Inkjet Printing for Site-Controlled Tunnel Pitting with High Aspect Ratio in Al

Abstract

High resolution inkjet printing was applied to the site control of the anodic tunnel etching of Al. In this method, a dot array of polymer resin was formed on Al͑100͒ by inkjet printing and was transferred to the oxide layer by anodization. The anodic etching of Al with a mask in a HCl electrolyte resulted in the site-controlled initiation of the tunnel etching of Al and the uniform tunnel pits with high aspect ratio. The interval of the tunnel pits could be successfully controlled by the inkjet patterning on the micrometer scales.Inkjet printing has attracted considerable interest for preparing various types of functional devices owing to its advantages for making desirable patterns on a substrate in noncontact mode. There have been several applications of inkjet printing for the preparation of a wide variety of functional devices, such as electronic or biological devices in addition to the printing of graphical materials. 1-4 One attractive application of inkjet printing is in the fabrication of fine structures with high aspect ratios. For such applications, novel processes combined with inkjet printing and an anisotropic fabrication technique, which allow the formation of structures with high aspect ratio, are essential. In addition, inkjet printing with high spatial resolution is desirable for this purpose. Recent progress in inkjet printing has demonstrated the possibility of patterning extremely high resolutions, e.g., an ϳ3 m interval in dot arrays. 5 In the present article, the fabrication of arrays of fine tunnel pits with high aspect ratios is described using the combined process of inkjet printing and anodic etching of Al. The formation of a fine pattern by high resolution inkjet printing and the subsequent anisotropic anodic etching of Al͑100͒ generated the site-controlled ordered array of tunnel pits with high aspect ratios. The site control of the tunnel pitting in Al was conducted by a method similar to previously reported articles. 6,7 In this process, the polymer mask formed by contact printing generated the selective tunnel pitting of Al during the anodic etching in the electrolyte containing Cl − . This process was originally developed for widening the surface area of electrodes in electric capacitors. [8][9][10][11][12] The introduction of inkjet printing allows the desirable arrangement of tunnel pitting in noncontact mode. The obtained fine structures are the first examples of the microscale hole array structures of metal with high aspect ratios based on inkjet patterning and are applied to various types of functional devices, which require a fine structure with a high aspect ratio besides its use in electric capacitors. Figure 1 shows the schematic of the site-controlled tunnel pitting of Al using the combined process of inkjet printing and anodic etching. An Al foil ͑99.99%, 110 m thick, Toyo Aluminum͒ with ͑100͒ plane ͑Ͼ95%͒ was electrochemically polished in a mixture solution of perchloric acid and ethanol. The fine pattern composed of the dot array of acrylic polymer was formed on the A...

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