On-chip high performance slow wave transmission lines using 3D steps for compact millimeter wave applications

Slow wave coplanar waveguide structures have been designed and implemented with the 3D steps; include alternating high and low impedance sections. The high impedance section is built with a narrow (w1), thin (t1) short (s) line and designed to have line inductance nL; the low impedance section is built with wide (w1), thick (t1) short (s) line and is designed with line capacitance nC, where L and C are the line inductance and capacitance per unit length of the conventional transmission line with given characteristic impedance respectively. The slow wave transmission line structures were achieved through IBM 45nm technology with multi-layer metals. Results for slow wave transmission lines are provided in the paper for design with different characteristics impedances. Results have shown that the inductance per unit length and capacitance per unit length of the line increased at least 40% compared with the conventional slow wave transmission line structure, which means a reduction of 30% wavelength and 50% chip area of a branch line coupler. The slow wave effect can be controlled by using different w1/w2, t1/t2 and s. In addition, detailed design guide to improve the slow wave effect are presented in the paper.