Design of 7T-2C a-IGZO based pixel circuit for flexible AMOLED displays

This work proposes an AC biased pixel circuit employing flexible amorphous-Indium Gallium Zinc Oxide (a- IGZO) thin film transistors (TFT) to compensate for threshold voltage, mobility, and OLED deterioration for AMOLED displays. In the circuit, there are seven TFTs and two capacitors and is voltage programmed. The designed circuit was simulated using the HSpice tool and an adapted level 61 model of a flexible a-IGZO TFT. It also increased the AMOLED’s lifetime because we employed an ac reversed biased OLED to enhance the OLED’s lifetime and electrical uniformity and reliability. Due to the AC bias, the OLED is reverse biased during the non- emission phase, which not only restricts the OLED’s emission during the other three programming periods to maintain a high contrast ratio display, but also suppresses OLED degradation and so extends the lifetime of the AMOLED display. It can compensate for a broad range of threshold voltage variations, from -1.5 V to 2.5 V, from the driver TFT’s standard 0.7 V. For the specified range, the greatest percentage error in AMOLED current was less than 0.7 percent. It can also endure 0.3 percent mechanical strain on the driver TFT, with a maximum OLED current inaccuracy of less than 0.0085 percent.