Solid-state image pickup device, its electric-charge transfer method and its fabrication method

Abstract

The present invention solves a smear problem caused by mixing of a noise signal with signal electric charge being transferred in an operation to transfer the signal charge obtained as a result of a process carried out on a received light beam having a large wavelength. In order to solve the problem, the present invention provides a solid-state image pickup device including a layered structure which includes photosensors and an electric-charge transfer section. The photosensors include a first photosensor ( 21 ) and a second photosensor ( 22 ) for receiving a light beam with a wavelength smaller than the wavelength of a light beam received by the first photosensor ( 21 ). The first photosensor ( 21 ) and the second photosensor ( 2 ) are provided at adjacent locations separated away from each other by a potential barrier section ( 12 ). A read gate ( 42 ) provided beneath the first photosensor ( 21 ) transports electric charge obtained as a result of a process carried out by the first photosensor ( 21 ) to an electric-charge transfer section ( 50 ) provided beneath the second photosensor ( 22 ).

1 . A solid-state image pickup device comprising:
 a photosensor section provided in a substrate as a section including a first photosensor and a second photosensor for receiving a light beam with a wavelength smaller than the wavelength of a light beam received by said first photosensor;   a first electric-charge transfer section provided beneath said first photosensor in said substrate;   a second electric-charge transfer section provided beneath said second photosensor in said substrate;   a first read gate provided in a side portion of said first photosensor in said substrate as a gate for transporting electric charge obtained as a result of a photoelectric conversion process carried out by said first photosensor to said first electric-charge transfer section;   a second read gate provided in a side portion of said second photosensor in said substrate as a gate for transporting electric charge obtained as a result of a photoelectric conversion process carried out by said second photosensor to said second electric-charge transfer section; and   a transfer gate provided between said first electric-charge transfer section and said second electric-charge transfer section in said substrate as a gate for transferring electric charge accumulated in said first electric-charge transfer section to said second electric-charge transfer section.   
     
     
         2 . A solid-state image pickup device according to  claim 1 , wherein said first photosensor receives a light beam of the red or green color and said second photosensor receives a light beam of the blue color. 
     
     
         3 . A solid-state image pickup device according to  claim 1 , wherein said first photosensor receives a light beam of the red color and said second photosensor receives a light beam of the green color. 
     
     
         4 . A solid-state image pickup device according to  claim 1 , wherein said first photosensor and said second photosensor are provided at adjacent locations separated away from each other by a potential barrier section. 
     
     
         5 . An electric-charge transfer method provided for a solid-state image pickup device comprising a photosensor section provided in a substrate as a section including a first photosensor and a second photosensor for receiving a light beam with a wavelength smaller than the wavelength of a light beam received by said first photosensor, wherein:
 a read gate provided in a side portion of said first photosensor in said substrate transports electric charge obtained as a result of a photoelectric conversion process carried out by said first photosensor to a first electric-charge transfer section provided beneath said first photosensor in said substrate; and   a transfer gate further transfers said electric charge to a second electric-charge transfer section provided beneath said second photosensor in said substrate.   
     
     
         6 . An electric-charge transfer method provided for a solid-state image pickup device in accordance with  claim 5 , wherein said first photosensor receives a light beam of the red or green color and said second photosensor receives a light beam of the blue color. 
     
     
         7 . An electric-charge transfer method provided for a solid-state image pickup device in accordance with  claim 5 , wherein said first photosensor receives a light beam of the red color and said second photosensor receives a light beam of the green color. 
     
     
         8 . An electric-charge transfer method provided for a solid-state image pickup device in accordance with  claim 5 , wherein said first photosensor and said second photosensor are provided at adjacent locations separated away from each other by a potential barrier section. 
     
     
         9 . A method of fabricating a solid-state image pickup device, said method comprising the steps of creating:
 a photosensor section in a substrate as a section including a first photosensor and a second photosensor for receiving a light beam with a wavelength smaller than the wavelength of a light beam received by said first photosensor;   an electric-charge transfer section beneath said second photosensor in said substrate; and   a read gate beneath said first photosensor in said substrate as a gate for transporting electric charge obtained as a result of a photoelectric conversion process carried out by said first photosensor to said electric-charge transfer section.   
     
     
         10 . A method of fabricating a solid-state image pickup device, said method comprising the steps of creating:
 a photosensor section in a substrate as a section including a first photosensor and a second photosensor for receiving a light beam with a wavelength smaller than the wavelength of a light beam received by said first photosensor;   a first electric-charge transfer section beneath said first photosensor in said substrate;   a second electric-charge transfer section beneath said second photosensor in said substrate;   a first read gate provided in a side portion of said first photosensor in said substrate as a gate for transporting electric charge obtained as a result of a photoelectric conversion process carried out by said first photosensor to said first electric-charge transfer section;   a second read gate provided in a side portion of said second photosensor in said substrate as a gate for transporting electric charge obtained as a result of a photoelectric conversion process carried out by said second photosensor to said second electric-charge transfer section; and   a transfer gate between said first electric-charge transfer section and said second electric-charge transfer section in said substrate as a gate for transferring electric charge accumulated in said first electric-charge transfer section to said second electric-charge transfer section.