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How a team defied odds in setting a smartphone standard

Posted December. 02, 2011 02:33,   


A team of researchers set a goal of making more than 300 holes in a 1-inch active-matrix organic light-emitting diode screen, or AMOLED, used in smartphones. The more holes the AMOLED screen has, the more pixels it gets.

The Samsung smartphone Galaxy S II has 217 pixels in a one-inch square, or 217 ppi. The Apple iPhone 4 uses LCD and has 326 ppi. Though AMOLED can reproduce natural colors, it lags behind the iPhone in the number of pixels because researchers had difficulty planting miniscule dots densely on the AMOLED screen, which is a newer technology compared to LCD.

The display industry said the production of an AMOLED screen with more than 300 ppi in several years is impossible. LG Display President Kwon Young-soo also told reporters in July, “With existing technology, making AMOLED with 270 ppi in the coming years is impossible.”

○ Jumping over the 300-ppi hurdle created by Steve Jobs

The negative industry outlook further prompted the “Dalli” team into action. Lee Jung-ho, a senior researcher in charge of circuit design, said, “Whenever we encountered news articles saying 300 ppi is impossible for AMOLED, we reaffirmed our determination to overcome this.”

In the wake of the death of Apple co-founder Steve Jobs, 300 ppi has suddenly become the standard for smartphone screens. The human eye can recognize 300 ppi at most at a distance of 30 centimeters. In June last year, Jobs called the iPhone 4 screen a "retina display" thanks to its more than 300 ppi.

To beat the iPhone in resolution, more than 10 members of the Dalli team had to break countless glass plates. AMOLED is made by attaching a thin plate with holes called a “mask” on a glass plate and putting a light-emitting material that produce colors into the holes. The small hole is thinner than a stand of hair and constitutes a pixel.

If the mask was thick, however, the light-emitting material was not smeared with the glass plate because of difficulty passing through holes. If the mask was too thin, the glass plate got bent when many holes were made. In addition, if the mask failed to adhere to the glass plate well, colors were mixed.

Senior researcher Kim Hyeon-cheol said, “While conducting sample tests and studying process improvement in mass production lines in the development period, we didn’t hesitate to break glass plates if they weren`t perfect,” adding, “Discarded glass plates can cover about 6,600 square meters of land.”

The area of 6,600 square meters is equivalent to one and a half soccer fields.

○ Smartphones show HD images

The Dalli team stayed up countless nights, being so busy that just one member attended a team member’s wedding. In the end, they made a new mask using new material. By completely sticking the mask on the glass plate, they pierced more than 300 holes.

This led to the development of a 4.65-inch, 1280×720 HD super AMOLED screen used for the Galaxy Nexus by making 316 pixels per inch.

Piercing 1,280 pixels on a horizontal line and 720 pixels on a vertical line of a TV screen 40 to 50 inches is not difficult. To achieve HD resolution on a smartphone, pixels should be densely planted.

Researcher Lee said, “On the Galaxy Nexus screen, the distance between each pixel is a fifth of the thickness of a strand of hair.”

Disputes over the picture quality of smartphones still rage on. As the number of colors a pixel produces is different, the AMOLED and LCD camps are locking horns over the standard for natural colors.

Dalli researcher Lee Hee-cheol said, "Whenever we hear criticism, we have lots of things to say. But we believe that consumers will appreciate our product in the end. As we put our energy into the product, we hope consumers will use it with care.”