  Spatial Atomic Layer Deposition (SALD) is a recent approach that is up to two
orders of magnitude faster than conventional ALD, and that can be performed at
atmospheric pressure and even in the open air. Previous works have exploited
these assets to focus on the possibility of high-rate, large-area deposition
for scaling up into mass production. Conversely, here we show that SALD indeed
represents an ideal platform for the selective deposition of functional
materials by proper design and miniaturization of SALD close-proximity heads.
In particular, we have used the potential offered by 3D printing to fabricate
custom close-proximity SALD injection heads. By using 3D printing, the heads
can be easily designed and readily modified to obtain different deposition
areas, free-form patterns, and even complex multimaterial structures. The heads
can be printed in different materials to adjust to the chemistry of the
precursors and the deposition conditions used. Polymeric heads can be used as
cheap (even disposable) heads that are both used for performing deposition and
for prototyping and optimization purposes. Finally, by designing a miniaturized
head with circular concentric gas channels, 3D printing of functional materials
can be performed with nanometric resolution in Z. This constitutes a new 3D
printing approach based on gaseous precursors. Because the selective deposition
strategies presented here are based on the SALD process, conformal and
continuous thin films of functional materials can be printed at low
temperatures and with high deposition rate in the open air. Our approach
represents a new versatile way of printing functional materials and devices
with spatial and topological control, thus extending the potential of SALD and
ALD in general, and opening a new avenue in the field of area-selective
deposition of functional materials.
