Microdisplay technologies for near-to-eye applications mostly
use a complementary metal-oxide semiconductor (CMOS) processing
chip as backplane for pixel addressing, with extensive post-processing
on top of the CMOS chip to deposit organic LED or liquid crystal layers.
Here, we examine the possibility of integrating emissive microdisplays
within the CMOS chip, with absolutely no post processing needed. This
will dramatically reduce the manufacturing cost of microdisplays and
may lead to new microdisplay applications. Visible electroluminescence
is achieved by biasing pn junctions into avalanche breakdown mode.
The most appropriate CMOS pn junction is selected and innovative techniques
are applied to increase the light extraction efficiency from the
CMOS chip using the metal layers of the CMOS process. An 8 × 64 dot
matrix microdisplay was designed and manufactured in a 0.35-μm CMOS
technology. The experimental results show that a luminance level
of 20 cd∕m2 can be reached, which is an adequate luminance value in
order to comfortably read data being displayed in relatively dark environments.
The electrical power dissipation per pixel being activated is
0.9 mW∕pixel. It is also shown that the pixels can be switched at a rate
faster than 350 MHz.