Non-volatile solid state image pickup device and its drive

A solid state image pickup device, comprising:

• a semiconductor substrate of a first conductivity type;
• a well region formed in said semiconductor substrate and having a second conductivity type that is opposite to the first conductivity type;
• a plurality of pn junction diodes, each of which has an embedded charge accumulation region of the first conductivity type formed within said well region;
• a plurality of first MOS transistor structures, each of which is associated with one of said embedded charge accumulation regions as a first source region, and has a first floating gate that is formed above said semiconductor substrate, a first control gate that is capacitively coupled to said first floating gate, and a first drain region that is formed within said well region;
• and
• second MOS transistor structures, each having a second source region and a second drain region, which are positioned in the vicinity of an associated one of said first MOS transistor structures and are formed within said well region, a second floating gate, which is formed above said semiconductor substrate and is electrically connected with said first floating gate, and a second control gate, which is capacitively coupled to said second floating gate.

A method of driving a solid state image pickup device comprising a semiconductor substrate of a first conductivity type, a well region formed in said semiconductor substrate and having a second conductivity type that is opposite to the first conductivity type, a plurality of pn junction diodes, each of which has an embedded charge accumulation region of the first conductivity type formed within said well region, a plurality of first MOS transistor structures, each of which is associated with one of said embedded charge accumulation regions as a first source region, and has a first floating gate that is formed above said semiconductor substrate, a first control gate that is capacitively coupled to said first floating gate, and a first drain region that is formed within said well region, and second MOS transistor structures, each having a second source region and a second drain region, which are positioned in the vicinity of an associate one of said first MOS transistor structures and are formed within said well region, a second floating gate, which is formed above said semiconductor substrate and is electrically connected with said first floating gate, and a second control gate, which is capacitively coupled to said second floating gate, said solid state image pickup device driving method comprising the steps of:

• (a) lefting light incident on said plurality of pn junction diodes and accumulating charges that express image information in said embedded charge accumulation regions,
• (b) applying a write control voltage to said well regions and said first MOS transistor structures and injecting at least a part of said charges that express image information as signal charges into said first floating gate, and
• (c) applying a control voltage to said second MOS transistor structures and detecting a threshold voltage.