Samsung Display planning to apply transparent polyimide substrate to foldable OLED panel

Samsung Display is planning to use a transparent polyimide substrate for its foldable OLED panels by 2024, TheElec has learned.

Using completely transparent polyimide instead of the yellowish ones used now will increase the light penetration through the panel and improve the quality of pictures in under panel camera, sources said.

Under panel cameras, as its name suggests, have the camera under the panel and expose the lens hole of the camera only when being used.

While the lens is exposed, it is still under the panel, and one of the challenges of under panel cameras is to absorb as much light as possible.

But the yellowish polyimide material used in the panel limits how much light can be absorbed by the sensors.

To offset this, Samsung Display intentionally reduced the pixel count of where the lens hole is to 187pixels per inch instead of 374ppi of the other areas of the panel for Galaxy Z Fold 3, which was the first phone from Samsung to use under panel cameras.

As there are fewer pixels in the same surface area, there are more areas where the light can pass through. The pixels on the lens hole area were also quadrupled in size to limit the resolution drop. However, the downside of all this was that the panel area where the hole is and other areas were immediately noticeable even when the under panel camera was not in use.

Using a transparent polyimide substrate will allow Samsung Display to place more pixels in the lens hole area to match the other areas of the panel.

However, the company will need to find a solution to transparent polyimide varnish being less durable and more expensive compared to conventional varnish.

Current polyimide substrates are made by putting the liquid varnish on a glass substrate. The varnish is hardened to solid form through hit and the glass substrate is cut off using a laser.

This process can’t be used for transparent polyimide varnish, sources said.