9 Laser-Induced Forward Transfer Towards Additive Manufacturing
277
LIFT has been successfully incorporated in industrial processing for electronics and
biological applications.
9.2.3 Advancement and Variations of LIFT
In the years that followed its initial use and owing to the technique’s simplicity and
versatility, LIFT has presented a steady increase in the number of potential applications and materials that could be investigated for organic electronics, bio-electronics,
sensors, etc. [10–20]. This is also highlighted in the number of publications [21]
and patents that were published during the last 10 years, showing an ever-growing
interest in the technique’s unique features such as the high-spatial-resolution and the
selectivity for drop-on-demand applications (Table 9.1 and Fig. 9.2).
Since 1986, where Bohandy et al. [4] firstly introduced the term “LIFT” and in an
effort to overcome the aforementioned LIFT limitations, some alternative methods
have been demonstrated. In these contexts, the main techniques that differ from
the traditional LIFT (liquid and solid phase, Fig. 9.3) are: Dynamic release layerLIFT (DRL-LIFT) [22], Laser-Induced Backward Transfer (LIBT) [23], Matrixassisted pulsed laser evaporation (MAPLE) [24], Blister-actuated LIFT (BA-LIFT)
[25], Absorbing film-assisted-LIFT (AFA-LIFT) [26] and Biological laser printing
(BioLP) [27]. More specifically, in DRL-LIFT the donor substrate, which in traditional LIFT is a transparent substrate, is usually coated with a thin absorbing layer
followed by the deposition of the material under investigation as can be seen in
Fig. 9.3 (right). In this case, as the laser beam irradiates the interface between the
donor and the thin absorbing layer, vaporization of the thin film occurs leading to the
ejection of the material towards the receiver substrate. The dynamic release layer is
usually a metallic one, where Au, Cr, Ti, and Cu are often used, however polymeric
DRL’s may be used as well, with thicknesses ranging between 20 and 100 nm for
the metallic and up to 1 µm for the polymeric ones. The first work involving the use
of a DRL was reported by Tolbert et al. [22], where multilayer films where used to
transfer inks. In the case of the polymeric DRL’s, during the irradiation of the donor
substrate, decomposition of the organic molecules takes place due to photothermal
and photochemical effects that enable the detachment of the material under transfer.
Thus, by adjusting the absorption coefficient of the DRL with respect to the desired
wavelength, it is possible to deposit materials with low absorption to the wavelength
used and also avoid direct exposure to the laser beam that could possibly alter their
structural and morphological characteristics. The most commonly used polymeric
DRL’s are photopolymers including triazene polymers (TP) that have been reported
in several applications [28–30]. AFA-LIFT and BioLP have been employed mainly
for the printing of biological materials, since the use of a 1–100 nm thick metallic or
metal oxide DRL enables the transfer and avoids the direct interaction of the beam
with these sensitive to degrade structures. LIBT on the other hand is an approach
that uses a transparent—to the desired—wavelength substrate and is performed in
the opposite to traditional LIFT direction. This means that the laser beam propagates
277
LIFT has been successfully incorporated in industrial processing for electronics and
biological applications.
9.2.3 Advancement and Variations of LIFT
In the years that followed its initial use and owing to the technique’s simplicity and
versatility, LIFT has presented a steady increase in the number of potential applications and materials that could be investigated for organic electronics, bio-electronics,
sensors, etc. [10–20]. This is also highlighted in the number of publications [21]
and patents that were published during the last 10 years, showing an ever-growing
interest in the technique’s unique features such as the high-spatial-resolution and the
selectivity for drop-on-demand applications (Table 9.1 and Fig. 9.2).
Since 1986, where Bohandy et al. [4] firstly introduced the term “LIFT” and in an
effort to overcome the aforementioned LIFT limitations, some alternative methods
have been demonstrated. In these contexts, the main techniques that differ from
the traditional LIFT (liquid and solid phase, Fig. 9.3) are: Dynamic release layerLIFT (DRL-LIFT) [22], Laser-Induced Backward Transfer (LIBT) [23], Matrixassisted pulsed laser evaporation (MAPLE) [24], Blister-actuated LIFT (BA-LIFT)
[25], Absorbing film-assisted-LIFT (AFA-LIFT) [26] and Biological laser printing
(BioLP) [27]. More specifically, in DRL-LIFT the donor substrate, which in traditional LIFT is a transparent substrate, is usually coated with a thin absorbing layer
followed by the deposition of the material under investigation as can be seen in
Fig. 9.3 (right). In this case, as the laser beam irradiates the interface between the
donor and the thin absorbing layer, vaporization of the thin film occurs leading to the
ejection of the material towards the receiver substrate. The dynamic release layer is
usually a metallic one, where Au, Cr, Ti, and Cu are often used, however polymeric
DRL’s may be used as well, with thicknesses ranging between 20 and 100 nm for
the metallic and up to 1 µm for the polymeric ones. The first work involving the use
of a DRL was reported by Tolbert et al. [22], where multilayer films where used to
transfer inks. In the case of the polymeric DRL’s, during the irradiation of the donor
substrate, decomposition of the organic molecules takes place due to photothermal
and photochemical effects that enable the detachment of the material under transfer.
Thus, by adjusting the absorption coefficient of the DRL with respect to the desired
wavelength, it is possible to deposit materials with low absorption to the wavelength
used and also avoid direct exposure to the laser beam that could possibly alter their
structural and morphological characteristics. The most commonly used polymeric
DRL’s are photopolymers including triazene polymers (TP) that have been reported
in several applications [28–30]. AFA-LIFT and BioLP have been employed mainly
for the printing of biological materials, since the use of a 1–100 nm thick metallic or
metal oxide DRL enables the transfer and avoids the direct interaction of the beam
with these sensitive to degrade structures. LIBT on the other hand is an approach
that uses a transparent—to the desired—wavelength substrate and is performed in
the opposite to traditional LIFT direction. This means that the laser beam propagates