Nanosecond laser ablation of polyvinylpyrrolidone (PVP) protected silver nanoparticle (20 nm diameter) film is studied using a frequency doubled Nd:YAG nanosecond laser (532 nm wavelength, 6 ns full width half maximum pulse width). In the sintered silver nanoparticle film, absorbed light energy conducts well through the sintered porous structure, resulting in ablation craters of a porous dome shape or crown shape depending on the irradiation fluence due to the sudden vaporization of the PVP. In the unsintered silver nanoparticle film, the ablation crater with a clean edge profile is formed and many coalesced nanoparticles of 50 to 100 nm in size are observed inside the ablation crater. These results and an order of magnitude analysis indicate that the absorbed thermal energy is confined within the nanoparticles, causing melting of nanoparticles and their coalescence to larger agglomerates, which are removed following melting and subsequent partial vaporization.
Additive direct writing has many advantages compared with the subtractive conventional MEMS fabrication process.
With its reduced manufacturing steps, the processing time is shortened and the overall process costs less. Also, the
process is non-toxic and its flexibility in the manufacturing gives the capability to alter printing patterns promptly.
Among many direct writing methods, electro-hydrodynamic (EHD) printing is also receiving a huge interest due to its
capability of high resolution printing. However, there are still many issues to be resolved for the high volume fabrication
process, such as the realization of multi-nozzle drop on demand system, etc. In this work, EHD printing was
demonstrated using a hole-type electrode with stainless steel nozzle to which the liquid is supplied from a constant
pressure reservoir. With varying square voltage pulses between the nozzle and the electrode, three types of jet emission
modes are observed; continuous mode, fine jet pulsating mode and droplet pulsating mode. Among these modes, the
droplet pulsating mode and the fine jet pulsating mode were optimized to print relatively large patterns and high
resolution patterns, respectively. In addition, to demonstrate near field printing for high position accuracy, EHD printing
was carried out with a nozzle penetrating the hole-type electrode, so that the distance between nozzle tip and the
substrate could be shortened.
The low temperature fabrication of active (field effect transistor) electrical components on flexible polymer substrates
is presented in this paper. A drop-on-demand (DOD) ink-jetting system was used to print gold nano-particles
suspended in organic solvent, PVP (poly-4-vinylphenol) in PGMEA (propylene glycol monomethyl ether acetate)
solvent, semiconductor polymer in organic solvent to fabricate passive and active electrical components on flexible
polymer substrates. Short pulsed laser ablation enabled finer electrical components to overcome the resolution
limitation of inkjet deposition. Continuous Argon ion laser was irradiated locally to evaporate the carrier solvent as
well as to sinter gold nano-particles. In addition, a new method for the selective ablation of multilayered gold
nanoparticle film was demonstrated.
Ablation of metal nanoparticle film using frequency doubled Nd:YAG nanosecond laser is explored to apply for
trimming drop on demand (DOD) inkjet printed electrical micro-conductor for flexible electronics. While elevated rim
structure due to expulsion of molten pool is observed in sintered nanoparticle film, the ablation of unsintered
nanoparticle film results in a Gaussian-shaped ablation profile, so that a clean precise patterning is possible. In addition,
the ablation fluence threshold of unsintered metal nanoparticle film is at least ten times lower than that of a
corresponding metal film. Therefore, by using nanosecond laser ablation, inkjet printed metal nanoparticles compatible
for flexible polymer can be patterned efficiently with a high resolution.
The low temperature fabrication of passive electrical components (conductor, capacitor) on the flexible polymer substrate is presented in this paper. A drop-on-demand (DOD) ink-jetting system was used to print gold nano-particles suspended in Alpha-Terpineol solvent and PVP in PGMEA solvent to fabricate passive electrical components on flexible polymer substrate. Short pulsed laser ablation enabled finer electrical components to overcome limitation of inkjet process. Continuous Argon ion laser was irradiated locally to evaporate carrier solvent as well as to sinter gold nano-particles. In addition, a self alignment technique for PVP layer was demonstrated taking advantage of the deliberate modification of surface wetting characteristics. Finally, a new selective ablation of multilayered gold nanoparticle film was demonstrated using the ablation threshold difference for sintered and non sintered gold nanoparticles.
Many applications require delivery of small quantities of functional materials into locations on a substrate in the form of liquid solution. Consequently, interest in nongraphical inkjet printing is growing. In addition, higher resolution for printing flexible electronics is becoming more critical to enhance the performance of printing electronics. Since the resolution of inkjet process is limited by the nozzle size and the statistical variation of droplet flight and spreading phenomena, hybrid inkjet printing has emerged as an attractive processing method. In this work, surface monolayer protected gold nanoparticle was printed in a liquid solution form and cured by laser irradiation to fabricate electrically conductive microlines on glass or polymer substrate at a reduced temperature. Continuous laser curing enabled local heating and the morphology could be controlled as well. Thermal penetration into the substrate could be minimized by using pulsed laser beam. Nanoparticle film was effectively removed by applying femtosecond laser, so that small feature size was obtained. Printing on a heated substrate has advantages over room temperature printing. The solvent evaporates soon after contact, so that a thick layer can be deposited with high jetting frequency. The rapid liquid evaporation also eliminated uneven wetting problems and the smaller feature size was obtained.