Young's Modulus and Coefficient of Linear Thermal Expansion of ZnO Conductive and Transparent Ultra-Thin Films

Naoki Yamamoto,Tetsuya Yamamoto,Hisao Makino

doi:10.1155/2011/136127

Naoki Yamamoto, Tetsuya Yamamoto + Show 1 more

Open Access

https://doi.org/10.1155/2011/136127

Copy DOI

Abstract

A new technique for measuring Young's modulus of an ultra-thin film, with a thickness in the range of about 10 nm, was developed by combining an optical lever technique for measuring the residual stress and X-ray diffraction for measuring the strain in the film. The new technique was applied to analyze the mechanical properties of Ga-doped ZnO (GZO) films, that have become the focus of significant attention as a substitute material for indium-tin-oxide transparent electrodes. Young's modulus of the as-deposited GZO films decreased with thickness; the values for 30 nm and 500 nm thick films were 205 GPa and 117 GPa, respectively. The coefficient of linear thermal expansion of the GZO films was measured using the new technique in combination within-situresidual stress measurement during heat-cycle testing. GZO films with 30–100 nm thickness had a coefficient of linear thermal expansion in the range of 4.3 × 10−6– 5.6 × 10−6 °C−1.

Highlights

Transparent and conductive ZnO films, such as Gadoped Zinc oxide (GZO) or Al-doped ZnO films, are attracting attention as alternative electrode materials to indium tin oxide (ITO), with good optical transparency and electrical conductive properties for liquid crystal displays (LCDs), flexible displays, touch-screens, and solar cells
The properties of the residual stresses in GZO films formed by reactive plasma deposition (RPD) and magnetron sputtering methods with various thicknesses, shown in Figures 4 and 5, were analyzed using heat-cycle testing
The thermal stress and the coefficient of linear thermal expansion of the GZO films formed on the thermally oxidized Si wafer of a single crystal with a (100) crystalline surface were obtained using the stress-temperature characteristics of the GZO film shown in Figure 4 and using (4) or (5)

Summary

Introduction

Transparent and conductive ZnO films, such as Gadoped Zinc oxide (GZO) or Al-doped ZnO films, are attracting attention as alternative electrode materials to indium tin oxide (ITO), with good optical transparency and electrical conductive properties for liquid crystal displays (LCDs), flexible displays, touch-screens, and solar cells. ZnO electrodes need to endure against mechanical forces caused by the thermal processing steps during the manufacture of electronic devices such as flat panel displays, flexible displays, touch-screens, and LEDs, and by the expansion or shrinkage of parts caused by thermally severe circumstances (during summer and winter, e.g.) in the case of solar cells. These external forces could enhance the frequency of peeling or cracking in the elements composing the systems, such as transparent electrodes, during the fabrication or operation of the devices. Young’s moduli and the coefficients of linear thermal expansion of GZO thin films were analyzed using the new technique

Experimental

Residual Stress in GZO Thin Films

Young’s Modulus of GZO Film

Summary