A Single Layer CCD Image Sensor with Wide Gap Electrode and Gradual Potential Channel

CCD is a continuum of MOS capacitors, so its big capacitance becomes one of the major disadvantages compared with CMOS image sensor, that cause not only large power dissipation but also other problems, such as generating an electro magnetic interference(EMI). Single-layer electrode CCD is one of the ways to reduce CCD capacitance compared with conventional two layer CCD electrode structure. On the other hand, image scanning system using linear image sensor is moving from lens reduction optics system to contact type optics system, because contact type system has smaller size than lens reduction system. Image sensor for contact optics requires much longer CCD pitch. It means that charge transfer in CCD becomes more difficult than short pitch CCD. We have developed a CCD linear image sensor, called "Gratron", with gradual potential channel CCD for the purpose of accelerating charge transfer in long channel single-layer CCD. A CCD that is driven by two phase clock is fabricated with single layer poly Si electrodes that have wider electrode gaps and longer electrode channel length. At the sensor that has 21um pitch pixel linear array with a single sided CCD register, high charge transfer efficiency (>99%) is obtained at 25MHz and small capacitance of CCD is realized.