| 摘要 |
In general, the output of a buried channel CCD is provided with a floating diffusion (4), which forms a storage site to determine the size of an electric charge. For this purpose, the floating diffusion may be connected to the input of an amplifier, such as a source follower (8). The charge is transferred to the floating zone from below an output gate OG to which a DC voltage is applied. To obtain a high sensitivity, i.e. a high voltage per electron, it is important to keep the capacitance of the floating zone as small as possible. The capacitance can be reduced by narrowing the channel at the output. This method of reducing C, however, is limited in known structures because this shape of the channel may induce an electric field in the channel which counteracts the transfer to the floating zone. To suppress this effect, the gate oxide (5) below the output gate is provided with a thicker part (5b) adjoining the floating diffusion (4). By virtue thereof, an additional field is induced below the output gate, which enhances the transfer of charge to the floating zone. This enables the channel to be narrowed, resulting in a low floating-zone capacitance, without decreasing the transfer efficiency. Said capacitance is reduced further by the thick oxide, which leads to a small capacitance between the floating zone and the output gate. |
