Design and measurements of 50 Ω on-chip slow-wave conductor-backed coplanar transmission lines up to 220 GHz

In this paper high performance slow-wave transmission lines are investigated. The conductor-backed coplanar wave-guides (CBCPW) are manufactured in the back end of line of an high-speed SiGe BiCMOS technology that offers bipolar transistors with ft, fmax of 300 and 500 GHz, respectively. It is therefore important to study the behaviour of transmission lines from below 1 GHz up to 220 GHz. Slow wave structures are compared with conventional CBCPW. The phase velocity of the slow-wave structures is 50 % slower than the conventional CBCPW. Since the wavelength is proportional to the phase velocity, slow-wave structures are more compact than conventional transmission lines. Different de-embedding methods are adopted in order to subtract the pads parasitic to the measurement of the transmission lines. The quality factor of the manufactured slow-wave line is 9.5 despite the small lateral dimension of 64 µm.