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Innovation Japan 2021 (August 23 - September 17)

Innovation Japan 2021 - Online
Topics for manufacturing process of oxide semiconductor were proposed one after another

August 23th, Innovation Japan 2021 - Online has started by the online method. Many demonstrations are disclosed until September 17th by a specific homepage. Topics for electronics device are closed up based on the homepage.

Transparent oxide conductive film is formed at RT

Picture 2. Cu film with low resistance

Picture 1. Sample of transparent conductive film
The research group of Kogakuin University announced an original manufacturing process "Molecular precursor method" as a forming process of transparent oxide conductive film. In this process, a precursor liquid composed of organic complex and alkylamine is coated on the substrate, and then, annealed. As a result, uniformly transparent conductive oxide film is obtained.

As first research result, a precursor liquid composed of dispersed Carbon Nano Tube was coated on the substrate, as a result, transparent conductive film in not only UV region, but also deep ultraviolet region was formed by UV irradiation process at R.T. Its adhesive is sufficient, and also, relatively good specific resistance same as 10-3cm. Moreover, chemical resistance and heat resistance are sufficient. It's useful for alternative of ITO and FTO, and also, effective for electrode of solar cell and deep ultraviolet LED because of widely transparent region.

In addition, pure P-type Cu2O film was formed by this method, and then, a p-n junction type solar cell with this film was pilot-produced.

Besides, low resistance Cu film was formed by coating Cu precursor liquid. In this film, reflectance can be controlled by film thickness.

Oxide film is patterned by the lift-off method using a-CaO sacrifice layer

The research group of Kanazawa University proposed the water lift-off (WLO) process as fine patterning process of oxide thin film without etching treatment.

Picture 3. Patterned sample by WLO process
Figure 1. Basic flow of WLO process
Figure 1 shows basic flow. In this process, amorphous CaO (a-CaO) is used as a sacrifice layer due to solubleness and high melting point, and pure water is used as a stripping liquid instead of alkali in the last lift-off process. As a result, it's possible to correspond to high temperature process, which is advantageous for crystal growth of oxide film. On the other hand, it's difficult to correspond to high temperature process by general lift-off process using alkali.

Picture 3 shows fine dot pattern same as square 7m on a side. It's possible to form various structures at will without deterioration of crystallizability, surface form, and electric property.

Correspond to flexible devices by stack of SiO2 buffer and ZnO semiconductor

The research group of Osaka Institute of Technology appealed that oxide semiconductor succeeded to be formed on the flexible device, which was generally difficult to form oxide semiconductor because of its solid and fragility.

Picture 4. Result of surface observation at COP substrate thickness 50m
Figure 2.Cross-section structure of oxide-TFT
Figure 2 shows pilot-produced oxide-TFT. ZnO series was formed on COP (cycloolefin polymer) substrate. And also, oxide layers were stacked by insert of SiO2 buffer layer.

In this estimate, if substrate thickness was thin, deformation was decreased. Concretely, it's 188 m, crack in ZnO film and AZO film was generated after 100 times curving test, and also, the substrate was broken after approximate 500 times test. On the other hand, as picture 4, at COP thickness = 50 m, crack has not been observed after 10,000 times test. It's reason why if substrate thickness is thin, durability of device was improved due to decrease of deformation against SiO2 film, ZnO film, and AZO film. In fact, oxide-device with high durability (10,000 times at 5 o curvature radius) has been pilot-produced.

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