Effects of Insertion of Ag Mid-Layers on Laser Direct Ablation of Transparent Conductive ITO/Ag/ITO Multilayers: Role of Effective Absorption and Focusing of Photothermal Energy.

Younggon Choi,Hong-Seok Kim,Eou-Sik Cho,Haunmin Lee,Sang Jik Kwon,Jae-Hee Han,Wonjoon Choi

doi:10.3390/ma14185136

Abstract

From the viewpoint of the device performance, the fabrication and patterning of oxide–metal–oxide (OMO) multilayers (MLs) as transparent conductive oxide electrodes with a high figure of merit have been extensively investigated for diverse optoelectronic and energy device applications, although the issues of their general concerns about possible shortcomings, such as a more complicated fabrication process with increasing cost, still remain. However, the underlying mechanism by which a thin metal mid-layer affects the overall performance of prepatterned OMO ML electrodes has not been fully elucidated. In this study, indium tin oxide (ITO)/silver (Ag)/ITO MLs are fabricated using an in-line sputtering method for different Ag thicknesses on glass substrates. Subsequently, a Q-switched diode-pumped neodymium-doped yttrium vanadate (Nd:YVO4, λ = 1064 nm) laser is employed for the direct ablation of the ITO/Ag/ITO ML films to pattern ITO/Ag/ITO ML electrodes. Analysis of the laser-patterned results indicate that the ITO/Ag/ITO ML films exhibit wider ablation widths and lower ablation thresholds than ITO single layer (SL) films. However, the dependence of Ag thickness on the laser patterning results of the ITO/Ag/ITO MLs is not observed, despite the difference in their absorption coefficients. The results show that the laser direct patterning of ITO/Ag/ITO MLs is primarily affected by rapid thermal heating, melting, and vaporization of the inserted Ag mid-layer, which has considerably higher thermal conductivity and absorption coefficients than the ITO layers. Simulation reveals the importance of the Ag mid-layer in the effective absorption and focusing of photothermal energy, thereby supporting the experimental observations. The laser-patterned ITO/Ag/ITO ML electrodes indicate a comparable optical transmittance, a higher electrical current density, and a lower resistance compared with the ITO SL electrode.

Highlights

Transparent conductive oxides (TCOs) such as indium tin oxide (ITO), indium zinc oxide, and aluminum-doped zinc oxide films have been used extensively as pixel electrodes and window layers in various optoelectronic and energy devices, including flat panel displays (FPDs), touch screen panels (TSPs), and solar cells [1–13]
Issues of general concern about possible disadvantages, such as more complicated fabrication process with increasing cost, still remain, in this work, we successfully demonstrated the fabrication of ITO/Ag/ITO MLs for transparent conductive oxide electrode applications with a higher FoM compared with that of ITO single layer (SL)
To analyze the effects of the Ag mid-layer on the laser direct ablation-assisted patterning of OMO ML films, a neodymium-doped yttrium vanadate (Nd):YVO4 laser was used in the direct etching of ITO/Ag/ITO MLs deposited for various Ag thicknesses using an in-line sputtering method

Summary

Introduction

Transparent conductive oxides (TCOs) such as indium tin oxide (ITO), indium zinc oxide, and aluminum-doped zinc oxide films have been used extensively as pixel electrodes and window layers in various optoelectronic and energy devices, including flat panel displays (FPDs), touch screen panels (TSPs), and solar cells [1–13]. Conventional metal electrodes such as Mo, Cu, Al, and Ag paste films have been replaced with TCO materials of higher optical transmittance to realize fully transparent optoelectronic devices. Replacing the metal electrodes with pure TCOs in large-sized FPDs or TSPs is not optimal because of their lower conductivities compared with those of metals. Despite the insertion of thin metal mid-layers between TCO films, the transparency of OMO MLs did not reduce significantly, whereas the electrical conductivities improved compared with those of pure TCO [23–25]. It has been reported that an optimized ITO/Ag/ITO ML possesses a high figure of merit owing to its high optical transmittance and low electrical resistivity [25,27]. Wang et al successfully reported the inorganic all-solid-state electrochromic device applications based on ITO/Ag/ITO ML electrodes with a high figure of merit [25]. To the authors’ best knowledge, there has been no study on the underlying mechanism by which Ag mid-layers play an important role of effective absorption and focusing of photothermal energy for patterning the ITO/Ag/ITO ML electrodes by using laser direct ablation

Methods

Results

Conclusion