Electrodeposited Copper Wire for Transparent Conductive Film

1. Introduction

ITO(indium tin oxide) is the most common transparent conductive film used for touch panel and solar cell.   However, the Indium is the rare metal and sputtering tool is expensive.   Hence there are drastic demands for the ITO substitutes.  

Silver nano-wire is a good candidate for the ITO substitute(1), however, cost is 60 times expensive than copper.   Furthermore, the resistivity of copper is almost same as silver.   Most conventional copper wire is produced by etching of photo lithographed copper foil(2), however, etching consumes most of the copper area, since we need high transparent film.  

By using the chromium electrodeposited mold, the copper electrodeposits preferentially into the mold cracks and forms copper wire.   Hence, the copper wires have been electrodeposited into the mold cracks and their characteristics as the transparent conductive film have been measured.

2.Experimantal

    The electrodeposits substrate is SUS 304.   The chromium mold has been electrodeposited onto this SUS 304 with Sargent bath at 600mA/cm² for 72min.   Then annealed at 150℃ for 5hours.   The copper wire has been electrodeposited preferentially into the chromium mold crack.   The bath consist of 25g/l of H₂SO₄, 200g/l of CuSO₄・5H₂O and the additive.   The current density is 10 to 50mA/cm²with  5 to 150s at room temperature.

The openings of copper wire(=Transparency) has been measured on the chromium mold.   The wire width, wire resistance and transmittance have been measured by removing the copper wire from the chromium mold.   Chromium etching solution has been used to remove the copper wire.

3.Results

1.Figue 1 shows the top view of copper wire and chromium mold.   Numerous numbers of copper wires are running along the chromium mold cracks.

2.For the copper wire of 30second electrodeposition time, the wire resistance is 0.18Ω/□ , wire width is 9.8μm and the transmittance is 84%.   These wire resistance, width and transmittance satisfy the requirements for the transparent conductive film.

3.Figure 2 shows the photo of display with the copper wire has been placed on the LCD.  Our copper wire have enough transmittance

References

1. http://www.cambrios.com/technology
2. http://panasonic.co.jp/news/topics/2013/112371.html
3. Nikkei Electronics,7-22,P14(2013)