Solid state image sensor and electronic device

Abstract

There is provided a solid state image sensor including a photoelectric conversion unit formed and embedded in a semiconductor substrate, an impurity region that retains an electric charge generated by the photoelectric conversion unit, and a transfer transistor that transfers the electric charge to the impurity region. A gate electrode of the transfer transistor is formed in a depth direction toward the photoelectric conversion unit in the semiconductor substrate, from a surface of the semiconductor substrate on which the impurity region is formed. A channel portion of the transfer transistor is surrounded by the gate electrode in two or more directions other than a direction of the impurity region, as seen from the depth direction.

What is claimed is: 
     
         1 . A solid state image sensor, comprising:
 a photoelectric conversion unit configured to generate an electric charge, wherein the photoelectric conversion unit is embedded in a semiconductor substrate;   an impurity region configured to retain the generated electric charge;   a transfer transistor configured to transfer the electric charge to the impurity region; and   a discharge transistor configured to discharge an unnecessary electric charge generated by the photoelectric conversion unit, wherein a gate electrode of the transfer transistor is adjacent to a gate electrode of the discharge transistor in a depth direction of the semiconductor substrate.   
     
     
         2 . The solid state image sensor according to  claim 1 , wherein the gate electrode of the transfer transistor is adjacent to the gate electrode of the discharge transistor in parallel in the depth direction of the semiconductor substrate, via an insulating film. 
     
     
         3 . The solid state image sensor according to  claim 1 , wherein the photoelectric conversion unit is a photo diode. 
     
     
         4 . The solid state image sensor according to  claim 3 , wherein the gate electrode of the transfer transistor and the gate electrode of the discharge transistor are in a position identical with a p-n junction plane of the photo diode. 
     
     
         5 . The solid state image sensor according to  claim 3 , wherein the gate electrode of the transfer transistor and the gate electrode of the discharge transistor are in a position deeper than a p-n junction plane of the photo diode. 
     
     
         6 . The solid state image sensor according to  claim 1 , wherein
 the gate electrode of each of the transfer transistor and the discharge transistor is connected to a part at which a carrier energy is lowest on a formation plane of a photo-diode of the photoelectric conversion unit.   
     
     
         7 . The solid state image sensor according to  claim 1 , further comprising
 a photoelectric conversion film including a material having a larger light absorption coefficient than the semiconductor substrate, wherein the photoelectric conversion film is located at a back side of the semiconductor substrate.   
     
     
         8 . The solid state image sensor according to  claim 1 , further comprising a channel portion including an electrical current path between the gate electrode of the transfer transistor and the gate electrode of the discharge transistor. 
     
     
         9 . The solid state image sensor according to  claim 8 , wherein an impurity concentration at the impurity region is higher as compared to an impurity concentration at the channel portion. 
     
     
         10 . An electronic device, comprising:
 a solid state image sensor including:
 a photoelectric conversion unit configured to generate an electric charge, wherein the photoelectric conversion unit is embedded in a semiconductor substrate; 
 an impurity region configured to retain the generated electric charge; 
 a transfer transistor configured to transfer the electric charge to the impurity region; and 
 a discharge transistor configured to discharge an unnecessary electric charge generated by the photoelectric conversion unit, wherein a gate electrode of the transfer transistor is adjacent to a gate electrode of the discharge transistor in a depth direction of the semiconductor substrate. 
   
     
     
         11 . The electronic device according to  claim 10 , wherein the gate electrode of the transfer transistor is adjacent to the gate electrode of the discharge transistor in parallel in the depth direction of the semiconductor substrate, via an insulating film. 
     
     
         12 . The electronic device according to  claim 10 , further comprising a channel portion including an electrical current path between the gate electrode of the transfer transistor and the gate electrode of the discharge transistor. 
     
     
         13 . The electronic device according to  claim 12 , wherein an impurity concentration at the impurity region is higher as compared to an impurity concentration at the channel portion. 
     
     
         14 . The electronic device according to  claim 10 , wherein the photoelectric conversion unit is a photo diode. 
     
     
         15 . The electronic device according to  claim 14 , wherein the gate electrode of the transfer transistor and the gate electrode of the discharge transistor are in a position identical with a p-n junction plane of the photo diode. 
     
     
         16 . The electronic device according to  claim 14 , wherein the gate electrode of the transfer transistor and the gate electrode of the discharge transistor are in a position deeper than a p-n junction plane of the photo diode. 
     
     
         17 . The electronic device according to  claim 10 , wherein
 the gate electrode of each of the transfer transistor and the discharge transistor is connected to a part at which a carrier energy is lowest on a formation plane of a photo-diode of the photoelectric conversion unit.   
     
     
         18 . The electronic device according to  claim 10 , wherein
 the solid state image sensor further includes a photoelectric conversion film including a material having a larger light absorption coefficient than the semiconductor substrate, and   the photoelectric conversion film is located at a back side of the semiconductor substrate.   
     
     
         19 . A solid state image sensor, comprising:
 a photoelectric conversion unit configured to generate an electric charge, wherein the photoelectric conversion unit is embedded in a semiconductor substrate;   an impurity region configured to retain the generated electric charge;   a transfer transistor configured to transfer the electric charge to the impurity region; and   a discharge transistor configured to discharge an unnecessary electric charge generated by the photoelectric conversion unit, wherein
 end portions, close to the photoelectric conversion unit, of a gate electrode of the transfer transistor is adjacent to a gate electrode of the discharge transistor are in a formation plane of the photoelectric conversion unit, and 
 a distance between the gate electrode of the transfer transistor and the gate electrode of the discharge transistor gradually increases as a depth from a surface of the semiconductor substrate becomes shallower.