Design and test results of different aluminum coating layers on the sCMOS sensors for soft X-ray detection

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 x 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 degrees C. 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.