The Island-Gate Varactor—A High-Q MOS Varactor for Millimeter-Wave Applications

A new accumulation MOS varactor with island-shaped poly gate layout is proposed to improve the quality factor ( Q-factor) at high frequency, which can be readily employed for CMOS-based millimeter-wave applications. Measured results up to 67 GHz show significant improvements in the Q-factor and the series resistance R
_s
over the conventional multi-finger MOS varactors with the same ground rule and gate area. The proposed island-gate MOS varactor is expected to improve the overall Q-factor of the LC tank of millimeter-wave oscillators.