Combination of OLED and reflective liquid crystal for high visibility and low power consumption

Nowadays, OLED screens and transmissive LCD screens used as displays for mobile products have clear images indoors, but their visibility is poor outdoors in sunny conditions. Moreover, screens account for a large proportion of the power consumption of mobile products. As a countermeasure to solve these problems, the Japan Semiconductor Energy Research Institute has developed a hybrid display that combines OLED and reflective liquid crystal. He delivered a relevant speech at the International Society for Display Technology "SID 2016" held recently. The company calls this display a "TR-Hybrid Display." T stands for Transmissive OLED and R stands for Reflective LC.

This hybrid display uses an OLED screen attached to the back of a reflective LCD screen, and holes are made on part of the reflective electrodes of the reflective LCD screen, and the light emitted from the OLED screen passes through the holes.

OLED display

Reflective LCD display

In terms of manufacturing technology, the peeling technology of flexible OLED displays is adopted. First, a release layer is applied to a glass substrate for transportation, and TFTs are formed on it. Next, a bottom-emitting OLED module that extracts light is formed on the TFT side, covered with a flat film, and glass is placed on top. Then peel off the release layer and remove the glass substrate for transportation. Finally, a liquid crystal color filter substrate is attached to the side of the TFT with the glass substrate removed, and liquid crystal material is injected.

The screen size of the trial display is 4.38 inches and the number of pixels is 768×1024. The fineness is 292ppi. In terms of aperture ratio, LCD is 76% and OLED is 3.9%. In order to further reduce power consumption, TFT uses an oxide semiconductor IGZO that can drive both low-frequency and OLED. Compared with the usual 60Hz drive, the power consumption of the reflective LCD screen can be reduced to approximately 1/180 by adopting 1/3Hz drive.

In addition, the driving method has also been optimized. This improves the display contrast ratio of the OLED screen from 1111:1 to 2850:1. OLED screens and reflective LCD screens are driven independently. Each pixel (sub-pixel) of OLED is equipped with 2 transistors and 1 capacitor, and each pixel (sub-pixel) of liquid crystal is equipped with 1 transistor and 1 capacitor.