Patent ID: 8450832

Claim:
A junction varactor comprising: a substrate having a varactor region in which the varactor is formed; first isolation regions in the varactor region, wherein the first isolation regions forming a first substrate surface region between inner edges of the first isolation regions; second isolation regions in the varactor region, wherein the first isolation regions are within the second isolation regions, the first and second isolation regions forming second substrate surface regions between outer edges of the first isolation regions and inner edges of the second isolation regions; third substrate surface regions from the outer edges of the second isolation regions; a first doped region of a first polarity type in the varactor region, the first doped region is disposed from the first substrate surface region between the inner edges of the first isolation regions to a first depth which is shallower than a bottom of the first isolation regions; a second doped region of a second polarity type in the varactor region, the second doped region is disposed from the second substrate surface regions to a second depth which is below a bottom of the second isolation regions and the bottom of the first isolation regions, the second doped region extends between bottoms of the second isolation regions, the first and second doped regions form a first junction between the first isolation regions; a third doped region of the first polarity type in the varactor region, the third doped region is disposed from the third substrate surface regions to a third depth which is below the second depth, the third doped region encompasses the first and second doped regions, the second and third doped regions form a second junction between and below the bottoms of the second isolation regions; a first varactor terminal coupled to the first and third substrate surface regions for coupling to the first and third doped regions; and a second varactor terminal coupled to the second substrate surface regions for coupling to the second doped region.