The Enhancement of Q Factor for Patterned Ground Shield Inductors at High Temperatures

摘要

We report on an effective way of using a patterned ground shield (PGS) to enhance the Q factor of on-chip spiral inductors. We fabricated PGS inductors using both 0.18 μm and 0.35 μm CMOS processes, with Ml and poly strip PGSs, respectively. The strip width and spacing of the PGSs are W{sub}g - 0.8 μm and S{sub}g = 0.45 μm, with metal thicknesses of t{sub}p = {0.54,0.2} μm in the 0.18 μm process, and t{sub}p = {0.6,0.3} μm in the 0.35 μm process. The separation distance D between PGS and top metal layer is different in both processes. We found that the Q factor degradation of inductors at high temperatures can be effectively compensated by using PGS. Among all geometric parameters of a PGS in the 0.18 μm process, the parameter D is the critical factor for the shielding effectiveness, and Ml PGS is much more efficient than poly strip PGS in improving the inductor performance over the temperature range of 298 K to 358 K. However, in the 0.35 μm process the latter is better than the former.