The 4,032ppi OLED micro-display developed by Sony
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Sony develops 4,032ppi OLED micro-display

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By Naoki Tanaka

Sony Corp says it has developed an OLED micro-display with a resolution as high as 4,032ppi.

Sony shortened pixel pitch from 7.8μm to 6.3μm and realized a resolution of UXGA (1,600 x 1,200) with a 0.5-inch screen. The company has already started to ship samples, planning to begin shipment of mass-produced products in November.

The newly-developed OLED micro-display is targeted at the EVFs (electronic viewfinders) of digital cameras. It is made by forming OLED elements on a monocrystalline silicon (Si) substrate. Because driving circuits and variation compensation circuits are formed on a monocrystalline Si substrate, which is suited for micro-fabrication, the resolution of the new display can be more easily improved, compared with OLED displays using glass substrates.

Currently, OLED micro-display are widely used for EVFs and expected to be used in the market for AR/VR head-mounted displays in the future.

For shortening the pixel pitch of an OLED micro-display, it is necessary to reduce the size of a transistor made on the monocrystalline Si substrate. In general, when the size of a transistor is reduced, it causes a variation in properties and the deterioration of withstand voltage.

This time, Sony developed its own compensation circuit and optimized the transistor layout and manufacturing process to reduce the variation in properties and the deterioration of withstand voltage.

Moreover, Sony shortened the distance to the organic EL light-emitting layer by forming a color filter on a Si substrate and realized both a high resolution and wide viewing angle by improving the color placement of the color filter.

In the case of a conventional OLED micro-display, a color filter is formed on a glass substrate opposed to a Si substrate. There is a resin layer between the Si substrate and glass substrate, and their thicknesses increase the distance between the organic EL light-emitting layer and the color filter. When the distance is long, colors tend to be mixed when viewed at an angle, making it difficult to ensure a wide viewing angle.

Furthermore, Sony newly designed a driving circuit to support a frame rate of 240fps, which is twice as high as before. As a result, it became possible to more accurately capture a fast-moving subject with a viewfinder and, therefore, to enjoy photographing with comfort without missing important photo opportunities.

Also, for use in HMDs (head-mounted displays), it helps improve the displacement of virtual video to be superimposed on the real world (for AR) and reduce sickness caused by VR, according to the company.

For the new OLED micro-display, Sony realized a low power consumption. Even though the pixel count increased by about 60%, the company realized a power consumption equivalent to that of its previous product by employing a newly-designed peripheral circuit that operates with a voltage 50% lower than in the past.

The maximum brightness, contrast and color gamut of the new OLED micro-display are 1,000cd/m2, 100,000:1 or higher, and 110% of the sRGB color space, respectively.

© Nikkei Technology Online

©2018 GPlusMedia Inc.

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