Screen-offset printing combines screen-printing on a silicone blanket with transference of the print from the blanket to a substrate. The blanket absorbs organic solvents in the ink, and therefore, the ink does not disperse through the material. This prevents blurring and allows fine patterns with widths of a few tens of micrometres to be produced. However, continuous printing deteriorates the pattern’s shape, which may be a result of decay in the absorption abilities of the blanket. Thus, we have developed a new technique for refreshing the blanket by substituting high-boiling-point solvents present on the blanket surface with low-boiling-point solvents. We analyse the efficacy of this technique, and demonstrate continuous fine pattern formation for 100 screen-offset printing processes.
We demonstrated a coating method of screen printing for discharging droplets of a high-viscosity resin on a substrate for ultraviolet (UV) nanoimprint lithography (NIL). Compared with a spin-coated resin film on a silicon substrate, discharged resin droplets on a silicon substrate were effective in terms of the uniformity of residual layer thickness (RLT) in contact with a mold with various pattern densities. Fluorescence microscope observations with a fluorescent-dye-containing UV-curable resin enabled the evaluation of the shapes of resin droplets discharged on a substrate surface. Widely used screen mesh plates composed of a stainless mesh covered with a patterned emulsion film caused defects of undischarged parts, whereas defects-free resin droplets with a narrow size distribution were discharged by mesh-free plates prepared with laser ablation. The pitch-to-diameter ratio in the configuration of 10-µm-diameter holes needs to be larger than 2.5 times for printing a resin having a viscosity of 12,800 mPa s.
Multiple sets of gold (Au) four-terminal microelectrodes comprising 100 μm-scale pad electrodes and 20 μm-wide lead lines were fabricated on a silicon substrate by a print-and-imprint method involving laser drilling and screen printing. Laser drilling of 12.5 μm-thick polyimide (PI) sheets with a picosecond-pulse laser enabled the fabrication of PI membranes with designed patterns of through holes. The through holes had a frustum shape, and the average hole diameters on both the laser entry and exit sides of the PI films enlarged with an increase in the applied repetition rate. The hole patterns designed with submicrometer position accuracy were prepared using a linear motor stage. Liquid ultraviolet (UV)-curable resin, exhibiting a high viscosity (11.0 Pa s) and a high dry-etching resistance to argon (Ar) ion beam milling after UV curing, was placed onto a substrate surface as droplets by screen printing, corresponding to the hole patterns of the PI through-hole masks. The average volume of the liquid droplets could be tuned in the range of 0.02–0.54 pl, which depended on the volumes of the laser-drilled frustum holes. The volumes of liquid resin necessary to fill the mold recesses were adjusted site-selectively by the number of resin droplets printed on a metal-deposited substrate surface. Fluorescence microscopy with a fluorescent dye-doped resin indicated that the imprinted resist patterns had a residual layer thickness in the range of 15–28 nm. The Au electrodes with a 30 nm-thickness could be fabricated by subsequent Ar ion beam milling and removal of a sacrificial metal layer.
Additive-type printing techniques such as gravure-offset printing and screen printing are effective for low-cost and ecofriendly electrode pattern formation. Gravure-offset printing is effective for fine pattern formation with widths on the order of 10–20 µm, whereas screen printing is effective for the formation of large-area patterns. However, it is difficult to simultaneously form fine and large-area patterns using these printing techniques. In this study, we demonstrate that fine (minimum width of 15 µm) and medium- as well as large-area patterns can be formed simultaneously using our developed screen-offset printing technique, which is a combination of screen printing on a silicone blanket and transfer printing from the blanket to a substrate. Furthermore, we demonstrate the application of our method to printing on adhesive materials, which allows electrode formation without applying heat to the film substrate.
The authors demonstrated a “print and imprint” method comprising screen printing and ultraviolet (UV) nanoimprinting for preparing sub-100-nm-wide cured resin patterns. In the screen printing, UV-curable resins with viscosities in the range of 6.26–266 Pa s were deposited as droplet shapes on Si surfaces using a polyimide through-hole membrane mask with a hole diameter of 10 μm and a hole pitch of 45 μm. The low-volatile high-viscosity resin of 12.8 Pa s had an advantage of maintaining the droplet shapes 3 h after deposition. The spherical segment-shaped droplets showed an average diameter of 18.9 μm and height of 1.63 μm. The average volume was approximately 230 μm3 (0.230 pl) which was close to that dispensed by ink-jet printing. The droplet resin on a modified Si surface was filled into recesses of a fluorinated silica mold, and the molded resin was cured by UV nanoimprinting. Although the displacement of resin droplets was periodically uniform on substrate surfaces, the thicknesses of residual layers were almost identical to 0.12 μm in 45, 60, 80, and 100-nm-wide line and space patterns in the range of 1 mm length. The authors confirmed that the resin droplets with a viscosity of 12.8 Pa s could be transformed into imprinted resin patterns with a residual layer thickness of 0.12 μm without obvious nonfill defects.
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