Liquid Crystal Polymer Film Research Articles

Multilayer Organic Multichip Module Implementing Hybrid Microelectromechanical Systems

We present the design and development of an organic package that is compatible with fully released RF microelectromechanical systems (MEMS). The multilayer organic package consists of a liquid-crystal polymer film to provide near hermetic cavities for MEMS. The stack is further built up using organic thin-film polyimide. To demonstrate the organic package, we have designed and implemented a 2-bit true-time delay X-band phase shifter using commercially available microelectromechanical switches. The packaged phase shifter has a measured insertion loss of 2.45 plusmn 0.12 dB/bit at 10 GHz. The worst case phase variation of the phase shifter at 10 GHz is measured to less than 5deg. We have also conducted temperature cycling (-65degC to 150degC) and 85/85 to qualify the packaging structures.

A DISTRIBUTED COMPUTING APPROACH TO THE SIMULATION OF LIQUID CRYSTAL LATTICE MODELS

We have studied a lattice spin model of nematic liquid crystal-polymer composite films by means of extensive Monte Carlo simulations over a distributed computing network. The Condor processing system installed on the Italian Nuclear Physics Institute computer network was used. The use of several geometries and boundary conditions allowed us to investigate a wide number of different realistic or speculative models. Many of the simulations differ only by a small number of parameters and they can be effectively performed in parallel. The results of the simulations can be analyzed globally when all the computations are completed and then for example, employed to extrapolate phase diagrams or other complex physical quantities. They provide an effective example of wide area distributed computing applications which could be also implemented in future GRID approaches.

P‐118: Alignment and Optical Properties of Retarder Film Made of Photoreactive Calamitic Liquid Crystals

AbstractHow the alignment and optical properties of liquid crystal polymer (LCP) film, formed by photo‐polymerization of reactive LCs, are affected by the alignment layer (AL) structure, the LC‐aligning method, and the polymerization conditions has been investigated. It has turned out that the alignment characteristics of LCP film greatly depend on the nature of AL and the polymerization condition and that its optical properties are governed by the degree of the in‐plane alignment of LC molecules. In the case of in‐air photo‐polymerization, a higher intensity of UV irradiation at a fixed exposure dosage has induced the higher degree of polymerization of LCP film and thus the better thermal stability than a lower intensity. The rubbed AL has induced the higher degree of the in‐plane alignment, with the tilted optic axis, and subsequently produced the better optical properties. On the other hand, photoalignment has generated the inferior LC alignment, with no tilt of the optic axis, indicating its low capability for aligning LC molecules.

Twisted phase gratings induced by photoregulated mesogenic molecules on the surface of photoreactive polymer liquid crystal film

Three-dimensional phase gratings with twisted structures were self-organized by photoregulated mesogenic molecules on the surface of photocrosslinkable polymer liquid crystal film. The molecules are selectively photoreacted only at the surface of the film under the polarization holographic illumination, and the resultant photocrosslinked mesogenic molecules induce the three-dimensional twisted gratings in the film during annealing process. The diffraction properties were well explained by means of Jones calculus and diffraction theory.

Measurement of Degree of Order in Mixed Polarised Fluorescent Polymer Liquid Crystal Films

Abstract Raman spectroscopy is used to investigate the degree of order found in in-situ photopoly-merised films exhibiting polarised emission. Studies indicate that the mixed system shows different degrees of order for its two molecular components. The degree of order was measured in the mesophase for the mixed monomers prior to polymerisation and was found to be in close agreement with the order of the two components measured in equivalent cured films. These studies have therefore provided an insight into the nature of molecular ordering in these mixed systems and shows that the in-situ photopolymerisation process does not greatly change the ordering in the system.

A Glassy Bending‐Mode Polymeric Actuator Which Deforms in Response to Solvent Polarity

AbstractSummary: We investigate a series of glassy polymer actuators which are found to bend rapidly and reversibly in response to changes in the solvent environment. The actuators are based on hydrogen‐bonded liquid crystal networks, and bending motion is created using director profiles engineered to take advantage of the network swelling anisotropy. Strongly polar solvents easily swell the network, forcing bending in one direction, while the less polar solvents extract water to force bending in the opposite direction.Shape variation of twisted configuration liquid crystal polymer films in acetone and water.magnified imageShape variation of twisted configuration liquid crystal polymer films in acetone and water.

Switching of Electrically Commanded Alignment Layers Probed by Optical Second Harmonic Generation

Optical second harmonic generation (SHG) was used to probe the response of a 200 nm thick electrically commanded alignment layer made of ferroelectric liquid crystal polymer (FLCP) film to an external DC electric field. The results show that for the field magnitudes in the range 0–2 V/μm the field induced reorientation effects represent only a relatively minor structural perturbation of the film. The switching process is monostable and shows characteristics of the “V-shaped” switching. The response time of the SHG signal is relatively longer than what is measured for the bulk FLCP. Several mechanisms are considered as possible reasons for that.

A polymer-based Chronic Nerve Interface Microelectrode Array

ABSTRACTThis paper will present ongoing work in the development of a thin, flexible, photolithographically-defined polymer-based electrode array based on Liquid Crystal Polymer (LCP) films and substrates. The goal of the effort is to develop and qualify a new platform technology that would allow accurate positioning of large numbers of electrode contacts in neural tissue for chronic applications. LCP films are a far greater match to the density of neural tissue than the competing wire and silicon arrays and thus will match the bending and flexing as the neural tissues change dimension. This flexibility would cause less neural damage and will maintain a more constant relationship with local neurons. Technology development activities include thin film metallization, interconnect insulation and device microfabrication.

Enhanced Cu/LCP adhesion by pre-sputter cleaning prior to Cu deposition

Liquid crystal polymer (LCP) and Cu thin film cleaned with radio frequency (RF) plasma in a vacuum pressure of 3.0/spl times/10/sup -3/ Pa followed by Cu deposition on LCP were bonded at room temperature. Immediately after bonding, the samples were unloaded, heated in air, argon, nitrogen, hydrogen, and oxygen gases, and subjected to peel strength measurements before and after heating to investigate the adhesion enhancement and the bonding mechanism of Cu/LCP. The interfacial adhesion was evaluated in terms of peel strength (180/spl deg/) measured by a peel tester (AGS-1 kNG, Shimadzu Corporation). The adhesion strength after the heat treatment depended on the heating environment and increased in the order of oxygen, air, nitrogen, and argon gas environments, respectively, but significantly declined in further heating in O/sub 2/ gas, approximating the level prior to heating. Visual and optical inspections on the delaminated samples showed bulk fractures or partial bulk fractures in LCP heated in all gas environments except in O/sub 2/ and its sequential treatments. X-ray photoelectron spectroscopy (XPS) analyses showed a carbon-rich LCP surface with a reduced amount of oxygen after sputter cleaning with RF plasma, which favorably reacted with the deposited Cu. Heating of bonded samples in various environments might enhance or suppress the interfacial reaction resulting in strong adhesion or poor adhesion depending on the heating environments. Depth profile on peeled LCP sample (which was heated first in Ar and then in oxygen prior to delamination) revealed thicker Cu oxide layers on delaminated LCP than natural Cu oxide layers. The new oxidized Cu layers produced across the interface were likely a result of the reaction of diffused oxygen in LCP with deposited Cu layers.

Fabrication of Liquid Crystal Polymer Films and Their Passivation Effect for Organic Devices

We have investigated the fabrication of liquid crystal polymer (LCP) thin films by thermal evaporation, and pulsed laser deposition (PLD). Due to the carbonization of LCP, no films were fabricated by thermal evaporation. The laser desorption time-of-flight mass spectra of a LCP target exhibited that the main ablation species were the fragments of the LCP in the case of low laser fluence, indicating the possibility of film fabrication by PLD. Thin films fabricated by PLD using a KrF excimer laser have a pale yellow color and a surface roughness of 1 nm, as measured by atomic force microscopy. The spectra obtained by Fourier transform infrared spectroscopy exhibit a peak corresponding to carbonyl bond at approximately 1730 cm-1, indicating a polyester structure similar to that of the original LCP. The breakdown field of the films was 1 MV/cm. We demonstrate that this film acts as a passivation films for organic field-effect transistors.

New fabrication method for anisotropic gratings formed in photocrosslinkable polymer liquid crystals

We present a new fabrication method, called ‘two-step ultraviolet exposure’, to prepare anisotropic gratings in photocrosslinkable polymer liquid crystal films. Using the controllability of the reorientation direction of mesogenic molecules, anisotropic phase gratings, in which the mesogenic molecules were periodically modulated in orthogonal directions, were prepared by the use of one grating photomask. The resultant gratings diffract the light and convert the polarization states at the same time, and have applications as diffraction optical devices.

Influence of substituents on the reorientational behavior in photocrosslinkable polymer liquid crystal films with p-substituted cinnamoyloxybiphenyl side groups by irradiating with linearly polarized ultraviolet light and annealing

This paper describes the synthesis and influence of the substituent on the reorientation behavior of photocrosslinkable methacrylate polymer liquid crystals (PPLCs), which contain p-substituted cinnamoyloxybiphenyl (CB) side groups. Irradiating with linearly polarized ultraviolet (LPUV) light induced optical anisotropy of all PPLC films due to an axis-selective photoreaction of the mesogenic groups. The thermally enhanced reorientation direction depended on the substituent groups and liquid crystalline nature of the PPLC. A high in-plane reorientational order ( S>0.6) parallel to the polarization of LPUV light was obtained for PPLCs with p-methoxy-CB and p-methyl-CB side groups, while out-of-plane reorientation was predominant for p-fluoro-CB and p-trifluoromethyl-CB side groups.

液晶ポリマーフィルム上への無電解銅めっき

It is well known that liquid crystal polymer (LCP) films exhibit excellent mechanical and physical characteristics compared with those of other polymers. In order to apply LCP films on printed circuit boards, the etching conditions required for LCP film to obtain a good anchor effect for electroless copper plating was studied. After etching the LCP film in a 10M KOH solution at 70 degrees for 60-90 minutes, we obtained a copper film with excellent adhesion strength using a plating bath having slow plating speed or using sodium phosphinate as a reducing agent.

FLEXIBLE LASERS MADE FROM CHOLESTERIC LIQUID CRYSTAL POLYMERS

Optically pumped mirrorless laser action has been observed in a dye-doped photopolymerized cholesteric liquid crystal (PCLC) polymer film. At high excitation energy above the threshold, the laser action is observed at an edge of the one-dimensional photonic band of the PCLC herical structure. This PCLC film possesses a mechanical flexibility, and laser action is observed even in a bent film. The helical pitch of the PCLC polymer has no temperature dependence, which is favorable for the laser device application.

Formation of pure polarization gratings in 4-methoxyazobenzene containing polymer films using off-resonant laser light

Polarization holographic recordings in polymer liquid-crystal films with azobenzene side groups were investigated using two orthogonal linearly polarized 633 nm He-Ne laser beams and subsequent annealing. Although the electric transitions of the polymer material were almost off-resonant, stable pure polarization gratings were created with a first-order diffraction efficiency greater than 30%.

Neural signal recording using microelectrode arrays fabricated on liquid crystal polymer material

Microelectrode arrays have been developed for simultaneous multi-channel recordings from nervous systems, typically using silicon substrates. However, it has been known that it is difficult to meet the biocompatibility and durability requirements using silicon and other dielectric materials (SiO 2, Si 3N 4), due to environmental moisture and ions. Additional disadvantage of silicon being the rigid material makes it hard to apply these materials in chronic recording situations. Liquid Crystal Polymer (LCP) was recently introduced as a candidate material for electronic packaging purposes. The material acts as efficient barrier against ions and moisture, a desirable feature for a substrate material of microelectrode arrays. In this paper, we report on the neural recording performed using the LCP-based microelectrode arrays. The cell adhesion on the new material was compared very favorably with that using silicon, SiO 2, or polyimide material. The microelectrode arrays were patterned with Ti (500 Å)/Au (3500 Å) on the LCP film and were employed in both stimulation and recording from rat sciatic nerve. The electrical characteristic of the recorded signal was as good as those using other substrate materials, proving this material as an excellent candidate for next generation microelectrode arrays.

ミリ波帯パッケージへの液晶ポリマーの適用

The high frequency characteristics of liquid crystal polymer (LCP) have been investigated using a microstrip line (MSL) on a silicon (Si) substrate to verify the possibility of the application of the material in millimeter-wave packaging. A LCP film was fabricated using a direct-bonding technique on Si substrate. Measured characteristics of insertion loss are compared between a LCP film and a SiO2 film. The loss of the LCP-MSL is approximately 1/2 of that of the SiO2-MSL. Moreover, a GaAs low noise amplifier (LNA) microwave monolithic integrated circuit (MMIC) was fabricated using a flipchip bonding technique on a LCP substrate to demonstrate an application for a millimeter-wave package. The measured output gain of the LNA package is over 11dB. The millimeter-wave LCP package is a promising technology in realizing low cost millimeter-wave radio equipment.

HOLOGRAPHIC IMAGE STORAGE IN POLYMER AZOBENZENE LIQUID CRYSTALS

Unique characteristics were observed in phase-type gratings which were formed in polymer liquid crystal (PLC) films. We have investigated the formation and the properties of the holographic gratings recorded in PLCs with azobenzene moieties (photoresponsive unit). Two types of PLCs were examined: homopolymers of azobenzene monomers (PALC) and copolymers with a tolane moiety (mesogenic unit with a high birefringence) in the side chain. The diffraction efficiency (η) was enhanced in the LC phase. We obtained the value of η of 31% while it was less than 1% in a glassy state in the Raman-Nath regime. This difference may be due to the modulation of refractive index (Δn) based on alignment change of mesogens in the PLC film. In addition, we attempted the holographic image storage of three-dimensional (3-D) objects in the PLC film. The 3-D object was reconstructed with high resolution (>5,000 lines/mm).

Reversion of Alignment Direction in the Thermally Enhanced Photoorientation of Photo-Cross-Linkable Polymer Liquid Crystal Films

Reversion of the in-plane reorientation direction of mesogenic groups has been observed for the first time in novel polymethacrylate liquid crystal (PLC) films substituted with a 4-methoxycinnamoyloxybiphenyl side group. The reversion was generated by irradiation with linearly polarized ultraviolet (LPUV) light and a subsequent annealing. Irradiation with LPUV light induces negative optical anisotropy of the films as a result of an axis-selective photoreaction of the side groups. The direction of the thermally enhanced reorientation is dependent on the degree of photoreaction and the distribution of photoproducts, while the induced orientational order in both directions, S, was larger than 0.5. The distribution of photoproducts in PLC films has been analyzed to elucidate their contribution to the thermally enhanced reorientation behavior. Initially upon photoreaction, thermal enhancement of the photoinduced negative optical anisotropy was observed. However, when the degree of photodimerization was 15% or greater, the direction of the thermally enhanced reorientation was found to be parallel to the polarization direction (E) of LPUV light. It is concluded that a small amount of photoproduct plays a role in the thermal amplification of the photoinduced negative optical anisotropy in a manner identical to that of PLC with azobenzene side groups. In contrast, photodimerized mesogenic groups generated reversion of the orientational direction and enhancement of positive optical anisotropy of the film through annealing.

Formation of intensity grating in a polymer liquid crystal with a side-chain azobenzene moiety by photoinduced alignment change of mesogens

We studied the behavior of photoinduced alignment change of a polymer liquid crystal (PLC) containing an azobenzene moiety in the side chain and formation of a grating by means of the photoinduced alignment of PLCs. The alignment change was evaluated by irradiation with s-polarized light at 488 nm. We investigated the effects of light intensity and incident angles of writing beams (two s-polarized (s + s) configuration) on grating formation in PLC films, and explored the relation between the alignment change and diffraction efficiency. The diffraction efficiency showed a maximum when the change in photoinduced alignment was almost complete in the bright area of interference patterns. The maximum value obtained for the modulation of the refractive index was 0.04. These results indicate that a PLC with an azobenzene moiety is effective under (s + s) polarization conditions, compared with other azopolymer systems.