Overcoming the limitations of silicon MMICs

Microwave circuits in silicon were improved by overcoming the three major limitations present in this technology: low quality passives, low levels of isolation due to the conductive silicon substrates, and the relative low speed of transistors in silicon.; Passives were improved by modifying existing post-process fabrication techniques to achieve higher substrate isolation. Transmission lines were implemented with copper and low-k dielectric with improvements of 30% in their useful operating frequency. Even lower attenuation was achieved using silver in place of copper metallization in coplanar waveguides (CPWs), a result shown to be particularly important for phase noise reduction in VCOs. This thesis also presents an optimized CPW with wavelength reduction aimed at improving passive performance by reducing attenuation, implementing larger phase shifts with shorter lines and by using slotted ground planes for increased cross-talk immunity.; An analysis of coupling or cross-talk effects in inductors, resonators and transmission lines is presented. A commercial EM simulator was used for a near-field full-wave solution of coupling effects in silicon substrates. To verify theory, a novel one-step calibration technique aimed at calculating on-chip coupling is presented here. Measurement results are very accurate and agree with EM simulation within 1 dB. To offset the relative low speed of silicon devices, distributed circuit techniques to increase the achievable bandwidth of silicon based circuits, a study on the gain-bandwidth limitations of silicon based distributed amplifiers is presented. This analysis was previously only available for GaAs technologies with different process constraints. As a demonstration, a 27 GHz distributed amplifier, fabricated in a standard CMOS technology and capable of 40 Gbit/sec transmission is reported. This amplifier shows the highest bandwidth ever achieved in standard CMOS technologies using cascode gain stages. Finally, this thesis will present a novel distributed amplifier gain cell with gain and bandwidth control. A four stage distributed amplifier with gain-bandwidth control was demonstrated using integrated varactors.