The inkjet technology

There are high expectations for the inkjet technology that sprays luminescent materials to make OLED displays like printers for personal computers. Though it has problems in display performance and reliability, it enables to easily make OLED displays.

The inkjet printing method does not require a vacuum environment at the time of production. Moreover, it eliminates the need for a mask (for applying luminescent materials of multiple colors), making it possible to apply luminescent materials to a large-area substrate. Also, it realizes an efficient use of luminescent materials.

Japan-based JOLED Inc commercialized the world’s first OLED display using the inkjet printing method. At SID 2019, the company’s displays were exhibited in the booth of Japan Display Inc (JDI).

Following JOLED, manufactures based in China, which is now the center of display production, are developing inkjet OLED displays at a high pace. At SID 2019, China Star Optoelectronics Technology Co Ltd (CSOT) and Tianma Microelectronics Co Ltd exhibited their latest displays.

CSOT exhibited a 31-inch panel. By employing a top-emission structure, which enables to easily improve aperture ratio, the company realized a 4k display with a resolution of 144ppi. For its driving board, oxide semiconductor IGZO TFTs were used.

The panel has a brightness of 100cd/m2 (peak brightness: 200cd/m2), contrast ratio of 100,000:1, 100% color gamut on NTSC standards and frame rate of 60Hz.

Tianma showcased a small-size panel for smartphones. It realizes a high resolution of 403ppi with an inkjet printing method, which makes it difficult to increase resolution. Its screen size and pixel count are 4.92 inches and 1,728 x 972, respectively.

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