Investigations of varactor depletion capacitance effects of fin field-Effect transistor devices

The effects of the depletion capacitance of a varactor between fin field-effect transistor (FinFET) and bulk planar devices are investigated. Fabricated NMOS varactors are characterized and studied. The depletion capacitance of an NMOS varactor in FinFETs is lower than that of the conventional bulk planar one. Thus, the NMOS FinFET varactor provides a larger tuning range (about 10.4 times with respect to minimal capacitance) than the bulk planar one (approximately 3.7 times). The simulation results of the proposed three-dimensional (3D) devices with FinFET and bulk planar varactors show that the depletion layer width of the NMOS varactors in FinFETs is more sensitive to the applied gate voltage than the bulk planar one.