Abstract
Hybrid sensor/display pixels and their operating schemes are proposed,
simulated, and characterized. The circuit design implemented a phototransistor
connected to a drive thin-film transistor (TFT) and an organic light-emitting
diode (OLED). The circuits were fabricated using hydrogenated amorphous-silicon
(a-Si:H) TFTs as a hybrid photosensor/switching device. The light sensitivity
of the phototransistors and response to incident illumination were modeled
and verified experimentally for different white-light intensities. The pixel
gray scale was determined by the pulse-height voltage modulation from the
phototransistor, which was varied by changing the light intensity. The resulting
circuits have a wide dynamic range with a light to dark output current ratio
of
$10^{4}$
for
TFTs having channel lengths of
$<{{10}}\
\mu{m}$
and light intensity up to
$\sim {{8}}\ {{mW/cm}}^{2}$
.
A 256-RGB-level imaging scale is possible with 5-nA steps for each grey scale
in a pixel array matrix having a refresh rate of more than 200 Hz.
© 2014 IEEE
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