Process technique for improving the tuning range in MOS varactors

This paper presents a new technique to improve the tuning range of MOS varactors in conventional CMOS technology. Poly-silicon depletion effect is intentionally incorporated in the gate electrode of varactor. It is demonstrated that the tuning range increases by 60% without degradation in Q factor. The process for the proposed poly-silicon depletion effect does not require any extra process steps, except the redefinition of the appropriate masks, making this technique compatible with current CMOS technology. An analytical model for this improvement is also discussed.