US Patent 7777168 Image sensor circuit and method comprising one-transistor pixels

A pixel is formed in a semiconductor substrate of a first doping type, a first layer of the second doping type covering the substrate, a second layer of the first doping type covering the first layer. A MOS-type transistor is formed in the second layer and has a drain area and a source area of the second doping type. The pixel includes a first area of the second doping type, more heavily doped than the first layer, crossing the second layer and extending into the first layer and connected to the drain area. The pixel further includes a second area of the first doping type, more heavily doped than the second layer and bordering the source area.