Implemented with matrix-addressed photodiode arrays, CMOS image sensor
(CIS) solutions take full advantage of the
economies of scale afforded by a highly
developed semiconductor-manufacturing
infrastructure. The chip industry's steady
march to finer submicron nodes, combined with adding more features on a per-pixel basis, continue to push CIS solutions
ahead of charge-coupled devices (CCDs).
In fact, CIS technology makes it possible to integrate imaging, timing, and readout functions all on the same device. This
leads to practical system-on-a-chip solutions that serve an expanding array of display-centric applications. While the noise
levels of both technologies are comparable, CIS technology has much more saturation capacity than CCD technology.
Recent CMOS-processing advances
have boosted CISs, particularly the virtual
elimination of "dark current." Dark current is produced by a photodiode array in
the absence of light. Such unwanted current is caused by volatile organic compounds (VOCs) in air, also known as "photochemical smog." VOCs can adversely
impact the ability of CIS photodiode arrays
to convert incident photon flux into high resolution digital images.
To overcome image degradation
caused by dark current, a team from
Dongbu took a three-pronged attack at
the CMOS substrate level. First, it built up
the P+ region at the junction of shallow
trench isolation (STI) and the photodiode,
eliminating "dark current" resulting from
defects caused by a non-uniform silicon
interface (). Second, it built up mask
polysilicon to create a protection pole,
enabling uniform colors up to 10 Mpixels
(). Third, it removed "image lagging"
by infusing tilt ions ().
