices. Enhanced characteristics of composite and multilayer films with selected examples from recent literature and the origin of enhancement are discussed and summarized. Finally, applications of the materials for the development of various electronic devices are also presented.     

ZnO薄膜的制备方法、性质和应用

介绍了宽禁带半导体ZnO薄膜的制备工艺、主要性质和器件应用等几方面内容.ZnO薄膜的制备方法大致分为物理法和化学法.前者主要包括溅射、脉冲激光沉积和分子束外延等;后者则涵盖化学气相沉积、喷雾热解和溶胶-凝胶法等.从晶体结构、光学及电学等角度概述了ZnO薄膜的主要性质.与这些性质相联系的器件应用有太阳能电池、发光器件和紫外探测器等.对器件应用领域中存在的一些问题及其解决思路作了探讨.     

金属网格对制备TiO2薄膜及其光学特征的影响

使用直流磁控溅射装置,通过在溅射过程中加入不同的金属网格,300 ℃条件下在玻璃衬底上制备了不同晶粒尺寸的TiO2薄膜.利用X射线衍射谱(XRD)、场发射扫描电子显微镜(SEM)对薄膜的结构和表面形貌进行了分析,并使用紫外一可见分光光度计研究了TiO2薄膜的透射和吸收光谱.研究结果表明:金属网格在磁控溅射过程中能有效减小TiO2薄膜的晶粒尺寸,金属网格的网孔尺寸越小,晶粒尺寸越小,吸收边蓝移越明显.     

Strain on ferroelectric thin films

Strain engineering aims to take advantage of the stress field imposed by substrates on thin films. It requires an understanding of the consequences of stress fields on the physical properties of the deposited materials. This is achieved in ferroelectric thin films through the use of misfit-strain phase diagrams that show the stability regions for the possible phases. These encompass bulk phases as well as new ones exhibiting symmetries that are not present in the bulk. For the solid solution lead zirconate–lead titanate, Pb(Zr_1−x Ti _x )O₃, monoclinic phases found in the bulk morphotropic phase boundary region and associated to concentrations exhibiting the highest properties can be stabilized on a wider range of composition in thin films. In addition, phases of lower symmetry can be stabilized through the use of anisotropic biaxial stress fields, generated by orthorhombic substrates for example. Another crucial aspect of the influence of biaxial stress fields is the generation of domain structures. Theoretical tools as well as experimental verifications have provided much insight on the underlying physics. We, therefore, present here an overview of the influence of both iso- and anisotropic biaxial stress fields on the structures and properties of ferroelectric thin films exemplified on Pb(Zr_1−x Ti _x )O₃.     

Dielectric strength and reliability of ferroelectric PLZT films deposited on nickel substrates

We have deposited ferroelectric (FE) Pb_0.92La_0.08Zr_0.52Ti_0.48O₃ (PLZT) films on nickel substrates by chemical solution deposition. Energy density of ≈ 46 J/cm³ has been measured with 1.15-µm-thick PLZT/LNO/Ni film-on-foil capacitors. A series of highly accelerated lifetime tests were performed to determine the reliability of these FE film-on-foil capacitors under high temperature and high field stress. Samples were exposed to temperatures ranging from 100 to 150 °C and electric fields ranging from 8.7 × 10⁵ V/cm to 1.3 × 10⁶ V/cm. The breakdown behavior of the FE PLZT film-on-foil capacitors was evaluated by Weibull analysis. The activation energy was determined to be ≈ 0.35 eV when an electric field of 1.05 × 10⁶ V/cm was applied. The voltage acceleration factor was ≈ − 6.3 at 100 °C. The mean time to failure was projected to be > 3000 h at 100 °C with a dc electric field of ≈ 2.6 × 10⁵ V/cm.     

Europium incorporated barium titanate thin films for optical applications

BaTiO₃:Eu (BT:Eu) thin films were deposited onto quartz substrates by RF magnetron sputtering. The effect on structural, morphological, optical and photoluminescence (PL) properties in the films with different Eu concentrations (0–5 wt%) were investigated. The X-ray diffraction (XRD) pattern of the undoped BT thin film revealed a tetragonal (T) phase with orientations along (101) plane. From XRD pattern, the crystallinity of the films increased with increase in Eu concentration. The SEM images revealed that the films exhibited tetragonal shape, crack free and good adherence to the substrate. Atomic force microscopy studies showed an increase of grain growth with doping concentration. The rms roughness value increased with increase in Eu concentration and the film surface revealed positive skewness and high value of kurtosis which make them suitable for tribological applications. X-ray photoelectron spectroscopy revealed the presence of barium, titanium, europium and oxygen in BT:Eu film. An average transmittance of >80 % (in visible region) was observed for all the films. Optical band gap of Eu doped BT films decreased from 3.86 to 3.53 eV. Such films with optical properties such as high transparency, decrease in band gap and high refractive index are suitable for optoelectronic applications. PL properties showed a sharp line at 625 nm and a broad line at 552 nm due to europium (Eu³⁺) transitions. PL phenomena were observed, owing to the electronic structure of Eu³⁺ ions as well as BT nanocrystallites in the films. The sharp and intense red luminescence is useful for photoelectric devices and optical communications.     

Fabrication and dielectric property of ferroelectric PLZT films grown on metal foils

We have grown ferroelectric Pb_0.92La_0.08Zr_0.52Ti_0.48O₃ (PLZT) films on platinized silicon and LaNiO₃-buffered nickel substrates by chemical solution deposition using a sol-gel process based on acetic acid chemistry. The following measurements were obtained under zero-bias field: relative permittivity of ≈960 and dielectric loss of ≈0.04 on the PLZT film grown on Pt/Si substrates, and relative permittivity of ≈820 and dielectric loss of ≈0.06 on the PLZT film grown on LNO-buffered Ni substrates. In addition, a relative permittivity of 125 and dielectric loss of 0.02 were measured at room temperature under a high bias field of 1 × 10⁶ V/cm on PLZT deposited on LNO-buffered nickel substrate. Furthermore, a steady-state leakage current density of ≈8.1 × 10⁻⁹ A/cm² and mean breakdown field strength of 1.7 × 10⁶ V/cm were measured at room temperature. Finally, remanent polarization (P_r) of ≈2.0 × 10⁻⁵ C/cm², coercive electric field (E_c) of ≈3.4 × 10⁴ V/cm, and energy density of ≈45 J/cm³ were determined from room-temperature hysteresis loop measurements on PLZT/LNO/Ni film-on-foil capacitors with 250-μm-diameter platinum top electrodes.     

Semiconducting transparent thin films: their properties and applications

The present state of the art of transparent, electrically conducting films, with special reference to In₂O₃, SnO₂ and Cd₂SnO₄, has been reviewed. Various production techniques currently in use, and typical parameters used in the processes have been discussed in detail. Electrical and optical properties of these films have been reported as a function of various parameters, e.g. substrate temperature, doping, oxygen pressure, etc. Finally, the applications of these films in research and industry have been discussed in detail.     

Preparation and characterization of PLZT thin films by sol-gel processing

The effect of acid catalysts on the sol-gel preparation of ferroelectric lead lanthanum zirconium titanate (PLZT) thin films was studied. High quality thin films were successfully produced by using suitable amounts of the drying control chemical additive formamide and also catalyst acids during the sol-gel processing followed by various annealing conditions. The dielectric constants of the PLZT (8/65/35) thin films produced in this study varied between 540 (100 kHz) for a film annealed at 600 °C for 30 mins to a maximum 870 °C (1 kHz), 700 (100 kHz) for a film annealed at 650 °C for 20 mins.