Most LCOS devices comprise a layer
of liquid crystal sandwiched between a top
sheet of glass coated with a transparent
electrode, and a pixelated silicon substrate
(or backplane) made by the complementary
metal–oxide–semiconductor (CMOS)
fabrication process. Because the silicon
is reflective, it serves as a mirror element
for each pixel, with the strength of the
reflection electronically controlled by the
amount of light transmitted through the
liquid crystal above. Separate channels of
red, green and blue light illuminate the
LCOS chip in turn, with electronic drive
signals controlling the transmission state
of each pixel to form an active-matrix
colour image. In some cases, a dedicated
LCOS chip is used for each colour channel.
This is a very simple and elegant design
concept: the backplane is formed from a
standard CMOS processed wafer and the
glass substrate has no patterning. Indeed,
the CMOS industry benefits from the heavy
investments made by other industries,
which allows for increases in pixel density
(and, thus, higher resolution) without the
need for LCOS manufacturers’ investment