  In recent years, tremendous progress has been made on complementary
metal-oxide-semiconductor (CMOS) sensors for applications as X-ray detectors.
To shield the visible light in X-ray detection, a blocking filter of aluminum
is commonly employed. We designed three types of aluminum coating layers, which
are deposited directly on the surface of back-illuminated sCMOS sensors during
fabrication. A commercial 2k * 2k sCMOS sensor is used to realize these
designs. In this work, we report their performance by comparison with that of
an uncoated sCMOS sensor. The optical transmissions at 660 nm and 850 nm are
measured, and the results show that the optical transmission reaches a level of
about 10-9 for the 200 nm aluminum layer and about 10-4 for the 100 nm aluminum
layer. Light leakage is found around the four sides of the sensor. The readout
noise, fixed-pattern noise and energy resolution of these Al-coated sCMOS
sensors do not show significant changes. The dark currents of these Al-coated
sCMOS sensors show a noticeable increase compared with that of the uncoated
sCMOS sensor at room temperatures, while no significant difference is found
when the sCMOS sensors are cooled down to about -15 degree. The aluminum
coatings show no visible crack after the thermal cycle and aging tests. Based
on these results, an aluminum coating of a larger area on larger sCMOS sensors
is proposed for future work.
