添加剂对聚酰亚胺液晶垂直取向剂性能的影响

研究了添加剂对PI取向性能、耐摩擦性、热稳定性以及透光率的影响。用均苯四甲酸二酐(PM-DA),对苯二胺(PDA),4-已氧基联苯酚-3’,5’-二胺基苯甲酸酯(C6-BBDA),制备了三元共聚型PI取向膜,并采用添加剂(封端剂和交联剂)对PI改性。通过调节添加剂的组成制备了4种PI。利用红外光谱仪(FT-IR)、热失重分析仪(TGA)、紫外分光光度计(UV-Vis)、偏光显微镜(POM)和预倾角测试仪对合成的PI进行了结构表征和性能测试。研究发现LC分子在4种PI膜上都获得了均匀的垂直取向;添加交联剂的PI膜具有良好的耐摩擦性,经摩擦强度为600mm摩擦后,仍对LC分子具有垂直取向的能力;加入添加剂的PI膜具有良好的热稳定性,此外,加入添加剂的PI膜仍具有较高的透光率。     

High thermal stability of AlCrTaTiZr nitride film as diffusion barrier for copper metallization

To inhibit rapid Cu diffusion in interconnect structures, an effective diffusion barrier layer with high thermal stability, low electrical resistivity and good interface adhesion is strongly demanded. Thus in this study, an amorphous nitride film of equimolar AlCrTaTiZr alloy with an N content of about 41 at.% was deposited by reactive radio-frequency magnetron sputtering. Thermal stability of the AlCrTaTiZr nitride film and its barrier property to Cu diffusion were investigated under thermal annealing at 700-900 °C. The AlCrTaTiZr nitride film remained an amorphous structure after thermal annealing at 700 °C and then crystallized at 800 °C. However, no interdiffusion between Si substrate and Cu metallization through the AlCrTaTiZr nitride film occurred. The electrical resistivity of the film remained at the low level of as-deposited value, indicating its good thermal stability as an effective diffusion barrier layer. With temperature further increasing to 900 °C, severe interdiffusion occurred, along with the formation of silicides and large pores. The electrical resistivity then significantly increased, implying the failure of the AlCrTaTiZr nitride film.     

Photo-induced liquid crystal alignment of poly(vinyl cinnamate) and fluorinated polyimide blends

Liquid crystal(LC) alignment properties were mainly affected by surface properties of alignment layers. In our previous work, we prepared poly(vinyl cinnamate) (PVCi) and polyimide blend alignment layer for thermally stable LC alignment. In this work, we utilized fluorinated polyimide for blend alignment layers in order to modify surface properties of alignment layers. For this purpose, polyimides containing fluorine unit were synthesized and used for the blend alignment layers. Fluorine containing diamine, 4,4′-bis[2-(4-aminophenyl)hexafluoropropyl]-diphenyl ether(BDAF), is used for the polyimide synthesis. We prepared the fluorinated polyimide and PVCi blend alignment layers and investigated the effect of fluorine on the LC alignment properties and pretilt angle of LC.     

Van der Waals force contribution to the vertical alignment of liquid crystal on Al2O3 films using ion-beam method

This study demonstrates liquid crystal (LC) alignment on Al₂O₃ films using the ion-beam (IB) method as well as the optimization of the IB irradiation condition. Uniform LC alignment was achieved at an IB incident energy of 1800 eV with an IB incident angle of 45°, while inferior LC alignments were observed in other tested conditions. The pretilt angles and transmittances of the LC cell were also shown as part of the same trend for the LC alignment states. This result was subject to van der Waals forces which were caused by topographical changes during the IB process.     

Use of polydimethylsiloxane thin film as vertical liquid crystal alignment layer

The possibility of the use of polydimethylsiloxane to align liquid crystals is studied. The polydimethylsiloxane thin films coated on glass substrates exhibit a very low surface free energy, and are found to be capable of vertical liquid crystal alignment. Comparing to thin films made using a typical polyimide polydimethylsiloxane films possess a more stable surface energetic state. The pretilt angle of the calamitic liquid crystal molecules sandwiched between the silicon elastomer thin films was virtually 90°, and the molecular tilt can be maintained in a wide temperature range. Liquid crystal sandwiched between the silicon-based polymer thin films can operate in the in-plane-switching mode.     

Homogeneously aligned liquid crystal display on silicon oxynitride thin film using ion beam bombardment

This paper introduces the homogeneously aligned liquid crystal (LC) display using ion beam (IB) bombardment of a new silicon oxynitride (SiON) alignment layer for the first time. The pretilt angle was shown to be a function of the IB incident energy, and possible mechanisms of LC alignment were investigated with physical and chemical methods. An X-ray photoelectron spectroscopy analysis showed that the LC alignment on the IB-bombarded SiON inorganic surface was due to the reformation of Si–O bonds as a major factor. The electro-optical characteristics were comparable to those of rubbed polyimide films.     

Effects of backbone conformation and surface texture of polyimide alignment film on the pretilt angle of liquid crystals

Polyimides (PIs) with different inclination angle of polymer backbones, together with polar hydroxyl group and/or nonpolar trifluoromethyl group at various sites of the backbone were synthesized and used as liquid crystal alignment layers. The molecular conformation, surface chemistry, surface energy, surface morphology, and pretilt angle of the PI film were investigated. The distributions of fluorinated group and hydroxyl group at different depths of the PI surfaces were analyzed by X-ray photoelectron spectroscopy. Effects of the conformation of the PI molecular backbone on the surface morphology of the rubbed PI layer, the pretilt angle and surface energy of the alignment film were studied. The PI which contains both nonpolar fluorinated groups sticking out of the surface and the polar hydroxyl groups on the surface exhibits high pretilt angle.     

Orientational control of liquid crystal molecules by reformed poly(dimethylsiloxane) alignment layer via ion-beam irradiation

We introduce an alternative approach to making a reformed PDMS layer as a pretilt controllable alignment layer, which can be used in the vertical alignment (VA) and twisted nematic (TN) modes, by varying the ion beam (IB) energy. Depending on different the dielectric anisotropy of surfaces, PDMS layers have been demonstrated to align LC molecules homogeneously and homeotropically. The electro-optic characteristics of aligned VA and TN-LCD based on PDMS layer were comparable to those of VA and TN-LCD based on polyimide, showing good potential of PDMS film as an alignment layer.     

Surface alignment of liquid crystal multilayers evaporated on photoaligned polyimide film observed by surface profiler

The investigation of the surface alignment of liquid crystal (LC) multilayers evaporated on photoaligned polyimide vertical alignment (PI-VA) film was carried out by means of the novel three-dimensional (3D) surface profiler. We report the first use of the surface profiler to visualize a microscopic image of the monolayer arrangement of LC molecules in contact with the surface of photo-treated PI-VA film. The photoinduced anisotropy of partially UV-exposed PI-VA film can be visualized as a topological image of LC multilayers. It seems that the topology of LC multilayers is indicating the orientational distribution of LC molecules on the treated film. It was found that the periodically photoaligned PI-VA film surface can align an adsorbed LC monolayer and the LC molecular alignment can be extended to the bulk via the epitaxylike LC–LC interaction, i.e. a short-range molecular interaction. With regard to the unexposed PI-VA film surface, noticeable anisotropy in the monolayer alignment was not observed, indicating that the long-range elastic interaction may be responsible for the bulk alignment. The appearance of small droplets in the masked region may be presumably related to the dewetting phenomena.     

Properties of indium tin oxide films deposited using High Target Utilisation Sputtering

Indium tin oxide (ITO) films were deposited on soda lime glass and polyimide substrates using an innovative process known as High Target Utilisation Sputtering (HiTUS). The influence of the oxygen flow rate, substrate temperature and sputtering pressure, on the electrical, optical and thermal stability properties of the films was investigated. High substrate temperature, medium oxygen flow rate and moderate pressure gave the best compromise of low resistivity and high transmittance. The lowest resistivity was 1.6 × 10^− 4 Ω cm on glass while that on the polyimide was 1.9 × 10^− 4 Ω cm. Substrate temperatures above 100 °C were required to obtain visible light transmittance exceeding 85% for ITO films on glass. The thermal stability of the films was mainly influenced by the oxygen flow rate and thus the initial degree of oxidation. The film resistivity was either unaffected or reduced after heating in vacuum but generally increased for oxygen deficient films when heated in air. The greatest increase in transmittance of oxygen deficient films occurred for heat treatment in air while that of the highly oxidised films was largely unaffected by heating in both media. This study has demonstrated the potential of HiTUS as a favourable deposition method for high quality ITO suitable for use in thin film solar cells.     

单胺添加剂对聚酰亚胺取向材料性能的影响

通过引入单胺添加剂，合成了三类、八种聚酰亚胺取向材料，采用热重分析对它们的热稳定性进行了研究。结果表明，单胺的加入使聚合物的分子量降低，粘度和热稳定性下降。对于不含强极性基团的聚酰亚胺取向材料，适当地加入单胺可增大预倾角；对于含有强极性基团的聚酰亚胺取向材料，单胺的加入对预倾角的影响很小。     

液晶种类及工艺条件对预倾角的影响

用均苯四羧酸二酐(PMDA),1,2,3,4-环丁烷四羧酸二酐(CBDA)和4((4-氨基苯基)-二(4-甲氧基苯基)甲基)苯胺共聚制备聚酰亚胺,并用做液晶取向膜。采用正交偏光显微镜和预倾角测试仪分别表征了液晶的取向效果及其预倾角;考察了液晶种类、二胺与二酐比例、摩擦深度、摩擦次数等工艺条件对预倾角的影响。结果表明,不同的液晶对预倾角有较大影响,普通液晶E7获得的预倾角只有3.5°左右,而ZLI-2293可获得4°以上稳定的预倾角,且液晶取向均匀良好。同时,得到了最佳的二胺与二酐配比、摩擦深度和摩擦次数。     

Photo-induced alignment behavior of azobenzene compound in thin film

Photo-induced molecular alignment behavior of spin-coated poly(4,4′-azobenzene pyromellitamic acid) (PAA(azo)) film was investigated by Fourier transform infrared spectroscopy measurement, atomic force microscope and transmission electron microscope observation. As-spun PAA(azo) flm was found to be smooth and uniform with an amorphous structure. Upon irradiation of linearly polarized ultraviolet light, the molecular ordering and crystallization were induced, and the film surface was roughened slightly. The PAA(azo) film converted to poly(4,4′-azobenzene pyromellitimide) (PI(azo)) film with higher ordering and crystallinity by subsequent thermal treatment. The PI(azo) film was useful as an active layer to introduce the molecular alignment of copper phthalocyanine (CuPc).     

Improved liquid crystal pretilt angles by patterned dual alignment coating structures

The pretilt angles for the optically compensated bend (OCB) mode liquid crystals have been improved using novel patterned dual alignment coating structures in this study. The transition from the splay configuration to the bend configuration can thus be effectively reduced. The dual alignment coating structures consisted of a horizontal alignment polyimide (PI) and a patterned vertical alignment liquid crystal polymer (LCP). Three patterning masks were designed for the photolithography process. The pretilt angles were demonstrated to be increased to 34 degrees for the triangle lattice array-patterned cells. It became 31 degrees for the square lattice array-patterned cells, and 24 degrees for the honeycomb lattice array-patterned cells. The improved pretilt angles were illustrated by the force balance model that can be predicted by the LCP area ratio. The effective control over the pretilt angle could improve the response time to 2 ms when the voltage was ramped up to 5.5 V for the OCB mode liquid crystal devices.     

High-temperature-dependent optical properties of ZnO film on sapphire substrate

In order to fabricate fiber-optic temperature sensors based on ZnO film, it is important to study the temperature-dependent optical properties of this material. In this work, we deposited ZnO films on c-plane (0001) sapphire substrate at 250 °C. Atomic force microscope and X-ray diffraction measurements show the smooth surface and high orientation along [0001] of ZnO film, respectively. The high-temperature-dependent optical properties of ZnO film were measured by ultraviolet-visible transmission with temperatures ranging from room-temperature to 300 °C and analyzed by theoretically fitting the optical absorption edge curve. It is observed that the band gap energy red shifts nonlinearly from 3.345 to 3.153 eV with increasing temperature. The sharp absorption edge of ZnO films after annealing at 300 °C is almost consistent with that of the as-deposited sample, indicating an excellent thermal stability and the potential application in fiber-optic temperature sensors.     

Improvement of white organic light emitting diode performances by an annealing process

White organic light emitting diode (OLED) devices with the structure ITO/PHF:rubrene/Al, in which PHF (poly(9,9-di-n-hexylfluorenyl-2,7-diyl)) is used as blue light emitting host and rubrene (5,6,11,12-tetraphenylnapthacene) as an orange dye dopant, have been fabricated. Indium tin oxide (ITO) coated-glass and aluminium were used as anode and cathode, respectively. The devices were fabricated with various rubrene-dopant to obtain a white light emission. The OLED device that composed of several concentrations of rubrene-doped PHF film was prepared in this study. It was found that the concentration of rubrene in the PHF-rubrene thin film matrix plays a key role in producing the white color emission. In a typical result, the device composed of 0.06 wt.% rubrene-dopant produced the white light emission with the Commission Internationale de L'Eclairage (CIE) coordinate of (0.30,0.33). The turn-on voltage and the brightness were found to be as low as 14.0 V and as high as 6540 cd/m², respectively. The annealing technique at relatively low temperature (50 °C, 100 °C, and 150 °C) was then used to optimize the performance of the device. In a typical result, the turn-on voltage of the device could be successfully reduced and the brightness could be increased using the annealing technique. At an optimum condition, for example, annealed at 150 °C, the turn-on voltage as low as 8.0 V and the brightness as high as 9040 cd/m² were obtained. The mechanism for the improvement of the device performance upon annealing will be discussed.     

Magnetic silica:epoxy composites with a nano- and micro-scale control

Multiscale composites with magnetic properties were prepared by incorporating Cu–Ni nanoferrites filled silica microparticles in an epoxy matrix. The size of the nanoferrites was controlled both by the structure of the silica template and the annealing temperature (700 and 900 °C) used during the synthesis procedure. The ferrite:silica particles prepared at 700 °C showed a narrow size distribution close to 8.3 nm with a superparamagnetic behaviour. A less symmetric size distribution was obtained when annealing was performed at 900 °C, with diameters ranging from 15 to 80 nm. The reinforcement incorporation increased up to 7 °C the glass transition temperature and 30 °C the decomposition temperatures of the composites. The proposed strategy permits the nanoscale control, by the trapping effect of the silica on the magnetic nanoparticles, as well as the control of the micro-scale distribution through a simple protocol. These composites could have potential applicability as EMI shielding materials, owing to their magnetic nature, lightweight and enhanced thermal stability.     

Effect of substrate temperature on the thermal stability of Cu/Zr-N/Si contact system

The effect of substrate temperature on the thermal stability of Cu/Zr-N/Si contact systems was investigated. Zr-N films were deposited on the Si substrates by RF reactive magnetron sputtering under various substrate temperatures. Cu films were in-situ sputtered onto the Zr-N films subsequently. The contact systems were characterized using four-point probe sheet resistance measurements (Rs), X-ray diffraction (XRD), and scanning electron microscopy (SEM) respectively. It was found that the sheet resistances of Cu/Zr-N (350 °C)/Si contact system were lower than those of Cu/Zr-N (150 °C)/Si specimens after annealing at 650 °C. Cu/Zr-N (350 °C)/Si contact systems showed better thermal stability so that the Cu₃Si phase could not be detected. It is indicated from the comparison analysis results that the Zr-N film showed better diffusion barrier performance deposited under higher substrate temperature.     

Enhancement of 1.5 μm emission in erbium-doped spin-on glass by furnace annealing

Characteristics of light emission from mixture of spin-on glass and erbium oxide nanoparticles were investigated. Such erbium-doped silica thin films after furnace annealing have exhibited a strong room temperature photoluminescence (PL) at ∼ 1.53 μm. The PL intensity of the erbium-doped thin film after annealing at 1000 °C was 30 times higher than those after low-temperature annealing. The chemical environment of the erbium ion in the thin film after annealing has been studied by Time-of-Flight Secondary Ion Mass Spectrometry (SIMS). The SIMS result confirmed that Er-O-Si complex was favored and OH group was eliminated in the erbium-doped silica film sample after annealing. Hence we accounted for the PL enhancement of erbium-doped silica by furnace annealing.     

Thermal stability of magnetron sputtering amorphous carbon nitride films

Magnetron sputtered amorphous carbon nitride films were annealed at different temperatures (450-900°C) and time (30-120 min). Compositional, bonding structural and surface morphological modifications of the films were characterized by Fourier transformation infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) and atomic force microscopy. The as-deposited film was found to have nitrogen content of 30 at%, and the carbon atoms were bonded to nitrogen atoms in the chemical structure state of CN, CN and CN bonds. The FTIR and XPS results showed that the films were thermally stable without an obvious change in the films as annealing temperature was lower than 600°C. The relative intensity ratio of CN over CN bonds reached a maximum at annealing temperature of 750°C, and then decreased gradually at annealing temperature up to 900°C. The CN bonds in the films decreased with the increase of annealing temperature and eliminated completely at annealing temperature of 900°C. These results revealed that annealing caused a substantial decrease in the number of weak bonds between carbon and nitride atoms. The CN bonds have higher thermal stability than CN bonds and CN bonds in the films. Simultaneously annealing also led to the formation of a large fraction graphitic-like carbon in the films while nitrogen escaped from the film. Besides, the surface roughness of the films increased with annealing temperature. However, when annealing time was increased from 30 to 120 min at annealing temperature of 750°C, only a slight effect of the annealing time on composition, bonding structure and the surface roughness of the films was observed.