[SID2019] What material is better for cover windows of foldable OLED? colorless PI or UTG?

Since Royole introduced ‘FlexPai’, a foldable OLED phone, Samsung Electronics and Huawei have also launched Foldable OLED phones, attracting great interest from the industry and the public.

The biggest change of the foldable OLED phone currently being commercialized or under preparation is that the cover window of the glass material used in the existing flexible OLED has been changed to colorless PI material.

Colorless PI is thinner than conventional cover window glass, which is advantageous in reducing the radius of curvature and has the advantage of not breaking. UTG (ultra-thin glass), which has good surface touch-feel and scratch-resistant glass as thin as possible, is also attracting attention as a cover window material for foldable OLEDs.

At the SID Display Week exhibition in San Jose, KOLON exhibited colorless PI with hard coating. KOLON, which has been ready for mass production of colorless PI since 2018, is currently supplying colorless PI for foldable OLED cover windows to AUO, BOE, LG Display, and Royole.

Hard coating company DNP and TOYOCHEM also exhibited colorless PI with hard coating. DNP’s company official said that the film is under development and its main business area is hard coating, and TOYOCHEM’s company official said that it supplied hard coating samples to KOLON and SKC.

Meanwhile, SCHOTT, a UTG development company, also attracted the attention of the audience by displaying UTG for foldable OLED cover windows. An official of SCHOTT said that the UTG currently being developed is a cover window product for out-folding, not in-folding, and that the thickness is currently in development from 0.7 mm to 2.5 mm in accordance with customer requirements.

As the smartphone set makers are expected to release foldable OLED phones in the near future, competition for related materials is also expected to be intense. Whether the Colorless PI will continue to dominate or whether UTG will be able to exercise its influence is highlighted.

초고해상도를 구현할 수 있는 FMM, 국산화 앞당겨지나

Fine metal mask(이하 FMM)은 화소와 RGB 유기물을 증착하는 역할을 하기 때문에 FMM은 OLED의 해상도와 수율을 결정짓는 요소로서 작용되나, 현재 FMM은 증착 공정시 열팽창이 일어나거나 무게에 의한 섀도우 현상이 발생하는 한계에 봉착해 있다.

또한, FMM 전량은 일본 히다치(Hitachi)금속이 생산한 압연 invar를 일본 다이니폰프린팅(DNP)에서 에칭 공정을 통해 만든 완제품 형태로 비싼 가격에 수입하고 있다.

이로 인해 국내외 관련 업계는 laser가공 등 다양한 방식으로 FMM 개발에 총력을 기울이고 있는 상황이나 아직까지 R&D 단계에 머물고 있는 실정이다.

이런 상황에서 지난 9일 순천대학교 신소재공학과 박용범 교수 연구팀은 전주도금 인바 제조기술을 개발에 성공했다고 밝혔다. 이는 전기도금을 활용하면서 음극에 부착된 금속을 박리한 후 형상이 있는 부품으로 만드는 기술이다.

<전주도금인바의 열팽창곡선과 미세조직, 출처: 순천대>

해당 기술을 통해 invar는 판재로도 생산할 수 있고, 패턴 된 음극의 형상을 그대로 복제할 수 있다. 또한, FMM의 두께를 지금보다 절반 정도 얇은 7 um 수준까지 구현할 수 있어 초고화질을 구현할 수 있다고 연구팀은 설명했다.

박 교수는 “전주도금 인바에 대한 일본의 연구 수준이 우리 연구팀 턱 밑까지 쫓아왔고, 중국은 대규모 자본을 앞세워 개발에 뛰어들었다.”며, “우리나라 기업들이 국제경쟁력을 선점하기 위해서는 학계가 적극 지원할 필요가 있다고 판단했다.”고 말했다.

이에 따라”지난 20년 가까이 연구해 구축한 모든 데이터베이스를 논문을 통해 공개하기로 결심했다.”고 덧붙여, 그간 전량 수입에 의존하던 FMM을 국산화 할 수 있을지 귀추가 주목된다.

Is accelerating the localization for FMM, which can realize ultra-high resolution?

Since Fine Metal Mask (FMM) plays a role of depositing pixel and RGB organic materials, FMM is a factor that determines the resolution and yield of OLED. However, FMM is currently confronted with some limitations that thermal expansion occurs during the deposition process or shadow effects arise due to its weight.

In addition, the total amount of FMM is imported at high prices in the form of finished products which are made by Japanese Dainippon Printing (DNP)’ etching process with the rolled invar produced by Hitachi Metals.

Under the circumstances, domestic and overseas related industries are concentrating on developing FMM in various ways such as laser processing, but they are still in R & D stage.

The research team of Professor Park Yong-Bum of New Material Engineering Department of Sunchon University announced on 9th May that it succeeded in developing the technology of electroforming invar manufacturing technology. This is a technique for separating the metal attached to the cathode while utilizing the electroplating, and making FMM.

<Thermal expansion curves and microstructure of electroforming invar, source: Suncheon University>

According to the research team, invar can be produced as a sheet material, and the shape of the patterned cathode can be copied as it is, through this technology. In addition, the thickness of FMM can be reduced to about 7μm, about half the thickness of the current FMM, which might be helpful to realize super high image quality.

Professor Park said, “The level of Japanese research on the electroforming invar has been pursued to the bottom of our research team, and China has entered into development with a large amount of capital.” In order for Korean companies to gain international competitiveness, I thought the academic circles needed to support it actively. Consequently, I have decided to publish all the databases that have been built and researched for nearly 20 years through papers.”

Attention is focused whether it is to be successful in localizing FMM, the total amount of which has been imported.