Osram creates gallium-nitride LED chips on silicon wafers
The technology is currently in the pilot stage, enabling the manufacturer to test it under practical conditions, meaning that the first LEDs on silicon from the company could hit the market in about two years.
According to Osram Semi project manager Peter Stauss, the researchers have optimized the quality of the gallium-nitride layers on the silicon substrates to the point where efficiency and brightness have reached competitive market levels.
The achievement is significant for LED technology for several reasons: Silicon offers very good thermal properties, and as the standard material in the semiconductor industry it is more cost effective than the somewhat exotic sapphire. As a consequence of its position in the chip industry, large wafer diameters are available at low cost. While in the research project at hand wafers with a diameter of 150mm were utilized, first structures have already been demonstrated on 200mm substrates. The larger wafer size boosts the productivity in LED manufacturing. Already the 150mm wafer accommodates 17.000 LED chips.
Production of a UX:3 chip on a silicon wafer. For full resolution, click here.
According to Osram, quality and performance data on the fabricated LED silicon chips match those of sapphire-based chips: the blue UX:3 chips in Osram’s standard Golden Dragon Plus package achieve a brightness of 634 mW at 3.15 volts, equivalent to 58 percent efficiency. The company points out that these are outstanding values for 1 mm² chips at 350 mA. In combination with a conventional phosphor converter in a standard housing – in other words as white LEDs – these prototypes correspond to 140 lm at 350 mA with an efficiency of 127 lm/W at 4500 K.
“For these LEDs to become widely established in lighting, the components must get significantly cheaper while maintaining the same level of quality and performance,” Stauss emphasizes. “We are developing new methods along the entire technology chain for this purpose, from chip technology to production processes and housing technology.”
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