Laser-Induced Forward Transfer Using Triazene Polymer Dynamic Releaser Layer

TLDR: In this paper, a short review of the use of triazene polymer as a dynamic release layer (DRL) for laser-induced forward transfer (LIFT), before looking at the latest research in more detail is presented.

Abstract: This article presents a short review of the use of triazene polymer as a dynamic release layer (DRL) for laser-induced forward transfer (LIFT), before looking at the latest research in more detail. The field of triazene polymer ablation only started around 20 years ago and has grown rapidly into a number of different application areas. Most promisingly, triazene ablation has been refined as a method for propulsion, bringing the benefits of LIFT to the deposition of sensitive transfer materials. The key to understanding LIFT with a triazene DRL is to understand the more fundamental nature of triazene polymer ablation in both frontside and backside orientations. This article focuses on the most recent experimental results on LIFT with a triazene DRL: the effect of picosecond pulse lengths compared with nanosecond pulse lengths; the effect of reduced air pressure; and the improvements in transfer in terms of range of transfer materials, and transfer across a gap. The results all help improve fundamental understanding of triazene-based LIFT, and the transfer of functioning OLEDs demonstrates the capability of the technique.

Figures

FIGURE 3. Flyer velocity as a function of fluence as calculated from shadowgrams (like those in Fig. 2). Reduced pressure flyer velocities (blue squares/blue solid line fit) and atmospheric flyer velocities (red circles/red dashed line fit) have been plotted and the fit lines were calculated according to Eq. 1.

Full text

Laser-Induced Forward Transfer Using Triazene
Polymer Dynamic Releaser Layer
James Shaw Stewart
a,b
, Thomas Lippert
b
, Matthias Nagel
a
, Frank Nüesch
a
and
Alexander Wokaun
b
a
Empa Swiss Federal Laboratories for Materials Testing and Research, Überlandstrasse 129, 8600 Dübendorf,
Switzerland
b
Paul Scherrer Institut, 5232 Villigen-PSI, Switzerland
Abstract. This article presents a short review of the use of triazene polymer as a dynamic release layer
(DRL) for laser-induced forward transfer (LIFT), before looking at the latest research in more detail. The
field of triazene polymer ablation only started around 20 years ago and has grown rapidly into a number
of different application areas. Most promisingly, triazene ablation has been refined as a method for
propulsion, bringing the benefits of LIFT to the deposition of sensitive transfer materials. The key to
understanding LIFT with a triazene DRL is to understand the more fundamental nature of triazene
polymer ablation in both frontside and backside orientations. This article focuses on the most recent
experimental results on LIFT with a triazene DRL: the effect of picosecond pulse lengths compared with
nanosecond pulse lengths; the effect of reduced air pressure; and the improvements in transfer in terms of
range of transfer materials, and transfer across a gap. The results all help improve fundamental
understanding of triazene-based LIFT, and the transfer of functioning OLEDs demonstrates the
capability of the technique.
Keywords: triazene polymer, laser transfer, LIFT, OLED
PACS: 81.16.Mk
INTRODUCTION
Laser-induced forward transfer is a precision deposition technique utilizing the high-
energy and fine-focussing of laser beams. The use of an intermediate layer, such as a triazene
polymer film, to absorb the energy and provide the mechanical energy for propulsion without
allowing light to impinge upon the transfer material can help minimise energy transfer into
the transfer material. This extends the benefits of LIFT to more sensitive and structured thin
film layers that cannot otherwise be deposited in such a controlled manner. To start off with
we will look at triazene polymer ablation, before reviewing the history of LIFT and how
these two separate research fields of converged to develop LIFT using an intermediate
triazene polymer DRL.
Triazene Polymer Ablation
The fundamental aspect of this method is the clean laser-ablation of the triazene polymer.
In the field of polymer ablation, triazene-based chemicals were originally used as dopants for
the ablation of other polymers
1, 2
using 308 nm wavelength light from the common XeCl
excimer laser. Fairly soon, the group at Bayreuth incorporated the triazene chromophore into
polymers themselves, firstly as a PMMA co-polymer with triazene side-chains
3
, and then
with the triazene chromophore along the polymer backbone
4
to improve the efficiency and
cleanness of the polymer-ablation process. These novel polymers proved to be much more
precise and clean in their ablation when compared to the doped PMMA
5
. In addition to the
789
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CP1278, International Symposium on High Power Laser Ablation 2010, edited by
C. R. Phipps
© 2010 American Institute of Physics 978-0-7354-0828-9/10/$30.00
EMPA20100774

high photosensitivity, it was seen that triazene polymers also exhibit remarkably high
thermostability, up to 230 ºC
6
.
Developments in triazene ablation
The ablation of triazene polymers was initially seen as a promising photoresist
technology
7
. However, the photosensitivity of the standard triazene polymers is matched by
their sensitivity to an acidic wet-etching processes
8
. This led to further structural alterations
to triazene polymers, such as the insertion of ester groups into the backbone, enabling photo-
cross-linking of the polymers without breaking up the polymers' backbones
9
. At the Paul
Scherrer Institut other applications were explored, such as micro-optics formed by precise
UV-ablation of the triazene, and laser-plasma thrusters for micro-satellites
10
. Also
investigated was a form of laser transfer known as laser molecular implantation, where
fluorescent molecules were contained within a triazene matrix and transferred via ablation
11
.
Imaging techniques were used to analyse the ablation process of triazene, and the first
attempts were made to understand the nature of the ablation process
12
. Further developments
in these time-resolved methods enabled a greater understanding of the energy generated by
this process
13, 14
. An improved triazene polymer synthesis procedure
15
, developed at Empa,
Dübendorf, has given more control to the structure of the triazene polymer, and therefore
opened up the possibility of creating polymers with different structures
16
, and possibly
different physical and chemical properties, such as solubility or reactivity.
Laser-Induced Forward Transfer
LIFT is a technique with some clear advantages. It has many of the benefits of the
traditional press-printing, but uses a laser to act as the press. The laser irradiates the sample
from behind as if pushing the material towards the receiving substrate. Only the material that
is irradiated will be transferred, which means that the laser defines the lateral shape of the
deposition. Precisely defined deposition can be obtained by controlling the path of the laser
beam using a beam steerer. The important factor here is the transfer material; with the
traditional printing press the transfer material was an ink which was robust and transferred
quite simply. In today's age, with hand-held high-resolution display devicesmore factors need
to be considered because we expect to transfer more things than a single ink, and in a more
reliable way. So in order to be transferred efficiently it is desirable that the transfer material
can absorb the wavelength of light used fairly well, and that it can also transfer this photon
energy into a mechanical energy fairly efficiently. For more detailed and precise printing – at
finer resolutions – this may be hard to achieve. The addition of an intermediate, dynamic
release layer (DRL) to carry out the energy transfer is beneficial in terms of both the quality
of the ablation, and also the reduction in degradation to the transfer material by light-
absorption, even managing to maintain the film morphology through the transfer. This is the
role which triazene polymer plays in laser-induced forward transfer, as a DRL.
LIFT Developments
The earliest report of LIFT, as it as been outlined above, comes from the simple "direct
writing" deposition of aluminium layers using a 193 nm ArF excimer laser
17
. The addition of
an intermediate layer was quickly adapted, originally as a thermally-activated DRL
18
, and
then as a matrix in a process known as matrix-assisted pulsed laser evaporation direct-write
(MAPLE-DW)
19
. The use of triazene in the molecular implantation process
11
was eventually
followed by the use of triazene as a DRL in the transfer of polymethyl methacrylate
20
. This
790
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Frequently asked questions

Q1. What are the contributions mentioned in the paper "Laser-induced forward transfer using triazene polymer dynamic releaser layer" ?

This article presents a short review of the use of triazene polymer as a dynamic release layer ( DRL ) for laser-induced forward transfer ( LIFT ), before looking at the latest research in more detail. This article focuses on the most recent experimental results on LIFT with a triazene DRL: the effect of picosecond pulse lengths compared with nanosecond pulse lengths ; the effect of reduced air pressure ; and the improvements in transfer in terms of range of transfer materials, and transfer across a gap. Most promisingly, triazene ablation has been refined as a method for propulsion, bringing the benefits of LIFT to the deposition of sensitive transfer materials. 

Q2. What is the main advantage of the LIFT technique?

The addition of an intermediate, dynamic release layer (DRL) to carry out the energy transfer is beneficial in terms of both the quality of the ablation, and also the reduction in degradation to the transfer material by lightabsorption, even managing to maintain the film morphology through the transfer. 

Q3. What was the first attempt to understand the nature of the ablation process?

Imaging techniques were used to analyse the ablation process of triazene, and the first attempts were made to understand the nature of the ablation process 12 . 

Q4. What is the effect of a shorter pulse length on the ablation of triazene?

According to the model a shorter pulse length should decrease the heat loss via diffusion, and therefore increase the efficiency of energy transfer from light into gas-pressure build up of the ablation products. 

Q5. What is the role of the laser in the transfer of triazene?

So in order to be transferred efficiently it is desirable that the transfer material can absorb the wavelength of light used fairly well, and that it can also transfer this photon energy into a mechanical energy fairly efficiently. 

Q6. What is the effect of adding an intermediate layer?

The addition of a stabilising lightemitting polymer layer (MEH-PPV) improves the transfer 30 , but not enough to transfer a pixel with functionality. 

Q7. What is the effect of shortening the pulse beyond the nanosecond regime?

Whilst it is known that when the UV-irradiation is for too long a period, no ablation oftriazene polymer will occur 26 , the effect of shortening the pulse beyond the nanosecond regime had not been studied previously. 

Q8. What was the important factor in the ablation process?

The important factor here is the transfer material; with the traditional printing press the transfer material was an ink which was robust and transferred quite simply. 

Q9. What is the role of the laser in the ablation process?

In today's age, with hand-held high-resolution display devicesmore factors need to be considered because the authors expect to transfer more things than a single ink, and in a more reliable way. 

Q10. What is the name of the paper?

Redistribution subject to AIP license or copyright; see http://proceedings.aip.org/about/rights_permissionsCP1278, International Symposium on High Power Laser Ablation 2010, edited by C. R. Phipps© 2010 American Institute of Physics 978-0-7354-0828-9/10/$30.00high photosensitivity, it was seen that triazene polymers also exhibit remarkably high thermostability, up to 230 ºC 6 . 

Q11. What was the first known method of converting a polymer to a matrix?

The addition of an intermediate layer was quickly adapted, originally as a thermally-activated DRL 18 , and then as a matrix in a process known as matrix-assisted pulsed laser evaporation direct-write (MAPLE-DW) 19 . 

Q12. What was the first use of triazene in the molecular implantation process?

The use of triazene in the molecular implantation process 11 was eventually followed by the use of triazene as a DRL in the transfer of polymethyl methacrylate 20 . 

Q13. What is the purpose of the article?

This extends the benefits of LIFT to more sensitive and structured thin film layers that cannot otherwise be deposited in such a controlled manner.