Last modified: 8 December 2021

FI: Frontside Illuminated

A CCD chip (on ACIS) in which X-rays are incident on the gate structure on the front of the chip. This blocks some low energy X-rays, but has lower background and (in the absence of parallel CTI) provides better energy resolution than BI (backside illuminated) chips.

See the ACIS entry for more details on the CCD chips.