Coplanar Waveguide Circuits Research Articles

Femtosecond electron beam probe of ultrafast electronics

The need for ever-faster information processing requires exceptionally small devices that operate at frequencies approaching the terahertz and petahertz regimes. For the diagnostics of such devices, researchers need a spatiotemporal tool that surpasses the device under test in speed and spatial resolution. Consequently, such a tool cannot be provided by electronics itself. Here we show how ultrafast electron beam probe with terahertz-compressed electron pulses can directly sense local electro-magnetic fields in electronic devices with femtosecond, micrometre and millivolt resolution under normal operation conditions. We analyse the dynamical response of a coplanar waveguide circuit and reveal the impulse response, signal reflections, attenuation and waveguide dispersion directly in the time domain. The demonstrated measurement bandwidth reaches 10 THz and the sensitivity to electric potentials is tens of millivolts or −20 dBm. Femtosecond time resolution and the capability to directly integrate our technique into existing electron-beam inspection devices in semiconductor industry makes our femtosecond electron beam probe a promising tool for research and development of next-generation electronics at unprecedented speed and size.

Evaluation of transmission characteristics of CVD-grown graphene and effect of tuning electrical properties of graphene up to 50 GHz

Graphene has been investigated as a transparent conductive film for use in a variety of devices, and in recent years it has shown promise for use in millimeter-wave devices as 5G technology. In this study, we applied single-layer (SL), triple-layer (3L), and P-type doped 3L graphene to coplanar waveguide (CPW) transmission lines and obtained transmission characteristics (S21) from 1 to 50 GHz, which covered the 5G band. Furthermore, an equivalent circuit model of the CPW used in the measurements was constructed and simulations were performed, which showed good agreement with the measured results. The results validated the transmission properties of the graphene and the contact impedance at the interface between electrodes and the graphene in CPW circuits, which are necessary parameters for designing antennas using graphene. In addition, by comparing the transmission loss of three types of graphene, the parameters for improving the transmission characteristics were clarified.

Fabrication of airbridges with gradient exposure

In superconducting quantum circuits, airbridges are critical for eliminating parasitic slotline modes of coplanar waveguide circuits and reducing crosstalks between direct current magnetic flux biases. Here, we present a technique for fabricating superconducting airbridges. With this technique, a single layer of photoresist is employed, and the gradient exposure process is used to define the profile of airbridges. In order to properly obtain the bridge profile, we design exposure dosage based on residual photoresist thickness and laser power calibrations. Compared with other airbridge fabrication techniques, the gradient exposure fabrication technique provides the ability to produce lossless superconducting airbridges with flexible size and, thus, is more suitable for large-scale superconducting quantum circuits. Furthermore, this method reduces the complexity of the fabrication process and provides a high fabrication yield.

Permeability and Ferromagnetic Resonance Study for Magnetic Nanowires Substrate With Copper Layer

In this letter, a straightforward accurate method for magnetic nanowires (MNWs) ferromagnetic resonance (FMR) frequency determination and permeability extraction is proposed. FMR frequencies are obtained using a one-port coplanar waveguide (CPW) circuit system. Relative permeability, defined as ${\mu } = {\mu }{'}\mathrm {-j} {\mu }{'}{'}$ , of MNW samples is extracted by “four steps” method, commonly used for thin films (Bekker et al. , 2004; Liu et al. , 2005; Wei et al. , 2015). MNW samples with and without copper (Cu) layer are compared. Samples with a Cu layer show stronger FMR resonances, negligible influences from board resonances, and low distortion ${\mu }{'}$ compared to those without a Cu layer. From ${\mu }{'}{'}$ , the average linewidth of a cobalt sample with and without Cu layer is 4.96 and 5.6 GHz, respectively. From the peak of ${\mu }{'}{'}$ , the FMR frequency of an iron sample is higher at low dc field when compared to cobalt. This can be beneficial for microwave device design when external dc field is limited, and higher operating frequency is required.

Laser-Assisted Additive Manufacturing of mm-Wave Lumped Passive Elements

The performance of additively manufactured microwave passive elements and interconnects continues to improve as better materials, and process techniques are developed. In this paper, laser-enhanced direct print additive manufacturing (LE-DPAM) is used to fabricate capacitors and inductors for coplanar waveguide (CPW) circuits. Acrylonitrile butadiene styrene is used as the dielectric that is printed using fused deposition modeling, and DuPont CB028 conductive paste is deposited using microdispensing. These two techniques are combined with picosecond-pulsed laser machining to achieve $\simeq 12$ - $\mu \text{m}$ slots on printed conductors, producing aspect ratios greater than 2:1. The same laser is used to fabricate vertical interconnections that allow for the fabrication of multilayer inductors. Inductances in the range of 0.4–3 nH are achieved, with a maximum quality factor of 21, selfresonance frequencies up to 88 GHz, and an inductance per unit of area of 5.3 nH/mm2. Interdigital capacitors in the range of 0.05–0.5 pF are fabricated, having a maximum quality factor of 1000, a capacitance per unit area of 1 pF/mm2, and selfresonances up to 120 GHz. All the components are made on the center line of a CPW that is 836- $\mu \text{m}$ wide. The results show that LE-DPAM enables the fabrication of compact passive circuits that can be easily interconnected with MMIC dies, which at the same time can be manufactured as part of a larger component. This enables the fabrication of structural electronics that are functional into the millimeter-wave frequency range. Bounds on the inductances and capacitances per unit area are related to material and geometry limitations.

1.4 µm-Thick Transparent Radio Frequency Transmission Lines Based on Instant Fusion of Polyethylene Terephthalate Through Surface of Ag Nanowires

Though a percolated network of silver nanowires (AgNWs) has been considered the most promising flexible transparent electrode because of it high conductivity, high transmittance, and excellent flexibility, fabrication of AgNW-based transmission lines designed to conduct high frequency signals has been scarcely reported. The fabrication and performance of extremely thin (1.4 µm thick) and low lossy (smaller than − 17 dB for reflection coefficient corresponding to 2.5 GHz) transmission lines with unprecedented transparency (higher than 90% for the entire visible light spectrum) are demonstrated in this study. AgNWs deposited onto a 1.4 µm-thick polyethylene terephthalate (PET) sheet were irradiated by intense-pulsed-light to selectively raise their temperature. The intensive photon energy delivered to the AgNWs simultaneously caused the active diffusion of Ag atoms and plasmonic welding, resulting in large drops in resistivity without drastic changes in their physical shape or the optical transmittance of the films. Furthermore, absorption of heat also thermally activated the underlying polymer and causing it to react with the surface of the AgNWs—this results in enhanced adhesion between the AgNWs and the PET. Measurements and simulation of specially designed coplanar waveguide circuits revealed that the fabricated electrode could simultaneously provide excellent transmission characteristics and mechanical stability and transparency.

Transparent and flexible high frequency transmission lines based on composite structure comprising silver nanowires and polyvinyl butyral

Percolated networks of silver nanowires (AgNWs) have attracted intensive attention because of their remarkable mechanical stability, along with their excellent optical and electrical performance for the fabrication of flexible transparent electrodes. Most prior research has mainly focused on fabricating transparent electrodes that can be used in optoelectronic devices such as touch sensors, light emitting diodes, and photovoltaics. However, fabrication of transparent and flexible transmission lines designed to conduct alternating current of high frequency has not been reported so far. Herein, we developed highly transparent, mechanically stable transmission line by employing inverted layer processing (ILP) in order to embed the AgNWs just below the surface of a free-standing transparent polymer. For this, we synthesized polyvinyl butyral (PVB), which can be prepared from polyvinyl alcohol by reaction with butyraldehyde, for AgNW support. AgNWs deposited on a preliminary substrate (glass) were plasmonically sintered to significantly enhance their conductivity, and then transferred to the surface of the cured PVB film by the ILP. Measurements and simulation of specially designed coplanar waveguide circuits comprising AgNWs and PVB revealed that the fabricated electrode can simultaneously provide impressive transmission performance as well as excellent mechanical flexibility and transparency. An interesting finding was that the transmission characteristics and mechanical stability are in a trade-off relationship, which needs to be carefully considered in the design and selection of materials for the flexible transmission lines.

Radio-Frequency Characteristics of Partial Dielectric Removal HR-SOI and TR-SOI Substrates

High-resistivity silicon-on-insulator (HR-SOI) and trap-rich high-resistivity silicon-on-insulator (TR-SOI) substrates have been widely adopted for high-performance rf integrated circuits. Radio-frequency loss and non-linearity characteristics are measured from coplanar waveguide (CPW) transmission lines fabricated on HR-SOI and TR-SOI substrates. The patterned insulator structure is introduced to reduce loss and non-linearity characteristics. A metal-oxide-semiconductor (MOS) CPW circuit model is established to expound the mechanism of reducing the parasitic surface conductance (PSC) effect by combining the semiconductor characteristic analysis (pseudo-MOS and C–V test). The rf performance of the CPW transmission lines under dc bias supply is also compared. The TR-SOI substrate with the patterned oxide structure sample has the minimum rf loss (<0.2 dB/mm up to 10 GHz), the best non-linearity performance, and reductions of 4 dB and 10 dB are compared with the state-of-the-art TR-SOI sample's, HD2 and HD3, respectively. It shows the potential application for integrating the two schemes to further suppress the PSC effect.

Environmentally-friendly cellulose nanofibre sheets for humidity sensing in microwave frequencies

This paper investigates environment friendly cellulose nanofibres (CNF) as new and sensitive material for humidity sensing in RF/microwave frequencies. CNF sheets were fabricated by sonocatalyzed TEMPO process and physically characterized. Humidity sensing investigation was performed with CNF sheets taped on the top of circuits in coplanar waveguide (CPW) technology. This investigation includes sensitivity and dynamic range analysis with reflected waves along the CPW circuit through resonant frequency shift, and transmitted waves through S21 phase shift. Moreover, sheets with various amounts of CNF were used to study the influence of CNF weight on humidity sensing performances. Regarding the resonant frequency shift, the best sensitivity was measured with the weightier CNF film (71g/m2), that is 2.82MHz/%RH from 55%RH to 100%RH. Regarding the phase shift, the same film sensitivity is 0.7°/%RH from 70%RH to 100%RH, with a figure of merit of 7.43°/dB as a phase shifter.

Co-sputtered MoRe thin films for carbon nanotube growth-compatible superconducting coplanar resonators

Molybdenum rhenium alloy thin films can exhibit superconductivity up to critical temperatures of . At the same time, the films are highly stable in the high-temperature methane/hydrogen atmosphere typically required to grow single wall carbon nanotubes. We characterize molybdenum rhenium alloy films deposited via simultaneous sputtering from two sources, with respect to their composition as function of sputter parameters and their electronic dc as well as GHz properties at low temperature. Specific emphasis is placed on the effect of the carbon nanotube growth conditions on the film. Superconducting coplanar waveguide resonators are defined lithographically; we demonstrate that the resonators remain functional when undergoing nanotube growth conditions, and characterize their properties as function of temperature. This paves the way for ultra-clean nanotube devices grown in situ onto superconducting coplanar waveguide circuit elements.

High Power 20-GHz Photodiodes With Resonant Microwave Circuits

We report the design, fabrication, and characterization of resonant microwave circuits integrated with InGaAs/InP modified unitravelling-carrier photodiodes. The photodiodes were flip-chip bonded on AlN substrates with coplanar waveguide circuits. The RF output power levels of 23 and 21.6 dBm at 20 GHz are demonstrated for microwave open stubs and shorted stubs, respectively.

CPW balun for printed balanced antennas

In coplanar waveguide (CPW) circuits, printed balanced antennas must be excited through baluns. These baluns often feature coplanar-to-slotline transitions that must be tuned and matched by electromagnetic optimisation, and may interfere with the antenna backward radiation. A new CPW balun for printed balanced antennas is presented and modelled. As its multimodal circuit model makes clear, it integrates an impedance-matching network within its structure that can be analytically designed. The balun has been experimentally tested, exhibiting good agreement with its circuit model and a weak electromagnetic interaction with the antenna radiation.

Design and characterization of microfluidic housing effects on coplanar waveguide microfluidic delay line performance

A fluid and its housing are integrated on a coplanar waveguide circuit surface, realizing a variable delay line. Performance tradeoffs for different fluidic housing shapes are investigated. Simulation and measurement results for two circuits are shown with the housing filled with air or de-ionized water. © 2012 Wiley Periodicals, Inc. Microwave Opt Technol Lett 55:789–793, 2013; View this article online at wileyonlinelibrary.com. DOI: 10.1002/mop.27434

Dielectric spectroscopy of a thin surface layer by differential time-domain reflectometry using a coplanar waveguide circuit line probe

Dielectric spectroscopy is a powerful method for measuring the relaxation properties of various materials, especially soft materials. Among these soft materials, living systems and artificial multilayer films have layered structures with a thickness on the order of nano- to micrometers. To measure the dielectric spectra of such a thin layer, the measurement probe for dielectric spectroscopy requires the structure to possess a low measurement depth that is comparable to the thickness of the thin layer. For this purpose, we developed a probe for measuring the dielectric spectra of material surfaces of various depths using differential time-domain reflectometry. The developed probes consist of coplanar waveguide circuits of 280 µm to 1 mm line width, which allows for the measurement of the dielectric spectra of the material surface layer with thicknesses in the range of 450 µm to 1.2 mm. The proposed structure of the measurement probe enables the dielectric spectroscopy of a thinner material surface layer by reducing the width and pitch of the coplanar waveguide circuit lines.

Dielectric thickness and ground width effect on multilayer coplanar components and circuits for ceramic multichip modules

AbstractThis article investigates the effect of dielectric thickness and ground width on the performance of multilayer conductor backed coplanar waveguide lumped elements and circuits fabricated on advanced multilayer photoimageable thick‐film ceramic multichip module (MCM) technology. From the S‐parameters, the effective dielectric constant is extracted to investigate the effect of dielectric thickness and ground‐width on transmission line dispersion. The equivalent circuit parameters for multilayer ceramic‐based capacitors and inductors are investigated for various dielectric thicknesses and ground‐plane widths. Finally, the practical effect of dielectric thickness and ground width are investigated for a highly compact and high performance lumped element low pass filter at 3 GHz, developed for cost‐effective MCM applications. © 2012 Wiley Periodicals, Inc. Microwave Opt Technol Lett 54:1127–1132, 2012

High Bandwidth Resonant Radio Frequency Circuit for Lipid Bilayer Detection

Research on ion channels are traditionally performed in the DC regime. Only a few attempts having been made to conduct RF measurements for probing ion channel properties. We present here simulations and subsequent measurements of an integrated coplanar waveguide and microfluidic tank circuit detecting bilayer formation. We observe a 5 MHz shift in resonant frequency and a 1.4 dB shift in amplitude when a lipid bilayer is formed. These measurements allow for in-vitro radio frequency recordings with nanosecond readout times. The designed structure also enables the incorporation of simultaneous RF and DC recordings from lipid bilayer embedded proteins such as ion channels.

The Impact of On-Wafer Calibration Method on the Measured Results of Coplanar Waveguide Circuits

This paper compares four commonly used on-wafer calibration methods including multiline thru-reflect-line (TRL), line-reflect-reflect-match, line-reflect-match, and short-open-load- thru, for three diverse coplanar waveguide (CPW) circuits. The magnitudes and phases of S 11 and S 21 of the CPW circuits are compared to quantify how the specific calibration method influences measured scattering parameters. Special care is taken to ensure that the measured scattering parameters are normalized to the same reference impedance and reference plane for accurate comparison. The measured results are compared with full-wave simulations to provide additional assessment of accuracy. A method to de-embed the discontinuity of the CPW at the probe tip and the CPW of the test structures is presented. The effect of probe-to-device-under-test discontinuity is effectively modeled by one- or two- section of shunt capacitor and series inductor. The results show that the multiline TRL calibration method provides the highest transmission coefficient repeatability on not well-matched circuits and highest accuracy on the three circuits in this paper up to 40 GHz.

Ultra-Wideband CPW-to-Substrate Integrated Waveguide Transition Using an Elevated-CPW Section

In this letter, an elevated-coplanar waveguide (ECPW) is proposed for an intermediate section of a coplanar waveguide (CPW)-to-substrate integrated waveguide (SIW) transition. The ECPW is used to attain a gradual mode matching and to achieve the consequent wide bandwidth. The measurement results show 70% fractional bandwidth at 10 dB return loss and 0.9 dB insertion loss from 19 to 40 GHz. We expect that the proposed SIW transition plays an important role for the integration of high-Q SIW with CPW circuits, such as millimeter-wave system-in-package (SiP) using SIW circuits.

Micromachined wide-band lithium-niobate electrooptic Modulators

We present our detailed study of a micromachined substrate approach for a wide-band lithium-niobate modulator and other ultra-wideband RF interconnection applications. Resonant substrate mode coupling often results in large RF loss that affects the frequency performance in LiNbO/sub 3/ modulators. Using the micromachining approach, we demonstrated significantly reduced resonant mode coupling loss in LiNbO/sub 3/ modulator electrodes. In this paper, the effects of substrate geometry and material combination on microwave transmission are experimentally investigated. Our investigation showed that the RF launch of the coplanar-waveguide circuit is a major contributor to the resonant mode coupling. Micromachining the launch area allows us not only to suppress resonant couplings, but also to retain substrate mechanical strength for high-yield production. Two micromachined modulator die configurations were proposed and experimentally demonstrated.

Power performance and scalability study of AlGaAs/GaAs double-recessed pseudomorphic high electron mobility transistors on unthinned substrate for coplanar waveguide circuit applications

We have investigated the power performance and scalability of AlGaAs/GaAs Double-Recessed Pseudomorphic High Electron Mobility Transistors (DR-PHEMTs) at 10 GHz on an unthinned GaAs substrate for CoPlanar Waveguide (CPW) circuit applications. It was found that the output power varied linearly with the logarithm of the device’s gate width ranging from 200 to 1000 μm. It increased at a rate of 0.01 dB/μm. That worked out to a doubling of output power (or 3 dB) for every 300 μm increase in the gate width. Gain decreased at a rate of about 0.005 dB/μm while PAE generally improved when the gate width was increased. As for DC measurement, the maximum transconductance of the device was about 375 mS/mm at V G = −0.5 V and V DS = 3 V. The gate-drain breakdown voltage (BV GD) measured was −20 V, defined at I G = −1 mA/mm. The microwave performance of the devices was measured on-wafer using a load-pull system at a bias of V G = −0.5 V and V DS = 8 V. For a device with a gate width of 1 mm, its saturated CW output power, gain and PAE value at 10 GHz was 27.5 dBm (0.55 W), 8 dB and 48%, respectively. At this same set of bias conditions, the value of f t and f max was 40 and 80 GHz, respectively.