Two-dimensional time delay integration visible cmos image sensor

Abstract

A two dimensional time delay integration CMOS image sensor having a plurality of pinned photodiodes, each pinned photodiode collects a charge when light strikes the pinned photodiode, a plurality of electrodes separating the plurality of pinned photodiodes, the plurality of electrodes are configured for two dimensional charge transport between two adjacent pinned photodiodes, and a plurality of readout nodes connected to the plurality of pinned photodiodes via address lines.

1 . An image sensor comprising:
 first and second regions, the first region located adjacent to the second region;   a first photodiode located adjacent to the first region;   a second photodiode located adjacent to the second region;   a first transfer gate positioned above the first region, and configured to transfer a charge from the first photodiode to the first region; and   a second transfer gate positioned above the second region, configured to receive the charge in the second region, and configured to transfer the charge from the second region to the second photodiode.   
     
     
         2 . The image sensor of  claim 1 , wherein the first and second regions are substantially free of any floating diffusion region or drain region. 
     
     
         3 . The image sensor of  claim 1 , further comprising:
 a first readout node located outside the first and second regions, and configured to collect a first charge from the first photodiode.   
     
     
         4 . The image sensor of  claim 3 , further comprising:
 a third transfer gate coupled between the first readout node and the first photodiode, and configured to facilitate the first node to collect the first charge from the first photodiode.   
     
     
         5 . The image sensor of  claim 1 , further comprising:
 a second readout node located outside the first and second regions, and configured to collect a second charge from the second photodiode.   
     
     
         6 . The image sensor of  claim 5 , further comprising:
 a fourth transfer gate coupled between the second readout node and the second photodiode, and configured to facilitate the second node to collect the second charge from the second photodiode.   
     
     
         7 . The image sensor of  claim 1 , wherein the first transfer gate is located directly adjacent to the second transfer gate. 
     
     
         8 . The image sensor of  claim 1 , wherein:
 the first photodiode has a first Fermi level,   the second photodiode has a second Fermi level substantially the same as the first Fermi level,   the first region has a first region Fermi level substantially higher than the first Fermi level, and   the second region has a second region Fermi level substantially the same as the first region Fermi level.   
     
     
         9 . The image sensor of  claim 8 , wherein:
 the first transfer gate creates a first well in the first region, such that the first well has a first quasi-Fermi level substantially lower than the first Fermi level when the charge is transferred from the first photodiode to the first well, and   the second transfer gate creates a second well in the first region, such that the second well has a second quasi-Fermi level substantially similar to the first quasi-Fermi level when the charge is transferred from the first well to the second well.   
     
     
         10 . The image sensor of  claim 9 , wherein:
 the first transfer gate restores the first region Fermi level in the first region after the charge is transferred from the first region to the second region, and   the second transfer gate restores the second region Fermi level in the second region to transfer the charge from the second region to the second photodiode.   
     
     
         11 . A method for transferring a charge between a first photodiode and a second photodiode, comprising the steps of:
 creating a first well adjacent to the first photodiode during a first time period; and   creating a second well adjacent to the first well and the second photodiode during a second time period partially but not entirely overlapping with the first time period.   
     
     
         12 . The method of  claim 11 , wherein the creating the first well step includes:
 adjusting, in a first region adjacent to the first photodiode, a first quasi-Fermi level substantially lower than a first Fermi level of the first photodiode.   
     
     
         13 . The method of  claim 12 , wherein the creating the second well step includes:
 adjusting, in a second region adjacent to the second photodiode and the first region, a second quasi-Fermi level substantially the same as the first quasi-Fermi level and substantially lower than a second Fermi level of the second photodiode.   
     
     
         14 . The method of  claim 11 , further comprising the steps of:
 collapsing the first well after the first time period; and   collapsing the second well after the second time period.   
     
     
         15 . The method of  claim 14 , wherein:
 the collapsing the first well step includes restoring, in a first region adjacent to the first photodiode, a first region Fermi level substantially higher than a first Fermi level of the first photodiode, and   the collapsing the second well step includes restoring, in a second region adjacent to the second photodiode and the first region, a second region Fermi level substantially higher than a second Fermi level of the second photodiode.   
     
     
         16 . The method of  claim 11 , wherein:
 the first time period has a first portion distinct from the second time period, and   the second time period has a second portion distinct from the first time period.   
     
     
         17 . A method for transferring a charge between a first photodiode and a second photodiode, comprising the steps of:
 applying a first voltage to a first electrode to adjust a first quasi-Fermi level of a first region located adjacent to the first photodiode during first and second cycles; and   applying a second voltage to a second electrode to adjust a second quasi-Fermi level of a second region located adjacent to the first region and the second photodiode electrode during the second cycle and a third cycle.   
     
     
         18 . The method of  claim 17 , wherein:
 the first quasi-Fermi level is substantially lower than a first Fermi level of the first photodiode, and   the second quasi-Fermi level is substantially the same as the first quasi-Fermi level and substantially lower than a second Fermi level of the second photodiode.   
     
     
         19 . The method of  claim 17 , further comprising the steps of:
 floating the first electrode to restore a first region Fermi level of the first region after the second cycle; and   floating the second electrode to restore a second region Fermi level of the second region after the third cycle.   
     
     
         20 . The method of  claim 19 , wherein:
 the first region Fermi level of the first region is substantially higher than the first Fermi level of the first photodiode, and   the second region Fermi level of the second region is substantially higher than the second Fermi level of the second photodiode.