AMOLED Reliability with a-Si TFT's in Normal vs. Inverted TFT/OLED Integration Scheme

An important technical issue associated with using a-Si for AMOLED displays is the direct voltage programming of the pixel by providing a constant current source to the OLED. Since only n-channel a-Si TFT's are available, this requires connecting the driver TFT to the OLED cathode rather than the OLED anode which is not conventionally possible without inverting the OLED stack. This paper reports on the luminance decay vs. time in either normal or inverted pixels may be predicted by measuring the drift in the characteristics of individual TFT and OLED component. Also, the luminance decay is lower in the inverted structure, because of the lack of dependence on the OLED voltage rise.