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Innovation Japan 2025 (August 21 - 22)


Innovation Japan 2025
Newly transparent films for flexible device were proposed one after another

August 21 - 22, Innovation Japan 2025 was held in Tokyo Big Site. New topics of electric device are closed up.


Support low resistance and high transmittance by grafen/Ag/grafen stack layer


Fig 1. Comparison of optical transmittance


Pic 1. Coated samples of grafen/Ag/grafen
First of all, Aoyama Gakuin University proposed three stack layer of grafen (0.34nm) /Ag (5nm) /grafen (0.34nm) as a newly transparent conductive film. As you know, specific resistance of grafen single layer is relatively high same as 550cm. For this reason, it's reduced to approximate 130cm by three stacking layer. And also, as figure 1, high transmittance at visual light range same as 90% and over was obtained by sandwich structure including Ag film.

In this experiment, a glass was used as a substrate, but plastic film will be used in near future. By the way, it can be patterned by photolithography + O2 dry etching or direct O2 dry etching using mechanical metal mask.


Pic 2. Emission demonstration of LED using CNT transparent electrode
Properties are not degraded in bending state by CNT series transparent film

Kogakuin University proposed a carbon Nano tube (CNT) with silicon complex ink as a newly transparent conductive film. This ink is coated by various coating methods, and then, treated by a specific acid. Of course, it can be directly coated on various plastic films. Its sheet resistance is approximate 500/, and optical transmittance is 90% and over.

Its flexibility is superior. Picture 2 shows LED system with this conductive film. If this sample is bend, LED keeps emitting state, and furthermore, emitting state is not changed, too.

Flexible organic film solar cell is pilot-produced by use of new polymer ink as anode


Pic 3. Flexible organic film solar cell
Kanazawa University appealed a new conductive polymer ink, and then, exhibited plastic type organic film solar cells using this transparent conductive film. This original ink is coated on substrates by various coating methods, and then, is cured at 80, as a result, low resistance (80/) and high transmittance (92%) can be supported. In short, PET film such as lowest thermal resistance film can be used.

As picture 3 shows roll type organic film solar cell (30~100cm) using this transparent anode. It's composed of all polymer material including p-type and n-type organic semiconductor. Power conversion efficiency (PCE) is relatively high same as 7% in spite of all solution polymer type device.

Amorphous ITO film is polycrystallized by excimer laser anneal

Kyushu University proposed that amorphous ITO film was polycrystallized by excimer laser anneal. Damage against substrate is minimized by local annealing to surface neighborhood of ITO film, which has high absorption of UV light.


Pic 4. EBSD image of poly-ITO film by excimer laser anneal
Film properties such as grain size and thermal damage against substrate can be controlled by laser process condition such as energy density, shot number, shot period, and so on. In short, it's effective for low thermal resistance substrate, which is necessary to use high quality ITO film.

Stretchability of device itself is enhanced by use of liquid metal as mounting connection

As concerns other field, National Institute of Advanced Industrial Science and Technology (AIST) reported a mounting technology of electric device by use of liquid metal. As you know, liquid metal such as Ga+In or Ga+Sn functions as liquid in wiring because of low melting point (30), and has high stretchability same as 500% and over.

In this time, the research group proposed to use this liquid metal as connection of device and wiring. In the first experiment using non stretchable wiring, stretchable resistance was increased at just stretch amount of liquid metal. And also, it's increased to 300% in connection area.


Fig 2. Effect sample of mount process using liquid metal

Figure 2 shows the next experiment using stretchable wiring and its result. Stretchable resistance of wiring itself is increased at 0.8 times, and that of device was greatly increased, too.


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