Florence Podevin

High-Q Slow-Wave Coplanar Transmission Lines on 0.35

In this letter, experimental results and trends for shielded coplanar waveguide transmission lines (S-CPW) implemented in a 0.35 μm CMOS technology are provided. Because of the introduction of floating strips below the CPW transmission line, high effective dielectric permittivity and quality factor are obtained. Three different geometries of S-CPW transmission lines are characterized. For the best geometry, the measured effective dielectric permittivity reaches 48, leading to a very high slow-wave factor and high miniaturization. In addition, measurements demonstrate a quality factor ranging from 20 to 40 between 10 and 40 GHz, demonstrating state-of-the-art results for transmission lines realized in a low-cost CMOS standard technology.

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This paper presents reflection-type phase shifters (RTPSs) with very high figure-of-merit (FoM) and low insertion-loss variation, achieving up to 360 ° relative phase shifts. Two compact topologies are proposed. They were implemented at the working frequency of 2 GHz on a printed circuit board technology. The reflection loads are based on the use of one transmission line loaded by varactors, forming L- or π-type networks. An automatic procedure is given to design the electrical length and the characteristic impedance of the transmission line of the reflection loads as well as the output impedance of the 3-dB branch-line coupler in order to get phase shifters with the highest possible FoM. Measurement results of the first L-type network RTPS showed a relative phase shift of 201 ° for only 0.54 dB ± 0.09 dB of insertion loss, leading to a FoM of 319 °/dB. A relative phase shift of 385 ° was achieved for the π-type network RTPS with insertion loss of only 0.98 dB ± 0.58 dB, leading to an FoM of 246 °/dB. In both cases, simulation and measurement results fit very well. Moreover, the return loss over a 10% bandwidth is always better than 10.9 dB for the first RTPS and better than 12.3 dB for the second one, respectively. The comparison with previous works shows more compact reflection loads with electrical performance equal to the state-of-the-art.

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In this paper, a physical model of the slow-wave (SW) microstrip lines based on a metallic-nanowire-filled-membrane substrate is presented for the first time. The model properly predicts the behavior of the SW transmission lines as shown by the experimental results. Two sets of transmission lines differing in oxide thickness with various widths were fabricated and characterized up to 70 GHz. The electrical model is valid for both oxide thicknesses and microstrips width. High-quality factors are obtained, above 40 from 30 GHz up to 70 GHz, paving the way for further designs of passive circuits, like power dividers or hybrid couplers, with good performance.

Design of Compact Reflection-Type Phase Shifters With High Figure-of-Merit

This paper proposes a new technology for slow wave microstrip lines based on a low-cost metallic-nanowire-filled-membrane substrate (MnM-substrate). These transmission lines can operate from RF to millimeter-wave frequencies. The MnM-substrate consists in a dielectric material containing vertical metallic nanowires connected to a bottom ground plane. The innovative concept of the slow-wave microstrip lines on MnM-substrate is presented, as well as the electromagnetic considerations, fabrication process, and measurement results. Initial results show high relative dielectric constants (up to 43). Hence, it is possible to reach high-quality factor transmission lines within a great range of impedances, from 20 to 100 Ω, without critical dimensions.

Modeling and Characterization of Slow-Wave Microstrip Lines on Metallic-Nanowire- Filled-Membrane Substrate

This paper presents the design of an integrated rat-race coupler for balun applications based on high quality factor Slow-wave CoPlanar Waveguides (S-CPW) transmission lines in millimeter wave frequencies. The 28 nm CMOS advanced digital technology by STMicroelectronics is used. The design procedure is detailed. Phase-inverter and optimized criteria for the transmission lines characteristics are used to minimize insertion losses and surface on the die. A 3D full wave EM software coupled to a circuit simulator is used to optimize the various building blocs. The compact and low-loss rat-race coupler shows state-of-art very exciting and promising performances. It occupies a 0.086 mm2 area. From 52 GHz till 67 GHz, return loss is better than 15 dB, while coupling factors are identical, varying between −4.2 and −4.4 dB, that means 1.4 dB maximal insertion loss. Finally between 13 and 85.5 GHz, the phase difference is kept constant, equal to 180°±1° while the isolation is better than 44 dB.

Slow-wave microstrip line on nanowire-based alumina membrane

A new concept of slow wave microstrip transmission lines (SW μTL) dedicated to mmW and sub-mmW applications (100 GHz and further) is described herein. The microstrip is deposited on a specific substrate consisting in a metallic nanowires-filled membrane (MnM) of alumina covered with a thin top layer of silicon oxide. The slow wave effect is obtained thanks to metallic nanowires that capture the electric field while the magnetic field can extend in the whole substrate. Despite of the strong miniaturization expected, such SW μTLs should reach a quality factor five times higher than the one obtained with a conventional microstrip line (without nanowires). Such SW μTL can act as interconnecting paths if the MnM substrate is used as a 3D-interposer.