Studies Of High-performance Electrodes In Thin Film Transistors By Inkjet Printing

As the marginal benefits of large-scale display diminishes,the drawbacks of traditional vacuum production processes have become increasingly prominent,providing a unique opportunity for the development of inkjet printed thin-film transistor?TFT?.Metal oxide thin film transistor?MOS-TFT?is a hot spot in current research due to its low process temperature and high performance.However,the mian research object for its inkjet printing preparation focuses on semiconductor layer.TFT electrodes simultaneously serve as the interconnection wires of the units in the fabrication of the backplane,thus the research of high-performance electrodes'inkjet printing is of great importance.Owing to the limitations of inkjet printing technology,the preparation of electrodes with high uniformity and high resolution is currently achieved by additional process steps,which makes inkjet printing technology lose its low-cost advantage in the fabrication of high-performance electrodes in TFT.Therefore,from the perspective of conductive ink,equipment,process,etc.,the droplet behavior of inkjet printing must be further discussed,and new methods and mechanisms for the direct patterning of high-performance electrodes should be proposed.The inkjet printed film achieves its uniformity through the control of the flow field of the liquid film during the evaporation process,while its high-resolution patterning is limited by the micro-droplets colascence mechanism.Accordingly,the content of this paper mainly includes the developing of new conductive inks,evaporation control,flow field adjustment of liquid film,coalescence mechanism of micro-droplets and the direct patterning of electrodes with high uniformity and high resolution.The main results are shown as follows:?1?It is proposed to regulate the“coffee ring”effect using the“drying micro-environment”,which essentially adjusts the evaporation uniformity of the liquid film along its surface by the mutual drying influence of inkjet printed film,causing the flow field to change,and realizing the continuous control of the profiles of dots,lines and films?concave,convex,and flat?.?2?The“dry micro-environment”was used to achieve continuous adjustment of the sizes and shapes of the ripples,and accurately suppress the formation of cracks on the surface of the film.At the same time,the intrinsic relationship between crack formation during solidification of metal organic decomposition?MOD?silver ink and evaporation of liquid film,flow field and the reduction process of silver nanoparticles was studied.?3?Developed a low-temperature?<150??,high-conductive and“gel-switchable droplet front”MOD ink for inkjet printing.The“sol-gel”transition is modulated by the ink chemistry and strong evaporation effect of micro-droplets.The process is such that the droplets are in the sol state in the jetting state,and the surface gelation occurs first in the periphery region within the deposition delay time.For the first time,large-scale uniformity of inkjet printed film is achieved,and the surface undulation is?h/?L<0.04%.?4?The existence of“air film”in inkjet printing process was indirectly verified by droplets self-alignment phenomenon.Its important role in droplets coalescence process was discussed.The relationship between the generation of the“air film”and the flow field on the surface of the droplet was verified by the targeted design of the conductive ink.An“interspace defects growth”method was invented to prepare high-resolution inkjet printed electrodes,an“air film”self-aligned short channel was achieved with the channel length of only 2.4?m,refreshing the direct graphic accuracy limit of piezoelectric inkjet printing?>20?m?.The intensity of the“air film”between droplets was controlled then by the“drying micro-environment”,making the length of the short channel of the electrodes continuously adjustable.The shortest channel is close to 1?m,and at the same time,uniform profiles of electrodes are satisfied.?5?Through the discussion of the solvent etching and the electrode/semiconductor interface contact characteristics,the effects of silver nanoparticles?SNPs?and MOD inks inkjet printed as source and drain electrodes on the electrical properties of MOS-TFT were compared.The results show that the TFT device fabricated with the MOD ink has the better electrical properties on leakage current and I_on/I_off.