The present invention provides a varactor that has increased tunability
and a high quality factor Q as well as a method of fabricating the
varactor. The method of the present invention can be integrated into a
conventional CMOS processing scheme or into a conventional BiCMOS
processing scheme. The method includes providing a structure that
includes a semiconductor substrate of a first conductivity type and
optionally a subcollector or isolation well (i.e., doped region) of a
second conductivity type located below an upper region of the substrate,
the first conductivity type is different from said second conductivity
type. Next, a plurality of isolation regions are formed in the upper
region of the substrate and then a well region is formed in the upper
region of the substrate. In some cases, the doped region is formed at
this point of the inventive process. The well region includes outer well
regions of the second conductivity type and an inner well region of the
first conductivity type. Each well of said well region is separated at an
upper surface by an isolation region. A field effect transistor having at
least a gate conductor of the first conductivity type is then formed
above the inner well region.