Visible ITO Pattern in Capacitive Touch Lens: Cause and Countermeasure
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Visible ITO Pattern in Capacitive Touch Lens: Cause and Countermeasure Duk Su Kim1, Gyeong-Geun Lee2, Jacob Yang1, and Dong Hyuk Shin1 1R&D Center, ELK Corporation, Daejeon, Korea, Republic of; 2 Nuclear Materials Research Division, Korea Atomic Energy Research Institute, Daejeon, Korea, Republic of. ABSTRACT Market demand for touch panel/lens has been exceptionally high for the recent years due to smartphones, tablet PCs, etc. Among the available technologies to envision touch functionality, capacitive touch screen has received the great attention due to the various superiorities over the competing ones. Capacitive touch screen features two transparent conductive electrodes, such as ITO (indium tin oxide). However, the difference in refractive indices of ITO, substrate, and air, ITO pattern is clearly visible if there is no proper countermeasure. Most of touch screen makers and ITO substrate supplier utilize “index-matching technology” to prevent this phenomenon. Even though of the attempts to minimize visible ITO pattern in final product, there are many technical and process challenges. In this study, the causes around visible ITO pattern were investigated to understand and provide the proper countermeasures. One of the possible causes for visible ITO pattern was improper annealing process in ITO especially for film substrate. According to XPS (X-ray photoelectron spectroscopy)/ESCA (electron spectroscopy for chemical analysis) and other analysis results, ITO, which is normally deposited through sputtering, is not fully transformed to oxidized state. After aligning and adjusting annealing condition, acknowledged visible ITO pattern was disappeared. Other causes for visible patterns were also discussed in detail, and the relevant countermeasures were provided. INTRODUCTION Recent development around touch panel/lens industry has been overwhelming for the last 3 years. Now, most of major mobile phone companies launched touch panel-installed handset to the market, and this phenomenon was started from Apple’s iPhone1, 2. Among the available technologies to envision touch functionality, capacitive touch screen has received the great attention due to the various superiorities over the competing ones3. Capacitive touch screen features two transparent conductive electrodes, such as ITO (indium tin oxide) on top of common substrates, i.e. PET film and glass. However, there is a significant difference in refractive indices between ITO, substrate, and air, and ITO pattern is clearly visible if there is no proper countermeasure. Most of touch screen makers and ITO substrate supplier utilize “index-matching technology” to prevent this
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phenomenon4. This specially developed process features an optical coating to compensate the difference in refractive indices of ITO and substrate. Even though of the attempts to minimize visible ITO pattern in final product, there are many technical and process challenges. Thin ITO layer and optical coating is fragile and sensitive to the external condition, and the most of processes around
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