As next generation displays, various displays are studied recently. Especially, throughout the world, many researchers have an interest about transparent displays.
In case of liquid crystal display(LCD), it is used widely from small size mobile display to large size digital TV. LCD have to be equipped with light source such as back light unit(BLU) because liquid crystal is not luminous materials. And LCD typically consists of color filter layer on the LC panel to make full color display. So, conventional LCD has not been considered as one of the future technology to realize transparent displays.
On the other hand, many researchers think that Organic light emitting diodes(OLED) is one of the possible devices to realize it. However, OLED has problems to fabricate large size display panel and it is not mature technology for displays until now.
Therefore, in this thesis, I focused on its hybrid type concept, “See-through full-color LCD”. Proposed concept is made of transparent OLED BLU and LC panel which was removed its BLU and color filter layer. Red, Green and Blue sub-pixels in LC panel have to match spatially patterned R, G, B sub-pixels in OLED BLU. And then, liquid crystal controlled R, G, B lights that were flowed out from OLED BLU.
For the realization of proposed concept, research goes forward two parts which are transparent LC panel and transparent OLED BLU part. Transparent LC panel was made by eliminating its BLU, color filter, etc. So, its transmittance was increased about 30%.
R, G, B pixels of transparent OLED BLU were fabricated using SU-8 patterning method. And then organic materials and metal were deposited by vacuum thermal evaporation method. Transparent OLED based on following structures : ITO / PEDOT:PSS AI4083 / NPB / EML(Alq3:DCM 1.0wt% for red, Alq3 for Green and DPVBi for blue) / Alq3 / LiF / Al / Ag / Alq3. Last Alq3 layer worked as refractive index matching layer to improve optical light output. So, transmittance of OLED was about 60%.
Finally, transparent LC panel, transparent OLED BLU, JIG, PCB, and driving circuits are assembled. And “See-through full-color LCD” prototype was demonstrated successfully. It was good chance to confirm the possibility of proposed concept as future transparent display.
전세계적으로 투명디스플레이에 대한 관심이 점차 높아지고 있다. 현재 LCD의 경우 소형에서부터 대형까지 그 생산되는 품목이 다양하며 기술 또한 성숙단계에 들어섰기 때문에 이를 이용한다면 보다 빨리 투명디스플레이 시장에 접근할 수 있을 것이다. 하지만 LCD의 경우 BLU 및 컬러필터 등으로 인해 투명 디스플레이로 가는데 한계가 있으며, 관심이 집중되고 있는 OLED의 경우 대면적화가 어려운 실정이다.
이에 본 연구에서는 “See-through full-color LCD”의 개념을 제안하고 이에 대한 시제품을 제작함으로써 그 가능성과 문제점을 타진해 보았다. 제안된 개념은 일반 LCD에서 BLU와 컬러 필터를 제거한 액정패널과 투명 OLED BLU를 결합한 형태를 갖는다. 이때 액정패널의 R, G, B Sub-pixel과 상응하는 각각의 위치에 유기물질이 패터닝된 투명 OLED BLU를 결합하고 이 투명 OLED BLU를 통해 발생되는 R, G, B 각각의 빛을 액정의 투명 픽셀전극을 통해 인가된 전압에 의해 액정의 각도를 조절함으로써 천연색을 표현할 수 있게 된다. 개념의 실현을 위해 BLU와 액정패널을 제거한 투명액정패널 및 SU-8 물질을 이용하여 공간적으로 R, G, B 픽셀을 패터닝한 투명 OLED BLU를 제작하였고 이를 구동회로와 연결한 시제품을 시연 함으로써 그 가능성과 문제점을 타진해 보았다.