A polyimide (PI) film bonded to glass with the new technology
A polyimide (PI) film bonded to glass with the new technology
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Suga Laboratory of the School of Engineering, the University of Tokyo, developed the "surface activated bonding" technology that bonds a polymeric film to glass in a way that it can be easily peeled off by applying heat.

For example, when a polyimide (PI) film, which is used as a material for flexible substrate, is formed on a glass plate for carriage (support), it is necessary to apply a laser to remove the film from the plate, lowering yield rate and increasing cost. The new technology makes it easy to remove the film.

In the manufacturing process of flexible devices, a thin film such as a PI film is used as a substrate. But it is difficult to carry such a film or form a device without a support. Therefore, it needs to be bonded to a glass carrier, etc. However, adhesives cannot be used because they increase thickness. So, liquid PI is calcined on a glass carrier.

On the other hand, with the new bonding technology, an argon (Ar) ion beam is applied to the surfaces of the glass carrier and PI film, removing the oxide and adsorption films and flattening the surfaces. Next, a 5-20nm-thick silicon (Si) intermediate layer is formed by ion beam sputtering.

Furthermore, when the bonding needs to be reinforced, an iron (Fe) nano adhesion layer with a thickness of 1nm or less is formed on the Si intermediate layer. Lastly, the Fe nano adhesion layer (or the Si intermediate layer) formed on each surface is pressure-bonded with a pressure of about 2.5MPa to strengthen the bonding.

The bonded glass carrier and PI film can be easily separated by heating them at a temperature of about 400°C for about an hour to reduce the bonding strength. It is possible to adjust the easiness of separating them from each other by changing the thicknesses of the Si intermediate layer and Fe nano adhesion layer.

Suga Laboratory considers that the new technology can be applied to the manufacturing process of flexible devices within a few years and that the overall manufacturing cost can be reduced to about 1/3, compared with conventional technologies. Because the sputtering process and pressure bonding take about 50μs, bonding based on a roll-to-roll process can be realized in the future, it said.