Sumitomo Heavy Industries' Proprietary RPD Method Contributes to Ultra-thin Zinc Oxide Transparent Conductive Film Deposition
Sumitomo Heavy Industries and Kochi University of Technology used the proprietary RPD method to successfully create the world's first 10nm thick crystallized zinc oxide (ZnO) transparent conductive film on a glass substrate, paving the way for indium-free materials.
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- 📰 Published: April 23, 2026 at 19:04
- 🔍 Collected: April 23, 2026 at 10:31
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Sumitomo Heavy Industries, Ltd. (Headquarters: Shinagawa-ku, Tokyo; Representative Director and President: Toshiro Watanabe; hereinafter "Sumitomo Heavy Industries") and Tetsuya Yamamoto, Director of the Materials Design Center at the Research Institute of Kochi University of Technology (Kami City, Kochi Prefecture; President: Shigeomi Chono) have jointly developed a technology to form the world's first 10-nanometer (a nanometer is one billionth of a meter) thick crystallized transparent conductive film using zinc oxide (ZnO) on a glass substrate, utilizing Sumitomo Heavy Industries' proprietary Reactive Plasma Deposition (RPD) method (*1). This has demonstrated the usefulness of the RPD method as a means of forming extremely thin, crystallized ZnO films on glass substrates, which are being researched as future transparent conductive films, buffer films, and seed films (*2).
Image of the deposition equipment used in this research.
[Background]
Transparent conductive films are essential materials for products that require a "surface that passes both electricity and light," such as solar cells, organic LEDs (OLEDs), and transparent heaters. They are used in a state where metal oxides like Indium Tin Oxide (ITO) and Indium Gallium Zinc Oxide (IGZO) are deposited on transparent substrates such as glass or plastic. ZnO transparent conductive films have long attracted attention because of the abundant resource of zinc, its property of absorbing ultraviolet rays, its high thermal conductivity, and the ability to control its flexibility according to the application. However, due to the difficulty of handling during deposition compared to conventional materials, its practical application as a transparent conductive film has been limited, largely remaining at the R&D stage in companies and universities.
Sumitomo Heavy Industries develops and manufactures equipment that deposits transparent conductive films like ITO and Gallium-doped Zinc Oxide (GZO) onto substrates such as glass, mainly for the solar cell, flat panel display, and OLED sectors. Aiming for fundamental research for the further development of the RPD method, joint research has been conducted with Center Director Yamamoto and his team until 2024. So far, they have developed methods such as depositing a crystallized Tungsten-doped Indium Oxide (IWO) transparent conductive film with a thickness of 5 nanometers using the RPD method (*3). This current achievement is the result of joint research conducted from 2023 to 2024, with Sumitomo Heavy Industries responsible for modifying the RPD equipment.
[Contribution of the RPD Method in This Research]
- While ZnO easily crystallizes even at low temperatures, it is a material prone to distortion in its crystal structure due to rapid growth in the initial stages of deposition. Characteristic control at ultra-thin levels was difficult because Physical Vapor Deposition (PVD) methods like sputtering lead to a mixture of multiple crystal structures, and direct deposition onto a substrate required a film thickness of 20 nanometers or more.
- The RPD method can freely control the momentum (energy) when metallic element ions and oxygen ions in a plasma state collide with the substrate. Through this energy control, a transparent conductive film with only a single crystal structure can be realized. Furthermore, this time, the existing RPD deposition equipment was modified for research to adjust the collision energy of metallic element ions and oxygen molecular ions against the substrate with even greater precision.
- As a result, they succeeded for the first time in the world in depositing a 10-nanometer-thick crystallized ZnO transparent conductive film with mitigated crystal structure distortion on a glass substrate.
- Because the RPD method features "low temperature, low damage" and "large area, high-speed deposition," it is a suitable method for practical application and for deposition on heat-sensitive substrates, for example.
[Future Outlook]
The technology to precisely form crystallized ZnO transparent conductive films has the potential to be utilized in the future for Indium (In)-free transparent conductive films and buffer/seed films that require strict precision. It is also expected to be a future technology that lowers resource risks. Going forward, Sumitomo Heavy Industries will continue to engage in research and development of technologies that fill people and society with kindness into the future, such as the creation and value enhancement of proprietary technologies like the RPD method.
Note that technical details are scheduled to be announced separately by Center Director Yamamoto's group.
Annotations
*1 Reactive Plasma Deposition (RPD). This is Sumitomo Heavy Industries' proprietary deposition method that creates high reactivity by guiding electrons emitted from a plasma gun to an evaporation material using a magnetic field, and activating the material sublimated by heating in a high-density plasma.
In the RPD method, the mechanism by which flying particles with positive charges are accelerated lies mainly in controlling the synergistic effect of the plasma potential distribution from the anode (positive electrode) potential (the evaporation source) to the substrate pushing out the positively charged flying particles, and the sheath potential formed at the substrate interface. Because of this feature, it is possible to keep damage to the substrate low while maintaining high reactivity, realizing the formation of dense thin films, and consequently, films with excellent crystallinity.
Reference: About vacuum deposition equipment
Image of the deposition equipment used in this research.
[Background]
Transparent conductive films are essential materials for products that require a "surface that passes both electricity and light," such as solar cells, organic LEDs (OLEDs), and transparent heaters. They are used in a state where metal oxides like Indium Tin Oxide (ITO) and Indium Gallium Zinc Oxide (IGZO) are deposited on transparent substrates such as glass or plastic. ZnO transparent conductive films have long attracted attention because of the abundant resource of zinc, its property of absorbing ultraviolet rays, its high thermal conductivity, and the ability to control its flexibility according to the application. However, due to the difficulty of handling during deposition compared to conventional materials, its practical application as a transparent conductive film has been limited, largely remaining at the R&D stage in companies and universities.
Sumitomo Heavy Industries develops and manufactures equipment that deposits transparent conductive films like ITO and Gallium-doped Zinc Oxide (GZO) onto substrates such as glass, mainly for the solar cell, flat panel display, and OLED sectors. Aiming for fundamental research for the further development of the RPD method, joint research has been conducted with Center Director Yamamoto and his team until 2024. So far, they have developed methods such as depositing a crystallized Tungsten-doped Indium Oxide (IWO) transparent conductive film with a thickness of 5 nanometers using the RPD method (*3). This current achievement is the result of joint research conducted from 2023 to 2024, with Sumitomo Heavy Industries responsible for modifying the RPD equipment.
[Contribution of the RPD Method in This Research]
- While ZnO easily crystallizes even at low temperatures, it is a material prone to distortion in its crystal structure due to rapid growth in the initial stages of deposition. Characteristic control at ultra-thin levels was difficult because Physical Vapor Deposition (PVD) methods like sputtering lead to a mixture of multiple crystal structures, and direct deposition onto a substrate required a film thickness of 20 nanometers or more.
- The RPD method can freely control the momentum (energy) when metallic element ions and oxygen ions in a plasma state collide with the substrate. Through this energy control, a transparent conductive film with only a single crystal structure can be realized. Furthermore, this time, the existing RPD deposition equipment was modified for research to adjust the collision energy of metallic element ions and oxygen molecular ions against the substrate with even greater precision.
- As a result, they succeeded for the first time in the world in depositing a 10-nanometer-thick crystallized ZnO transparent conductive film with mitigated crystal structure distortion on a glass substrate.
- Because the RPD method features "low temperature, low damage" and "large area, high-speed deposition," it is a suitable method for practical application and for deposition on heat-sensitive substrates, for example.
[Future Outlook]
The technology to precisely form crystallized ZnO transparent conductive films has the potential to be utilized in the future for Indium (In)-free transparent conductive films and buffer/seed films that require strict precision. It is also expected to be a future technology that lowers resource risks. Going forward, Sumitomo Heavy Industries will continue to engage in research and development of technologies that fill people and society with kindness into the future, such as the creation and value enhancement of proprietary technologies like the RPD method.
Note that technical details are scheduled to be announced separately by Center Director Yamamoto's group.
Annotations
*1 Reactive Plasma Deposition (RPD). This is Sumitomo Heavy Industries' proprietary deposition method that creates high reactivity by guiding electrons emitted from a plasma gun to an evaporation material using a magnetic field, and activating the material sublimated by heating in a high-density plasma.
In the RPD method, the mechanism by which flying particles with positive charges are accelerated lies mainly in controlling the synergistic effect of the plasma potential distribution from the anode (positive electrode) potential (the evaporation source) to the substrate pushing out the positively charged flying particles, and the sheath potential formed at the substrate interface. Because of this feature, it is possible to keep damage to the substrate low while maintaining high reactivity, realizing the formation of dense thin films, and consequently, films with excellent crystallinity.
Reference: About vacuum deposition equipment