Solid state image pickup device and its driving method

A solid state image pickup device, comprising:

• a semiconductor substrate;
• a plurality of vertical charge transfer elements formed in one surface of said semiconductor substrate, each having (i) a vertical charge transfer channel having a first conductivity type and (ii) a plurality of vertical transfer electrodes formed on a first electrically insulating layer formed on the one surface of said semiconductor substrate, the vertical transfer electrodes traversing the vertical charge transfer channels as viewed in plan;
• a plurality of photoelectric conversion elements formed in the one surface of said semiconductor substrate in a matrix shape in rows and columns, each of said photoelectric conversion elements being electrically connectable to corresponding one of said vertical charge transfer elements;
• a horizontal charge transfer element formed in the one surface of said substrate and being electrically connectable to each of said vertical charge transfer elements, said horizontal charge transfer element having (i) a horizontal charge transfer channel having the first conductivity type and (ii) a plurality of horizontal transfer electrodes formed on the first electrically insulating layer formed on the one surface of said semiconductor substrate, each horizontal transfer electrode traversing the horizontal charge transfer channel as viewed in plan;
• a drain region formed in the one surface of said semiconductor substrate along the horizontal charge transfer channel, at a side thereof opposite the vertical charge transfer channel, said drain region having the first conductivity type;
• and
• a barrier region for charge formed between the horizontal charge transfer channel and said drain region, wherein the horizontal charge transfer channel, said drain region and said barrier region constitute a two-electrode element;
• wherein the horizontal charge transfer channel includes a potential barrier region and a potential well region alternately and repetitively disposed in this order from an upstream side to a downstream side, the potential barrier region having a relatively low effective impurity concentration and the potential well region having a relatively high effective impurity concentration, and a width of the potential well region as viewed in plan gradually or stepwise broadens toward said barrier region.

A solid state image pickup device, comprising:

• a semiconductor substrate;
• a plurality of vertical charge transfer elements formed in one surface of said semiconductor substrate, each having (i) a vertical charge transfer channel having a first conductivity type and (ii) a plurality of vertical transfer electrodes formed on a first electrically insulating layer formed on the one surface of said semiconductor substrate, the vertical transfer electrodes traversing the vertical charge transfer channels as viewed in plan;
• a plurality of photoelectric conversion elements formed in the one surface of said semiconductor substrate in a matrix shape in rows and columns, each of said photoelectric conversion elements being electrically connectable to corresponding one of said vertical charge transfer elements;
• a horizontal charge transfer element formed in the one surface of said substrate and being electrically connectable to each of said vertical charge transfer elements, said horizontal charge transfer element having (i) a horizontal charge transfer channel having the first conductivity type and (ii) a plurality of horizontal transfer electrodes formed on the first electrically insulating layer formed on the one surface of said semiconductor substrate, each horizontal transfer electrode traversing the horizontal charge transfer channel as viewed in plan;
• a drain region formed in the one surface of said semiconductor substrate along the horizontal charge transfer channel, said drain region having the first conductivity type;
• and
• a barrier region for charge formed between the horizontal charge transfer channel and said drain region, wherein the horizontal charge transfer channel, said drain region and said barrier region constitute a two-electrode element;
• wherein:
• the horizontal charge transfer channel includes a potential barrier region and a potential well region alternately and repetitively disposed in this order from an upstream side to a downstream side, the potential barrier region having a relatively low effective impurity concentration and the potential well region having a relatively high effective impurity concentration;
• each of the horizontal transfer electrodes covers the potential well region or potential barrier region under the first electrically insulating layer and said barrier region under the first electrically insulating layer;
• and
• a width of each of the horizontal transfer electrodes covering the potential well region and said barrier region is broad above the potential well region and narrow above said barrier region.