9 Laser-Induced Forward Transfer Towards Additive Manufacturing
275
9.2 Fundamentals of LIFT
9.2.1 Origins of LIFT
The concept of material transfer using lasers has been a research objective for over
40 years now, where Levene et al. [3] were the first to report the transfer of black ink
using a Nd:YAG (λ = 1.06 µm) laser source in 1970, while almost 15 years later,
Bohandy et al. [4, 5], introduced for the first time the term LIFT for the transfer
of copper metal features using a pulsed excimer laser source (λ = 193 nm, 15 ns),
on silicon and fused silica substrates, reporting resistivities between 3 and 50 times
the resistivity of bulk copper. The experiment was conducted in vacuum conditions,
however, LIFT nowadays may be performed in ambient conditions as well [6]. Few
years before, in 1979, Deutsch et al. also demonstrated the transfer of metal patterns
using “laser-initiated heterogeneous photochemical reactions” through UV photolysis of gas precursors [7], while in 1983 Osgood et al. introduced for the first time to
the term “laser initiated chemistry” for the deposition and removal of materials [8, 9].
In brief, the principle idea behind LIFT requires the use of (1) a pulsed laser source,
where the wavelength may range between the UV and the IR regions of the spectrum
depending on the optical absorption of the material under transfer to the specific
wavelength and the type of the application, (2) a donor substrate that is a transparent
substrate (sometimes referred to as carrier) coated with a thin film of the material
under investigation and (3) a receiver substrate on the surface of which the material
is deposited. During LIFT, the donor and receiver substrates are brought closely or
in contact to each other and as the laser pulse irradiates the interface between the
carrier and the thin-coated film from the back side of the donor substrate, the material is ejected and therefore deposited on the surface of the receiver substrate as it
is depicted in Fig. 9.1. The theory and the mechanism of LIFT, regarding liquid and
solid-phase printing, will be described in more detail in the next paragraphs.
Apart from the aforementioned basic requirements for LIFT, the system is usually
accompanied by mechanical components namely computer-controlled, highly accurate, and fast translation stages that facilitate the transfer of pre-programmed digital
patterns as well as optical parts such as galvanometer scanners that enable—if
desired—rapid and large area printing.
9.2.2 Limitations of the Technique
Despite the successful implementation of LIFT in a variety of applications, there are
certain aspects related to the technique that needs to be addressed before it can be
used in massive industrial processes and large-area manufacturing. More specifically,
since many LIFT applications involve the printing of metal features namely metal
films and metallic nanoparticles (NPs) inks, which are rapidly oxidized when they are
exposed to ambient conditions, the fast-melting and evaporation during transfer may
275
9.2 Fundamentals of LIFT
9.2.1 Origins of LIFT
The concept of material transfer using lasers has been a research objective for over
40 years now, where Levene et al. [3] were the first to report the transfer of black ink
using a Nd:YAG (λ = 1.06 µm) laser source in 1970, while almost 15 years later,
Bohandy et al. [4, 5], introduced for the first time the term LIFT for the transfer
of copper metal features using a pulsed excimer laser source (λ = 193 nm, 15 ns),
on silicon and fused silica substrates, reporting resistivities between 3 and 50 times
the resistivity of bulk copper. The experiment was conducted in vacuum conditions,
however, LIFT nowadays may be performed in ambient conditions as well [6]. Few
years before, in 1979, Deutsch et al. also demonstrated the transfer of metal patterns
using “laser-initiated heterogeneous photochemical reactions” through UV photolysis of gas precursors [7], while in 1983 Osgood et al. introduced for the first time to
the term “laser initiated chemistry” for the deposition and removal of materials [8, 9].
In brief, the principle idea behind LIFT requires the use of (1) a pulsed laser source,
where the wavelength may range between the UV and the IR regions of the spectrum
depending on the optical absorption of the material under transfer to the specific
wavelength and the type of the application, (2) a donor substrate that is a transparent
substrate (sometimes referred to as carrier) coated with a thin film of the material
under investigation and (3) a receiver substrate on the surface of which the material
is deposited. During LIFT, the donor and receiver substrates are brought closely or
in contact to each other and as the laser pulse irradiates the interface between the
carrier and the thin-coated film from the back side of the donor substrate, the material is ejected and therefore deposited on the surface of the receiver substrate as it
is depicted in Fig. 9.1. The theory and the mechanism of LIFT, regarding liquid and
solid-phase printing, will be described in more detail in the next paragraphs.
Apart from the aforementioned basic requirements for LIFT, the system is usually
accompanied by mechanical components namely computer-controlled, highly accurate, and fast translation stages that facilitate the transfer of pre-programmed digital
patterns as well as optical parts such as galvanometer scanners that enable—if
desired—rapid and large area printing.
9.2.2 Limitations of the Technique
Despite the successful implementation of LIFT in a variety of applications, there are
certain aspects related to the technique that needs to be addressed before it can be
used in massive industrial processes and large-area manufacturing. More specifically,
since many LIFT applications involve the printing of metal features namely metal
films and metallic nanoparticles (NPs) inks, which are rapidly oxidized when they are
exposed to ambient conditions, the fast-melting and evaporation during transfer may