Femtoliter-Scale Patterning
by High-Speed, Highly
Scaled Inverse Gravure Printing
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Abstract
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<sub>p</sub>) of a feature
can be constructed by incorporating these basis functions. By relating <i>Ca</i> and φ<sub>p</sub>, 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