Wide emitting lens for LED useful for backlighting

#This invention relates to light emitting diodes (LEDs) and, in particular, to certain lens designs and a technique for forming a lens over an LED die.

#LED dies typically emit light in a lambertian pattern. It is common to use a lens over the LED die to narrow the beam or to make a side-emission pattern. A common type of lens for a surface mounted LED is preformed molded plastic, which is bonded to a package in which the LED die is mounted. One such lens is shown in U.S. Pat. No. 6,274,924, assigned to Lumileds Lighting and incorporated herein by reference.

#A technique for forming a lens for surface mounted LEDs is described herein along with various designs of lenses. One particularly useful lens creates a wide emission pattern so that light from multiple LEDs in a backlight is thoroughly mixed to create a homogenous light source in a liquid crystal display (LCD) backlight.

#FIG. 1 is a side view of four LED dice mounted on a support structure, such as a submount, and a mold for forming a lens around each LED die.

#FIG. 2 is a side view of the LED dice being inserted into indentations in the mold filled with a liquid lens material.

#FIG. 3 is a side view of the LED dice removed from the mold after the liquid has been cured, resulting in a lens encapsulating each LED die.

#As a preliminary matter, a conventional LED is formed on a growth substrate. In the example used, the LED is a GaN-based LED, such as an AlInGaN LED, for producing blue or UV light. Typically, a relatively thick n-type GaN layer is grown on a sapphire growth substrate using conventional techniques. The relatively thick GaN layer typically includes a low temperature nucleation layer and one or more additional layers so as to provide a low-defect lattice structure for the n-type cladding layer and active layer. One or more n-type cladding layers are then formed over the thick n-type layer, followed by an active layer, one or more p-type cladding layers, and a p-type contact layer (for metallization).

#Various techniques are used to gain electrical access to the n-layers. In a flip-chip example, portions of the p-layers and active layer are etched away to expose an n-layer for metallization. In this way the p contact and n contact are on the same side of the chip and can be directly electrically attached to the package (or submount) contact pads. Current from the n-metal contact initially flows laterally through the n-layer. In contrast, in a vertical injection (non-flip-chip) LED, an n-contact is formed on one side of the chip, and a p-contact is formed on the other side of the chip. Electrical contact to one of the p or n-contacts is typically made with a wire or a metal bridge, and the other contact is directly bonded to a package (or submount) contact pad. A flip-chip LED is used in the examples of FIGS. 1-3 for simplicity.

#Examples of forming LEDs are described in U.S. Pat. Nos. 6,649,440 and 6,274,399, both assigned to Lumileds Lighting and incorporated by reference.