Image sensor having ito electrodes with an ono layer

Abstract

By incorporating an ITO electrode which is more transparent than polysilicon, and designing the pixel such that it has asymmetric gates with as much as possible of its light sensitive region covered by an ITO electrode, light sensitivity is increased. To solve the problem of impurity diffusion from the ITO electrode into the silicon below, the conventional Silicon Dioxide gate dielectric was replaced with an Oxide/Nitride/Oxide stack. Employing at least some polysilicon electrodes with ITO electrodes is desirable to allow entrance passages through which hydrogen passivation can be accomplished. The pixel architecture can be designed to increase sensitivity further by other design choices. The first of these choices is to incorporate a lenslet on each pixel such that as much as possible of the light falling on the pixel is made to pass through the portion of the pixel covered with ITO. The pixel light sensitivity improves not only because the light passes through the more transparent ITO electrode, but also because some of the light that would have fallen on the LOD region and would be lost, is now collected. The second method is for color CCD sensors with color filter patterns, such as the 'BAYER' color filter pattern to name just one, to have the overlap of the color filters, which does not allow light transmission, to occur over the less sensitive area of the pixel, which is the area covered with the polysilicon electrode. For proper operation a slight modification of the vertical clock timing is needed.