Inkjet Printing at High Resolution

Abstract

Inkjet printing has been used as a manufacturing tool for a wide range of applications beyond its original use for text and graphics printing. This thesis aims to investigate the stability and electrical properties of inkjet printed line structures at high spatial resolution, using piezoelectric drop on demand (DOD) printing and electro-hydrodynamic (EHD) inkjet printing. An experimental study of the stability of lines produced by DOD printing drops of volume in the range 1 -10 pL using an ink/substrate combination with zero receding contact angle is presented. These results are used to validate existing models of the limiting bounds for the formation of stable parallel-sided lines as a function of drop spacing and printing speed. The model for the maximum drop spacing bound shows good agreement with our results. The minimum drop spacing bound is limited by a bulging instability and our results agree with the existing model, except for the printings with large drop volumes at low temperature. It is shown that in this circumstance there is a different mechanism for bulging that occurs after printing over a period of minutes, if the liquid bead is present on the surface for a significant period of time before drying. A study of the stability of lines printed on ink/substrate combinations with finite receding contact angles is also presented, over the same range of droplet size as the zero receding contact angle work. In this case, all the printed structures are found to be unstable, showing either individual large drops or continuous lines showing irregular periodic bulges at lower values of advancing and receding contact angles. The morphology change is shown to be due to the change of boundary conditions for the liquid bead at decreased contact angle. A dynamic model based on previous analysis methods is developed to predict the mean wavelength of the bulging morphology. It is further shown that stabilized line structures can be obtained on substrates with finite receding contact angle by pre-depositing droplets to generate small regular disturbances that initiate the formation of controlled periodic bulges, thus making the ridges relatively stable due to loss of liquid to the adjacent bugles. Finally, a study is presented on the stability and electrical properties of lines printed at ultra high resolution using an EHD inkjet printing system. Stable DOD EHD printing using femtolitre volume droplets is achieved by controlling the flow rate and pulse width time. The stability model for the formation of parallel-sided lines is shown to agree well with the results on the low contact angle silicon substrates and also with results in the literature. However, large deviations were observed for results from high contact angle substrates. We hypothesize that this is possibly due to the deviations from the calculated ejected volume per pulse. Stable inkjet printed line electrodes with sub ten micrometre width are successfully achieved, with conductivities within an order of magnitude of bulk silver.

Date of Award	1 Aug 2021
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Brian Derby (Supervisor)