Lithography onto curved surfaces

A recent three-dimensional method is summarized in Figure 3.10 [33].

2 mm silver-coated ) glass capillary

Coat capillary with photoresist

Make electrical connection; electroplate nickel; dissolve substrate

Figure 3.10 Scheme [33] for fabricating a chain using a flexible photomask and electrochemical welding. (A) Metallized glass capillaries coated with photoresist, by pulling them slowly from bulk solution. (B) Capillaries hard-baked at 105 °C for 3 min. Exposure (8s) of coated capillary to UV light through a flexible mask (design shown in (C)) wrapped around its surface. (D) Under optical microscope align two patterned capillaries to be in close proximity with their patterns matched to form a

Figure 3.10 Scheme [33] for fabricating a chain using a flexible photomask and electrochemical welding. (A) Metallized glass capillaries coated with photoresist, by pulling them slowly from bulk solution. (B) Capillaries hard-baked at 105 °C for 3 min. Exposure (8s) of coated capillary to UV light through a flexible mask (design shown in (C)) wrapped around its surface. (D) Under optical microscope align two patterned capillaries to be in close proximity with their patterns matched to form a chain. (E) (Links correspond to openings in the photoresist. Dotted lines represent links on the undersides of the capillaries that are not visible from the top). Electroplating nickel for 30 min. at density 20 mA/cm2 welded together the ends of the chain links, in those areas defined by the photoresist. Finally, release the nickel chain by dissolving photoresist in acetone, dissolving silver metallization in aqueous ferricyanide bath, and dissolving the titanium and glass in concentrated H F [33]

250 Jim

Figure 3.11 Optical micrograph of a free-jointed nickel chain formed by the process shown in Figure 3.10[33]. The final thickness of the nickel was about 50|nm

This method depends upon a flexible mask, that can be curved around the glass capillary tubes. The size of objects that can be made by this method is limited in part by the relative alignment of the two cylinders that is needed. Generalizations are discussed in [33].

The authors suggest that applications of such fully three-dimensional structures could include ultralight structures for micro air and space vehicles, components for microelectromechanical systems, 3D metallic membranes and electrodes, and, at smaller dimensions, dielectric structures for photonic band gap materials.

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