Research On Small Molecular Fluorescent Organic Light Emitting Diode And Design Of Its Driving System

Organic light-emitting diode is considered as the most rational and potential ofthe third generation Flat Panel Displays (FPDs) technology. Compared to LCD,OLEDs have many advantages, such as non-backlighting, ultra-thin and light,transparent, flexible, high brightness, contrast and fast response. However, the OLEDmanufacturing technique is not mature yet. High performance luminescent materials,which impede industrialization process of the OLED, still need to explore. In order tosolve those issues, this article, based on the organic material and degradationmechanism, fabricates the small molecule green fluorescent OLED devices. Based onthe theoretically analysis of the PMOLED driving characteristics and methods, thispaper designs two high efficient display driving system and uses some keytechnologies, such as the self-compensated algorithm, which solve the cross effect andbrightness non-uniformity problems existing in the device. The dissertation mainlyincludes the following aspects:The energy band matching, thickness matching, refraction ratio matching, carrierinjection mechanism between carrier (hole or electron) transporting layer and organiclayer are researched. Based on the qualitative and quantitative analysis of the carrierinjection and interface barrier impacted by anode thin film and buffer layer, a highperformance six layer bottom emitting small molecular green fluorescent OLED isfabricated using vacuum vapor deposition technology. The hole injection layer andhole transport layer influence on the device performance are also researched.Monochrome2×12matrix PMOLED panel is fabricated with anode layer,insulating layer, cathode layer and Cr layer design. According to the I-V experimentalcurve of fabricated panel, one fitting function is established to approximate threetransporting mechanism. Using the pixel aging theory, power on and off sequence forcurrent driving is described. Combined the matrix analysis method and resistance ofindium tin oxide thin films and metal, the PMOLED equivalent circuit and descriptionfunctions of pixel voltage drop and electrode resistor are established. Based on thecharacteristic of current mode device, the influence of the driving signal frequency,positive bias voltage duty ratio, reverse bias voltage location and the current peak onthe driving circuit are explored.Utilizing new elaborated the bandgap reference output stage, a high performance non-curvature compensation BiCMOS bandgap reference and its current source withno Early effect and low output resistance are proposed. With the cascode PTATcurrent source, the system PSR performance is enhanced. Combined the row andcolumn driving circuit, the whole driving system is established. The system has beensimulated using CSMC0.5um60V BCD technology. The results indicate that thereference current has high precision, low temperature coefficient and high stability.Based on the control signals of row and column circuit, driving current can beaccurately increased from1.2mA to1.4mA, and then1.5mA.PMOLED display driving system is set up combined with FPGA developmentplatform. According to the relationship among the pixel aging speed, driving currentand driving voltage, the control of pixel is realized by adjusting duty cycle of PWMsignal. Based on the proposed self-compensated algorithm, the driving voltage dropbecause of pixel inner resistance is compensated and the display luminance uniformitycharacteristic is improved. The pixel driving current is also regulated within certainrange which is decided by the relationship between luminance and current and thedriving current offset compared to the normal pixel current. The experimental resultsshow that when the duty cycle of PWM signal increases from66.6%to94.9%, thedriving current of aged pixel rises from1.53mA to2.18mA. Correspondingly, thepixel driving voltage reaches to0.88V which is higher than the normal pixel drivingvoltage0.55V. In this paper, the research results has the theoretical significance andapplication value in terms of improving PMOLED display driving system, solving thebrightness non-uniformity, and cross effect, and increasing display lifetime.The research is supported by Smart Power Integration&Semiconductor DevicesResearch Group in Toronto University.