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.

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 λ/8, 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, β, and the effective permittivity, ε eff , 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 β of 0.53~2.96 rad/mm and an ε eff 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.

In this paper, various types of transmission lines employing the periodically arrayed ground structure (PAGS) were fabricated on silicon substrate, and their RF characteristics were thoroughly investigated for a decision of optimal structure design. According to the results, with-contact showed wavelength shorter than other types of transmission lines and insertion loss value lower than other types of transmission lines. In addition, with-contact showed effective permittivity and propagation constant value higher than other types of transmission lines. Above results indicate that the with-contact is most appropriate for application to a miniaturization of RF components on silicon substrate.