Stacked LED Sub-Pixels to Limit Surface Recombination
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Solution Overview
Problem
Conventional light emitting diode (LED) displays face challenges in reducing the size of LED chips for increased pixel density, which leads to increased non-radiative surface recombination and decreased external quantum efficiency, while also requiring longer manufacturing times and occupying more area due to the need for excessive LED chips per pixel.
Innovation Solution
A light emitting device with a stack structure of LEDs, including a first, second, and third LED stack with conductivity type semiconductor layers and surface protection layers, bonded together with planarization and insulation layers, and buried vias to enhance light emission and reduce surface recombination, allowing for a larger pixel area and reduced manufacturing time.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of moving object
If the size of LED chips is reduced to increase pixel density, then the number of LEDs per pixel increases, but non-radiative surface recombination increases and external quantum efficiency decreases
Solution Approach 1:
The patent transitions from a two-dimensional arrangement of LED chips to a three-dimensional stacked structure. Multiple LED stacks are arranged vertically along the thickness direction, allowing sub-pixels to be positioned at different heights. This vertical stacking enables increased pixel density without reducing individual LED chip size, thereby maintaining external quantum efficiency while achieving higher resolution displays.
Solution Approach 2:
The patent divides each pixel into multiple sub-pixels arranged in different spatial layers. Each sub-pixel contains LED stacks with specific conductivity types (n-type or p-type) positioned at different heights. This segmentation allows independent optimization of each sub-pixel's LED chip size and arrangement, preventing current leakage between adjacent sub-pixels while maintaining high efficiency.
2Adaptability or versatility
If individual LED chips are arranged in each sub-pixel on a two-dimensional plane, then color display is achieved, but the number of LED chips increases and mounting time increases
Solution Approach 1:
The patent merges multiple LED chips into vertically stacked configurations where n-type and p-type LED stacks are bonded together. This stacking approach reduces the total number of separate mounting operations required compared to placing individual LED chips in each sub-pixel on a two-dimensional plane. The bonded LED stacks function as integrated units, significantly reducing mounting process time while maintaining full color display capability through the combination of different LED emissions.
3Quantity of substance
If LED chip size is reduced to fit more sub-pixels in a restricted area, then pixel density increases, but mounting difficulty increases
Solution Approach 1:
The patent resolves the mounting difficulty by moving from two-dimensional placement to three-dimensional stacking. Multiple sub-pixels are arranged vertically at different heights rather than being compressed into a restricted two-dimensional area. This allows each LED chip to maintain a practical size for mounting while achieving high sub-pixel density through vertical arrangement. The stacked structure naturally accommodates multiple sub-pixels without requiring excessively small or difficult-to-mount LED chips.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution increases the area of each sub-pixel, reduces current leakage, and enhances light extraction efficiency by minimizing non-radiative recombination, thereby improving the external quantum efficiency and manufacturing efficiency of LED displays.
Implementation Method 1
reduction in size of LED chips increases effect of non-radiative surface recombination, thereby lowering the external quantum efficiency of the light emitting diodes
Implementation Method 2
a surface protection layer at least partially covering side surfaces of the first LED stack, the second LED stack, or the third LED stack
Implementation Method 3
Light emitting diodes have been used in various fields including displays
Implementation Method 4
reduction in size of LED chips increases effect of non-radiative surface recombination, thereby lowering the external quantum efficiency of the light emitting diodes
Data Source
AI summary
A light emitting device for a display including a first LED stack, a second LED stack disposed under the first LED stack, a third LED stack disposed under the second LED stack, and including a first conductivity type semiconductor layer and a second conductivity type semiconductor layer, a surface protection layer at least partially covering side surfaces of the first LED stack, the second LED stack, or the third LED stack, a first bonding layer interposed between the second LED stack and the third LED stack, a second bonding layer interposed between the first LED stack and the second LED stack, lower buried vias passing through the second LED stack and the first bonding layer, and electrically connected to the first conductivity type semiconductor layer and the second conductivity type semiconductor layer of the third LED stack, respectively, and upper buried vias passing through the first LED stack.