X-ray CCD with low noise charge injection structure

A frame transfer CCD designed for X-ray detection in space 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. The amount of injected charge can be controlled with very high accuracy. Precise measurements were performed of signal and noise as a function of gate voltages and injection timing parameters helping to extract physical characteristics of the charge injection structure. Very small charge packets can be reproducibly injected with noise as low as 5 electrons rms. We demonstrate that this charge injection structure is an extremely useful tool in studying and mitigating radiation effects in CCDs. It allows for fast and accurate calibration of radiation damage suffered by CCDs in space environment. Charge loss in each column of a CCD can be determined with just a few frames of data. Applying the results of these measurements to data analysis allows to correct for column-to-column nonuniformities and improves energy resolution of a damaged CCD. Charge loss as a function of charge has been measured down to very low signal levels, this dependence is also an important factor in developing CTI-correction algorithms. Studying variance of the trap distribution over different columns of a CCD we were able to make certain conclusions about a about charge state of the traps. This technique can be used in studying trap composition of devices. We experimentally confirmed that periodically injecting charge-filled rows it is possible to significantly improve CCD charge transfer inefficiency that was induced by irradiation of a device. Injecting rows filled with charge fills the traps, they stay charged for some time and do not contribute to a charge loss. This technique has been tested and proved useful. Both CTI and energy resolution of the device have shown significant improvements.