Showing papers on "Coplanar waveguide published in 1998"

Distributed MEMS true-time delay phase shifters and wide-band switches

Abstract: Wide-band switches and true-time delay (TTD) phase shifters have been developed using distributed microelectromechanical system (MEMS) transmission lines for applications in phased-array and communication systems. The design consists of a coplanar waveguide (CPW) transmission line (W=G=100 /spl mu/m) fabricated on a 500 /spl mu/m quartz substrate with fixed-fixed beam MEMS bridge capacitors placed periodically over the transmission line, thus creating a slow-wave structure. A single analog control voltage applied to the center conductor of the CPW line can vary the phase velocity of the loaded line by pulling down on the MEMS bridges to increase the distributed capacitive loading. The resulting change in the phase velocity yields a TTD phase shift. Alternatively, the control voltage can be increased beyond the pull-down voltage of the MEMS bridges such that the capacitive loading greatly increases and shorts the line to ground. The measured results demonstrate 0-60 GHz TTD phase shifters with 2 dB loss/118/spl deg/ phase shift at 60 GHz (/spl sim/4.5-ps TTD) and 1.8 dB loss/84/spl deg/ phase shift at 40 GHz. Also, switches have been demonstrated with an isolation of better than 40 dB from 21 to 40 and 40 to 60 GHz. In addition, a transmission-line model has been developed, which results in very close agreement with the measured data for both the phase shifters and switches. The pull-down voltage is 10-23 V, depending on the residual stress in the MEMS bridge. To our knowledge, this paper presents the first wide-band TTD MEMS phase shifters and wide-band switches to date.

Millimeter-wave Ti:LiNbO/sub 3/ optical modulators

Abstract: The design, fabrication, and characteristics of ridged Ti:LiNbO/sub 3/ optical modulators that work in the millimeter-wave region are presented. A new concept of design under velocity matching is demonstrated for the proposed modulator. It has been shown by calculation that impedance matching is achieved and conductor loss is greatly reduced under velocity matching with wider gaps and a thicker coplanar waveguide electrode in conjunction with a ridge structure. Two types of Mach-Zehnder optical intensity modulators for the wavelength of 1.5 /spl mu/m are developed. A fully packaged module for 40 Gb/s transmission with a half-wave voltage of 3.5 V and a broadband modulator responsible up to 100 GHz with a half-wave voltage of 5.1 V.

Empirical model of the microwave properties of high-temperature superconductors

Abstract: This paper presents simple correct models of high-temperature superconductor (HTS) film parameters at microwave frequencies. The models are based on the enhanced two-fluid model of a superconductor. The quasi-particle scattering and peculiarities of the normal conductivity of the HTS at microwaves, including residual resistance of a material, are taken into account. The difference between the known Gorter and Casimir two-fluid model of low-temperature superconductor and the enhanced two-fluid model of HTS is proven. A simple quasi-static model of current distribution across the microstrip line and coplanar waveguide is used for a simulation of a contribution of the superconductor transport processes into impedance per unit length of the transmission lines considered. The models developed were applied to a simulation of microstrip line and coplanar waveguide resonators. Good agreement of simulated results and measurements in a wide temperature range has been demonstrated. The model presented can be considered as a starting point for the formation of the computer-aided design (CAD) package of HTS microwave components.

Characterization of broad-band transmission for coplanar waveguides on CMOS silicon substrates

Abstract: This paper presents characteristics of microwave transmission in coplanar waveguides (CPW's) on silicon (Si) substrates fabricated through commercial CMOS foundries. Due to the CMOS fabrication, the metal strips of the CPW are encapsulated in thin films of Si dioxide. Many test sets were fabricated with different line dimensions, all on p-type substrates with resistivities in the range from 0.4 /spl Omega//spl middot/cm to 12.5 /spl Omega//spl middot/cm. Propagation constant and characteristic impedance measurements were performed at frequencies from 0.1 to 40 GHz, using a vector-network analyzer and the through-reflect-line (TRL) deembedding technique. A quasi-TEM equivalent circuit model was developed from the available process parameters, which accounts for the effects of the electromagnetic fields in the CPW structure over a broad frequency range. The analysis was based on the conformal mapping of the CPW multilayer dielectric cross section to obtain accurate circuit representation for the effects of the transverse fields.

112-GHz, 157-GHz, and 180-GHz InP HEMT traveling-wave amplifiers

Abstract: We report traveling-wave amplifiers having 1-112 GHz bandwidth with 7 dB gain, and 1-157 GHz bandwidth with 5 dB gain. A third amplifier exhibited 5 dB gain and a 180 GHz high-frequency cutoff. The amplifiers were fabricated in a 0.1-/spl mu/m gate length InGaAs/InAlAs HEMT MIMIC technology. The use of gate-line capacitive-division, cascode gain cells and low-loss elevated coplanar waveguide lines have yielded record bandwidth broad-band amplifiers.

A class of novel uniplanar series resonators and their implementation in original applications

Abstract: A class of novel millimetric uniplanar series resonators are presented, which can be used in monolithic and hybrid uniplanar microwave integrated circuits (MIC's). The proposed structures are able to demonstrate low radiation and compactness characteristics, which are attractive for passive and active monolithic and hybrid integrated circuits. A principle of achieving these high-quality circuits is described and also confirmed by experimental and theoretical results, which are in good agreement up to 50 GHz. To illustrate the features of the proposed series resonators and demonstrate their effectiveness, two classes of miniature coplanar waveguide (CPW) filters (namely, low-pass and bandpass) are designed using these resonators. The developed low-pass filter has some important advantages such as low insertion loss in passband, very wide stopband, high cutoff rates, small size, low number of elements, and an effective control of spurious signals. On the other hand, the newly developed bandpass filter provides an alternative, yet compact, structure to classical filters. Obviously, many other classes of filters or passive components can also be designed.

Characteristics of periodically loaded CPW structures

Abstract: A capacitively loaded coplanar waveguide (CPW) resonator has been studied. It has been shown that the proposed resonator can be used to achieve a slow-wave effect without occupying extra surface area and it has a good performance as compared with the conventional half-wavelength CPW resonator. Furthermore, dispersive effects have been increased with the number of slots in periodically loaded structures.

Doped Ba0.6Sr0.4TiO3 thin films for microwave device applications at room temperature

Abstract: The dielectric property comparison between laser-ablated Mn-doped and undoped Ba0.6Sr0.4TiO3 (BST) thin films at low frequency (100 kHz) and at microwave frequencies has been demonstrated. The dielectric properties were characterized at low frequency using interdigital capacitors, and at microwave frequencies with coplanar waveguide (CPW) meander-line phase shifters. With 1% Mn-doped BST films, results to date gave a dielectric constant as high as 2100, a tunability of 85% with DC bias field of 88 kV/cm, and a loss tangent without DC bias as low as 0.0033 at 100 kHz and room temperature. At 10 GHz, our best result to date was also obtained with 1% Mn-doped BST film deposited on MgO substrate, which at room temperature possess a dielectric constant of 1820 with a tunability of 56% at 40 kV/cm DC electric field, and a loss tangent of 0.006 at zero bias.

Frequency-dependent propagation characteristics of coplanar waveguide electrode on 100 GHz Ti:LiNbO3 optical modulator

Abstract: The microwave propagation characteristics of a coplanar waveguide electrode in the frequency range 45 MHz – 110 GHz were studied in order to evaluate the factors which limit the performance of a high-speed ridged Ti:LiNbO3 optical modulator. Since the effective microwave index is constant in the higher frequency range, neither structure nor material dispersions of the modulator are observed. In addition to the conductor loss, the dielectric loss also increases above 20 GHz. The dielectric loss is shown to originate not only in the LiNbO3 substrate, but also in the silicon oxide buffer layer.

Accurate Characteristic Impedance Measurement on Silicon

Abstract: This paper presents a new method that accurately determines the characteristic impedance of planar transmission lines printed on lossy dielectrics even when contact-pad capacitance and conductance are large. We demonstrate the method on a coplanar waveguide fabricated on fused silica and a microstrip line fabricated on a highly conductive silicon substrate.

Coplanar microwave circuit having suppression of undesired modes

Abstract: Lossy resistive films (220, 220') and longitudinally extending coplanar conductors (206, 210) of a radio frequency transmission line are defined on the planar surface (204) of an insulating substrate (202). The resistive films (220, 220') may be positioned away from or in the space between parallel conductors (206, 210). The coplanar conductors may be configured as a two conductor coplanar slotline (206, 210) or as part of a three conductor coplanar wave guide (206, 210, 230). The resistive film (338) may also be extended (sea of resistor) over otherwise unused portions of the substrate. Still another embodiment provides a signal attenuating coplanar resistive structure (350) between a coplanar signal conductor (356) and a coplanar ground conductor (370). The coplanar resistive structure (400, 500) may include a meandering, or serpentine conductor (510) or interdigitated comb-like resistive film fingers (412a, 416).

Transmission lines and passive elements for multilayer coplanar circuits on silicon

Abstract: In this paper, propagation properties of both standard and multilayer coplanar lines on different types of silicon substrates, as well as a number of quasi-lumped and stub-type circuit elements, are investigated. For the transmission lines, emphasis is placed on losses. As examples for circuit elements, a lumped parallel resonator and a high-low impedance low-pass filter are demonstrated.

RF and mechanical characterization of flip-chip interconnects in CPW circuits with underfill

Abstract: RF characterization of flip-chip interconnects in coplanar waveguide (CPW) circuits with underfill is reported. The scattering-parameters have been measured up to 40 GHz for GaAs CPW through-line chips flip-chip mounted on an alumina substrate with and without an underfill epoxy. A lumped-element model of flip-chip interconnect has been developed for flip-chip assemblies with and without epoxy. Fatigue life of flip-chip assemblies has been computed for different chip sizes and substrates. The results show feasibility of using underfill encapsulant in microwave/millimeter-wave frequency range.

Coplanar passive elements on Si substrate for frequencies up to 110 GHz

Abstract: This paper provides both modeling and design information on coplanar passive elements on a silicon substrate. The influence of substrate resistivity on coplanar waveguide (CPW) loss is discussed, and elements of a cell library for coplanar monolithic microwave integrated circuits (MMIC's) on high-resistivity substrates are presented. The elements include discontinuities, junctions, and spiral inductors. The models are based on field-theoretical simulations and verified by S-parameter measurements up to 110 GHz.

Improvement in performance of electrically tunable devices based on nonlinear dielectric SrTiO3 using a homoepitaxial LaAlO3 interlayer

Abstract: Improved structural and dielectric properties of nonlinear dielectric SrTiO3 thin films on LaAlO3 substrates were accomplished by incorporating a homoepitaxial LaAlO3 interlayer between the substrate and the dielectric film. Using this interlayer, the quality factor of SrTiO3 films with high-temperature superconducting YBa2Cu3O7−x electrodes on LaAlO3 substrates was improved by more than 50% at 4.2 GHz and 4 K. This improvement, combined with no change in nonlinearity, led to greater than a 50% enhancement of the finesse factor (defined as the product of the quality factor and the fractional shift resonant frequency) for the coplanar waveguide microwave resonators. The reduced planar defect density in the SrTiO3 films was attributed to this improvement.

A flip-chip MMIC design with coplanar waveguide transmission line in the W-band

Abstract: This paper describes a design method for flip-chip monolithic millimeter-wave integrated circuits (MMICs) with a coplanar waveguide (CPW) transmission line for W-band applications. We proposed a test structure for obtaining accurate flip-chip CPW line models. We examined the transmission line characteristics of the CPW line using the test structure in the millimeter-wave range and modeled them. Using the CPW line models, we designed and fabricated both two- and three-stage amplifiers using 0.15-/spl mu/m InGaP/InGaAs high electron-mobility transistor technology. The maximum power gain of the two-stage amplifier is 12 dB at 79 GHz. The three-stage amplifier has a maximum power gain of 16 dB at 77 GHz. The agreement of measured S-parameters with calculated results demonstrates that the proposed test structure is suitable for characterizing flip-chip CPW lines and provides very accurate models.

A novel coplanar transmission line to rectangular waveguide transition

Abstract: Waveguides (WG) are often utilised for antenna or filter design. This paper presents a new, easy to build transition from a coplanar line to a WG, which is often needed to embed WGs into MMIC designs or vice versa. In contrast to the well known E-plane probe-transitions and ridged waveguide-transitions, the proposed waveguide transition does not require modifications of the waveguide and the planar design. The transition was optimised for a low radiation pattern on the top side and for a broadband transmission using the Finite Difference Time Domain Method (FDTD). Measurements for verification are also presented.

W-Band finite ground coplanar waveguide (FGGPW) to microstrip line transition

Abstract: fA uniplanar transition from finite ground coplanar waveguide (FGCPW) to microstrip line operating at W-Band has been developed. The design is uniplanar and does not require viaholes or wirebonds. The transition, centered at 94 GHz, results in 0.2 dB insertion loss with a bandwidth of 20%. The return loss is better than -17 dB from 85 GHz to 100 GHz. To our knowledge, this simple transition shows state-of-the-art performance, and can be very useful for CPW-probe to microstrip circuit measurements.

RF and mechanical characterization of flip-chip interconnects in CPW circuits with underfill

Abstract: RF characterization of flip-chip interconnects in CPW circuits with underfill has been investigated by measuring the scattering-parameters up to 40 GHz for GaAs coplanar waveguide (CPW) through line chips flip-chip mounted on alumina substrate with and without underfill epoxy. Fatigue life of flip-chip assemblies has been computed for different chip sizes and substrates. The results show feasibility of using underfill encapsulant in microwave/mm-wave frequency range.

Low cost wideband RF port structure for microwave circuit packages using coplanar waveguide and BGA I/O format

Abstract: A MMIC package comprises a trace pattern of a coplanar wave guide which matches impedances at all transitions to enhance signal transmission and avoid reflection. The invention employs metalization on a dielectric substrate material wherein this metalization is patterned in order to provide gaps and signal carrying conductors which enhance the signal propagation and reduce impedance mismatches in order to provide a package capable of handling high frequency microwave signals.

Avoiding cross talk and feed back effects in packaging coplanar millimeter-wave circuits

Abstract: The impact of the packaging configuration on cross talk and feed back effects caused by parasitic substrate modes is investigated for coplanar millimeter-wave circuits. It is demonstrated theoretically and by means of several circuit examples that both the mounting configuration and the thickness of the semiconductor substrate of coplanar MIMICs have to be chosen appropriately, in order to avoid circuit degradation or even failure.

Measured attenuation of coplanar waveguide on CMOS grade silicon substrates with polyimide interface layer

Abstract: The measured propagation constant of a coplanar waveguide on CMOS grade silicon with a polyimide interface layer is presented. It is shown that the transmission line can have an attenuation comparable to other transmission lines on Si substrates if the proper polyimide thickness is used.

In-line polymeric construct for modulators, filters, switches and other electro-optic devices

Abstract: A coplanar waveguide polymeric in-line fiber construct (CPW-PILF) formed on an optic half coupler substrate base or D-fiber wherein the surface is polished down through the cladding on the optical fiber so as to form an evanescent coupling region on the surface. Co-planar, spaced-apart electrodes are deposited on the surface with their gap aligned over the coupling region, and an electro-optic (EO) polymeric waveguide is deposited over the electrodes and between the electrode gap. Light transmitted thorough the optical fiber is evanescently coupled to said waveguide and modulated by a signal applied to the electrodes. Alternatively, the waveguide is deposited on the surface of the substrate and the electrodes are deposited over the waveguide.

Electrode optimization for high-speed traveling-wave integrated optic modulators

Abstract: Different electrode configurations for LiNbO/sub 3/-based Mach-Zehnder traveling-wave electrooptic modulators are analyzed. It is found that the Z-cut coplanar waveguide (CPW) configuration provides the best compromise between the characteristic impedance, the half-wave voltage, and the driving power. To increase the bandwidth and simultaneously reduce the half-wave voltage, an optimum design of multisection phase reversal electrode is proposed. To verify the theoretical predictions experimentally, two modulators, both using the Z-cut LiNbO/sub 3/ CPW configuration, were fabricated and characterized, one with an optimized five-section phase reversal electrode and the other with a conventional single-section electrode. By comparing the performances of these two devices, it is confirmed that significant improvements on the bandwidth to half-wave voltage ratio and the flatness of the frequency response can indeed be obtained from using an optimized multisection phase reversal electrode.

Characteristics of trenched coplanar waveguide for high-resistivity Si MMIC applications

Abstract: A novel low RF loss trenched coplanar waveguide (CPW) transmission-line structure fabricated using evaporated aluminum tracks on a high-resistivity (10-k/spl Omega/ cm) silicon (HRS) substrate is reported. By assuming that Schottky contact boundaries exist at the metal silicon substrate interface in the CPW line, the finite-element analysis method is used to determine the simulated behavior of the structure. The distributed capacitance, leakage conduction current, and dynamic shunt conductance for the line are shown to be a function of dc bias applied to the line, and also to reduce as a function of trench depth in the normal bias regime. Experimental results show: (1) the reduction of RF losses in comparison with conventional aluminum conductor CPW line structures may be as much as 0.5 dB/cm at 30 GHz; (2) by proper positive dc biasing of a CPW line on a p-type HRS substrate, a further reduction (0.2 dB/cm) in RF loss at 30 GHz can be achieved; (3) predicted trends in line leakage current, capacitance, and relative characteristics impedance are experimentally verified. The proposed waveguide structure may be utilized in a special fabrication process designed for RF/microwave applications.

Transition between circuit transmission line and microwave waveguide

Abstract: A transition is provided for interfacing a coplanar waveguide with a three dimensional microwave waveguide. The transition includes three coplanar conductors that are formed integrally with and extend from the coplanar waveguide. The transition extends into the microwave waveguide through a slot, with the plane of the transition being perpendicular to the direction of propagation of the electric field in the waveguide. The center conductor of the transition is a patch whose width increases. The other two conductors are attached to the side conductors of the coplanar waveguide and to the exterior of the waveguide. They flank the patch and have curved edges complementary to those of the patch. The gaps are initially narrow, and become wider gradually. Further, as each guide steers the electric field while changing direction by 90°, it rotates the orientation of the electric field vector by the same amount.

Fabrication and investigation of YBa2Cu3O7−δ/Ba0.05Sr0.95TiO3 thin film structures for voltage tunable devices

Abstract: High-temperature superconducting/ferroelectric thin film structures were deposited by laser ablation. Three types of voltage tunable devices were fabricated and investigated-trilayer capacitor, planar interdigital capacitor and coplanar waveguide. As ferroelectric the solid solution BaxSr1-xTiO3 was chosen with barium content x = 0.05 because its Curie temperature is close to the liquid nitrogen boiling point (77 K). Temperature and voltage dependences of the Ba0.05Sr0.95TiO3 dielectric constant epsilon(r,BSTO) were studied. High epsilon(r,BSTO) values were determined-up to 3000 at 75 K, 20 GHz and zero de bias. Efficient voltage tunability was demonstrated (up to 40%) at loss level tan delta=0.01-0.1. Compact YBa2Cu3O7-delta/Ba0.05Sr0.95TiO3 coplanar waveguide with as narrow gap as 18 mu m was tested as electrically tunable phase-shifter and field-induced phase shifts of more than 180 degrees were obtained by 35 V de bias at 20 GHz. This improvement was attained by proper choice of the ferroelectric material, accomplished epitaxial growth of the films and decrease of the specific dimensions. (C) 1998 Published by Elsevier Science B.V. All rights reserved.

Investigation of microstrip and coplanar transmission lines on lossy silicon substrates without backside metallization

Abstract: Silicon circuits, now penetrating well into the microwave frequency range, use lossy silicon substrates. Consequently, the microwave performance of transmission lines on this substrate becomes increasingly important and has been investigated here up to 20 GHz. It is shown that transmission lines on 20-/spl Omega//spl middot/cm substrates have no need for backside metallization and backside via holes. Two models for different line types are derived from measurements and verified against them. A coplanar waveguide (CPW) with an overall width of less than 30 /spl mu/m was fabricated with an attenuation of 0.5 dB/mm at 20 GHz, which is acceptable for monolithic microwave integrated circuit (MMIC) design.

Broadband and low driving-voltage LiNbO3 optical modulators

Abstract: Travelling-wave type LiNbO3 (LN) optical modulator structures employing thicker coplanar waveguide (CPW) electrodes are presented, for achieving a lower driving-voltage and broader bandwidth characteristic with an impedance and velocity match condition. To design a high-performance device-structure, a figure of merit p is introduced for travelling-wave type optical modulators, which can make an excellent modulator with a smaller value of p. Microwave characteristics of the modulators with a ridged type LN-substrate are theoretically compared to those of planar-type modulators. As a result, the characteristic-impedance and the product of driving-voltage and interaction-length of the electrodes in modulators are shown to be almost determined only by the buffer-layer thickness for any modulator-structure under a velocity-matching condition. By utilising a wider gap and accordingly thicker electrodes with a ridged LN-substrate, LN modulator structures having a 40 GHz-band and far less than a 3 V driving-voltage have been clarified under a 50 Ω characteristic-impedance system.