Charge-Coupled Devices

Charge-coupled devices(CCDs) belong to a wider class of what are called charge-transfer devices(CTDs).

In recent years, CCDs have come to be used in microelectronics as solid-state imaging devices (SSIDs) used instead of conventional TV tubes, memory elements, delay lines, filters, signal-processing circuits, and logic ga­tes.

A major advantage of CCDs is their simple design. The general arrangement of a CCD is shown in Fig. 8.11. This is a three-phase sym­metrical CCD consisting of a chain of MOS capacitors on a common p -type substrate. At the input and output, this chain may have diodes or FETs. The metal electrodes positioned along the device measure 10 to 15 um and the spacing between them is 2 to 4 um. The row of metal electrodes is separated from the p- type substrate by a layer of Si0₂ with a thickness of 0.1 um.

Fig. 8.11. IC using charge-coupled devices

Electrodes 1, 2and 3make up a single cell of a CCD. The input electrode injects electrons across the n⁺-p junction. The injection current can be controlled by varying the gate voltage. Charge transfer from electrode 1to electrode 2and so on can take place only if the voltage applied to the electrodes is positive and the voltage at the next electrode exceeds that at the preceding one or is equal to it, that is, if , then , and so on.

References

1. Normal Lurch. Fundamentals of Electronics. Wiley, N.Y. 1991.
2. Zherebtsov J. Basic Electronics. Mir, M., 1989.
3. Rabah K. V. A Study of IGBT. 1995.

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