Color-Tunable and Phosphor-Free White-Light Multilayered Light-Emitting Diodes

A tightly integrated 3-D RGB light-emitting diode (LED) stack is demonstrated. Chips of identical dimensions are stacked on top of each other, with wire bonds embedded within. This is achieved by integrating laser-micromachined channels onto the sapphire face of InGaN LEDs, serving to accommodate wire bonds from the chip beneath. The resultant structure eliminates leakage of monochromatic light from individual chips, producing optimally mixed emission through the top aperture. The device can emit a wide range of colors and is an efficient phosphor-free white-light LED as well. When emitting at correlated color temperatures (CCTs) of 2362 K, 5999 K, and 7332 K, the device generates ~ 20 lm/W, exhibiting performance invariant of CCT. Thermal characteristics of this multilayered device are investigated via infrared thermometry.