The Design Of Micro-LED Active Driver Pixel Circuit Based On Metal Oxide TFT

Micro-LEDs have been receiving much attention recently as an emerging display technology,due to their outstanding characteristics of lower power consumption,higher brightness,faster responds time than traditional TFT LCD and AMOLED display.Metal oxide TFTs have a high application prospect for the merits of high mobility,good uniformity,low off-current and so on.The combination of TFT backplane technology and Micro-LED display shows great potential in wearable display devices,transparent display,and other display applications.In this article,we summarize the developments,bottlenecks,driving methods,and the pixel circuit design of Micro-LED display,and design three active-matrix Micro-LED pixel circuits based on MO TFTs.The designed pixel circuits are inverter pixel circuit,pull-up control pixel circuit,and compensatory pixel circuits,belong to analog PWM driving method.In the design of inverter pixel circuit,a triangular wave is used to control the light emission of Micro-LEDs.When Micro-LEDs are light up,the driving TFT is operating in saturation model to serve constant current.The experimental results for 60Hz flash rate show that the maximum pulse width and the proportion of light-emitting time can reach 13.3ms and83%,respectively,which improves the analog data can control pulse with of current to achieve PWM driving.Moreover,the inverter pixel circuit has a simple driving method,which only needs six signals to achieve the analog PWM driving.In the pull-up control pixel circuit,the experimental results of individual pixel show the data signal can change the current pulse width to change the lightness of Micro-LED and keep the current flowing though Micro-LED constant without the influence of Vdata,which can avoid the color of Micro-LED shift with the current density.We also fabricated a Micro-LED array based on the pull-up control driving method by IZO TFTs backplane.The array has a size of 600?m×600?m and the resolution of 48×29.The array also can achieve completely switch off without leakage when Vdata<-2.4 V,3200 cd/m~2 maximum lightness when Vdata>-8 V,and 74%lightness uniformity.This pixel circuit needs seven driving signals and has the merit of simple structure,small area,and constant current PWM driving.In the design of compensatory pixel circuit,a threshold voltage compensation method is applied in the pull-up control pixel circuit to eliminate the uneven light for degradation of TFTs.A 16×15 Micro-LED array is fabricated by IZO TFTs backplane.Data signal can control the lightness of Micro-LED array which can achieve completely switch off without leakage when Vdata>0V,970 cd/m2 maximum lightness when Vdata<-5V.The compensatory pixel circuit has an obvious improvement of brightness uniformity although employed more TFTs.The lightness uniformity of the compensatory array can reach 88%,which is better than pill-up control array with 14%.