High Thermal Stability Electrooptic Chromophores and new Integrated Optical Polymer Devices
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n 3r/E Figure 1 523 Mat. Res. Soc. Symp. Proc. Vol. 328. ©1994 Materials Research Society
New optical grade, low loss polyimides 3 have been developed to act both as passive waveguides and as hosts for EO chromophores in active regions of devices. The new polyimide copolymers easily withstand standard semiconductor device manufacturing conditions (T>3250C). Most organic chromophores, however, cannot withstand the stringent thermal and chemical stability conditions required in polyimide-based fabrication processes and device assembly steps. Recently, we successfully developed a new class of high thermal stability (T>365°C) fused-ring EO chromophores, 1,8-naphthoylene-benzimidazoles (Figure 2), designed for their structural similarity to polyimide repeat units and consequent easy incorporation into host polyimides. 4 These new high thermal stability chromophores are the first realization of high EO coefficient guest molecules to qualify under real semiconductor fabrication conditions, thereby representing a critical step in the progress toward a practical optical device technology.
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R
R'
Material
H
H
SY156
H
OCH 3
SY165
H
SY177
SH
SY215
NH2
Figure 2 II. CHROMOPHORE MATERIAL PROPERTIES The new EO guest chromophores were developed by computer aided molecular design following structural guidelines that simulate basic features of the host polyimide repeat units, yet with substantial microscopic second order optical coefficients Iijk(-(O3;O01,o02). Members of this series are highly colored, comparatively soluble in common organic solvents, and very stable in polyamic acid solutions. As shown by the spectral data of Figure 3 for the new series, the wavelength of the first electronic transition is tunable from 430 to 630 nm through side group substitution. The transition gives both liquid solutions and polymer thin films of the chromophores their bright color. The transparency range can, thereby, be selected as required for optical device applications.
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Figure 3: Linear absorption spectra for SY series in 1,4-dioxane The thermal stabilities of the pure EO chromophores have been studied by thermal gravimetric analysis (TGA) and differential scanning calorimetry (DSC) methods. The TGA data for the pure chromophores are shown in Figure 4. In reference to the parent SY156, the thermal stability increases upon substitution with donor groups of increased strength. The strong amine donor substituted SY215 is thermally stable up to 400'C. Thermal stability studies were also carried out for the SY series dissolved in the new high temperature polyimides. In one study, the absorption spectra of the systems were measured before and after heating under nitrogen. In the important case of SY215, for example, there are no spectral changes for the guest-host system up to 325°C. 10 0 CD
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...... SY156 -- SY165 ...........SY177 SY215
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