Light emitting diode chip and method of fabricating the same

What is this patent about?

’440 is related to the field of light emitting diodes (LEDs) and, more specifically, to high-efficiency chip architectures that utilize multi-layered reflective structures to maximize light extraction. In conventional LED designs, metal reflectors often suffer from limited reflectivity and susceptibility to oxidation, while standard distributed Bragg reflectors typically only provide high performance within a narrow wavelength band or for light incident at specific angles. This creates a significant bottleneck for white-light LED packages where light must be reflected across a broad visible spectrum, including light that has been backscattered or converted by phosphors.

The underlying idea behind ’440 is a specialized asymmetric dielectric stack that achieves ultra-wideband reflectivity by grouping dielectric pairs based on their optical thickness relative to a central visible wavelength. Rather than using a uniform thickness throughout the stack, the invention organizes the layers into distinct zones: one group where both layers are thinner than a quarter-wavelength, another where both are thicker, and a transitional pair that bridges the two. This specific gradient or grouping allows the reflector to maintain high efficiency across the entire 400 nm to 700 nm range and at steep angles of incidence, which is critical for capturing light that would otherwise be lost to the substrate.

The claims of ’440 focus on an LED chip featuring an alternating lamination bottom structure positioned beneath the substrate, characterized by three specific types of dielectric pairs. The first type consists of material layers where both have an optical thickness less than λ/4, the second type features one layer below and one layer above λ/4, and the third type consists of layers where both exceed λ/4. These independent claims protect the specific arrangement of these pairs—either moving from thin to thick or vice versa—to ensure the device reflects light across the visible spectrum regardless of the entry angle.

In practice, the invention functions as a broadband optical mirror integrated directly onto the back of the growth substrate. By utilizing materials with high and low refractive indices, such as TiO2 and SiO2, and arranging them in this tiered thickness configuration, the stack achieves a simulated reflectance of over 98%. This performance is further enhanced by a metal reflector placed at the very bottom of the stack, which not only catches any residual light but also serves as a thermal path to dissipate heat generated during high-power operation.

This approach differentiates itself from prior art by solving the design complexity inherent in wideband reflectors. By categorizing the stack into thickness-defined zones, the inventor provides a systematic way to add or adjust layers without disrupting the entire optical profile of the chip. Furthermore, the inclusion of a top lamination structure—which is tuned to be transparent to the LED's primary emission but reflective to longer-wavelength phosphor light—creates an optical cage that forces converted light out of the package, significantly increasing the overall luminous efficiency compared to standard reflective coatings.