Phosphor in inorganic binder for LED applications
A method for fabricating an LED/phosphor structure is described where an array of blue light emitting diode (LED) dies are mounted on a submount wafer. A phosphor powder is mixed with an organic polymer binder, such as an acrylate or nitrocellulose. The liquid or paste mixture is then deposited over the LED dies or other substrate as a substantially uniform layer. The organic binder is then removed by being burned away in air, or being subject to an O 2 plasma process, or dissolved, leaving a porous layer of phosphor grains sintered together. The porous phosphor layer is impregnated with a sol-gel (e.g., a sol-gel of TEOS or MTMS) or liquid glass (e.g., sodium silicate or potassium silicate), also known as water glass, which saturates the porous structure. The structure is then heated to cure the inorganic glass binder, leaving a robust glass binder that resists yellowing, among other desirable properties.
1. A method for fabricating a luminescent structure comprising:
depositing an intermediate phosphor layer on a supporting structure, the intermediate phosphor layer comprising phosphor powder mixed with a first binder;
removing the first binder, leaving a porous phosphor layer on the supporting structure, wherein the phosphor layer comprises phosphor grains sintered together;
after the step of removing the first binder, infusing the porous phosphor layer with sol-gel or liquid glass; and
curing the sol-gel or liquid glass to form an inorganic transparent glass binder.
2. The method of claim 1 wherein the step of removing the first binder comprises heating the first binder to evaporate the first binder and sinter the phosphor grains.
3. The method of claim 1 wherein the step of removing the first binder comprises subjecting the first binder to an O 2 plasma to oxidize the first binder.
4. The method of claim 1 wherein the step of removing the first binder comprises dissolving the first binder.
5. The method of claim 1 wherein the first binder comprises acrylate.
6. The method of claim 1 wherein the supporting structure comprises a glass substrate.
7. The method of claim 1 further comprising singulating the supporting structure to form luminescent tiles and affixing one of the tiles over a light emitting diode.
8. The method of claim 1 wherein the supporting structure comprises a submount wafer populated with light emitting diode dies.
9. The method of claim 1 wherein the supporting structure comprises a releasable film, where the method further comprises:
prior to the removing step, laminating the intermediate phosphor layer on the releasable film over light emitting diodes mounted on a submount wafer;
removing the releasable film; and
then proceeding to the removing step, the infusing step and the curing step.
10. The method of claim 1 wherein the supporting structure comprises a lens over a light emitting diode.
11. The method of claim 1 wherein the sol-gel, after curing, forms a layer of either sodium silicate or potassium silicate.