  In recent years, scientific CMOS (sCMOS) sensors have been vigorously
developed and have outperformed CCDs in several aspects: higher readout frame
rate, higher radiation tolerance, and higher working temperature. For silicon
image sensors, image lag will occur when the charges of an event are not fully
transferred inside pixels. It can degrade the image quality for optical
imaging, and deteriorate the energy resolution for X-ray spectroscopy. In this
work, the image lag of a sCMOS sensor is studied. To measure the image lag
under low-light illumination, we constructed a new method to extract the image
lag from X-ray photons. The image lag of a customized X-ray sCMOS sensor
GSENSE1516BSI is measured, and its influence on X-ray performance is evaluated.
The result shows that the image lag of this sensor exists only in the
immediately subsequent frame and is always less than 0.05% for different
incident photon energies and under different experimental conditions. The
residual charge is smaller than 0.5 e- with the highest incident photon charge
around 8 ke-. Compared to the readout noise level around 3 e-, the image lag of
this sensor is too small to have a significant impact on the imaging quality
and the energy resolution. The image lag shows a positive correlation with the
incident photon energy and a negative correlation with the temperature.
However, it has no dependence on the gain setting and the integration time.
These relations can be explained qualitatively by the non-ideal potential
structure inside the pixels. This method can also be applied to the study of
image lag for other kinds of imaging sensors.
