Molybdenum disulfide as a 2D semiconductor material has a very good performance, that is, they are easy to bend. Electrons can move rapidly in such a semiconductor. At the same time, because only about one atom is thick, such semiconductors are transparent. These characteristics make them ideal materials for making flexible OLED displays. However, when the manufacturer tries to process molybdenum disulfide into a transistor that controls OLED pixels, the resistance between molybdenum disulfide (MoS2) and the source and drain of the transistor will be too high to make this excellent material impossible to apply.

Now, engineers in South Korea find a way to apply molybdenum disulfide transistors to a flexible OLED display. They use the transistor to make a simple 6 * 6 dot matrix on a plastic sheet with a thickness of only 7 microns, which can be attached to the human skin. This simple plastic display screen is very soft, bending with less than 1 centimeters of bending radius will not damage.

Jong Hyun Ahn, a flexible electronics expert at the Yonsei University in Seoul, explained that "carrier mobility (Carrier mobility)" is the key performance that they need to tackle. This performance is measured by the rate of charge passing through the semiconductor. For example, materials used to fabricate most chips - the carrier mobility of crystalline silicon is 1400 square centimeter / volt second (cm2 / V - s). The semiconductor, which consists of the backboard of the display screen, is a system for switching and lighting pixels. The carrier mobility required must be able to drive sufficient current to operate the pixels and to meet the video code rate requirements. "For traditional LCD liquid crystal displays, their backboards can be made of amorphous silicon with lower carrier mobility." The electron mobility of the material is about 1 square centimeter / volt second, Ahn said.

But the OLED display requires higher carrier mobility. OLED display manufacturers, including LG and Samsung, use high mobility materials such as polysilicon (> 10 square centimeters / volts seconds) and oxide semiconductors. But, "these materials are hard and crisp." Ahn said. They can bend to a certain extent, but they can not be repeated.

A molybdenum disulfide transistor is clamped by two layers of three oxide two aluminum (Al2O3) from the top two directions. This device has high mobility, and high mobility is crucial to the delivery of current to the pixels of the OLED display. To make ultra-thin flexible OLED display, Ahn and its team need to release molybdenum disulfide from the transistor that "grabs" it.

Ahn said: "the contact resistance between molybdenum disulfide and transistor electrodes is very high, and high resistance will reduce carrier mobility of MoS2 transistors." The key to solve the problem is to realize that 2D semiconductor is very susceptible to the influence of surrounding materials. Unlike the commonly used means of placing transistors on the surface of silicon oxide, the surface of Ahn's team is very smooth and easy to control. They clamped the transistor into two layers of insulating aluminum oxide. Three the interface between oxidized two aluminum and molybdenum disulfide increases the electrons in semiconductors, similar to the doping of chemicals into silicon materials to make it a semiconductor phenomenon. This enhancement effect overcomes the problem of high contact resistance and improves the charge carrier mobility. In addition, the smooth dielectric material does not produce a potential spot, which further increases the mobility to 17 to 20 square centimeters / volt seconds.