Search

A physics-based equivalent-circuit model for on-chip symmetric transformers is presented with all the model elements driven from fabrication specifications. Two extra coupled transformer loops are used for each coil to model the parameters of skin effect, proximity effect, and reflective effect of the substrate eddy current, respectively. Model accuracy under free space is first demonstrated using an electromagnetic field solver without considering substrate loss. Several sets of transformers were fabricated on a standard 0.18-[micro]m 1P8M RF CMOS technology to further verify the accuracy and scalability of the proposed model. By careful comparison of S-parameters, coil inductance, quality factor, coupling coefficient, and maximum available gain between measured data and simulated data, model accuracy, and scalability are verifed over a wide range of geometry configurations. Index Terms--Baluns, eddy current, equivalent circuit, physical model, transformers.

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 [micro]m and 0.35 [micro]m CMOS processes, with M1 and poly strip PGSs, respectively. The strip width and spacing of the PGSs are [W.sub.g] = 0.8 [micro]m and [S.sub.g] = 0.4.3 [micro]m, with metal thicknesses of [t.sub.p] = {0.54.0.2} [micro]m in the 0.18 [micro]m process, and [t.sub.p] {0.6, 0.3} [micro]m in the 0.35 [micro]m 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 [micro]m process, the parameter D is the critical factor for the shielding effectiveness, and M1 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 [micro]m process the latter is better than the former. Index Terms--Pattern ground shield (PGS) inductors, performance enhancement, Q factor, shielding effectiveness, temperature.