Sep 5, 2008
Laser printing made easy
A new laser printing technique can produce arbitrary patterns of nanoparticles over large areas using just a single laser pulse. The method, which overcomes the problems encountered in conventional laser printing, could be used to fabricate electronic devices like transistors, in a simple way.
The most widely used laser printing technique, laser-induced forward transfer (LIFT), relies on spot-by-spot transfer of material, which makes it difficult to fabricate patterns of different geometrical shapes and feature sizes. The new parallel laser printing method, devised by Myeongkyu Lee of Yonsei University in Seoul, Korea, and colleagues, is based on pulsed laser-induced thermal desorption of nanoparticles. Since the threshold energy density for material transfer in this process is much lower than that in LIFT, it is possible to print arbitrary patterns over large areas using a single laser pulse, explains Lee.
The researchers began by solution depositing a nanoparticulate silver film, around 150 nm to 1 µm thick, on a glass source substrate using a commercial silver nano-ink with an average particle size of 25 nm. This film was then dried at room temperature.
Next, a Nd:YAG pulsed laser beam (with a wavelength of 1.064 µm, pulse width of 6 ns, repetition rate of 10 Hz and maximum average power of 8.5 W) was spatially modulated by a photomask in contact mode. The pulse was incident on the film from the back of the substrate.
Lee and colleagues then locally desorbed the material and transferred it onto the receiver substrate (silicon, glass or plastic) in contact with the film, which generated a printed pattern on it. "Any kind of pattern can be fabricated using this technique, once a corresponding mask is used," said Lee.
Any kind of pattern can be fabricated using this technique, once a corresponding mask is used Myeongkyu Lee, Yonsei University, Seoul, Korea,
To make transistors, the team laser-printed source and drain electrodes onto a heavily doped silicon wafer with a 200 nm thick SiO2 dielectric layer. After curing the printed electrodes at 225 °C, a pentacene semiconductor layer was deposited between two electrodes by thermal evaporation. The researchers say that they would also like to fabricate a transistor using all-solution processes, rather than just by thermal evaporation of the pentacene active layer.
They stress that the process is not only useful for printing metal nanoparticles but also nanoparticulate semiconductor and dielectric films as well.
The work was reported in Appl. Phys. Lett.
About the author
Belle Dumé is contributing editor at nanotechweb.org