Characterization of TFT-LCD and OLEDs Devices by Phase Modulated Spectroscopic Ellipsometry for Display Applications
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Characterization of TFT-LCD and OLEDs Devices by Phase Modulated Spectroscopic Ellipsometry for Display Applications Eric Teboul1, Li Yan1, and Melanie Gaillet2 1 Thin Film Division, HORIBA Jobin Yvon, 3880 Park Avenue, Edison, NJ, 08820 2 Thin Film Division, HORIBA Jobin Yvon, 5 Avenue Arago, Chilly-Mazarin, 91380, France ABSTRACT Spectroscopic ellipsometry is an accurate and reliable optical technique to characterize polymers, liquid crystals (LCs) and organic light emitting diodes (OLEDs). Because these devices are formed by complex structure including optical anisotropy, absorbing and graded materials, the correct use of spectroscopic ellipsometer required a combination of the proper choice of hardware and the appropriate ellipsometric model. In this work, we presents ellipsometric results obtained by a commercially available phase modulated spectroscopic ellipsometer (PMSE) on a full Thin Film Transistor-Liquid Crystal Display (TFT-LCD) structure characterized from UV to NIR. As expected, strong anisotropy and inhomogeneous optical properties were found respectively on LCs and ITO materials. We also presents measurements of film thickness and optical constants of each layer constituing an OLED structure. INTRODUCTION Performances such as brightness and contrast ratio of TFT-LCD are directly related to the optical properties and film thickness of each layer. On the other hand, OLED based displays have aroused a significant interest and benefit from a wider viewing angle and higher emission efficiency. For both technologies, the accurate knowledge of the optical properties and film thickness of individual layer is important to optimize their performances. As a none destructive optical technique, spectroscopic ellipsometry characterized accurately and simultaneously, film thickness and optical properties for TFT-LCD and OLEDs devices. INTRODUCTION TO SPECTROSCOPIC ELLIPSOMETRY Based on the measurement of the change in light polarization upon reflection from a sample surface, ellipsometry derives thin films thickness, refractive index and absorption coefficient with extreme accuracy. The two components of the electromagnetic field: one “in the plane of incidence” (p), and the other perpendicular (s) to the plane of incidence, experience different attenuation and phase shift at the reflection as shown in Figure 1.
Figure 1. Incident and reflected components of the electromagnetic field.
Ellipsometry measures the ratio of these reflection coefficients, and is usually described by a set of two data, Psi (Ψ) and Delta (∆) related by the following expression: ρ=
Rp Rs
= tan Ψ ei∆
(1)
where Rp and Rs are linked to the material refractive index (through Fresnel’s law), film thickness and materials optical properties such as composition, crystallinity, anisotropy and uniformity [1]. Data analysis overview In order to get films thickness and optical constants, a fitting procedure of the ellipsometric data is required. This procedure can be described by 3 steps [2]. - Create a model that represents the nu
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