New CMOS-Compatible Micromachined Embedded Coplanar Waveguide

This paper proposes a new robust micromachined embedded coplanar waveguide (CPW). The central and ground plates are partially bent and overlapped within the trench, and due to tight coupling of the E -field between the overlapped plates, the micromachined embedded CPW line is capable of a wide range characteristic impedance (17.9-92.3 Ω), in a compact size. Furthermore, the area in which the E -field radiates into the substrate of the micromachined embedded CPW is quite narrow compared to conventional CPWs, and therefore, the dielectric loss of the micromachined embedded CPW can be effectively suppressed. Compared with conventional CPW lines, the embedded CPW lines have shown a marked reduction in loss, especially in the low-impedance range. The micromachined embedded CPW lines on the high-resistivity silicon substrate (ρ_s = 15 000 Ω · cm) achieve a measured loss as low as 0.81 dB/cm at 50 GHz. Moreover, the fabrication process of the micromachined embedded CPW line is compatible with the CMOS process. These features make micromachined embedded CPW a promising transmission line for RF integrated circuit application.