Page 299 - Organic Electronics in Sensors and Biotechnology

276 Chapter Seven

film is about 10 mJ/cm² using a frequency triple Nd:YAG laser emit-
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ting 150 ps pulses at 355 nm.
7.3.5 Replication: Imprint Techniques
Imprinting plastics is one key to low-cost mass production. The first
microstructures molded in polymer materials were fabricated with
the well-known hot embossing process. The basic process steps are
depicted in Fig. 7.9. The microstructure is replicated by pressing a
master onto a substrate at temperatures above the substrate materi-
51
al's glass temperature. With the introduction of vacuum embossing
of plastics it became possible to imprint large areas uniformly since it
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avoids an air cushion between stamp and sample. As the master
may be damaged by the embossing step, the so-called LIGA process
was adapted to fabricate a durable metal imprinting tool of the mas-
ter microstructure.
LIGA is the German acronym for the main steps of the process, i.e.,
lithography, electroforming, and plastic molding. 53–55 The single pro-
cess steps are shown in Fig. 7.10. To generate the metal tool by elec-
troforming the insulating master structure, a conducting starting
layer is deposited onto the master. This is usually done by evaporat-
ing a gold layer upon the master structure. By electroplating these
structures, the negative pattern of the resonator structure is formed as
a secondary metallic structure. Commonly used metals for plastic

Force

Heat

(a) (b) (c)
FIGURE 7.9 Processing steps for hot embossing.

(a) (b) (c)
FIGURE 7.10 Fabrication scheme of a Ni shim following the LIGA process.