Page 313 - Organic Electronics in Sensors and Biotechnology

290 Chapter Seven

(b) the realization of a photochemically altered surface layer for
increasing the refractive index. Straight single-mode waveguides and
multimode interference couplers for the NIR spectrum fabricated by
this approach have already been demonstrated. 95
Waveguide-Coupled Organic Semiconductor Lasers
The above-mentioned fabrication techniques enable the fabrication of
an integrated waveguide-coupled organic semiconductor laser. A
first success was the coupling of amplified spontaneous emission
generated in an organic semiconductor layer into an underlying deep
96
UV patterned waveguide. Recently, an integrated laser with strongly
25
(20×) enhanced coupling efficiency has been demonstrated. This
waveguide-coupled laser was fabricated with three main process
steps.
• Hot embossing of first-order DFB laser resonators
• Waveguide definition through deep UV exposure of PMMA
• Deposition of the active laser material Alq :DCM
3
By keeping the complete process chain compatible with 4 in wafers,
the mass production potential was shown. The whole process includes
several steps, which are schematically illustrated in Fig. 7.24.
With a possible target application being a high-volume produc-
tion, a simple and fast tool replacement is necessary. Therefore the
hot embossing process makes use of a nickel shim, which is based on
a master fabricated by electron beam lithography and dry etching
out of an oxidized silicon wafer (see Sec. 7.3). With the silicon wafer

Force DUV

Heat
(a) (b) (c)

Vapor deposition

(d ) (e) (f )
FIGURE 7.24 Schematic of the process chain for the fabrication of integrated
waveguide-coupled organic solid-state lasers.