High Q-factor of coplanar waveguide on low-k polymer layer

This paper presents experimental results for line-to-line coupling between adjacent coplanar waveguide (CPW) transmission lines. The CPW lines are fabricated on glass and low resistivity CMOS grade Si substrates coated with a 20/spl mu/m cyclotene polymer. From the measurement results it is found that the coupling increases with frequency on low resistivity silicon substrate while the coupling on glass shows relatively constant peaks. A spacing of 600/spl mu/m between CPW lines is required to avoid parasitic coupling less than 30dB for frequencies up to 30GHz when fabricated on low resistivity silicon, while a spacing of 200/spl mu/m is required when fabricated on glass. The conductor width (W) and the slot width (S) for low resistivity silicon is 80/spl mu/m and 45/spl mu/m, and on the glass substrate W = 150/spl mu/m, S = 30/spl mu/m. Based on full-wave EM simulation results, it is argued that the primary coupling mechanism is through the interaction of higher-order modes.

In this paper, a novel technological solution using both silicon surface micromachining and thick polymer layer deposition on low resistivity silicon substrate (20 /spl Omega//cm) has been investigated. The proposed structure achieves both a low attenuation level and a high quality factor. The silicon etching into the coplanar slots leads indeed to a noticeable decrease of the losses, whereas filling the gaps with the polymer BCB avoids a degradation of the effective permittivity.

We present a new method for discriminating organic vapors based on the variation of capacitance changes of an interdigitated CMOS capacitor with the thickness of the sensitive polymer layer. By carefully adjusting the thickness of the polymer layer, discrimination potential in addition to the chemical selectivity of the polymer is provided by the fact that the interdigitated capacitor signals depend on the layer thickness. At polymer thicknesses small compared to the center-to-center spacing of the electrodes, an increase in capacitance is observed for all analytes, whereas for thick layers, the direction of the capacitance changes depends on the dielectric constant of the analyte. Sensors can be designed to be insensitive towards a certain analyte by varying the polymer thickness. Measurements for volatile organic compounds using CMOS capacitors coated with different polymer thicknesses are presented to demonstrate the new way of increasing sensor selectivity.

Solid-state complexes of flexible polymers with surfactants (surf) exhibit mesomorphic phase and microphase-separated lamellar morphology. Because the surf molecules are strongly associated with the polymer backbone, the ordered packing of the alkyl tails should be cooperative with the chain packing in the polymer layers which is influenced by chain topology. In this study, the supramolecular structure and thermal properties of the complexes of a highly branched poly(ethylenimine) (PEI) with dodecylbenzenesulfonic acid (DBSA) were investigated. Polarized optical microscopy and small-angle X-ray scattering (SAXS) revealed the presences of mesomorphic phases and microphase-separated lamellar morphology in the complexes. The ordered supramolecular structure was observed not only for the stoichiometric composition but over a wide composition range. The thicknesses of polymer and surf layers were determined from the one-dimensional correlation function. The surf layer thickness varied with complex composition. The glass transition temperature of polymer layers was raised by complexation because of the stiffening of polymer chains. Complexation with DBSA also enhanced the thermal stability of PEI, where the thermal decomposition temperature can be raised by as much as 50 °C.

Because of their interesting electrical, mechanical and thermal properties at high frequencies, polymers are becoming more and more attractive in the development of RF and millimeterwave applications. Their process ease and characteristics indeed permit improvement in the performance of passive components as well as their integration especially with active devices. Investigated in this paper are a few technological solutions based on the use of thick polymer layers. The first one consists of a thick organic layer that may be employed as a dielectric membrane on bulk silicon micromachined substrates in order to realize suspended components, which exhibit thus very low losses and dispersion on a large frequency range. The elevation of passive circuits through thick polymers represents another attractive solution to minimize the losses induced by the silicon substrate, which through a low thermal budge provides a particularly attractive method for post-processing over active devices. The use of polymers for additional surface micromachining into coplanar slots on silicon substrates can also improve both losses and quality factor. Finally, an application using a thin polymer layer as dielectric protection for a MEMS device is described.

Electromagnetic band gap (EBG) structures can exhibit high impedance surface (HIS) performance on a lossless substrate. However, the performance of an EBG structure is not only determined by the type of element or physical dimensions, but also by the electrical characteristics of the dielectric substrate. The evolution of an EBG structure from HIS to metamaterial absorber with different lossy silicon substrates is analyzed and presented in a reflection magnitude and phase graph. The conductivity of the used substrate is introduced to represent the loss tangent of the silicon substrate. An equivalent circuit model is developed that models the EBG on a lossy silicon substrate. The small differences between calculated and simulated results are explained by ignoring the patch series inductance Ls and the capacitance Ch between the patch and ground plane. Based on the analysis of the reflection characteristics on lossy silicon substrates, this planar EBG structure provides an acceptable performance in BiCMOS technologies, but cannot be used in low-Ohmic CMOS technologies.

This paper deals with a novel technological solution based on the use of surface micromachining in coplanar slots that are filled with a thick organic dielectric layer. This technique enables both Q factor and losses improvements of passive circuits realized on low resistivity silicon substrate. It permits indeed to achieve much better attenuation level without an important decrease of the effective permittivity.

This paper describes fabrication, characterization and simulation of low-loss coplanar waveguide (CPW) interconnects on low-resistivity silicon substrate. The fabrication of CPWs is low-temperature (below 250/spl deg/C) and incorporates a spin-on low-k dielectric benzocyclobutene (BCB) and self-aligned electroplating of copper. The performance of CPWs is evaluated by high-frequency characterization and EM simulation. CPWs with different line width (W) and line spacing (S) are investigated and compared. Using a BCB layer as thick as 20 /spl mu/m, CPW fabricated on a low-resistivity silicon substrate exhibits an insertion loss of 3 dB/cm at 30 GHz.

Grafting‐to polymer coatings are typically easy to apply, but the thickness of such coatings is typically limited to a few nanometers, which may hamper applications. This paper presents a grafting‐to coating approach that yields polymer brushes up to an unprecedented thickness of 19 nm. To this aim, an easy‐to‐apply poly(dopamine) (PDA) primer layer is optimized. PDA is an easy‐to‐apply, but highly complex and chemically not well understood primer layer. In this study, PDA is deposited on silicon substrates using several deposition protocols (pH 4–7 in presence of NaIO4, and from Tris solution at pH 8.5). The modified surfaces are characterized using X‐ray photoelectron spectroscopy, spectroscopic ellipsometry, static water contact angle measurements, and atomic force microscopy. Subsequently, block copolymers of poly(glycidyl methacrylate)20‐b‐poly(N‐isopropylacrylamide)n are attached onto the PDA films using a grafting‐to approach. The results indicate that the conditions of PDA deposition and the PDA film thickness strongly influence the stability and grafting efficiency of the block copolymers. PDA films deposited at pH 7 with NaIO4 are stable, and yield the most efficient grafting, with grafted polymer layers as thick as 19 nm. Polymer layers of such thickness are rarely achieved using grafting‐to procedures from solution.

The results of experimental study of comparative efficiency of vibrational energy dissipation in materials of metal-polymer-metal (M–P–M) layered structure with different thickness of polymer layer are presented. It is shown that if the thickness of the polymer layer is significantly less than the thickness of the metal layer, it has little effect on the efficiency of energy dissipation in M–P–M structures. In addition, the vibration-absorbing film VPS-2.5 demonstrates high dissipation of vibrational energy in M–P–M structures in the frequency ranges from 1 to 6000 Hz, including low frequencies (f ≤ 200 Hz) even at a thickness of 0.2 mm.

Differences in probe-tip-to-line geometry and substrate permittivity between measurement and calibration wafer deteriorate measurement accuracy. This is especially the case when measurements are performed on lossy Silicon substrates. Two novel general techniques are presented which characterise the discontinuities near the probe-tip based on the measurement of two lines with different length. The equivalent elements representing the discontinuity are extracted at each frequency point together with the propagation constant and the characteristic impedance of the line. The obtained results are superior to previous methods with a reduced number of measurements. The validity of the method is demonstrated with measurements of CPW-lines on low and high resistivity Silicon and GaAs.

The properties of transmission lines on low-resistivity silicon substrate (/spl rho/=10 /spl Omega/.cm) are investigated. Coplanar lines on silicon substrate with a 10 /spl mu/m dielectric film show that losses of 0.6 dB/mm can be obtained at 50 GHz. A new embedded ultra-low loss coplanar line is proposed, with a broad interval of characteristic impedance.

Laser Raman spectroscopy is an effective tool for the study of biodegradable polymers, which play a vital role in the new developments in coronary implants such as stents. There is much excitement around the potential capabilities of synthetic biodegradable polymers and the effect they will have on the design and function of implanted devices. In the present investigation, heparin‐conjugated biodegradable copolymers were evaluated for their durability as drug‐eluting stent coatings. Laser Raman spectroscopic studies were carried out and spectra recorded and analyzed of explanted stents coated with different amounts of polymer alone, showing the existence of different levels at different quantities of polymer. The polymer was detected on every stent analyzed. On the stents coated with a thick layer of polymer, a firm layer of polymer still existed on the stent. In contrast, this layer was degraded and spread around on the stents coated with only a thin layer of the polymer. This indicates that the polymers used in the stents in the present investigation exhibit acceptable biodegradability. Such polymers can be used as efficient drug carriers, as these materials show good degradation after the stipulated period. Copyright © 2009 John Wiley & Sons, Ltd.

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> This paper reports the theoretical and experimental studies of high-<formula> <tex>$Q$</tex></formula> suspended microinductors produced by flip-chip assembly for multigigahertz RF integrated-circuit applications. The effects of device and substrate parameters on the <formula formulatype="inline"><tex>$Q$</tex> </formula> factor of the inductor devices are studied by numerical simulation using Ansoft's High Frequency Structure Simulator electromagnetic field simulation package. Suspended inductor devices are realized using a flip-chip assembly method in which the inductor structures with the supporting pillars are fabricated on a low-cost polyimide thin-film carrier and then assembled onto a low resistivity (3–4 <formula formulatype="inline"><tex>$\ \Omega\,\cdot\,$</tex></formula>cm) silicon substrate by flip-chip bonding. Individual and 2<formula formulatype="inline"> <tex>$\,\times\,$</tex></formula>2 arrays of meander and spiral inductor designs have been successfully fabricated with air gap heights ranging from 15 to 31 <formula formulatype="inline"><tex>$\mu$</tex></formula>m. Maximum <formula> <tex>$Q$</tex></formula> factors of <formula formulatype="inline"><tex>${\sim}$</tex> </formula>15 and <formula formulatype="inline"><tex>${\sim}$</tex></formula>13 at <formula formulatype="inline"><tex>${\sim}$</tex></formula>1 GHz have been achieved for meander and spiral suspended inductor devices before pad deembedding. It is shown that the optimal air gap between the inductor and substrate surface is <formula formulatype="inline"><tex>${\sim}{\hbox{15}}\ \mu$</tex></formula>m beyond which no further enhancement in the <formula formulatype="inline"> <tex>$Q$</tex></formula> factor can be obtained for devices on low-resistivity substrates. The experimental results are in excellent agreement with that of theoretical simulation. The inductor assembly method requires minimal chip/wafer processing for integration of high-<formula><tex>$Q$</tex></formula> inductors. </para>

This paper describes a method to vary the flexural bending stiffness of a multi-layeredbeam. The multi-layered beam comprises a base layer with polymer layers on the upperand lower surfaces, and stiff cover layers. Flexural stiffness variation is based on theconcept that when the polymer layer is stiff, the cover layers are strongly coupled tothe base beam and the entire multi-layered beam bends as an integral unit. Ineffect, we have a ‘thick’ beam with contributions from all layers to the flexuralbending stiffness. On the other hand, if the shear modulus of the polymer layers isreduced, the polymer layers shear as the base beam undergoes flexural bending,the cover layers are largely decoupled from the base, and the overall flexuralbending stiffness correspondingly reduces. The shear modulus of the polymer layeris reduced by increasing its temperature through the glass transition. This isaccomplished by using embedded ultra-thin electric heating blankets. From experimentsconducted using two different polymer materials, polymer layer thicknesses and beamlengths, the flexural stiffness of the multi-layered beam at low temperature wasobserved to be between two and four times greater than that at high temperature.