Low-Loss Coplanar Waveguides Interconnects on Low-Resistivity Silicon Substrate

Vertical-cavity surface-emitting lasers with vertically integrated electro-absorption modulators (EAM-VCSELs) potentially can reach higher modulation bandwidths than directly current-modulated VCSELs. The aforementioned device modulation capabilities are, however, currently restricted by their electrical contact parasitics. It, thus, becomes critical to optimize their access line to improve performance. In this paper, we numerically and experimentally demonstrate that a microstrip (MS) access line using a planarized benzocyclobutene (BCB) layer exhibits improved high-frequency characteristics compared to the coplanar waveguide (CPW) access line used to-date, since it reduces the losses induced by the doped substrates. We also use this opportunity to introduce an innovative technique for BCB layer planarization, which is not only compatible with the EAM-VCSEL double-mesa structure, but is also independent of the device pitch. The resulting BCB layer dielectric permittivity and losses are measured up to 100 GHz, and a side-by-side comparison of the electrical response of three-electrodes MS and CPW access lines is subsequently carried out. Finally, using the measured pad and access line RF responses and the EAM modulation characteristics, the devices with MS access are shown to be no longer limited by their electrode parasitics, but by the modulator internal impedance.

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.

This paper reports the design, fabrication, electrical characterization and packaging of micromachined shunt capacitive switch with low actuation voltage. These switches are fabricated on a low resistive silicon substrate using only a four mask surface micromachining process. The co-planar waveguide is patterned using chrome/gold layer. Positive photoresist S1813 is used as the sacrificial layer. The top beam membrane is made of gold. The membranes are released through a wet release process through Piranha solution. Supercritical point drying tools were used for the top beam release after wet etching to provide anti-stiction. The switches are 300 µm long with 10 μm holes on the top membrane to lower both residual stress and pull-in voltages. These switches exhibit low actuation voltages in the range of 5.5–6.4 V. The RF characterization shows that these switches have low insertion loss and high isolation in the frequency range of interest. The packaging was carried out using commercially available surface mount style RF packages. However, the whole packaging process is performed under low temperature in order to free the MEMS structures of thermally induced stress which otherwise would affect the performance of the switch. The adhesion of the die to the bottom package is excellent and is tested by die shear test. The packaged switch has passed the non-destructive pull test.

This paper presents a whole benzocyclobutene (BCB) film encapsulated 0-level packaging using a wafer level BCB bonding technique. Wafer-scale membrane transfer technique using silicon carrier wafers was used to make BCB membrane caps for encapsulation placed above the device wafers. The RF characteristics using coplanar waveguide (CPW) lines were measured to evaluate the effect of BCB film package. The insertion loss change of CPW lines by BCB membrane package is below 0.01 dB up to 90 GHz, while the glass packaged CPW lines show about 0.1 dB deviation from 20 GHz to 110 GHz

In this paper, we design and implement a coplanar waveguide (CPW) bandpass filter utilizing defected ground structure (DGS) technology. The CPW DGS technology, which only needs one or a series connection of a few cells to exhibit the bandgap characteristics, can provide the attenuation poles in the upper and lower bands to improve the rolloff characteristics of the bandpass filter. Moreover, the equivalent lump values of the CPW DGS are also calculated and good agreement between EM simulation and numerical calculation is obtained. The measured results show that the improved selectivity of upper and lower bands are 10.7 and 46.5 dB/GHz, respectively. © 2004 Wiley Periodicals, Inc. Microwave Opt Technol Lett 42: 331–334, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.20294

Correlation of printing faults with the RF characteristics of coplanar waveguides (CPWs) printed on nonwoven textiles

In this paper, technological solutions based on the use of thick low-k polymer layers on low-resistivity (LR) silicon substrate have been investigated. These thick organic layers provide an insulation of interconnects and passives circuits from the lossy silicon substrate and thus minimize its dramatic impact on the performances. Different thicknesses of polymer layer have been tested. Both EM-simulations and high-frequency characterizations have shown an important benefit in coplanar waveguide performances by employing a large polymer thickness (30 /spl mu/ in our case). A noticeable increase of the Q-factor close to 16% has been achieved with burying the realized CPW lines into a quasi-homogeneous polymer medium.

We present the design and development of an ultra-violet (UV) LIGA (a German acronym for electroplating, lithography and molding) micromachining process on silicon substrates at microwave/millimeter wave frequencies. The process employs an ultra-thick negative photoresist SU-8 that can be spin-coated and processed using conventional lithography techniques. Using this process, we have developed micromachined coplanar waveguide (CPW) interconnects on Si substrates. The conductor-backed micromachined CPW on Si (7.2 /spl Omega/-cm) achieves a measured attenuation of 0.18 dB/cm at 20 GHz.

We present experimental and simulation data of subterahertz attenuation of coplanar waveguides (CPWs) with wide and narrow ground planes. Experimental data are obtained by using a subpicosecond measurement technique based on electrooptic sampling. While time-domain data qualitatively describe the attenuation characteristics, they are converted to the frequency domain by a Fourier transform to give a quantitative interpretation. Simulation data are obtained by full-wave analysis and compared with the experimental results. It is shown that the simulation results consistently agree with experimental results. Furthermore, in the case of CPWs with wide ground planes, both of them are consistent with analytical theory. While CPWs with narrow ground planes have not been analytically studied, our results show that they suffer considerably lower attenuation, which we attribute to a reduced coupling between the CPW mode and substrate modes. The effects of ground-plane width and line dimensions on the attenuation characteristics are discussed in detail.

In this paper the Single Layer Reduction (SLR) technique is presented to compute dispersion characteristics of multilayer coplanar waveguide (CPW) with finite conductor thickness. The effective relative permittivity for the multilayer structure is derived from conformal mapping. Then SLR technique is used to convert multilayer CPW structure to an equivalent single layer structure. The dispersion characteristic of equivalent CPW structure is calculated from the closed form expressions.

Superconducting digital integrated circuits (ICs) are driving increasing demand for low-loss, high-bandwidth vertical interconnects to support advanced cryogenic systems. In this work, broadband superconducting through-silicon coplanar waveguides (CPWs) are fabricated within wet-etched vias by sputtering and patterning niobium (Nb) on the via sidewalls, establishing an effective architecture for high-frequency vertical signal transmission. By systematically optimizing the CPW geometry and introducing sidewall transition compensation within the via, the proposed structure mitigates impedance discontinuities and enhances transmission performance. Experimental measurements demonstrate stable broadband operation, with S<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</sub> ≤ −15 dB and S<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">21</sub> ≥ −3.5 dB from 0.01 to 48 GHz. De-embedded results further indicate that a single through-silicon CPW achieves S<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</sub>​ ≤ −15 dB and S<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">21</sub> ≥ −1 dB up to 37 GHz, confirming low reflection and reduced transmission loss in the via region. These results demonstrate the feasibility of superconducting through-silicon CPWs as high-bandwidth vertical interconnects and provide a scalable pathway toward three-dimensional integration in superconducting computing and cryogenic microwave systems.

The characteristics of proton-exchanged LiNbO3 waveguides fabricated using pyrophosphoric acid process are reported. Using this process, high index change waveguides with step profile have been realized. Low-loss (0.7 dB/cm) channel waveguides have been also obtained by pyrophosphoric acid process. The loss is much lower than that given by conventional benzoic acid process. We show that the reason for low-loss waveguide fabrication is due to the uniform proton-exchange formed by this process, compared with the benzoic acid process.

A grounded co-planar waveguide (GCPW) MEMS switch is presented. The proposed switch has a movable SiN membrane with a signal line and ground lines above a dielectric-air-metal (DAM) cavity on which a ground metal is patterned, resulting in a structure of GCPW transmission line. The electrostatic force makes an RF short path to the ground metal on the bottom of the DAM cavity with metal-to-metal contact. The ground metal which covers silicon substrate makes the switch to be on a low-resistivity silicon substrate. The measured results of the switch validate the proposed structure of the switches utilizing the DAM cavity.

Finite-difference time-domain method is adopted in this paper to build models and simulate full-space coplanar waveguide and shielded coplanar waveguide. The propagation constant and characteristic impedance of coplanar waveguide in different models are obtained and compared with the results of traditional modeling. Finally, the effects of different modeling on electromagnetic characteristics of coplanar waveguide are presented.

Using the method of lines and the separation of even/odd mode, the dispersion characteristics of broadside-coupled coplanar waveguides (CPW) are analyzed. It is found that the structure has a very weak dispersion in a wide frequency band. The theoretical basis is laid for the application of broadside-coupled CPW in three dimensional microwave integrated circuits, and using the quasi-static TEM approach to analyze and design the circuit in wide frequency band.