A high-packing density pixel with punchthrough read-out method for an HDTV interline CCD

Abstract

A new pixel structure for a high-packing-density interline CCD is proposed, in which signal charges are read out from the photodiodes to the vertical CCD by a punchthrough mechanism. This read-out method makes it possible to reduce the depth of the VCCD channel and the second p-well by implanting these two layers after diffusion of the photodiode n layer. Spreading resistance measurements on dummy wafers show that the depths of these layers are 0.28 /spl mu/m and 0.6 /spl mu/m, respectively. Moreover, the photodiode n-layer is covered with a surface p/sup +/-layer, even at the transfer region. We describe the results of simulations and experiments on a test image sensor with pixel dimensions of 7.3 /spl mu/m (H)/spl times/7.6 /spl mu/m (V). From the experimental data, we estimate the characteristics of an image sensor with pixel dimension 5.0 /spl mu/m (H)/spl times/5.2 /spl mu/m (V). Such a device should have a maximum charge handling capability of 1.4/spl times/10/sup 5/ electrons, a smear level of -88 dB, a sensitivity of 1.5/spl times/10/sup 3/ electrons/Ix with a 30% fill factor, no image lag, and a low photodiode dark signal of less than 14 electrons at 60/spl deg/C. These results indicate that an IL-CCD with a punchthrough readout structure is suitable for image sensors with a high pixel density such as 2/3 inch 2 million pixel image sensors for high-definition TV applications. >