RESUMO
The high-resolution array is the basic structure of most kinds of microelectronics. Electrohydrodynamic jet (E-Jet) printing technology is widely applied in manufacturing array structures with high resolution, high material compatibility and multi-modal printing. It is still challenging to acquire high uniformity of printed array with micro-nanometer resolution, which greatly influences the performance and lifetime of the microelectronics. In this paper, to improve the uniformity of the printed array, the influence of each parameter on the uniformity of the E-jet printed dot array is studied on the cobuilt NEJ-E/P200 experimental platform, finding the applied voltage plays the most important role in maintaining the uniformity of the printed array. By appropriately adjusting the printing parameters, the dot arrays with different resolutions from 500 pixels per inch (PPI) to 17,000 PPI are successfully printed. For arrays below and over 10,000 PPI, the deviations of the uniformity are within 5% and 10% respectively. In this work, the dot array over 15,000 PPI is first implemented using E-jet printing. The conclusions acquired by experimental analysis of dot array printing process are of great importance in high resolution array printing as it provides practical guidance for parameters adjustment.
RESUMO
A droplet impacting on a rectangular pixel with an offset is prone to cause the liquid to spread out of the pixel and adhere to adjacent pixels in organic light-emitting diode (OLED) inkjet printing. Therefore, the coalescence of a droplet impacting on a rectangular pixel is crucial in understanding the reliable OLED inkjet printing. In this paper, an assumption is established that the rectangular coalescence process is divided into the fusion part and spread part. On this basis, a dynamics model is introduced to analyze the coalescence behavior of a droplet impacting on a rectangular pixel. According to the law of conservation of mass and energy, dynamic equations are developed to obtain the maximum spread length as a function of time. In addition, the volume of the fluid method is used to simulate coalescence dynamics of a droplet impacting on a rectangular pixel by using the software of FLUENT, and the analytical solutions are consistent with the simulation results. Furthermore, the effects of the positioning error and initial velocity on the coalescence dynamics are analyzed. The results show that small initial velocity and positioning error of the droplet are helpful for the reliable OLED inkjet printing.
RESUMO
In the manufacture of the emissive layer and the encapsulation layer of organic light-emitting diode panels, inkjet printing has the advantages of high material utilization, low cost, flexibility in patterning, and large-area production. Especially for emissive layer printing, the micro-pixel array brings a higher requirement of droplet positioning accuracy and volume of the liquid in a pixel. To achieve a uniform deposit morphology, several droplets are usually needed in the inkjet printing of emissive layers. As the printing process continues, these droplets coalesce, and its equilibrium outcome can be roughly approximated by a section of an ellipsoidal cap under the interaction of the surface tension and gravity. The existence of the "ellipsoidal cap" enlarges the spread, and the maximum allowable out-of-pixel spreading length is decreased because of the "ellipsoidal cap" in the neighboring pixel. In this research, the volume of fluid method is used to study the behavior of the last droplet deposition into the wetted microcavity. The effects of wettability, droplet deposition speed, and initial volume of the liquid in the pixel on the printable region are investigated, and printing parameter spaces that result in successful printing are established.
