18 January 2018
Solar-Tectic and Blue Wave granted US patent for material that can improve TFT displays and yield GaN-on-Si monolithic micro-LEDs
© Semiconductor Today Magazine / Juno PublishiPicture: Disco’s DAL7440 KABRA laser saw.
Solar-Tectic LLC of Briarcliff Manor, NY, USA (which specializes in thin-film solutions for the solar, display, and glass industries) and Blue Wave Semiconductors Inc (which provides thin-film deposition equipment as well as coating services) say that a material for improving the performance of thin-film transistors (TFTs) used in almost all displays on the market, including LCD, LED and OLED, has been patented by the US Patents and Trademarks Office (USPTO).
US Patent no. 9,856,578 is for making crystalline films on glass at low temperature with a high degree of crystal orientation (‘texture’). The particular material demonstrated is magnesium oxide (MgO). The insulating material is not only highly transparent but also has very high thermal conductivity, high thermal stability, and a high melting point. Most importantly, the new material has an unusual (111) orientation, which can enhance the preferred orientations of silicon and germanium.
Silicon is used in almost all TFTs made currently using the LTPS (low temperature polysilicon) process, and the new MgO material promises to enhance the LTPS process (as well as the common a-Si TFT process) because of its high (111) crystal orientation which, by inducing texture in the silicon without chemical degradation, can greatly increase electron mobility. This is due to the resulting aligned crystals along the c-axis. The electrical performance and homogeneity of semiconductor layers can also be enhanced by the highly crystalline and oriented MgO film.
The thin film can be grown in a wide range of thicknesses, and deposited on a variety of technical glasses, including soda-lime or alkali-free glass, at temperatures as low as ~450°C or less. When deposited on soda-lime glass, the MgO film serves as a diffusion barrier, preventing impurities such as sodium (Na) from contaminating the silicon layer along with enhancing the crystallography along the (111) plane.
“With this new material, we can now grow oriented silicon films with high mobility on which III-V materials such as GaN can then be grown for micro-LEDs,” says CEO Ashok Chadhari. “GaN on highly crystalline silicon thin-film would allow for monolithic micro-LED fabrication.”
Last month Solar-Tectic announced an entirely new low-temperature process for making TFTs, which can replace LTPS and IGZO-CAAC (C-axis aligned crystalline indium-gallium-zinc oxide), and the MgO material is an essential part of that technology.
Solar-Tectic and Blue Wave also recently received a US patent (no. 9,719,165 B2) for a new ceramic glass technology for use with displays.