A New Pixel Circuit Compensating for a Decrease in Luminance of the Stretchable Active Matrix Organic Light Emitting Diode Display

The stretchable display is a next-generation flexible display because it is possible to implement free-form with free change, and various studies are being conducted. The most likely display technology for implementing a stretchable display is the organic light emitting diode (OLED), which is suitable for forming on flexible substrates because it can emit light on its own without using the back light unit (BLU). In addition, through advantages such as high contrast ratio, fast response time, and wide viewing angle, OLED is applied from small size panels such as mobile to large size panels such as televisions. Thin film transistor, a device applied to drive active matrix of OLED, is represented by the amorphous silicon (a-Si), low temperature poly silicon (LTPS), and oxide TFT such as amorphous In-Ga-Zn-oxide(a-IGZO). The a-IGZO, which has advantages such as high filed effect mobility and low leakage current compared to a-Si:H, is used as a backplane of commercial OLED panels. In addition, it is suitable for application to flexible substrates due to low process temperature, and high transmittance in the visible area due to band gap energy of about 3.1 eV can be applied to transparent display. In research to minimize damage to TFTs or OLEDs when the area of flexible substrates increases, rigid island structures protect devices from damage by forming rigid structures on soft substrates. Devices protected from damage caused by increasing the area can maintain performance, and each pixel can maintain brightness. However, when the area of the panel is increasing, the gap between the pixels increases, which leads to a decrease in the luminance of the panel. Among the studies to compensate for the decrease in brightness by increasing the area of the stretchable display, Kang et al. proposed a stretchable pixel circuit for AMOLED displays, which compensates for the reduced luminance by bootstrapping. The proposed circuit increases luminance through a variable capacitor with a strain-dependent capacity change. However, compensation for TFT's threshold voltage and voltage drop, which are possible causes of luminance reduction in OLED were not considered. The threshold voltage or power voltage of a different drive TFT for each pixel affects the current supplied from the backplane to the OLED electrode, and the current supplied differently for each pixel affects the light intensity of the OLED device, so compensation should be considered. In this study, we propose a no