Conclusions

DC characterization provides a fast, accurate, and thorough means for evaluating incoming CCD-based detectors. Though DC characterization does not replace full EO testing it does allow the build up of complex and expensive multi-detector FPA to proceed with high confidence that all CCD detectors are "healthy" and have the necessary clock and bias tolerance ranges. DC characterization on CCD detectors early in a program can identify processing and design problems undetectable by some detector vendors and most EO camera systems. Furthermore, DC testing is extremely useful, if not mandatory, when performing burn-in, accelerated life, and radiation tolerance testing on CCD detectors for use in space-based applications. The DC tests discussed herein are easily implemented on an automated DC test station, which allows for hundreds of measurements to be taken in only a few minutes. This, in turn, enables the DC testing to be performed at multiple points in the build up process of complex focal plane assemblies - yielding a high confidence in the reliability of the resultant focal plane assembly.

Some recent examples of the usefulness of DC testing are presented below. Figure 5 shows two examples where the DC gain measurements showed non-optimal performance. In Fig. 5 (left) the vendor-recommended operating point for reset drain is clearly too close to the reset gate cutoff point and in Fig 5. (right) the curve shows the recommended output drain bias is too low. Fig. 6 is an example of channel potential curves for two parallel register phases yielding significantly different inversion voltages, which would have resulted in one phase not running into inversion during integration.

Figure 5. (left) Example of non-optimal RD and (right) OD operating point.

Figure 5. (left) Example of non-optimal RD and (right) OD operating point.

Figure 6. Example of non-optimal clock-low voltage for a parallel clock.

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