Experimental Investigation of a Linear 500-Element 3-Phase Charge-Coupled Device

The principle of charge coupling was first conceived using a 3-phase technique with simple, nondirectional transfer electrodes. 1 This approach using all identical electrodes in a single level of metallization has been successfully demonstrated on several successive designs of linear devices; each structure has a greater number of elements with smaller electrode length than the previous design. 2-4 Correspondingly, improved efficiency at higher frequencies has been observed. The charge-coupled device (CCD) discussed in this paper was designed as a high-resolution linear image sensor with 500 three-phase elements at a spatial period of 18 /im, capable of reading half a line of 581 a normal page of printed material. 4 The device has also been demonstrated as an analog shift register able to delay a line of the Picturephone® video signal. 5 In these demonstrations, a few of the best devices have been used, and their performance has been described in the context of these particular demonstrations only. The following discussion enlarges the description of the performance of 3-phase single-level metal C C D ' s by reporting more representative results obtained in a study of m a n y devices. T h e goal of this study was to obtain an understanding of the functional dependences of charge-handling ability, transfer efficiency, and dark current on operating potentials, frequency, and temperature. In addition, devices with different electrode lengths and different fabrication technologies have been compared.