There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

Shape-memory polymers

Fundamentals, processes and applications of high-permittivity polymer–matrix composites

Due to the unprecedented growth in wireless applications over the past decade, development of low-cost solutions for RF and microwave communication systems has become of great importance. This practical new book is the first comprehensive treatment of lumped elements, which are playing a critical role in the development of the circuits that make these cost-effective systems possible. The books offers you an in-depth understanding of the different types of RF and microwave circuit elements, including inductors, capacitors, resistors, transformers, via holes, airbridges, and crossovers. Supported with over 220 equations and more than 200 illustrations, it covers the practical aspects of each element in exceptional detail. No other single volume treats this subject matter in such depth. From materials, fabrication, and analyses - to design, modeling, and physical, electrical, and thermal applications, this unique resource offers you complete coverage of the critical topics you need understand for your work in the field. Offering the most comprehensive, up-to-date body of knowledge on lumped elements, the book is an indispensable professional reference and serves as an excellent text for senior undergraduate and graduate-level courses in RF and microwave circuit design.

Lumped Elements for RF and Microwave Circuits

Shape-memory polymers are stimuli-responsive materials. Upon exposure to an external stimulus, they have the capability of changing their shape. A change in shape initiated by a change in temperature is called thermally induced shape-memory effect. The shape-memory effect results from the polymer's structure, that is, its morphology in combination with a certain processing and programming technology.



The polymer is processed into its permanent shape by conventional methods. Afterwards, it is deformed and the desired temporary shape is fixed. The latter process is called programming. Heating the programmed polymer above a temperature higher than the transition temperature Ttrans results in activating the shape-memory effect. As a consequence, the recovery of the memorized, permanent shape can be observed. The described effect is called a “one-way” shape-memory effect.



The shape-memory effect can be quantified by cyclic thermomechanical investigations. Important quantities describing the shape-memory properties of the material for a certain strain ɛm are the strain recovery rate Rr and the strain fixity rate Rf. The strain recovery rate Rr quantifies the ability of the material to memorize its permanent shape. The strain fixity rate Rf describes the ability of the material to fix the mechanical deformation ɛm which has been applied during the programming process.


Keywords:

block copolymers;
elastomers;
networks;
shape-memory polymers;
stimuli-sensitive polymers;
structure–property relations

Shape-Memory Polymers

Integral passives are becoming increasingly important in realizing next generation electronics industry needs through gradual replacement of discretes. The need for integral passives emerges from the increasing consumer demand for product miniaturization thus requiring components to be smaller and packaging to be space efficient. In this paper, the feasibility of integration of polymer/ceramic thin film (∼5 μm thick) capacitors (C) with other passive components such as resistors (R) and inductors (L) has been discussed. An integrated RC network requiring relatively large capacitance and resistance is selected as a model for co-integration of R and C components using low temperature PWB compatible fabrication processes. This test vehicle is a subset of a large electrical circuit of a functional medical device. In order to produce higher capacitance density and reduce in-plane device area, multi-layer (currently two-layer) capacitors are stacked in the thickness direction. A commercially available Ohmega-Ply resistor/conductor material is selected for integral resistors. Resistors were fabricated using a multi-step lithography process with the utilization of two separate masks. Bottom copper electrodes for capacitors were also defined during the resistor fabrication process. Photodefinable epoxies filled with a high permittivity ceramic powder were used for fabrication of thin film capacitors. Epoxy and ceramic powders were mixed in the required proportion and blended using a high shear apparatus. The coating solution was homogenized in a roll miller for 3 to 5 days prior to casting in order to prevent settling of the higher density ceramic particles. Capacitors were fabricated by spin-coating on the sub-etched copper electrodes. The deposited dielectric layers were dried, exposed with UV radiation, patterned, and thermally cured. Top capacitor electrodes (copper) were deposited using a metal or an e-beam evaporator. The electrodes were patterned using the standard photolithography processes. Selected good samples were used for depositing the second capacitor layer. The RC network is extended to incorporate electroplated polymer/ferrite core micro-inductors through the fabrication of an industry prototype low pass RLC filter. Meniscus coating was evaluated for large area manufacturing with high process yield. A capacitance density of ∼3 nF cm−2 was obtained on a single layer capacitor with ∼6 μm thick films. The capacitance density was increased to ∼6 nF cm−2 with the two-layer deposition process. The capacitors were relatively stable up to a frequency range of 120 Hz to 100 KHz. Meniscus coating was qualified to be a viable manufacturable method for depositing polymer/ceramic capacitors on large area (300mm x 300mm) PWB substrates. Dielectric constant values in the range of 3.5 to 35 with increase in filler loading up to 45 vol% were achieved in the epoxy nanocomposite system where the dielectric constant of the host polymer was limited to ∼3.5. Higher dielectric constant polymers are required to meet the increasingly higher capacitance needs for the next generation electronics packaging. Possible avenues for achieving higher capacitance density in polymer/ceramic nanocomposite system have been discussed.

Next generation integral passives: materials, processes, and integration of resistors and capacitors on PWB substrates

From cell phones to biomedical systems, modern life is inexorably dependent on the complex convergence of technologies into stand-alone products designed to provide a complete solution in small, highly integrated systems with computing, communication, biomedical and consumer functions. The concept of system-on-package (SOP) originated in the mid-1990s at the NSF-funded Packaging Research Center at the Georgia Institute of Technology. This can be thought of as a conceptual paradigm in which the package, and not the bulky board, as the system and the package provides all the system functions in one single module, not as an assemblage of discrete components to be connected together, but as a continuous merging of various integrated thin film technologies in a small package. In the SOP concept, this is accomplished by codesign and fabrication of digital, optical, RF and sensor functions in both IC and the package, thus distinguishing between what function is accomplished best at IC level and at package level. In this paradigm, ICs are viewed as being best for transistor density while the package is viewed as being best for RF, optical and certain digital-function integration. The SOP concept is demonstrated for a conceptual broad-band system called an intelligent network communicator (INC). Its testbed acts as both a leading-edge research and teaching platform in which students, faculty, research scientists, and member companies evaluate the validity of SOP technology from design to fabrication to integration, test, cost and reliability. The testbed explores optical bit stream switching up to 100 GHz, digital signals up to 5-20 GHz, decoupling capacitor integration concepts to reduce simultaneous switching noise of power beyond 100 W/chip, design, modeling and fabrication of embedded components for RF, microwave, and millimeter wave applications up to 60 GHz. This article reviews a number of SOP technologies which have been developed and integrated into SOP test bed. These are: 1) convergent SOP-based INC system design and architecture, 2) digital SOP and its fabrication for signal and power integrity, 3) optical SOP fabrication with embedded actives and passives, 4) RF SOP for high Q-embedded inductors, filters and other RF components, 5) mixed signal electrical test, 6) mixed signal reliability, and 7) demonstration of SOP by INC prototype system.

/pdf/the-sop-for-miniaturized-mixed-signal-computing-rd4m8a7iu7.pdf

The SOP for miniaturized, mixed-signal computing, communication, and consumer systems of the next decade

Integral passives for next generation of electronic packaging: application of epoxy/ceramic nanocomposites as integral capacitors

Polymer ceramic composites form a suitable material system for low temperature fabrication of embedded capacitors appropriate for the MCM-L technology. Improved electrical properties such as permittivity can be achieved by efficient filling of polymers with high dielectric constant ceramic powders such as lead magnesium niobate-lead titanate (PMN-PT) and barium titanate (BT). Photodefinable epoxies as the matrix polymer allow fine feature definition of the capacitor elements by conventional lithography techniques. The optimum weight percent of dispersant is tuned by monitoring the viscosity of the suspension. The dispersion mechanism (steric and electrostatic contribution) in a slightly polar solvent such as propylene glycol methyl ether acetate (PGMEA) is investigated from electrophoretic measurements. A high positive zeta potential is observed in the suspension, which suggests a strong contribution of electrostatic stabilization. By optimizing the particle packing using a bimodal distribution and modified processing methodology, a dielectric constant greater than 135 was achieved in PMN-PT/epoxy system. Suspensions are made with the lowest PGMEA content to ensure the efficiency of the dispersion and efficient particle packing in the dried film. Improved colloidal processing of nanoparticle-filled epoxy is a promising method to obtain ultra-thin capacitor films (<2/spl mu/m) with high capacitance density and improved yield. Capacitance of 35 nF/cm/sup 2/ was achieved with the thinnest films (2.5-3.0 /spl mu/m).

Colloidal processing of polymer ceramic nanocomposites for integral capacitors

This paper presents the design, fabrication and testing of capacitive copper RF MEMS switches with various hinge geometries, fabricated on high-resistivity silicon substrates. The switches were fabricated using a simple low-cost four-mask process and 0.6-1.0 /spl mu/m thick membranes were made out of sputtered copper. The capacitive airgap in between the membrane and the signal line is 1.5-2.0 /spl mu/m. The lowest actuation voltage measured on the fabricated switches is 9 V. The measured insertion loss of a fabricated switch and its associated transmission time was 0.9 dB (mainly contributed by the transmission line itself) and the isolation was measured to be 25 dB at 40 GHz.

/pdf/low-cost-low-actuation-voltage-copper-rf-mems-switches-5g8b7ze6t8.pdf

Swapan K. Bhattacharya

Papers

Next generation integral passives: materials, processes, and integration of resistors and capacitors on PWB substrates

The SOP for miniaturized, mixed-signal computing, communication, and consumer systems of the next decade

Integral passives for next generation of electronic packaging: application of epoxy/ceramic nanocomposites as integral capacitors

Colloidal processing of polymer ceramic nanocomposites for integral capacitors

Low-cost low actuation voltage copper RF MEMS switches