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nano tech 2020/Advanced Printing Technology Exhibition 2020/neo functional material 2020/JFex2020
(January 29 - 31)


Cnano tech 2020/Advanced Printing Technology Exhibition 2020/neo functional material 2020/JFex2020
New faces announced to go into the material market for flexible device

January 29 - 31, nano tech 2020/Advanced Printing Technology Exhibition 2020/neo functional material 2020/JFex2020 were held in Tokyo Big Sight. Main topics in these exhibitions are picked up.

Nippon Shokubai exhibited a new flexible OLED with 3 μm thickness

As regards devices, Nippon Shokubai demonstrated several flexible OLED devices. The company firstly exhibited OLED last year, and also, announced to go into the lighting device market. In this year, as picture 1, a mush prototype was exhibited as a new sample. Its thickness is mere 3 μm.


Picture 1. Flexible OLED
This device is an inverted structure (cathode/electron injection layer/electron transport layer/emitting layer/hole transport layer/hole injection layer/anode), which was jointly developed with NHK in the past. In this device, two PET films were used as the both substrates. It's not necessary to use a gas-barrier layer, such as Si series because of high durability in atmosphere. In short, an original EIL material with organic and inorganic materials is used instead of Alkali buffer material, which is unstable in atmosphere. As a result, high gas barrier property is obtained essentially. In fact, required water vapor permeability is 10-3g/m2/day order. As you know, this value is 3 digits higher than that of the conventional device with Alkali buffer layer. For this reason, emission lifetime (50 %) of Green device is 10,000 hours (@1000cd/m2).

By the way, in last exhibition, the company announced to release OLED devices in 2022, but in this time, accelerate in 2021.

Organic film　solar cell is used as auxiliary power of smartphone

With respect to organic film solar cell, Toray exhibited a flexible device using an originally ultra-thin transparent polyimide film as a substrate. It's a bulk-hetero junction polymer device with original p-type semiconductor and n-type C60 series semiconductor. Its total thickness is mere 50 μm.


Picture 3. Glasses using EC modulated light sheet

Picture 2. Organic film solar cell and smartphone
As picture 2, a sample was exhibited for smartphone use in the booth. In short, device was built in the whole area of the rear plane and frame area of the front　plane. In this case, it's not a main power, but auxiliary power. However, buttery lifetime can be extended.

Transmittance of glasses is controlled by EC light beam

Ricoh appealed an electrochromic (EC) modulated light sheet. As you know, EC phenomenon indicates that color of film is changed reversibly by electrochemical redox reaction. ECD has wide view angle property and memory property, so that, it is useful for E-paper display.

As picture 3, the company proposed that it was used for electric control glasses in this time. It's possible to control transparence of this glass from transparent state to gray state (dark glasses) at will by switching.

CNF sheet emerges as a substrate of flexible device

As concerns materials, Oji Holdings demonstrated a flexible substrate, which was based on new concept. It's a transparent sheet and film using Nonosize cellulose Nano fiber (CNF) as a main component. In a word, it's assimilated into dirt finally because of woody material. And also, in the case of scrapping, it's simply burned. In short, it's greatly ecological material.


Picture 5. Patterned sample of Ag pattern
Transmittance of all light beam
91.4 %
Haze
0.5 %
Tensile strength
 15 MPa
Elastic modulus 10 GPa
Linear expansion coefficient  7.2 ppm
(@60～100℃)
Tg   None (@200℃ and under) 
Decomposition temperature   5 % wt shrinkage:270 ℃
Decomposition peak:320 ℃ 
Flexibility   Without breaking at 1 mm diameter

Table 1. Main specifications (@25 μm thickness)

Picture 4. CNF transparent sheet
As table 1, linear expansion coefficient is 7.2 ppm/℃ (@60 - 100℃), which is almost same as that of glass. Of course, in spite of sufficient mechanical strength, flexibility is superior. Furthermore, chemical resistance is high, too. As a result, it's possible to correspond to etching process using acid and so on.

In the booth, a patterning sample of Ag pattern was exhibited, too. It's patterned by making use of surface treatment technology effectively. Concretely, first of all, a hydrophobic photoresist is coated on this sheet, and then, it's exposed by masked exposure of vacuum-ultraviolet light. As a result, hydrophobic area and hydrophilic area are separated in the substrate. The next, Ag ink is coated on the whole, as a result, it's gotten together in hydrophobic area selectively. By the way, adhesion of Ag film and the substrate was sufficient.

Kao announced to go into the market of CNT ink


Figure 1. Transfer characteristic of CNT-TFT

Picture 6. Semiconductor type CNT ink and metal type CNT ink
As to CNT, Kao announced to develop a semiconductor type CNT ink in the first time. Its purity is 99 % and over by making use of original separate extraction technology. And also, defect in the ink was minimized, too.

The company has pilot-produced a wettable CNT transistor (silicon wafer/thermally oxidized SiO2 film/source drain/CNT semiconductor layer) using this CNT INK as semiconductor material. Its carrier mobility and ON/OFF current ratio were 17 cm2/Vs and 1.6×105. These values mean that it can be used for display use. Furthermore, as figure 1, hysteresis phenomenon has not been almost observed.

Tosoh appealed a new wettable organic semiconductor material with atmospheric stability


Figure 3. Transfer characteristic of organic-TFT


Figure 2. New wettable organic semiconductor material
For organic-TFT, Tosoh introduced a new wettable organic semiconductor material. Figure 2 shows molecular structure. It has high thermal resistance (melting point：190 ℃) and high durability in atmosphere. In short, if organic-TFT using this material is left to atmosphere environment after manufacturing, it has not almost degraded. Of course, it can be coated and patterned by use of various methods, inclusive of ink jet printing method.

Figure 3 shows device characteristics of pilot-produced device (bottom gate/bottom contact structure) using this material. In this device, practical carrier mobility and hysteresis-free property were obtained. And also, Yamagata University has succeeded to drive a 3.2-inch full-color OLED (128 × 100 pixel) by this organic-TFT.

Specific resistance and work function of ITO film is controlled by laser annealing


Figure 4. Result of laser anneal treatment
As regards manufacturing process, National Institute of Advanced Industrial Science and Technology (AIST) proposed new manufacturing technology of transparent conductive film for flexible display, such as quantum dot display. If a plastic film is used as a substrate of flexible display, in general, it's difficult to adopt high temperature process. For this reason, first of all, a conventional ITO film is deposited by the sputtering method. The next, it's annealed by excimer laser irradiation. As a result, it's possible to control not only specific resistance, but also work function of ITO film.

Figure 4 shows relationship of laser fluence and specific resistance and work function. It indicates that these characteristics can be controlled by condition of laser annealing.

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