Patent ID: 6882029

Claim:
A PN-junction varactor, comprising: a first N-well formed on a semiconductor substrate; a first gate situated over said first N-well; a first gate dielectric layer provided between said first gate and said first N-well; a second gate situated at one side of said first gate and overlying said first N-well; a second gate dielectric layer provided between said second gate and said first N-well; a P + doping region located in said first N-well between said first gate and said second gate, and serving as an anode of said PN-junction varactor, wherein said P 30 doping region is encompassed by a second N-well, and wherein said second N-well has a doping concentration that is higher than that of said first N-well; a first N + doping region located at one side of said first gate that is opposite to said P + doping region within said first N-well; and a second N + doping region located at one side of said second gate that is opposite to said P + doping region within said first N-well, and said second N + doping region being electrically coupled to said first N + doping region for serving as a cathode of said PN-junction varactor.