Two-transistor pixel with buried reset channel and method of formation

Abstract

A two-transistor pixel of an imager has a reset region formed adjacent a charge collection region of a photodiode and in electrical communication with a gate of a source follower transistor. The reset region is connected to one terminal of a capacitor which integrates collected charge of the photodiode. The charge collection region is reset by pulsing the other terminal of the capacitor from a higher to a lower voltage.

1 - 30 . (canceled)  
   
   
       31 . A method of resetting an imager pixel, said pixel comprising: 
 a charge collection region; and    a reset region in contact with said charge collection region said method comprising:    pulsing a voltage to said reset region through a capacitor.    
   
   
       32 . The method of  claim 31  further comprising providing a first voltage level to one side of said capacitor during a charge integration period, the other side of said capacitor being coupled to said reset region, and pulsing said voltage to said one side of said capacitor to a second voltage level lower than the first during a reset period.  
   
   
       33 . An imager pixel comprising: 
 photo diode;    a capacitor having one terminal coupled to a charge collection of said photodiode;    a first transistor having a gate coupled to said charge collection region for providing a pixel output signal;    a second transistor for selectively coupling a pixel output signal from said first transistor to an output conductor; and    a voltage source for providing a first voltage signal to another terminal of said capacitor during a period when said photodiode photo converts an incident light signal and a second lower voltage level to said another terminal during a period when said photodiode is reset.    
   
   
       34 . The pixel of  claim 33  wherein said second voltage level is substantially zero volts.  
   
   
       35 . A method of operating an imager pixel, said method comprising: 
 providing a photodiode below a surface of a substrate;    coupling a first terminal of a capacitor to a charge collection region of said photodiode;    coupling a gate of a first transistor to said charge collection region for providing a pixel output signal;    providing a second transistor for selectively coupling said pixel output signal from said first transistor to an output conductor; and    providing a first voltage signal to a second terminal of said capacitor during a period when said photodiode photo converts an incident light signal, and providing a second lower voltage level to said second terminal during a period when said photodiode is reset.    
   
   
       36 . The method of  claim 35 , wherein said second voltage level is substantially zero volts.  
   
   
       37 . The method of  claim 35  further comprising forming a reset region below said surface of said substrate and in contact with said charge collection region, said reset region forming with said charge collection region an extended charge collection region, said reset region being operable to apply a reset signal to said extended charge collection region.