Liquid Crystal Polymer Research Papers (original) (raw)

This paper describes an effort to develop a thin film packaging technology for microfabricated planar antennas on polymeric substrates based on silicon carbide (SiC) films deposited by physical vapor deposition (PVD). The antennas are coplanar waveguide fed dual frequency folded slot antennas fabricated on liquid crystal polymer (LCP) substrates. The PVD SiC thin films were deposited directly onto the antennas by RF sputtering at room temperature at a chamber pressure of 30 mTorr and a power level of 300 W. The SiC film thickness is 450 nm. The return loss and radiation patterns were measured before and after the SiC-coated antennas were submerged into perchloric acid for 1 hour. No degradation in RF performance or physical integrity of the antenna was observed.

- by and +1
- •
- Physical Vapor Deposition, Silicon Carbide, Thin Film, Room Temperature

In this study, we provide the experimental results of the binary blends of a semi-flexible nematic liquid crystal polymer (LCP1) and polycarbonate (PC) within their phase diagram. The LCP1/PC blends were investigated by Differential Scanning Calorimetry (DSC), Optical Microscopy (OM), Wide-angle X-Ray Diffraction (WXRD), Fourier Transfer Infrared (FTIR), Gel Permeation Chromatography (GPC), and Nuclear Magnetic Resonance (NMR) techniques and observed the evidence of chemical reaction between LCP1 and PC in their heat-treated blends possibly by transesterification mechanism.

- by Lifescience Global Canada and +1
- •
- Polycarbonate, Liquid Crystal Polymer, Binary Blends

Two CPW-fed compact elliptical monopole UWB antennas are introduced with band rejection characteristic at the band used for wireless LAN applications. The antennas are fabricated on ultra thin (100 µm) liquid crystal polymer (LCP) and the band notch is caused by the presence of a resonating slot within the elliptical radiator. The two investigated antennas have a U-shaped slot and a Cshaped slot respectively. From the presented return loss and VSWR measurements, the C-shaped slot causes a wider rejection band compared to the U-shaped slot that could be used for the design of UWB antennas with reconfigurable sub bands. Both designs present almost identical radiation pattern behavior with the design without any slot with the exemption of the gain in the frequency notch band, which is maintained negative.

- by Manos M Tentzeris
- •
- APMC, Wireless Lan, Ultra Wideband, Liquid Crystal Polymer
- by nicola scaramuzza
- •
- Liquid Crystals, UV light, Liquid Crystal Polymer, Liquid Crystalline

A reflective-type polymer-stabilized cholesteric liquid crystal (PSCLC) cell was demonstrated at ! ¼ 1550 nm laser wavelength. It showed a high attenuation range ($30 dB), a low operating voltage ($12 V rms), a highly efficient polarizationindependent behavior and flat wavelength dependence in the range of 1525-1575 nm. The combined effects of curing temperature, chiral dopant, and monomer concentration were investigated and optimized to maximally improve the PSCLC properties. The potential application of PSCLC as a polarization-independent variable optical attenuator is emphasized.

- by Kyongok Kang
- •
- Analytical Chemistry, Colorimetry, Liquid Crystals, Functional Materials

Composites were synthesized by ''in-situ'' polymerization of polyazomethine, a liquid crystal polymer (LCP), in presence of multi-walled carbon nanotubes (MWNTs) previously dispersed in one of the employed monomers. Fiber processing was carried out by extrusion from the composites containing 1 and 10 wt.% of MWNTs at the mesophase temperature. We have observed that the typical highly oriented internal fibrillar structure can be significantly disrupted by increasing the nanotube content in the composite fibers. Evidences of MWNT alignment were found in the studied LCP/MWNT composites. D

- by Ana Benito
- •
- Materials Science, Biomedical Engineering, Carbon Nanotube, In Situ Polymerization

This article describes several European cooperative research examples in the field of polymer composite materials. The projects, which were carried out in collaboration between industrial and academic partners, were all supported by the European Union. They deal, e.g., with (a) the manufacturing and crash testing of thermoplastic composite structures, (b) the production of thermoplastic composite preforms, and (c) the energy absorption behavior of aluminum foams, and other interesting subjects.

- by Michael Maier
- •
- Materials Science, European Union, Composite Material, Energy absorption

In this paper, blends of Nylon 6,6 with the liquid crystal polymer Vectra A950 are considered; speci®cally we focused our attention on Nylon 6,6 modi®cations by interchange reactions that can occur in the melt, as a function of mixing conditions and blend compositions. Two matrix samples have been used, characterised by a slightly different relative amount of amine and carboxylic end groups, being the latter predominant in both cases. The dried polymers Nylon 6,6/Vectra, combined in weight ratios between 95/5 and 50/50, were subjected to reactive blending with different methods (single-screw extruder, Brabender, pyrex reactor). Pure Nylon samples have been also investigated as reference materials. The soluble Nylon 6,6-rich fraction of each blend was separated from the insoluble Vectra-rich one and used for molecular and spectroscopic characterisations. Thermal and morphological analyses, as well as testing of tensile properties, were carried out on the blends. Evidences of the occurrence of interchange reactions are given and the most probable ones are suggested. q

- by Luciano Falqui
- •
- Engineering, Polymer, CHEMICAL SCIENCES, Tensile Properties

Microdisplays of the liquid crystals on silicon (LCOS) type have gone through a rapid evolution during the last decade. We present an overview of how vertically aligned nematic (VAN) LCOS have evolved from an attractive, but notoriously difficult and even infamous technology, to the mainstream microdisplay technology that it is today. At the same time, we highlight a number of remaining issues and concerns, and present some ideas of how to remedy them.

- by Herbert De Smet
- •
- Optics, Medical Imaging, Fiber Optics, Telecommunications

With the maturation of the information display field, liquid-crystal materials research is undergoing a modern-day renaissance. Devices and configurations based on liquid-crystal materials are being developed for spectroscopy, imaging and microscopy, leading to new techniques for optically probing biological systems. Biosensors fabricated with liquid-crystal materials can allow label-free observations of biological phenomena. Liquid-crystal polymers are starting to be used in biomimicking colourproducing structures, lenses and muscle-like actuators. New areas of application in the realms of biology and medicine are stimulating innovation in basic and applied research into these materials.

- by Scott Woltman
- •
- Materials Engineering, Materials Science, Microscopy, Liquid Crystals

Applications of thermally stimulated depolarisation current (TSDC) technique to a variety of systems with different dispersion phases such as disperse and porous metal oxides, polymers, liquid crystals, amorphous and crystalline solids, composites, solid solutions, biomacromolecules, cells, tissues, etc. in gaseous or liquid dispersion media are analysed. The effects of dipolar, direct current (dc) and space charge relaxations are linked to the temperature dependent mobility of molecules, their fragments, protons, anions, and electrons and depend on thermal treatment, temperature and field intensity of polarisation, heating rate on depolarisation or cooling rate on polarisation. Features of the relaxation mechanisms are affected not only by the mentioned factors but also by morphological, structural and chemical characteristics of materials. The interfacial phenomena, especially the role of interfacial water, received significant attention on analysis of the TSDC data. Comparison of the data of TSDC and dielectric relaxation spectroscopy (DRS), differential scanning calorimetry (DSC), 1 H NMR spectroscopy with layer-by-layer freezing-out of bulk and interfacial water, adsorption/desorption of nitrogen, water and dissolved organics demonstrates high sensitivity and information content of the TSDC technique, allowing a deeper understanding of interfacial phenomena.

- by Polycarpos Pissis
- •
- Engineering, NMR Spectroscopy, Differential scanning calorimetry, Cooling Rate

Liquid crystal micro-composites based on ferroelectric liquid crystal and a chiral photocrosslinkable liquid crystal polymer are studied. Their ferroelectric properties are closely connected to their polymerization process. The effect of the UV curing conditions on the ferroelectric behavior is discussed. Low UV intensity applied for a long time treatment leads to a polymer network that introduces little variations on the

- by Alain Boudet
- •
- Physics, Condensed Matter Physics, Ferroelectrics, Liquid Crystal

POLICRYPS (an acronym of polymer liquid crystal polymer slices) is a nano/microcomposite structure made of slices of almost pure polymer alternated with films of well aligned nematic liquid crystal (NLC). The structure is obtained by irradiating a homogeneous syrup of NLC, monomer and curing agent molecules with an interference pattern of UV/visible light under suitable experimental and geometrical conditions; the spatial periodicity can be easily varied from an almost nanometric (200 nm) to a micrometric (15 µm) scale. Where the effect on an impinging reading light beam is concerned, the POLICRYPS can be utilized either in a transmission or a reflection configuration (depending on the geometry and substrate used) with negligible scattering losses, while the effect of spatial modulation of the refractive index (from polymer to NLC values) can be switched on and off by applying an external electric field of the order of few V µm-1. In this paper, we start by reviewing the general features of the POLICRYPS structure, that is the 'recipe' to fabricate it, along with a chemical-diffusive model that indicates the right physical and chemical conditions to make samples exhibiting good morphological, optical and electro-optical properties. We then show some possible utilizations of POLICRYPS with a light beam impinging almost perpendicularly to the structure: a switchable diffraction grating and a switchable optical phase modulator. Furthermore, we put into evidence that POLICRYPS channels can become an array of mirrorless optical micro-resonators for lasing effects. Finally, we report about utilization of POLICRYPS with a light beam impinging parallel to the structure and perpendicular to the channels, demonstrating that, in this case, the structure becomes a tuneable Bragg filter. Performances exhibited in all above applications put the POLICRYPS structure at the top level of the state of art of application oriented research in optics of liquid crystalline composite materials.

- by Giuseppe Strangi and +1
- •
- Refractive Index, Composite Material, Optical physics, Microstructures

We present the observation of an all-optical switching effect that takes place when a light beam of suitable wavelength irradiates a "layered" structure made of polymer slices alternated to films of well aligned liquid crystal ͑LC͒ which contain also a small percentage of azo-LC molecules. The simple and reliable fabrication procedure exploits a holographic UV curing technique. The observed switching effect takes place in samples that exhibit diffraction efficiency as high as 85% and is induced in less than 0.5 s by an unfocused pump beam of 245 mW/ cm 2 power density.

- by Alessandro Veltri
- •
- Engineering, Liquid Crystals, Optical Switch, Physical sciences

We have investigated the effects of electric field and gamma radiation on the permittivity of a liquid crystal (E8), polymer-matrix (C135) and their composite polymer-dispersed liquid crystal (PDLC). The permittivity data are analyzed in terms of the Debye model, which provides insight into the effects of radiation-induced charges on the relaxation time constants. The effect of gamma-ray dose on the electro-optical response of the PDLC is studied by modeling PDLC as a composite material consisting of either isolated or interconnected liquid-crystal droplets embedded in a polymer matrix.

- by Suresh Sharma
- •
- Condensed Matter Physics, Quantum Physics, Composite Material, Liquid Crystal

The state-of-the-art in the field of molecular design, synthesis, phase behaviour and photooptical properties of photochromic liquid crystalline (LC) side chain polymers, their blends with chiral and photochromic low-molar-mass dopants, hydrogen-bonded photochromic LC polymer systems, as well as photoresponsive LC dendrimers, is reviewed. The molecular architecture of the LC polymers and photochemical reactions of the main types of low-molar-mass achiral and chiral photochromes are briefly described. Recent advances in research dealing with the synthesis and study of optical and photooptical properties of a series of photochromic LC polymers bearing nematogenic and photochromic side groups forming nematic, smectic and cholesteric mesophases are considered.

- by Valery Shibaev
- •
- Engineering, Photochromism, Data storage, Memory Systems

The damping function has been a concept introduced in rheology since more than 30 years ago, and although a similar concept was already earlier implemented in studying rubber materials, its implementation in the modeling of polymer melts was an essential step forward in the classification and understanding of nonlinear viscoelasticity phenomena. It is the objective of this contribution to give an overview on the theoretical background and physical interpretation of the concept of the damping function for different types of deformation, as well as a review on the experimental results including the experimental artefacts to be considered. Besides homopolymers, a summary is given on different investigations of other types of systems, where the concept of the damping function has also been applied, for example, rubbers, rubberlike materials, block copolymers, polymer composites, liquid crystals, polymer blends, suspensions, emulsions, micellar systems, and in food rheology.

- by manfred wagner
- •
- Mechanical Engineering, Chemical Engineering, Viscoelasticity, Modeling

We study the smectic director structure of the rodlike liquid crystal 4-n-dodecyl-4Ј-cyanobiphenyl ͑12CB͒ confined in cylindrical cavities of 200 nm diameter in porous alumina templates by means of combined broadband dielectric spectroscopy, optical birefringence, and neutron scattering measurements. We show that the collective molecular orientation differs between entering the smectic A phase upon cooling from the isotropic state and entering the same phase upon heating while melting the confined crystal. We discuss this collective molecular realignment in terms of a competition between weak planar anchoring at the p-Al 2 O 3 / 12CB interface and a preferred texture typical of the crystallization of rodlike molecules in nanochannels ͑Bridgman growth͒.

- by Patrick Huber and +1
- •
- Engineering, Mathematical Sciences, Dielectric Spectroscopy, Physical sciences

The Micro-and Nano-mechanics Working Group of the Chinese Society of Theoretical and Applied Mechanics organized a forum to discuss the perspectives, trends, and directions in mechanics of heterogeneous materials in January 2010. The international journal, Acta Mechanica Solida Sinica, is devoted to all fields of solid mechanics and relevant disciplines in science, technology, and engineering, with a balanced coverage on analytical, experimental, numerical and applied investigations. On the occasion of the 30 th anniversary of Acta Mechanica Solida Sinica, its editor-in-chief, Professor Q.S. Zheng invited some of the forum participants to review the state-of-the-art of mechanics of heterogeneous solids, with a particular emphasis on the recent research development results of Chinese scientists. Their reviews are organized into five research areas as reported in different sections of this paper. §I firstly brings in focus on micro-and nano-mechanics, with regards to several selective topics, including multiscale coupled models and computational methods, nanocrystal superlattices, surface effects, micromechanical damage mechanics, and microstructural evolution of metals and shape memory alloys. §II shows discussions on multifield coupled mechanical phenomena, e.g., multi-fields actuations of liquid crystal polymer networks, mechanical behavior of materials under radiations, and micromechanics of heterogeneous materials. In §III, we mainly address the multiscale mechanics of biological nanocomposites, biological adhesive surface mechanics, wetting and dewetting phenomena on microstructured solid surfaces. The phononic crystals and manipulation of elastic waves were elaborated in §IV. Finally, we conclude with a series of perspectives on solid mechanics. This review will set a primary goal of future science research and engineering application on solid mechanics with the effort of social and economic development. Supports from NSFC and MOST are acknowledged. · 2 · ACTA MECHANICA SOLIDA SINICA 2011 I. MICRO-AND NANO-MECHANICS 1.1

- by Xi-Qiao Feng
- •
- Materials Engineering, Mechanical Engineering, Civil Engineering, Ophthalmology

In recent years, pulsed microwave imaging in the gigahertz range has been suggested as a promising complementing methodology to the currently existing detection and imaging techniques. This technique is based on significant electrical contrast between the cancerous and healthy breast tissue in the microwave range. In this paper, we investigate tumor detection capabilities of the CPW-fed Elliptical Slot Antenna with a Tuning Uneven U-shape Stub on flexible liquid crystal polymer (LCP) in the UWB Microwave range of frequencies. This topology features excellent capabilities to detect tumors of different sizes and orientations and could potentially revolutionize the detection of ultra-small tumors through the use of antenna-array conformal diagnostic "pouches".

- by N. Tavassolian and +1
- •
- Gynaecology, Cancer, Breast Cancer, Biomedical Imaging

We have used thermal treatment and rubbed polyimide alignment layers to produce large domains of poly(9,9-dioctylfluorene-cobithiophene) alternating copolymer (F8T2). The direction of rubbing on the polyimide surface determines the orientation of these domains, allowing us to create thin-film transistors with channel lengths parallel and perpendicular to the liquid-crystal polymer director. We show that thermal annealing at 280 • C brings F8T2 into a mesophase as observed by X-ray diffraction and differential scanning calorimetry. Polarized optical microscopy and polarized UV-vis absorption spectroscopy show that this ordered phase is associated with very large ordered domains and corresponds to a thermotropic, nematic liquid-crystal phase. We investigated thermal annealing effects on both F8T2 structural ordering and the associated anisotropic electrical properties of the thin-film transistors (TFTs). Enhanced mobility of holes is observed with ordering. Field-effect mobility parallel to the polymer backbone is as much as 6.5 times greater than the perpendicular configuration.

We proposed a method of making a flexible depthtype neural probe using liquid crystal polymer. Conventional depth neural probes made of metal or silicon have the limitations of a single recording site per shank or the brittleness of the silicon substrate. To avoid these drawbacks, polymer-based depth neural probes have been developed with biocompatible polymers such as polyimides or parylenes. However, those have suffered from the difficulty of inserting the probes into brain tissues due to their high flexibility, requiring mechanical reinforcements. Herein, we report the first attempt to use a flexible material, liquid crystal polymer (LCP), as a substrate for a depth-type neural probe. The LCP-based probe offers a controllable stiffness vs. flexibility and compatibility with thin-film processes in addition to its inherent characteristics such as high reliability and biocompatibility. In the present study, an LCP neural probe was fabricated to have enough stiffness to penetrate the dura mater of rodent brains without a guide tool or additional reinforcement structures. A simultaneous multichannel neural recording was successfully achieved from the somatosensory motor cortex of the rodents. Immunohistochemistry showed that the electrodes could be inserted into the desired regions in the brain. He is a Project Incharge of the research group for the development of bionic interface technology to control neural information.

- by Changkyun Im
- •
- Biomedical Engineering, Silicon, Immunohistochemistry, Polymers

Two CPW-fed elliptical monopoles were fabricated on liquid crystal polymer (LCP) with reconfigurable rejection band (band-notch) characteristics in the frequency range between 5 and 6 GHz. The first antenna uses a 2 long, U-shaped slot and the second antenna uses two symmetrically placed 4 long, inverted L-shaped stubs as resonating elements. Microelectromechanical system (MEMS) switches are used to activate and deactivate the resonating elements without the need of dc bias lines due to a novel design of the switch geometry. Transmission line models and surface current distributions are used to explain the effect of the added resonating elements. Reflection coefficient radiation pattern and gain measurements are presented to verify the design concepts featuring a very satisfactory performance. Index Terms-Band-notch, microelectromechanical system (MEMS), reconfigurable, ultrawideband (UWB) .

We report a simple evanescent field fiber optic electric field sensor constructed by coating the exposed fiber optic core with a Ž . polymer-dispersed liquid crystal PDLC . It is well known that the effective refractive index of the liquid-crystal polymers has a large dependence on the direction and the magnitude of an applied electric field. This dependence was large enough in our devices to enable simple transmission measurements to detect the presence of an applied electric field across the fiber optic. The sensors showed good sensitivity and reproducibility with its response dominated by the RC time constant of the structure rather than the response of the PDLC. Its response time was approximately 3 min with 15-20 min relaxation time. Using an electric circuit model of the device, we also discuss how the sensor's response time can be improved by many orders of magnitude. q 2000 Elsevier Science S.A. All rights reserved.

We develop a continuum theory of linear viscoelastic response in oriented monodomain nematic elastomers. The expression for the dissipation function is analogous to the Leslie-Ericksen version of anisotropic nematic viscosity; we propose the relations between the anisotropic rubber moduli and new viscous coefficients. A new dimensionless number is introduced, which describes the relative magnitude of viscous and rubber-elastic torques. In an elastic medium with an independently mobile internal degree of freedom, the nematic director with its own relaxation dynamics, the model shows a dramatic decrease in the dynamic modulus in certain deformation geometries. The degree to which the storage modulus does not altogether drop to zero is shown to be both dependent on frequency and to be proportional to the semi-softness, the non-ideality of a nematic network. We consider the most interesting geometry for the implementation of the theory, calculating the dynamic response to an imposed simple shear and making predictions for effective moduli and (exceptionally high) loss factors.

- by Eugene Terentjev
- •
- Mathematical Sciences, Physical sciences, Dynamic Response, Degree of Freedom

We present a Frank-Oseen elasticity theory for the shape and structure of deformable nematic droplets with homeotropic surface anchoring in the presence of a magnetic field. Inspired by recent experimental observations, we focus on the case where the magnetic susceptibility is negative, and find that small drops have a lens shape with a homogeneous director field for any magnetic-field strength, whereas larger drops are spherical and have a radial director field, at least if the magnetic field is weak. For strong magnetic fields the hedgehog configuration transforms into a split-core line defect that, depending on the anchoring strength, can be accompanied by an elongation of the tactoid itself. We present a three-dimensional phase diagram that shows the tactoid shape and director field for a given anchoring strength, tactoid size, and magnetic-field strength. Our findings rationalize the different shapes and structures that recently have been observed experimentally for nematic droplets found in dispersions of gibbsite platelets in two types of solvent.

- by Paul Van Der Schoot
- •
- Engineering, Complex Fluids, Mathematical Sciences, Physical sciences
- by M. Vasnetsov and +1
- •
- DFB laser, Oscillations, Second Order, Bragg Grating

We create polymer liquid crystals (PLCs) on a computer and subject them to constant-force tensile deformations. Molecular dynamics simulation procedure is used and graphical models and animations of crack formation and propagation as a function of time are generated. Special attention is given to realistic rigid LC island geometry and the island spatial distribution in the material. Internal fracture processes can now be easily studied. As a result of the numerous animations recorded, clear patterns in PLC crack initiation and propagation emerge. With the help of the animations, the structure of PLCs may be understood without having to resort to costly laboratory experimentation.

- by Ricardo Simões
- •
- Materials Engineering, Computer Animation, Materials, Crack propagation

The feasibility of using near-hermetic organic materials for microwave and millimeter-wave packaging is investigated. The effects of moisture on both passive and active components on/inside the nonhermetic materials are tested. Microstrip patch antennas on three low moisture absorption substrates (0.1% or less) are subjected to immersion tests until saturated and the corresponding measured frequency shifts are found to be less than 0.25% for two of the three materials tested. The recovery time from saturation to normal operation is found to occur from natural evaporation at room temperature in 10 min or less. One of the three materials, a promising organic laminate material called liquid crystal polymer (LCP), showed no measurable change in weight or in antenna resonance frequency between the ambient (air) state and that after extended submersion in water. In addition, a novel laminated LCP package for a 13-25 GHz monolithic microwave integrated circuit (MMIC) formed from seven thin layers of laser-machined LCP is subjected to immersion testing. The seal for the embedded chip cavity (formed by the LCP conforming around the feeding transmission lines) is found to be robust for protecting the embedded chip. Standard hermetic materials are suggested to be a potentially unnecessary requirement for reliable, long-lifetime, high-performance RF systems.

This paper presents an ultra-thin and flexible polymer-based capacitive pressure sensor for intraocular pressure (IOP) monitoring in a mouse eye. Due to the size limitation of the anterior chamber in the mouse eye, a volume of approximately 700×700×150 μm 3 on a small substrate is available for the MEMS capacitive pressure sensor. Moreover, the sensor would ideally be easily injectable into place. Further complicating the sensing is the need to operate the device on the curved surface of the anterior chamber with minimum damage to the eye tissue. Therefore, a thin and flexible substrate is required. We fabricate sensors by exploiting Parylene as a biocompatible structural material in a suitable form factor and 25 μm thick liquid crystal polymer (LCP) as a soft and flexible host substrate. Using our approach, the flexibility and small form factor necessary for a mouse eye implant is achieved, along with the sensitivity required to monitor IOP fluctuations. This device will allow better study of glaucoma through close monitoring in mice after integration with other components.

- by Wilhelmine Vries
- •
- Materials Engineering, Biomedical Engineering, Life Sciences, Polymers

This paper presents the characteristics of a compact and conformal ultra wideband (UWB) antenna fabricated on Liquid Crystal Polymer (LCP) substrate to be used in wearable applications. The presented return loss and radiation pattern measurements demonstrated that the characteristics of the antenna are not compromised when the antenna is bent or even folded. The antenna shows similar and reliable electrical and mechanical performances in wearable electronics, where their planar condition cannot be guaranteed. The antenna's ability to work under adverse environments (i.e. under heating and in water) are also investigated and negligible impact of these conditions on antenna performance promises the use of such antenna in wearable applications.

- by Qammer H. Abbasi
- •
- Environmental Conditions, Wearable Electronics, Substrates, Ultra Wideband

A standard non-metallized liquid crystal polymer (LCP) 4 mil thick microwave substrate with depthcontrolled laser-micromachined cavities was investigated as a system-level packaging layer for integrated packaging of monolithic microwave integrated circuits (MMICs) and radio frequency microelectromechanical systems (RF MEMS) switches. The RF characteristics of air/dielectric discontinuities at the cavity interfaces were first simulated and the results show that LCP's low dielectric constant enables cavity dimensions to be arbitrarily chosen without significantly affecting the RF performance. To test this packaging concept a 4 mil LCP sheet with twelve 1 mm x 2.4 mm x 2 mil deep cavities was fabricated. Air-bridge type RF MEMS switches were fabricated on a base LCP substrate and measured before and after introducing the laser-micromachined superstrate layer. The measurements show almost no difference in packaged and unpackaged form for frequencies up to 40 GHz. The concept of a system-level package on a flexible, low-cost, organic substrate has been demonstrated for the first time. The same technique could be used for integrating MMICs all in a near-hermetic low-cost LCP module.

- by Manos M Tentzeris
- •
- Micromachining, RF MEMS, Thin Film, Radio Frequency

We report on diffraction gratings consisting of continuous and well-aligned nematic films separated by polymer slices, which are originated in nematic-containing polymer composites when cured by a UV interference pattern. The diffraction efficiency of these gratings is experimentally investigated in detail; its temperature dependence reveals a rather complex, nonmonotonic shape, with a next-to-unit maximum at high temperatures and a next-to-zero minimum at lower ones. When the influence of an external electric field is investigated, the dependence of the diffraction efficiency on the applied voltage appears to be nonmonotonic too, the particular shape depending on the actual value of the sample temperature; in general, both switch-on and switch-off of the diffraction mechanism can be observed as an effect of the external field. For this kind of grating, a Kogelnik-like model has been implemented that makes use of only real values of some physical quantities, without the necessity of any fitting parameter. Numerical solutions account for the temperature dependence of the diffraction efficiency with good accuracy.

- by Alessandro Veltri and +1
- •
- Applied Mathematics, High Temperature, Temperature Dependence, Optical physics

In this paper, we present an RF MEMS switch developed on a low cost, flexible liquid crystal polymer (LCP) substrate. LCP's very low water absorption (0.04%), low dielectric loss and multi-layer circuit capability make it very appealing for RF systems-on-package (SOP). Here we present for the first time capacitive MEMS switch fabrication on an LCP substrate and its characterization and properties up to 40 GHZ.

- by Manos Tentzeris
- •
- Surface Roughness, RF MEMS, Radio Frequency, Water Absorption

A lamination technique for liquid crystal polymer (LCP)/Cu was developed for high speed and high performance printed circuit boards (PCB). This approach was accomplished by using a modified surface activated bonding (SAB) process to achieve enhanced adhesion and a smooth interface. Systematic investigation of peel strength of four categories of samples, namely “as bonded”, “annealed”, “Cu-deposited”, and “Cu-deposited and annealed”

- by Tadatomo Suga
- •
- Engineering, Materials Science, Packaging, Surface Roughness

Electronics packaging evolution involves system, technology, and material considerations. In this paper, we present a novel three-dimensional (3-D) integration approach for system-on-package (SOP)-based solutions for wireless communication applications. This concept is proposed for the 3-D integration of RF and millimeter (mm) wave embedded functions in front-end modules by means of stacking substrates using liquid crystal polymer (LCP) multilayer and BGA technologies. Characterization and modeling of high-Q RF inductors using LCP is described. A single-input-single-output (SISO) dual-band filter operating at ISM 2.4-2.5 GHz and UNII 5.15-5.85 GHz frequency bands, two dual-polarization 2x1 antenna arrays operating at 14 and 35 GHz, and a WLAN IEEE 802.11a-compliant compact module (volume of 75 35 0.2 mm 3) have been fabricated on LCP substrate, showing the great potential of the SOP approach for 3-D-integrated RF and mm wave functions and modules.

04ld 1'e'44? I hojur Or ' CWsOnsC including tile tine to, reviewingq ifltruCt,0n1l %earthingq tri'It data I I~t'~ IIII~~ii itltniiii ij ll .h4P th~e .3Ijecjop of ,nforn'art If end comments regarding thr$ burden #trflnatC 0t any ot 4.PC 0 otrllII(I'IIII~IC I lii rden. t0 tVash,n 1 ,o, Had .at r i'ce. Directorate fior informino pe'tons and Repo(., "is t II~~~~iI~~I IIiI IIIIII i~ii.e o' maaq~emn md Budget. Paperwork Reduction Pro~ect (O7O4_C1BS). Washrrngton. OC 20503

- by Coleen Pugh
- •
- Engineering, Liquid Crystals, Glass, Polymerization

The current work demonstrates a liquid crystalline polymer microlens array (LCP MLA) with an alloptically tunable and multistable focal intensity through photochemical phase transition. The operational mechanism of the optical tuning is associated with the photoisomerization effect. The proposed LCP MLA device has a focusing unit based on a birefringence LCP and a tuning unit with a light responsive material to control the polarization state of the incident probe beam. The optically variable refractive indices of LCP enable a positive or negative MLA that can control the polarization of incident light to be realized.

- by Andy Fuh
- •
- Mechanical Engineering, Liquid Crystals, Applied Optics, Optical physics

- by Qammer Abbasi
- •
- Environmental Conditions, Wearable Electronics, Substrates, Ultra Wideband

Molecular chirality, and the chiral symmetry breaking of resulting macroscopic phases, can be topologically imprinted and manipulated by cross-linking and swelling of polymer networks. We present a new experimental approach to stereo-specific separation of chiral isomers by using a cholesteric elastomer in which a helical director distribution has been topologically imprinted by cross-linking. This makes the material unusual in that is has a strong phase chirality, but no molecular chirality at all; we study the nature and parameters controlling the twist-untwist transition. Adding a racemic mixture to the imprinted network results in selective swelling by only the component of ''correct'' handedness. We investigate the capacity of demixing in a racemic environment, which depends on network parameters and the underlying nematic order.

- by Eugene Terentjev
- •
- Polymers, Physical sciences, Chiral Symmetry Breaking, Silicones

Analytical and numerical tools for the analysis and design of actuated polymer films (APFs) are developed and described in this paper. Computational micromechanical models are set up and correlated in order to calculate the deformation and power requirement to actuate an APF taking into account hyperelastic and viscous effects. A method is developed to correlate material parameters in the viscous branch of the Bergström-Boyce model to available experimental data. The effects of various geometric and material parameters are elucidated by a parametric study including coherent versus non-coherent actuators, excitation frequency and magnitude, modulus of elasticity of the actuator and the top film, and actuator volume fraction.

One emerging market for electrically conductive resins is for bipolar plates for use in fuel cells. Adding carbon fillers to thermoplastic resins increases composite electrical conductivity and viscosity. Current technology often adds as much of a single type of carbon filler as possible to achieve the desired conductivity, while still allowing the carbon-filled thermoplastic matrix material to be extruded and molded into a bipolar plate. In this study, varying amounts of two different types of carbon, one carbon black and one synthetic graphite, were added to Vectra A950RX liquid crystal polymer. The resulting single filler composites were then tested for electrical conductivity and rheological properties. The electrical conductivity followed that typically seen in polymer composites with a percolation threshold at 4 vol % for carbon black and at 15 vol % for synthetic graphite. Over the range of shear rates studied, the viscosity followed a shear-thinning power law model with power-law exponent (n − 1) = −0.5 for neat Vectra A950RX and (n − 1) = −0.7 for highly filled composite materials. Viscosity increased with increasing filler volume fraction for all shear rates. The viscosity–enhancement effect was more rapid for the composites containing carbon black when compared with those containing synthetic graphite. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 2680–2688, 2006

- by Mariana Cruz
- •
- Engineering, Materials Engineering, Polymer Composites, Applied

Liquid crystal polymer (LCP) and Cu thin film cleaned with radio frequency (RF) plasma in a vacuum pressure of 3.0 10 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 ) 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 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 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.

- by Matiar Howlader
- •
- Heat Treatment, Adhesion, Manufacturing Engineering, Thin Film

boardthe likely answer is of course with embedded Miniaturization with increased functionality at reduced components. Although embedded passives have received cost historically has been the key driver for the evolution of attention in the industry over the past 5 years, the net effect in miniaturization with embedded passives is not yet electronics products. However, the size reduction was sinfctdu tonhrtmaealcntantwh R C, L, Filter, the consumer demands in miniaturization and portability of Digital TV and Set Box C, L, R, Filter Memory! consumer electronics products. With the increased level of ___________________Logic/Linear interconnections and flexibility in System-in-Chip and High End Server! C, L, R, Filter System-on-Package, the size of the device is becoming Computer_______________ more often the size of the circuit board than anything else. So, the next question is how to reduce the size of the circuit 1-4244-1 186-6/07/$25.OO ©2007 IEEE

- by Amin Rida and +1
- •
- Real Estate, Copper, Thin Film, Long Range

POLICRYPS (an acronym of polymer liquid crystal polymer slices) is a nano/microcomposite structure made of slices of almost pure polymer alternated with films of well aligned nematic liquid crystal (NLC). The structure is obtained by irradiating a homogeneous syrup of NLC, monomer and curing agent molecules with an interference pattern of UV/visible light under suitable experimental and geometrical conditions; the spatial periodicity can be easily varied from an almost nanometric (200 nm) to a micrometric (15 µm) scale. Where the effect on an impinging reading light beam is concerned, the POLICRYPS can be utilized either in a transmission or a reflection configuration (depending on the geometry and substrate used) with negligible scattering losses, while the effect of spatial modulation of the refractive index (from polymer to NLC values) can be switched on and off by applying an external electric field of the order of few V µm −1 . In this paper, we start by reviewing the general features of the POLICRYPS structure, that is the 'recipe' to fabricate it, along with a chemical-diffusive model that indicates the right physical and chemical conditions to make samples exhibiting good morphological, optical and electro-optical properties. We then show some possible utilizations of POLICRYPS with a light beam impinging almost perpendicularly to the structure: a switchable diffraction grating and a switchable optical phase modulator. Furthermore, we put into evidence that POLICRYPS channels can become an array of mirrorless optical micro-resonators for lasing effects. Finally, we report about utilization of POLICRYPS with a light beam impinging parallel to the structure and perpendicular to the channels, demonstrating that, in this case, the structure becomes a tuneable Bragg filter. Performances exhibited in all above applications put the POLICRYPS structure at the top level of the state of art of application oriented research in optics of liquid crystalline composite materials.

- by Antonio d'Alessandro and +3
- •
- Refractive Index, Composite Material, Optical physics, Microstructures

The rate of domain growth in nematic side chain polymer samples is measured using the worm like path model for multiple scattering of light. The worm like path model which describes multiple scattaering in terms of the optical persistence length is found to apply both to multiple scattering in liquid crystal polymer films as well as to model polystyrene despersions.

- by Stephen Picken
- •
- Growth Kinetics, Multiple Scattering, Scaling Law, Liquid Crystal Polymer

We discuss the use of a double exponentially tapered slot antenna (DETSA) fabricated on flexible liquid crystal polymer (LCP) as a candidate for ultrawideband (UWB) communications systems. The features of the antenna and the effect of the antenna on a transmitted pulse are investigated. Return loss and E and H plane radiation pattern measurements are presented in several frequencies covering the whole ultra wide band. The return loss remains below 10 dB and the shape of the radiation pattern remains fairly constant in the whole UWB range (3 110 6 GHz). The main lobe characteristic of the radiation pattern remains stable even when the antenna is significantly conformed. The major effect of the conformation is an increase in the cross polarization component amplitude. The system: transmitter DETSA-channel -receiver DETSA is measured in frequency domain and shows that the antenna adds very little distortion on a transmitted pulse. The distortion remains small even when both transmitter and receiver antennas are folded, although it increases slightly. Index Terms-Conformal antenna, distortion, double exponentially slot antenna (DETSA), liquid crystal polymer (LCP), ultrawideband (UWB), ultrashort pulse.