Anne-Laure Franc

High-Performance Shielded Coplanar Waveguides for the Design of CMOS 60-GHz Bandpass Filters

This paper presents optimized very high performance CMOS slow-wave shielded CPW transmission lines (S-CPW TLines). They are used to realize a 60-GHz bandpass filter, with T-junctions and open stubs. Owing to a strong slow-wave effect, the longitudinal length of the S-CPW is reduced by a factor up to 2.6 compared to a classical microstrip topology in the same technology. Moreover, the quality factor of the realized S-CPWs reaches 43 at 60 GHz, which is about two times higher than the microstrip one and corresponds to the state of the art concerning S-CPW TLines with moderate width. For a proof of concept of complex passive device realization, two millimeter-wave filters working at 60 GHz based on dual-behavior-resonator filters have been designed with these S-CPWs and measured up to 110 GHz. The measured insertion loss for the first-order (respectively, second-order) filter is -2.6 dB (respectively, -4.1 dB). The comparison with a classical microstrip topology and the state-of-the-art CMOS filter results highlights the very good performance of the realized filters in terms of unloaded quality factor. It also shows the potential of S-CPW TLines for the design of high-performance complex CMOS passive devices.

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 describes a new concept of substrate integrated waveguide (SIW): a slow-wave substrate integrated waveguide (SW-SIW). Compared to a conventional SIW, the proposed topology requires a double-layer substrate with a bottom layer including internal metallized via-holes connected to the bottom conductive plane. The slow-wave effect is obtained by the physical separation of electric and magnetic fields in the structure. Electromagnetic simulations show that this topology of SIW allows decreasing the longitudinal dimension by more than 40% since the phase velocity is significantly smaller than that of a classical SIW. Simultaneously, the lateral dimension of the waveguide is also reduced. By considering a double-layer technology, SW-SIWs exhibiting a cutoff frequency of 9.3 GHz were designed, fabricated, and measured. The transversal dimension and the phase velocity of the proposed SW-SIW are both reduced by 40% as compared to a classical SIW designed for the same cutoff frequency, leading to a significant surface reduction. Moreover, an original kind of taper is proposed to achieve a good return loss when the SW-SIW is fed by a microstrip transmission line.

m CMOS Process

This paper presents a new physical model for shielded slow-wave coplanar waveguide structures. This lossy electrical model is based on physical behavior of the transmission lines. It allows a better understanding of the losses distribution along the structure. The ohmic losses in the coplanar strips, as well as the ohmic losses and the eddy current losses in the floating shield strips are studied for transmission lines having different geometrical dimensions and hence electrical characteristics. The model is then validated on different CMOS technologies and leads to the efficient optimization of the slow-wave transmission lines, especially concerning the floating shield dimensions.

Slow-Wave Substrate Integrated Waveguide

Based on a CMOS slow-wave coplanar-waveguide transmission-line topology, a novel compact millimeter-wave phase shifter is presented. The tunability is accomplished by using a liquid crystal (LC) material as a tunable dielectric between the coplanar signal strip and the shielding plane of the slow-wave transmission line. The device tunability is considerably enhanced by moving the free-standing signal strip with the application of a bias voltage. Combining the miniaturizing benefits of the slow-wave effect with the continuous tuning of LC material, the proposed device occupies only 0.38 mm2 and exhibits high performance. The phase shifter was characterized up to 45 GHz for a maximum bias voltage of 20 V without significant power consumption. The reproducible measurements show a figure-of-merit (ratio between the maximum phase shift and the maximum insertion loss) of 51°/dB at 45 GHz.

A Lossy Circuit Model Based on Physical Interpretation for Integrated Shielded Slow-Wave CMOS Coplanar Waveguide Structures

High-performance integrated slow-wave coplanar waveguides (S-CPW) are compared with conventional coplanar waveguides (CPW) fabricated in a 65-nm High-Resistivity-SOI (HR-SOI) CMOS technology. As expected, S-CPW demonstrates better performance at millimeter-wave frequencies in term of higher effective dielectric permittivity, which is due to the patterned floating shield inserted between the transmission line and the substrate. In addition, S-CPW shows a lower attenuation constant despite of the added metallic patterned floating shield on HR substrate. For demonstration purpose, both low- and high- characteristic impedance S-CPW and CPW are characterized. For 28-Ω S-CPW and 65-Ω S-CPW, the effective dielectric permittivity is improved by a factor of 6 and 2, respectively. Meanwhile, attenuation constants of slow-wave structures are lower than 0.9 dB/mm and 0.57 dB/mm at 60 GHz, compared to CPW ones which are as high as 1.5 dB/mm and 0.95 dB/mm, respectively. Furthermore, the loss distribution for the S-CPW structure is detailed by varying the patterned floating shield length for both standard Bulk and HR-SOI substrates.

Compact and Broadband Millimeter-Wave Electrically Tunable Phase Shifter Combining Slow-Wave Effect With Liquid Crystal Technology

This letter presents an original method based on Patterned Shielded CoPlanar Waveguides transmission lines (patterned S-CPW TLines) for the wideband characterization of thin dielectric materials, up to millimeter-wave frequencies. The proposed method is easy to use and a very promising candidate to reach a better precision than classical methods. The dynamic for the relative permittivity (respectively the dielectric loss tangent) determination is 3.8 times (respectively, 1.9 times) higher compared to classical methods. The method is experimentally validated by the characterization of a thin SiO2 layer (1 μm).

Performance Improvement Versus CPW and Loss Distribution Analysis of Slow-Wave CPW in 65 nm HR-SOI CMOS Technology

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.

Characterization of Thin Dielectric Films up to Mm-Wave Frequencies Using Patterned Shielded Coplanar Waveguides

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.