Modeling spiral inductors in SOS processes

Existing models for simulating spiral inductors fabricated in silicon processes are outgrowths of the PI structure originally employed by Nguyen and Meyer (1990). This structure and its subsequent elaborations work well for inductors in which the dominant loss mechanism is the underlying substrate. For newer processes with very high resistivity or insulating substrates such as Silicon-on-sapphire however, the model breaks down since inductor quality factor Q is then determined predominantly by series trace resistance. Models suitable for use in such processes are proposed and compared with measured data. The new models contain only four to six elements and, unlike the classic PI model, provide a broadband match to measured impedance behavior in both differentially driven and single-ended circuit applications.