Feature: Machine vision
Figure 1: Wafer with standard visible range anti- reflective coating (ARC) layer (left) and with back illumination, including the near-infrared ARC layer (right)
X-FAB enhances image sensor performance through back
illumination By the X-FAB technical team
image sensor performance through back illumination. Prepared for next- generation image sensor fabrication, the new back illumination (BSI) capability is immediately available for X-FAB’s XS018 180nm CMOS semiconductor process. Trough BSI, imaging devices’
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performance characteristics can be significantly enhanced. It means that the back-end process metal layers do not block incident light from reaching the pixels, increasing fill factors by up to 100%. Tis enchances pixel light sensitivity in low-level illumination situations. BSI also significantly reduces crosstalk between neighbouring pixels, due to shorter light paths, leading to better image quality. Although small-pixel BSI solutions
for 300mm wafers with high-volume consumer use are widely found, there are very few options available for image sensors with stitched large- pixel arrangements for 200mm wafers,
66 July/August 2024
www.electronicsworld.co.uk
-FAB, a specialty foundry group for analogue/mixed- signal semiconductor technologies, has achieved enhanced
especially when additional customisations are required. Te new X-FAB BSI capability brings new possibilities, allowing customers with even the most demanding application requirements to be served – like those developing X-ray diagnostic equipment, industrial automation systems, astronomical research equipment, robotic navigation, vehicle front cameras, and so on.
Machine vision applications By leveraging the XS018 platform, which offers high readout speeds and exhibits low dark currents, image sensors with multiple epi options will be produced. An anti-reflective coating (ARC) layer can be added and adjusted to particular customer requirements. Te accompanying X-FAB support package covers a full workflow from initial design through to the shipment of engineering samples. “BSI technology has become increasingly
prevalent in modern imaging devices, thanks to its ability to boost image quality by placing light-sensitive elements closer to the light source, and avoiding unwanted circuitry obstructions. Tis is proving very useful in environments where light is limited,” states Heming Wei, Technical Marketing Manager for Optical Sensors at X-FAB. “Tough much of this uptake has been within the consumer electronics sector, there are now numerous opportunities emerging in the industrial, automotive and medical markets. Via access to X-FAB’s BSI foundry solution, it will now be possible for these to be properly addressed, with a compelling offering that brings together heightened sensitivity, enlarged image sensor dimensions and bigger pixel capacities, too.” With this solution, X-FAB is opening
a foundry route to medical, automotive and industrial customers that combines boosted sensitivity, larger pixel size and larger sensor area.
Figure 2: Schematic cross section of backside illumination architecture
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