Voltage-variable capacitor with increased current conducting perimeter

Abstract

A parallel-plate, voltage-variable capacitor is designed to have an increased current conducting perimeter relative to its area. In one approach, the perimeter is increased by changing the shape of the plates. In another approach, the varactor is implemented by a number of disjoint plates, which are coupled in parallel.

What is claimed is:  
     
         1 . A parallel plate varactor comprising: 
 a bottom electrode;    a top electrode;    a dielectric layer sandwiched between the bottom electrode and the top electrode, wherein a permittivity of the dielectric layer varies according to an electric field applied to the dielectric layer; the bottom electrode, dielectric layer, and top electrode are integrated on a substrate; and an overlap between the bottom electrode, dielectric layer, and top electrode defines an active region for the varactor; and    wherein, for at least one of the electrodes: 
 a resistance of the active region of the electrode is significantly higher than a resistance of a bulk region of the electrode;  
 the active region has a lateral area A, the electrode has a current conducting perimeter P; and a ratio R of the perimeter P to a square root of the area A is at least 2.0.