Modeling and Applications of Highly-Scaled Gravure Printing

Pattern printing techniques have advanced rapidly in the last decade, driven by their potential applications in printed electronics. Several printing techniques have realized printed features ≤10 µm, but unfortunately they suffer from disadvantages that prevent their deployment in real applications; in particular, process throughput is a significant concern. Direct gravure printing delivers high throughput and has a proven history of being manufacturing worthy. Unfortunately, it suffers from scalability challenges due to limitations in roll manufacturing and lack of understanding of the relevant printing mechanisms. Gravure printing relies on individual processes namely filling, wiping, transferring and spreading to achieve high quality printing. As gravure printed features are scaled, the associated complexities are increased, and a detailed study of the various processes involved is needed.In this thesis, the various gravure-related fluidic mechanisms are studied using a novel inverse direct gravure printer. The underlying mechanisms of gravure printing are presented. A simple model of gravure printing is proposed. This model demonstrates that individual fluidic processes can be studied separately and a comprehensive understanding of the wiping process in gravure printing is analyzed carefully due to the importance of this process in producing high-fidelity patterns. We report two critical wiping mechanisms that generate drag-out and lubrication residues, which are fundamental scaling limitations for highly-scaled gravure printing. Third, the filling process is investigated, leaded to explanations of air entrapment in gravure cells. In addition, we provide designs and operation conditions for the ultimate reduction of the residues, leading significant scaling of printed features. Printed lines as small as 2 µm are realized at printing speeds as high as ~1 m/s, attesting to the potential of highly-scaled gravure printing.In addition to comprehensive printing mechanism studies, we demonstrate a fabrication process for a high-resolution roll based on advanced microfabrication techniques. The fabrication process incorporates the design guidelines developed previously to deliver the optimized cell geometry and pattern arrangement. Furthermore, electrically functional high-resolution lines are integrated in a fabrication process for fully printed high performance thin film transistors (TFTs). Highly-scaled TFTs demonstrated with channel lengths as small as 3 µm, leading to devices with transition frequency above 1 MHz; this represents a significant advancement over the state of the art

Lubrication-Related Residue as a Fundamental Process Scaling Limit to Gravure Printed Electronics

In gravure printing, excess ink is removed from a patterned plate or roll by wiping with a doctor blade, leaving a thin lubrication film in the nonpatterned area. Reduction of this lubrication film is critical for gravure printing of electronics, since the resulting residue can lower device performance or even catastrophically impact circuit yield. We report on experiments and quantitative analysis of lubrication films in a highly scaled gravure printing process. We investigate the effects of ink viscosity, wiping speed, loading force, blade stiffness and blade angle on the lubrication film, and further, use the resulting data to investigate the relevant lubrication regimes associated with wiping during gravure printing. Based on this analysis, we are able to posit the lubrication regime associated with wiping during gravure printing, provide insight into the ultimate limits of residue reduction, and, furthermore, are able to provide process guidelines and design rules to achieve these limits

Cell Filling in Gravure Printing for Printed Electronics

Highly scaled direct gravure is a promising printing technique for printed electronics due to its large throughput, high resolution, and simplicity. Gravure can print features in the single micron range at printing speeds of ∼1 m/s by using an optimized cell geometry and optimized printing conditions. The filling of the cells on the gravure cylinder is a critical process, since the amount of ink in the cells strongly impacts printed feature size and quality. Therefore, an understanding of cell filling is crucial to make highly scaled gravure printed electronics viable. In this work we report a novel experimental setup to investigate the filling process in real time, coupled with numerical simulations to gain insight into the experimental observations. By varying viscosity and filling speed, we ensure that the dimensionless capillary number is a good indicator of filling regime in real gravure printing. In addition, we also examine the effect of cell size on filling as this is important for increasing printing resolution. In the light of experimental and simulation results, we are able to rationalize the dominant failure in the filling process, i.e., air entrapment, which is caused by contact line pinning and interface deformation over the cell opening

Femtoliter-Scale Patterning by High-Speed, Highly Scaled Inverse Gravure Printing

Pattern printing techniques have advanced rapidly in the past decade, driven by their potential applications in printed electronics. Several printing techniques have realized printed features of 10 μm or smaller, but unfortunately, they suffer from disadvantages that prevent their deployment in real applications; in particular, process throughput is a significant concern. Direct gravure printing is promising in this regard. Gravure printing delivers high throughput and has a proven history of being manufacturing worthy. Unfortunately, it suffers from scalability challenges because of limitations in roll manufacturing and limited understanding of the relevant printing mechanisms. Gravure printing involves interactions between the ink, the patterned cylinder master, the doctor blade that wipes excess ink, and the substrate to which the pattern is transferred. As gravure-printed features are scaled, the associated complexities are increased, and a detailed study of the various processes involved is lacking. In this work, we report on various gravure-related fluidic mechanisms using a novel highly scaled inverse direct gravure printer. The printer allows the overall pattern formation process to be studied in detail by separating the entire printing process into three sequential steps: filling, wiping, and transferring. We found that pattern formation by highly scaled gravure printing is governed by the wettability of the ink to the printing plate, doctor blade, and substrate. These individual functions are linked by the apparent capillary number (<i>Ca</i>); the printed volume fraction (φ_p) of a feature can be constructed by incorporating these basis functions. By relating <i>Ca</i> and φ_p, an optimized operating point can be specified, and the associated limiting phenomena can be identified. We used this relationship to find the optimized ink viscosity and printing speed to achieve printed polymer lines and line spacings as small as 2 μm at printing speeds as high as ∼1 m/s

Systematic Design of Jettable Nanoparticle-Based Inkjet Inks: Rheology, Acoustics, and Jettability

Drop-on-demand inkjet printing of functional inks has received a great deal of attention for realizing printed electronics, rapidly prototyped structures, and large-area systems. Although this method of printing promises high processing speeds and minimal substrate contamination, the performance of this process is often limited by the rheological parameters of the ink itself. Effective ink design must address a myriad of issues, including suppression of the coffee-ring effect, proper drop pinning on the substrate, long-term ink reliability, and, most importantly, stable droplet formation, or jettability. In this work, by simultaneously considering optimal jetting conditions and ink rheology, we develop and experimentally validate a jettability window within the capillary number–Weber number space. Furthermore, we demonstrate the exploitation of this window to adjust nanoparticle-based ink rheology predictively to realize a jettable ink. Finally, we investigate the influence of mass loading on jettability to establish additional practical limitations on nanoparticle ink design