Exploiting CMOS reverse interconnect scaling in multigigahertz amplifier and oscillator design

The increasing number of interconnect layers that are needed in a CMOS proc ess to meet the routing and power requirements of large digital circuits al so yield significant advantages for analog applications. The reverse thickn ess scaling of the top metal layer can be exploited in the design of low-lo ss transmission lines. Coplanar transmission lines in the top metal layers take advantage of a low metal resistance and a large separation from the he avily doped silicon substrate. They are therefore fully compatible with cur rent and future CMOS process technologies. To investigate the feasibility o f extending CMOS designs beyond 10 GHz, a wide range of coplanar transmissi on lines are characterized. The effect of the substrate resistivity on copl anar wave propagation is explained. After achieving a record loss of 0.3 dB /mm at 50 GHz, coplanar lines are used in the design of distributed amplifi ers and oscillators. They are the first to achieve higher than 10-GHz opera ting frequencies in a conventional CMOS technology.