A tin oxide transparent-gate buried-channel virtual-phase CCD imager

A large-area (17.5 × 17.5 mm) tin oxide transparent-gate full-frame CCD imager has been developed using virtual-phase (VP) CCD-imager fabrication technology. The tin oxide gate structure substantially increases the quantum efficiency in the blue region and increases the average QE over the visible spectrum: 60 percent from 420 to 700 nm. The intrapixel response uniformity is drastically improved in the blue, and substantially improved over the complete spectrum. The device is composed of a 420 × 420 imaging array formed of 40 × 40 µm pixels and a 425 × 1 serial register composed of 40 × 80 µm cells. The maximum serial data rate is 2 MHz, and the imager sensitivity is 0.5 µV/electron measured at the output. The well capacity exceeds 1 × 10⁶electrons in the imaging array, while the serial capacity exceeds 2 × 10⁶electrons and the floating diffusion detection node will accept 4 × 10⁶electrons. A modification to the usual VP pixel structure was necessary to obtain good CTE for very low fight conditions in this unusually large pixel. In the initial devices produced, the array noise is dominated by the minimum channel current at about 70 electrons.