A HIGH-PACKING DENSITY PIXEL WITH PUNCHTHROUGH READ-OUT METHOD FOR ANHDTV INTERLINE CCD

A new pixel structure for a high-packing-density interline CCD is prop osed, 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-w ell by implanting these two layers after diffusion of the photodiode n layer. Spreading resistance measurements on dummy wafers show that th e depths of these layers are 0.28 mum and 0.6 mum, respectively. Moreo ver, the photodiode n-layer is covered with a surface p+-layer, even a t the transfer region. We describe the results of simulations and expe riments on a test image sensor with pixel dimensions of 7.3 mum (H) x 7.6 mum (V). From the experimental data, we estimate the characteristi cs of an image sensor with pixel dimension 5.0 mum (H) x 5.2 mum (V). Such a device should have a maximum charge handling capability of 1.4 x 10(5) electrons, a smear level of -88 dB, a sensitivity of 1.5 x 10( 3) electrons/lx with a 30% fill factor, no image lag, and a low photod iode dark signal of less than 14 electrons at 60-degrees-C. These resu lts indicate that an IL-CCD with a punchthrough readout structure is s uitable for image sensors with a high pixel density such as 2/3 inch 2 million pixel image sensors for high-definition TV applications.