–
V
+
Electron-transport layer
(e. g. Alq3) Light-emitting layer (e. g. Doped Alq3) Hole-transport layer T(e.g. NPB)
CHRIS CLAYPOOL
Indium tin oxide
Glass
he spectacular growth of the organic-light-emitting-device (OLED) industry over the Electroluminescent light past couple of years has highlighted the technical challenges faced in the manufac- FIGURE 1. Electroluminescent light is produced in an organic light- turing of these devices. The accuracy, repeat- emitting device when electrons and holes recombine in the light-
ability, and uniformity of the organic-layer thicknesses is emission layer. The accuracy, repeatability, and uniformity of the
a critical manufacturing issue for OLED displays because organic film thicknesses are important manufacturing issues to
these parameters directly affect the brightness and color which reflection and transmission spectroscopy can be applied.
uniformity of pixels in the display. Further-
more, knowledge of the optical properties of An advanced metrology tool optical constants (refrac-
the organic layers is necessary for optimizing tive index n and extinc-
the design of the OLED display, including characterizes multilayer tion coefficient k). These
the design of microcavities, and in under- techniques, however, have
standing device properties such as external thin-film OLED structures limitations when applied
light-coupling efficiency. Reflection and to OLED-related applica-
transmission spectrophotometry is a fast, based on power-spectral- tions in which the organic
noncontact, and nondestructive character- density analysis of films of interest tend to be ization method that is ideally suited for these thin and highly absorbing
OLED manufacturing challenges. spectroscopic multiangle in the UV range and are
deposited on transpar-
Contending with OLED absorption polarized reflection, polarized ent substrates. Although
Optical-metrology methods, including reflectometry (reflec-
reflectometry and spectroscopic ellipsometry, transmission, and spectro- tion spectrophotometry)
have found widespread use in the silicon in- methods can readily de-
dustry for monitoring layer thicknesses and scopic ellipsometric data. termine film thickness (t)
if the optical constants of
the film are known (fixed), the technique does not inherent-
CHRIS CLAYPOOL is chief technical officer of Scientific Computing International, 6355 Corte Del Abeto, Suite C-105, Carlsbad, CA 92009; ly contain enough measured information to solve n, k, and t e-mail: chris@sci-soft.com; www.scie-soft.com. of the film independently.
References:
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