Developed polycrystalline oxide semiconductor "Poly-OS" that can be applied to various displays

Idemitsu Kosan began developing the polycrystalline oxide semiconductor material IGO (Indium Gallium Oxide) in 2006. IGO is characterized by its high mobility, which is on the same level as low-temperature polysilicon (LTPS) ⁴, which was not possible with conventional oxide semiconductors. Furthermore, it has process suitability for large-scale lines of 8th generation and above, making it possible to manufacture thin film transistors (TFTs) ⁵.

Using its unique backplane technology, JDI succeeded in commercializing the world's first polycrystalline oxide semiconductor "Poly-OS" on the 6th generation mass production line at the Mobara Plant (Mobara City, Chiba Prefecture).
The Poly-OS created by JDI has achieved field effect mobility four times higher than conventional technology, and was announced as JDI's proprietary technology "HMO (High Mobility Oxide)" on March 30, 2022. (News release: "World's first 6th generation mass production line realizes oxide semiconductor TFT with field effect mobility four times higher than conventional products").

The two companies will work to popularize the polycrystalline oxide semiconductor "Poly-OS" technology so that it can be applied by a wide range of industry participants, as well as contribute to the evolution of display performance, the development of the industry, and the creation of a low-carbon society by reducing the power consumption of displays. We will work to make this a reality.

¹ Polycrystalline oxide: A polycrystalline thin film composed of metal elements and oxygen.
² Backplane: A circuit board on which minute semiconductor elements are mounted, which form the basis of thin displays.
³ Off-leakage current: Unintended current that leaks when the transistor is in the off state.
^4Low-temperature polysilicon (LTPS): Polycrystalline silicon formed on a glass substrate at low temperatures. High electron mobility.
^5Thin film transistor (TFT): A thin transistor made of silicon or other materials on a glass substrate.

[About polycrystalline oxide semiconductor “Poly-OS” technology]

<Technology overview>

Transistors using existing oxide semiconductors (Oxide), like amorphous silicon (a-Si) ⁶, are easy to manufacture in large areas and can reduce power consumption due to low off-leakage current. On the other hand, the issue has been that the mobility is low compared to LTPS, which is mainly used in current small and medium-sized displays. The innovative polycrystalline oxide semiconductor "Poly-OS" technology developed by both companies has significantly improved mobility and succeeded in achieving high performance similar to LTPS. This makes it possible to create products that combine the performance of existing backplane technologies (a-Si, Oxide, LTPS) (Fig. 1).

<Classification of oxide semiconductors>

Until now, oxide semiconductors with crystal structures such as amorphous and C-axis Aligned Crystal/nano crystal ⁷ have been used in the active layer of transistors and have been commercialized. IGO, a polycrystalline oxide semiconductor material developed by Idemitsu Kosan, is characterized by the ability to achieve a poly-crystalline state (Fig. 2) using the same process (450°C or less) as for existing amorphous oxide semiconductors. is. By using this polycrystalline oxide semiconductor in the active layer, it is possible to maximize the mobility of the original oxide semiconductor.

<Process technology>

Oxide semiconductor materials with high mobility have difficult to control carrier concentration, making it difficult to obtain stable TFT characteristics. By combining the process know-how such as CVD ⁸ / sputter ⁹ / annealing ¹⁰ / etching that JDI has cultivated over many years, stable TFT operation with high mobility and low off-leakage current has become possible (Fig. 3,4). The optimal Top Gate Self Align structure ¹² (Fig. 5) is adopted to further increase the on-current ¹¹, and stable TFT characteristics independent of channel width are obtained even at a channel length of 2 µm, providing current driving power equivalent to LTPS. (Fig.6).

^6Amorphous silicon (a-Si): Amorphous silicon used in thin film transistors.
⁷ C-axis Aligned Crystal/nano crystal: Crystal structure of a semiconductor film with c-axis alignment or microcrystals.
⁸ CVD: A process in which a thin film is formed on the surface of a substrate through a chemical reaction.
⁹ Sputtering: A process in which ions collide with a target (thin film raw material) to form a thin film.
¹⁰ Annealing: A treatment process that improves the film quality by applying heat to thin films etc. on glass substrates.
^11On current: Current that flows when a transistor is in the on state.
¹² Top Gate Self Align structure: TFT structure that reduces parasitic capacitance and enables high-speed operation.
^13Mother glass: Large-sized glass used for the glass substrate of flat-screen displays.

[Reference materials] Overview of each social company *Capital and sales are as of the fiscal year ending March 2022