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4-4 MEMS: Design and Fabrication

1976]. This IBM work was an extension of through-mask plating, also pioneered by Romankiw et al. in
1969, and was geared toward the fabrication of thin film magnetic recording heads [Romankiw et al., 1970]
(see Figure 4.30). The addition of plastic molding to the lithography and plating process was realized by
Ehrfeld et al. (1982) at the Karlsruhe Nuclear Research Center (the Kernforschungszentrum Karlsruhe, or
KfK), in 1982. By adding molding, these pioneers recognized the broader implications of LIGA as a new
means of low-cost manufacturing of a wide variety of micro parts with unprecedented accuracies from
various materials previously impossible to batch fabricate [Becker et al., 1982]. In Germany, LIGA origi-
nally developed almost completely outside of the semiconductor industry. In the United States, it was
the late Henry Guckel who, starting in 1988, repositioned the field in light of semiconductor process
capabilities and brought it closer to standard manufacturing processes.
The development of the LIGA process initiated by KfK was intended for the mass production of
micron-sized nozzles for uranium-235 enrichment (see Figure 4.3) [Becker et al., 1982]. The German
group used synchrotron radiation from a 2.5GeV storage ring for the exposure of the poly(methyl–
methacrylate) (PMMA) resist.
Today, LIGA and LIGA-like processes are researched in many laboratories around the world, and devel-
oping the ideal means of fabricating micromolds for the large-scale production of precise micromachines

Light fraction
UF
6
H
2

Heavy
fraction
Medium fraction

50 µm

FIGURE 4.3 Scanning electron micrograph of a separation nozzle structure produced by electroforming with nickel
using a micromolded PMMA template. This nozzle represents the first actual product ever made by LIGA. (Reprinted
with permission from Hagmann, P. et al. [1987] “Fabrication of Microstructures with Extreme Structural Heights by
Reaction Injection Molding,” presented at First Meeting of the European Polymer Federation, European Symposium on
Polymeric Materials, Lyon, France.)

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