CCD Charge Injection Structure at Very Small Signal Levels

A frame transfer charge-coupled device (CCD) designed for X-ray detection on board the SUZAKU spacecraft includes an input serial register and a charge injection structure which allows a very uniform injection of extremely small charge packets into the imaging section of the device. A variation of the fill-and-spill method was implemented to inject charge into the CCD. Very small charge packets (down to just a few electrons) can be reproducibly injected with noise as low as five-electron rms. The operation of the structure is described, and the results of the measurements are compared with the simulations. We have measured electron ldquoevaporationrdquo over potential barrier as a function of time, results being in excellent agreement with our model. By fitting a model to the data, it is possible to determine the internal capacitance of the input node. Charge injection noise as a function of signal charge was measured, and the results are also in agreement with theory. The designed structure can be used as a tool for studying and mitigating radiation damage effects in CCDs.