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[IMID 2022] SEL Develops 5,291ppi Micro OLED Display Integrating Si CMOS and OSFET

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At IMID 2022 held from August 24th to the 26th, Semiconductor Energy Laboratory (SEL) announced that it has developed a 5,291ppi micro OLED display for AR/VR that integrates Si CMOS and OSFET.

OLED, OS, Si structure/SEL

OLED, OS, Si structure/SEL

According to SEL’sannouncement, two problems arise when manufacturing an OLED display with high pixel density by integrating the existing Si FET. The first is that the source/gate drivers are located outside the display area, which increases the bezel width. A thin bezel width is a prerequisite for a decent AR/VR device size. The second issue is the high mobility of Si FETs and the balance between pixels. In order to apply Si FET to Micro OLED, it is necessary to reduce the transistor size while suppressing the increase in current.

In order to solve these problems, SEL announced that it has manufactured an OLED micro-display prototype that integrates Si CMOS and OSFET. SEL states that, “The mobility of OSFETs is not as high as Si FETs, but it is sufficient to drive OLED devices. Through the OLED/OS/Si structure in which OS (OSFET) and OLED are combined on CMOS, the width of the bezel area can be reduced by up to 40%. In addition, in the characteristic evaluation of OSFETs, it was possible to implement deep black and drive a low rate of fire, and the good distribution in a channel length of 200 nm and a breakdown voltage of about 20 V made it suitable for high voltage OLED driving of white-tandem OLED devices.”

The size of the 5,291ppi micro OLED display announced by SEL is 0.51 inches, the resolution is 1920×1920, and the pixel size is 4.8×4.8 μm. The backplane is a combined structure of 130 nm Si FET and 60 nm OSFET.

5,291ppi Micro OLED display specification/ SEL

5,291ppi Micro OLED display specification/ SEL

[2015 OLED Evaluation Seminar] Oxide TFT Technology that 2015 should Spotlight

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By Hyun Jun Jang

 

During the 2015 OLED Evaluation Seminar (December 4) hosted by UBI Research, Professor Jin-Seong Park of Hanyang University gave a presentation titled OLED Oxide TFT Technology Trend, discussing oxide TFT, related industry, and technological issues as well as TFT technology that should receive the spotlight in 2016.

 

Oxide TFT has an advantage of high mobility and large area uniformity compared to a-Si TFT. As such, it is being more applied to large area OLED panel and used in LG Display’s OLED TV.

 

Park revealed that there are mainly 4 issues regarding oxide TFT and led with the reliability issue. Oxide TFT is essentially in amorphous state but when crystalized, the density and crystallizability increase; as oxygen does not move away and stay in place, defects occur less and reliability is high. Japan’s SEL and Sharp published CAAC (C-Axis Aligned Crystal) structure related oxide TFT paper, and Cornell University produced CAAC oxide TFT by increasing the substrate temperature and adjusting oxygen’s partial pressure.

 

The second issue is composition ratio. Park reported that composition ratio is the most closely related characteristic to TFT’s mobility. He revealed that recently research is being carried out centering around IGZO (indium gallium zinc oxide), but also oxide TFT research with different composition ratio is continually published. For example, ITZO (indium tin zinc oxide)’s mobility has been reported to reach 30cm/Vsec, and BOE is working on the related research. Research results, which showed increased mobility and reliability for IGZTO, which is IZTO with G added, was published, as well as ZnON (zinc oxide nitride) TFT’s 100cm/Vsec mobility. BOE demonstrated ZnO TFT applied 14.1inch AMOLED.

 

The third issue is the device structure. Park explained that efficiency can increase when top gate structure is used to oxide TFT as parasitic capacitor is not needed, but that the process is difficult. However, Park reported that JOLED revealed when self-alignment is used the number of masks used can be reduced and increases performance. This structure is applied to OLED TV by LG Display.

 

Lastly, Park gave the safety of device as the last issue. Oxide TFT can exhibit degradation effects from light, oxygen, hydrogen, and moisture. Park reported that hydrogen particularly has great effect on the safety. He explained that although the current prevailing OLED TFT is LTPS, as the panel becomes larger there will be technological competition between oxide and LTPS. Reporting that TFT which is cost efficient and shows high performance in diverse factors such as resolution will dominate the market, Park concluded his presentation.