Integration of YAG:Ce Thin Film Wavelength Converter on III-V Blue LED via a Laser Lift-Off Process

Abstract

In this work, we have investigated fabrication of the thin films of down conversion layers for solid state lighting applications. We have developed a process to transfer a thin film of YAG:Ce to a LED top surface using an intermediate sacrificial layer (SL). A prerequisite for this layer is to dissociate upon absorption of laser radiation without degrading the thin film phosphor. This investigation is focused on identifying suitable optical, thermal and chemical properties of material for the laser lift-off process. In the present approach, a thin layer of phosphor is deposited on a sacrificial layer on a sapphire substrate. Both the phosphor and sacrificial layers are deposited using a pulsed laser ablation technique. The stack of YAG:Ce/SL/sapphire is glued to a blue LED with the sapphire substrate facing outward. This assembly of LED package is then irradiated by a 248 nm beam from an excimer laser for separating the SL from the sapphire substrate. It is observed that the dissociation occurs at the interface of sapphire and the sacrificial layer. The sapphire substrate is then easily separated from the stack leaving a thin film of phosphor layer on LED. The underlying dissociation process allowing a smooth transfer of the thin film of phosphor is discussed.