Coplanar waveguide varactors with bottom metal trenched in silicon

This paper reports the effects of embedding the bottom metal of a thin-film ferroelectric varactor into the wafer substrate. By embedding the bottom metal to a height flush with the surrounding dielectric, a smooth surface remains for the ferroelectric and top metal layers. This parallel stack of layers reduces the coupling between the two metal layers and the resulting capacitance. The design of the device and measured data of etched and non-etched varactors is also presented.