Image sensor

Abstract

A buried oxide is provided in a substrate of a photodiode so as to be opposed to a cathode and is in contact with a lower end of a depletion layer. The buried oxide is polarized owing to charges forming the depletion layer and thus works as a capacitor. A capacitor formed in the depletion layer and the additional capacitor made by the buried oxide are, therefore, connected in series, which reduces a total junction capacitance Cs. Increase in photo-detection voltage Vs results in according to an equation, Vs=Qp/Ct, since an amount of photocharge Qp is constant. The increase in the photo-detection voltage Vs allows an improvement in the SN ratio of the photodiode. Further, easy formation of the buried oxide, for example, by implanting oxygen ions, permits low-cost manufacturing of the photodiode.

1 . An image sensor, comprising:
 a semiconductor substrate of a first conductivity type having a photo-detecting surface on one side;   a semiconductor region of a second conductivity type disposed under the photo-detecting surface, and making a junction with the semiconductor substrate; and   a dielectric body disposed in the semiconductor substrate, and polarized owing to charges forming a depletion layer region, the depletion layer region being generated by the semiconductor substrate and the semiconductor region.   
     
     
         2 . An image sensor according to  claim 1 , wherein the dielectric body comprises an oxide of a semiconductor constituting the semiconductor substrate. 
     
     
         3 . An image sensor according to  claim 1 , wherein the dielectric body is in contact with the depletion layer region. 
     
     
         4 . An image sensor according to  claim 1 , wherein at least a part of the dielectric body is provided in the depletion layer region. 
     
     
         5 . An image sensor according to  claim 2 , wherein the dielectric body is in contact with the depletion layer region. 
     
     
         6 . An image sensor according to  claim 2 , wherein at least a part of the dielectric body is provided in the depletion layer region.