Abstract
In this paper, we examine the effect of switch thin-film transistor
(TFT) leakage and charge injection on the operation and driving of amorphous
silicon (a-Si) active matrix organic light-emitting diode (AMOLED) displays.
Charge injection causes an undesirable and immediate drop in the data voltage
stored on the storage capacitor C<sub>S</sub> when the switch TFT is turned off, and the leakage of
the switch TFT causes the charge on C<sub>S</sub> to gradually leak out over the frame time. While making
the row line negative helps reduce the leakage, it increases the voltage swing
on the row line and causes more charge injection. We have demonstrated that
for a given V<sub>DD</sub>,
there is an optimal negative gate drive voltage on the switch TFT that minimizes
the overall drop in data voltage on C<sub>S</sub> over the frame time. In addition, we have also shown that
even though this optimal driving point changes with aging of the display since
both leakage and V<sub>T</sub> increase
over time, it is possible to keep the voltage drop on C<sub>S</sub> constant irrespective of aging. The analysis
provides the designer with a means to improve the long term grey-scale performance
of the AMOLED display.
© 2006 IEEE
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