Nano 3D Fabrication of Devices by Expanding of LIFT Printing

The development of a novel material research strategy in the context of next-
generation fuel cell development is the focus topic of the EU project Nanostacks.
A central element of this strategy is a screening approach based on the fabrication
of small arrays of stacked devices derived from OLED and solar cell architectures.
These model systems allow the systematic investigation and optimization of mate-
rial combinations for the development of functional fuel cell components.
Laser-Induced Forward Transfer (LIFT) was selected as the fabrication method be-
cause of its high flexibility regarding material classes and its capability to deposit
functional materials with high spatial precision. In this process, a laser pulse is
focused onto a donor substrate, initiating the transfer of material onto an acceptor
substrate. Depending on the ink system, different transfer mechanisms are em-
ployed. In one configuration, a polyimide absorber layer converts the laser radiation
into heat, initiating material transfer, while in another configuration the laser radi-
ation is absorbed directly by the ink itself.
This work investigates the extension of the LIFT process toward the fabrication of
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electricalcomponentsinadot-by-dotprintingmode. Twodemonstratordeviceswere
selected that represent different dimensional regimes: an OLED with layer thick-
nesses in the nanometer range and a capacitor with structures in the micrometer
range. It is demonstrated that LIFT can be used to fabricate electrical components
with strongly differing thickness and material requirements within the same printing
platform.
To achieve this goal, the material transfer process was systematically analyzed and
optimized. A printing strategy based on overlapping individual transfer spots was
developed, enabling a lateral resolution in the range of 50 µm to 100 µm. This
allowed the fabrication of functional structures with dimensions of approximately
1 mm2. Process optimization promoted controlled merging of adjacent spots, re-
sulting in smooth thin films with a surface roughness of Ra = 2.78 ± 0.25 nm. By
adjusting process parameters and ink concentration, layer thickness could be tuned
in the range of 20 nm to 140 nm, enabling the fabrication of closed OLED layers
with thicknesses of approximately 20 nm.
Further improvements in lateral definition were achieved by implementing mi-
crostructuredacceptorsubstrates. Itwasshownthatpillarstructureswithheightsof
approximately 80 µm enable selective deposition on pillar tops, expanding the range
of material options and allowing higher-density device arrays. In addition, the use
of polyimide as an absorber layer was investigated in detail. Both commercial foils
and ultrathin spin-coated polyimide layers were evaluated, revealing physical limits
for efficient light-to-heat conversion for layers below 1 µm.
A major focus of this work was the development of inks tailored to the LIFT pro-
cess. Organic small-molecule materials such as PEDOT:PSS, TCTA, Rubrene and
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BPhen were successfully employed to fabricate OLED layers, while nanoparticle inks
such as silver and titanium dioxide were used for conductive tracks and capacitor
fabrication. Capacitors were realized by printing multilayer structures consisting of
conductive and dielectric nanoparticle inks, whereas OLED layers were transferred
in their dried state through local remelting in a contact-based configuration.
To support rapid material development, a dedicated LIFT test printer was designed
and built in collaboration with TECNAN. This mobile system enables on-site ink
qualificationusingastandardizedtestingroutineinwhichdefineddropletsaretrans-
ferredandevaluatedoptically. Thesystemestablishesarapidfeedbackloopbetween
ink formulation and process testing, significantly reducing ink development time.
The LIFT toolbox developed in this work consists of an optimized setup, tailored
inks, customized substrates and adapted printing strategies. It enabled fabrication
of different functional electronic devices with most diverse requirements and ma-
terials. Conductive tracks printed with silver ink reached resistivity values close
to those specified by the manufacturer after thermal post-treatment. Parallel-plate
capacitors fabricated from silver and titanium dioxide nanoparticle inks showed
capacitance values in the pF range with a yield of 54 %. Due to the dot-by-dot fab-
rication principle, the capacitance can be tuned with a resolution of approximately
0.4 pF per printed dot.
Furthermore, different OLED architectures were successfully fabricated using the
developed printing process. A hybrid OLED combining spin coating and LIFT
printing exhibited electroluminescence and a fully printed multilayer OLED struc-
tureadditionallyshowedsignificantlyimproveddevicestabilityandlifetime. Optical
and electrical characterization as well as analytical methods confirmed light emis-
sion and verified the correct layer structure.
Overall, this work demonstrates that LIFT is highly suitable for the fabrication of
complex electronic devices. The method enables the deposition of nanometer-scale
organic layers as well as micrometer-scale nanoparticle structures within a single
system. Beyond the demonstrated devices, the method shows strong potential for
the fabrication of further functional structures such as solar cells or fuel cells, making
it a promising technology for future material screening and device prototyping.