A new method for fabricating metal dies for the use of micro-lens array molding or stamping was proposed and investigated. As a metal, nickel was used, and the nickel dies were fabricated by replicating the primary resist molds that were directly printed using projection lithography on silicon wafers coated with approximately 10-μm thick positive resist PMER P-LA900PM. Lens array patterns with quasi-spherical cross sections were printed by selecting a wavelength of 405-nm, defocuses between +100 and +200 μm and exposure times of 20-30 min. After printing resist mold patterns of a lens array, a thin gold film was spattered on it, and nickel was electroplated next. The aimed nickel dies were obtained by removing the resist molds from the electroplated nickel blocks. The diameters of nickel dies were faithfully corresponded to those of the resist molds. In addition, the surfaces of nickel dies were very smooth, and the peak-to-valley roughness was almost less than a quarter of visible light wavelengths. The new method will be promisingly effective for fabricating micro-lens arrays.

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To develop artificial compound eyes, sizes of element lenses of typical insects were actually investigated, and a new simple and low-cost method for fabricating plastic micro-lens arrays was developed. It was thought essential to research on artificial compound eyes that lens parameters were freely controllable by our minds. For this reason, a new easy and low-cost fabrication method had to be developed. In the new method, original molds of micro-lens arrays with concave profiles were formed lithographically in a thick resist film. The concave resist patterns were printed using a handmade 1/19 reduction projection exposure system by only one exposure. Using intentionally defocused exposure, curvature radiuses were controllable in a very wide range of 21-85 μm for the same transparent hexagon patterns with an inscribed circle diameter of 26.3 μm. It was also verified that the resist-mold patterns were faithfully replicated to epoxy resin. After pouring the liquid resin onto the silicon wafer chip with resist-mold patterns, hardened solid resin with micro-lens arrays was separated from the wafer chip by peeling off the wafer chip mechanically. It is promising to fabricate microlens arrays with aimed lens parameters although some more subjects should be cared from now on.

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