Thin-film Transmission Lines Research Articles

Tolerance Considerations for MHMIC Manufacturing Process at Millimeter-Wave Band.

This paper investigates the manufacturing uncertainties at a 60 GHz millimeter-wave band for the monolithic hybrid microwave integrated circuits (MHMIC) fabrication process. It specifically deals with the implementation tolerances of thin-film gold microstrip transmission lines, titanium oxide thin-layer resistors, microstrip quarter-wavelength radial stubs, and active device implementation using the gold-bonding ribbons. The impacts of these manufacturing tolerances are assessed and experimentally quantified through prototyped MHMIC circuits. This allows us, on one hand, to identify the acceptable amount of dimensional variation enabling reasonable performances. On the other hand, it aims to establish a relationship between the manufacturing tolerances and the circuit parameters to provide more flexibility for the tolerance compensation and accuracy enhancement of the MHMIC fabrication processes.

Separation of Loss Mechanisms in Nb Superconducting Thin-Film Transmission Lines

Separation of Loss Mechanisms in Nb Superconducting Thin-Film Transmission Lines

Low Temperature Loss Measurement of Aluminium Thin Film Transmission Lines

Low Temperature Loss Measurement of Aluminium Thin Film Transmission Lines

Influence of the Surface Morphology of the Microwave Microstrip Line on Its Transmission Performance

The main morphological parameters of 50-ohm Au/i-GaAs{100} thin-film microwave microstrip gold coplanar transmission lines of the length lW affecting the active resistance of their skin layer R and inductance L are determined. It is found that the lateral character of the grain distribution and developed relief of their surfaces causes the appearance of additional electron scattering both at grain boundaries and at relief inhomogeneities. The small grain size dx 10 GHz transforms an abnormal skin-effect into the normal one. Herewith, the linear dependence of R on lW in the local approximation is provided by the fractal geometry of the surface relief and near-surface region of coplanar transmission lines, while the nonlinear dependence of the inductance L on lW is provided not only by the fractal relief features of the two-dimensional surface of coplanar transmission lines but also by the fractal features of the three-dimensional distribution of its grains.

Parametric Amplification at Ka Band via Nonlinear Dynamics in Superconducting 3D Cavities

Modern parametric amplifiers are based on lithographically produced superconducting thin-film planar transmission line structures. These paramps rely on resonant structures with embedded nonlinear elements to stimulate intermodulation with a stronger pump tone that gives rise to signal gain when certain conditions are satisfied. Such paramps have not yet been realised in superconducting 3D waveguide resonators. Possible applications of these devices include detector systems that are based on 3D waveguide such as dark matter detectors and quantum computers. Reported here are the results of an investigation of a 30.64 GHz series circular waveguide resonance machined from bulk niobium showing parametric gain of up to 2 dB in the presence of a stronger pump tone 10 kHz above in frequency. The gain is largest on abrupt jumps of the transmission spectra of the resonance, which may be a result of weak-link formation on the superconducting surfaces.

Broadband 300-GHz Power Amplifier MMICs in InGaAs mHEMT Technology

In this article, we report on compact solid-state power amplifier (SSPA) millimeter-wave monolithic integrated circuits (MMICs) covering the 280–330-GHz frequency range. The technology used is a 35-nm gate-length InGaAs metamorphic high-electron-mobility transistor (mHEMT) technology. Two power amplifier MMICs are reported, based on a compact unit amplifier cell, which is parallelized two times using two different Wilkinson power combiners. The Wilkinson combiners are designed using elevated coplanar waveguide and air-bridge thin-film transmission lines in order to implement low-loss 70-Ω lines in the back-end-of-line of this InGaAs mHEMT technology. The five-stage SSPA MMICs achieve a measured small-signal gain around 20 dB over the 280–335-GHz frequency band. State-of-the-art output power performance is reported, achieving at least 13 dBm over the 286–310-GHz frequency band, with a peak output power of 13.7 dBm (23.4 mW) at 300 GHz. The PA MMICs are designed for a reduced chip width while maximizing the total gate width of 512 μm in the output stage, using a compact topology based on cascode and common-source devices, improving the output power per required chip width significantly.

Low-loss cable-to-cable parallel connection method for thin-film superconducting flexible microwave transmission lines

We describe a superconducting (SC) cable-to-cable connection method for thin-film flexible (Nb/polyimide) parallel transmission line cables that exhibits low loss from DC to microwave frequencies. Design, fabrication procedures, assembly methods and characterization results are reported. The connector assembly incorporates a monolithic array of short superconductive bridging traces that function as a ganged electrical splice between two ribbon cables. The assembly is micro-mechanically self-aligned and uses pressure to make simultaneous electrical contacts between multiple 50 μm wide microstrip signal traces, as well as between ground planes. Each contacting surface comprises thin SC Nb overcoated with ultra-thin Au, providing nearly zero DC resistance and very good RF performance. A simulation model of the microwave performance of microstrip-to-microstrip interconnections at 4.2 K was successfully matched to measurement results. This new cable-to-cable connection approach exhibited an insertion loss <0.12 dB and a return loss >15 dB up to 14 GHz. The connections performed reproducibly throughout multiple thermal cycles and multiple disassembly/reassembly cycles.

Broadband Thin-Film Transmission-Line Characterization for Accurate High-Frequency Measurements of On-Wafer Components

A high-frequency fine-pitched (i.e., very narrow line width) thin-film transmission line (TL) characterization technique is presented. A new dielectric permittivity determination technique for thin-film TL structures is developed. Multi-layered mixed dielectric materials are then accurately characterized in a broad frequency band, to be followed by the TL characterization. For experiments, various lengths of TL and extra patterns were designed and fabricated by using both a ${\hbox{0.18-}}\mu{\hbox{m}}$ SK Hynix CMOS process and ${\hbox{0.13-}}\mu{\hbox{m}}$ Samsung CMOS process. S-parameters for the test patterns were measured by using a vector network analyzer from 10 MHz to 50 GHz. It is shown that not only the inherent de-embedding problems associated with wafer-level high-frequency characterizations can be conveniently eliminated, but also the frequency-variant characteristic impedance of a thin-film TL can be readily determined using the proposed technique. It can be exploited for accurate high-frequency wafer-level component characterizations including miniaturized transistors, frequency-variant interconnect lines, and other circuit components.

Kinetic Inductance Parametric Up-Converter

We describe a novel class of devices based on the nonlinearity of the kinetic inductance of a superconducting thin film. By placing a current-dependent inductance in a microwave resonator, small currents can be measured through their effect on the resonator’s frequency. By using a high-resistivity material for the film and nanowires as kinetic inductors, we can achieve a large coefficient of nonlinearity to improve device sensitivity. We demonstrate a current sensitivity of 8pA/√Hz, making this device useful for transition-edge sensor (TES) readout and other cutting-edge applications. An advantage of these devices is their natural ability to be multiplexed in the frequency domain, enabling large detector arrays for TES-based instruments. A traveling-wave version of the device, consisting of a thin-film microwave transmission line, is also sensitive to small currents as they change the phase length of the line due to their effect on its inductance. We demonstrate a current sensitivity of 5pA/√Hz for this version of the device, making it also suitable for TES readout as well as other current-detection applications. It has the advantage of multi-GHz bandwidth and greater dynamic range, offering a different approach to the resonator version of the device.

Basic Study on RF Characteristics of Thin-Film Transmission Line Employing ML/CPW Composite Structure on Silicon Substrate and Its Application to a Highly Miniaturized Impedance Transformer

A thin-film transmission line (TFTL) employing a microstrip line/coplanar waveguide (ML/CPW) was fabricated on a silicon substrate for application to a miniaturized on-chip RF component, and the RF characteristics of the device with the proposed structure were investigated. The TFTL employing a ML/CPW composite structure exhibited a shorter wavelength than that of a conventional coplanar waveguide and that of a thin-film microstrip line. When the TFTL with the proposed structure was fabricated to have a length of <TEX>${\lambda}/8$</TEX>, it showed a loss of less than 1.12 dB at up to 30 GHz. The improvement in the periodic capacitance of the TFTL caused for the propagation constant, <TEX>${\beta}$</TEX>, and the effective permittivity, <TEX>${\varepsilon}_{eff}$</TEX>, to have values higher than those of a device with only a conventional coplanar waveguide and a thin film microstrip line. The TFTL with the proposed structure showed a <TEX>${\beta}$</TEX> of 0.53~2.96 rad/mm and an <TEX>${\varepsilon}_{eff}$</TEX> of 22.3~25.3 when operating from 5 to 30 GHz. A highly miniaturized impedance transformer was fabricated on a silicon substrate using the proposed TFTL for application to a low-impedance transformation for broadband. The size of the impedance transformer was 0.01 mm2, which is only 1.04% of the size of a transformer fabricated using a conventional coplanar waveguide on a silicon substrate. The impedance transformer showed excellent RF performance for broadband.

InP DHBT Amplifier Modules Operating Between 150–300 GHz Using Membrane Technology

In this paper, we present WR05 (140–220 GHz) and WR03 (220–325 GHz) five-stage amplifier modules with novel membrane microstrip-to-waveguide transitions. The modules use a 250-nm InP double heterojunction bipolar transistor (DHBT) technology and multilayer thin-film microstrip transmission lines. The waveguide transitions use $E$ -plane probes on 3- $\mu$ m-thin GaAs membrane substrate. Beam lead connectors integrated on the transition eliminate the need of highly reactive bond wires. In addition, process steps such as backside metallization, backside vias, and nonrectangular dicing of the integrated circuits (ICs) are not required. The WR05 amplifier module demonstrates a peak gain of 24 dB at 245 GHz and more than 10-dB gain from 155 to 270 GHz. The WR-03 module has 19-dB gain from 230 to 254 GHz with input and output return loss better than 10 dB from 225 to 330 GHz. The two modules were also characterized in terms of noise. The minimum noise figures were measured to 9.7 dB at 195 GHz and 10.8 dB at 240 GHz for the WR05 and WR03 modules, respectively. To the authors' best knowledge, these are the first published results on an InP DHBT amplifier modules operating at these high frequencies. It is also the first time that membrane technology is used for IC packaging, regardless of IC technology.

실리콘 RFIC 상에서 무선 통신 시스템의 소형화를 위한 마이크로스트립/코프레너 복합구조를 가지는 박막필름 전송선로의 등가회로 및 대역폭에 관한 연구

실리콘 RFIC 상에서 무선 통신 시스템의 소형화를 위한 마이크로스트립/코프레너 복합구조를 가지는 박막필름 전송선로의 등가회로 및 대역폭에 관한 연구

Metal Layer Losses in Thin-Film Microstrip on LTCC

Thin-film microstrip transmission lines fabricated using a Ti adhesion layer followed by layered Cu, Pt, and Au films are measured to determine tradeoffs between manufacturability issues and microwave performance. Since Ti metal has approximately 25 times the resistance of Cu, and currents in a microstrip line flow mainly at the interface with the substrate where the Ti is located, there is the possibility of increased RF signal losses with this structure. It is found that Ti adhesion layers of ≤200-nm thickness cause minimal loss through 40 GHz on DuPont 9K7 low-temperature cofired ceramic substrates, so there is no significant electrical penalty for employing a metal stackup optimized for mechanical durability. These measurements, together with analysis and simulations suggest this will hold in general as long as the thinner, higher resistance adhesion metal is well below one skin depth in thickness at the operating frequency.

Broad frequency-band characterizations of electromagnetic energy propagation in planar thin-film transmission lines

Thin-film transmission lines are experimentally characterized in the frequency range from 10 MHz to 110 GHz. Scattering (S-) parameters for several test lines are measured. Then, two important transmission line parameters (i.e., the propagation constant and characteristic impedance) are determined in the measured frequency range. The resonances, which are inevitable in a practical experimental environment, are carefully eliminated by de-embedding parasitic effects and by determining the frequency-variant dielectric permittivity based on the Debye model. Based on the experimental work, we showed that the conventional skin-effect model may not be accurate for high-frequencies. Further, the 3-dimensional (3D) numerical field solver does not reflect the radiation loss at high-frequency. Finally, in the millimeter (mm)-wave region, all the three loss mechanisms due to the skin-effect, dielectric polarization, and electromagnetic radiation have to be taken into account.

A Short Wavelength and Low Loss Thin-Film Transmission Line Employing ML/CPW Composite Structure on Silicon Substrate

In this work, a thin-film transmission line (TFTL) employing microstrip line/coplanar waveguide (ML/CPW) on silicon substrate was proposed, and its RF characteristics were investigated. The TFTL employing ML/CPW composite structure exhibited the wavelength shorter than conventional coplanar waveguide and thin-film microstrip line. Concretely, at 10 GHz, the wavelength of conventional coplanar waveguide and thin film waveguide is 10.35 and 7.83 mm, while the wavelength of the TFTL employing ML/CPW composite structure was 6.26 mm, which was 60.5 % of the conventional coplanar waveguide. The TFTL employing ML/CPW composite structure with a length of λ/8 showed the loss less than 1.12 dB up to 30 GHz, which was lower than conventional coplanar waveguide and thin-film microstrip line. Above results indicates that the TFTL employing ML/CPW composite structure is a promising candidate for application to a miniaturization of RF components on silicon RFIC.

Experimental characterisations of thin film transmission line losses

New frequency-variant losses of planar thin film transmission lines are experimentally investigated in a broad frequency range. The frequency-variant transmission line parameters are accurately determined in the measured frequency band (i.e. from 40 MHz to 50 GHz). Then, it is shown that there are three critical frequencies that characterise the loss mechanism of thin film transmission lines. The conventional skin-effect model is not accurate in thin and fine transmission lines.

A novel transmission line characterisation based on measurement data reconfirmation

Due to inherent resonance effects and frequency-variant dielectric properties, it is very difficult to experimentally determine the stable and accurate circuit model parameters of thin film transmission line structures over a broad frequency band. In this article, a new, simple and straightforward frequency-variant transmission line circuit model parameter determination method is presented. Experimental test patterns for high-frequency transmission line characterisations are designed and fabricated using a package process. The S-parameters for the test patterns are measured using a vector network analyzer (VNA) from 100 MHz to 26.5 GHz. The parasitic effects due to contact pads are de-embedded. The frequency-variant complex permittivity and resonance-effect-free transmission line parameters (i.e., the propagation constant and characteristic impedance) are then determined in a broad frequency band.

Frequency Tuning and Spurious Signal Generation at Microwave Frequencies in Ferroelectric ${\hbox{SrTiO}}_{3}$ Thin-Film Transmission Lines

This paper evaluates the RF tuning and the microwave nonlinear response of SrTiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> thin films by measuring the third harmonics and third-order intermodulation (IMD) products of several coplanar waveguide transmission lines fabricated directly on SrTiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3 </sub> thin-film samples. From these measurements, we obtained the distributed nonlinear capacitance per unit length as a function of RF bias voltage C(V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">rf</sub> ) using an accurate equivalent circuit to model the spurious signal generation. A unique value of C(V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">rf</sub> ) is used to describe the third-harmonic generation at frequencies 3f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub> and 3f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> , and the IMD products at frequencies 2f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub> +f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> and 2f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> +f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub> , where f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub> and f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> represent the fundamental frequencies of the two-tone excitation signal. We compare C(Vrf) with the distributed nonlinear capacitance measured as a function of the dc-bias voltage C(V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">dc</sub> ) and obtain excellent agreement at 50 and 76 K. From these results, we conclude that full tunability can be achieved on nanosecond time scales, and that spurious signals generated in SrTiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> ferroelectric transmission lines at microwave frequencies can be modeled based on dc-biased measurements

Slit-patterned CoNbZr∕Nb∕CoNbZr magnetic film for rf noise suppressor

In this paper, we discuss the elimination of magnetic closure domains in a micropatterned film in order to have the desired loss generation profile against the operating frequency and describe a demonstration of the rf loss generation profile over a thin-film coplanar transmission line using micropatterned films with various slit designs. It was demonstrated that the micropatterned film causes loss in the transmission line in a narrow frequency band and the loss ratio in the other bands is smaller than in the nonpatterned film we measured. The peak frequency of loss generation is controllable according to the pattern dimension of the magnetic film. This technique is useful as a notch filter for integrated transmission lines.

The integration of thin-film microstrip and coplanar technologies for reduced-size MMICs

This paper proposes the integration of coplanar waveguide (CPW) and thin-film microstrip transmission lines to achieve size reduction of monolithic microwave integrated circuits (MMICs). The proposed structures take advantage of the multilevel metallization processes offered in MMIC technology. A very compact 90/spl deg/ CPW branchline coupler, operating at 44 GHz, is used to illustrate the technique. In comparison with conventional hybrid couplers, this coupler offers lower insertion loss and significantly smaller dimensions. The area of the coupler is approximately 65% of a conventional coupler. This paper also presents a family of novel series/shunt matching stub structures based on the CPW/thin-film microstrip combination. The technique allows a reduction in the length of matching stubs of approximately 50% by collocating multiple stubs together. Simulated and experimental results are presented in support of the novel structures.