Characteristics of submicrometer gaps in buried-channel CCD structures

A planar-gate buried-channel charge-coupled-device (CCD) structure with deep submicrometer gaps was investigated. CCD test structures with gap widths from 0.15 to 0.45 μm were fabricated using electron-beam lithography and reactive ion etching. Typical measured gap leakage currents were on the order of 0.3 pA/mm gap lengths for all gap widths. Potential wells, not barriers, were detected in the channel under the gaps. Measured potential well depths ranged from 0.15 to 1.0 V for gap widths from 0.15 to 0.45 μm, respectively. The wells could be eliminated by applying a 1- to 4-V potential difference on adjacent electrodes for the above gap width range. Measured well depths correlate well with two-dimensional device simulation data. These results indicate that the planar-gate CCD is a viable structure for efficient charge transfer, especially for direct imaging applications