Stacked LED Pixel Structure to Reduce 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 while maintaining luminosity and efficiency, leading to issues with surface recombination and external quantum efficiency.
Innovation Solution
A light emitting device with a stack structure of LEDs, including a first, second, and third LED stack with surface protection layers and bonding layers, and buried vias to enhance light emission and reduce surface recombination, allowing for increased pixel area and efficient mounting processes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If LED chips are reduced in size to increase pixel density, then the number of pixels per unit area increases, but the luminous area of each LED chip decreases
Solution Approach 1:
The patent transitions from a two-dimensional arrangement of LED chips to a three-dimensional stacked configuration. Multiple LED stacks are arranged vertically, allowing each LED chip to maintain a larger area while achieving high pixel density through vertical stacking rather than horizontal packing.
Solution Approach 2:
The pixel structure is segmented into multiple LED stacks (first, second, and third LED stacks) arranged vertically. Each stack contains multiple LED chips that can be independently controlled to emit different colors, allowing the pixel to be divided into functional segments that collectively provide full-color display capability with larger individual chip areas.
2Area of stationary object
If LED chips are reduced in size to fit more sub-pixels in a restricted area, then the area occupied by each pixel is reduced, but the mounting difficulty increases
Solution Approach 1:
The invention moves from planar mounting to vertical stacking, where multiple LED stacks are bonded together in the thickness direction. This three-dimensional arrangement allows each LED chip to maintain a practical size for mounting while achieving high pixel density through vertical integration rather than horizontal miniaturization.
Solution Approach 2:
Multiple LED stacks are merged vertically through bonding layers, combining multiple larger LED chips into a single pixel structure. This merging approach maintains ease of mounting for individual larger chips while achieving the functional equivalent of a high-density pixel through the combined vertical structure.
3Quantity of substance
If LED chips are reduced in size to increase pixel density, then more chips can be arranged in a restricted area, but surface recombination effects increase
Solution Approach 1:
The patent employs vertical stacking of multiple LED chips in the thickness direction rather than horizontal arrangement. This three-dimensional configuration allows each LED chip to maintain a larger active area with reduced surface-to-volume ratio, thereby minimizing surface recombination effects while still achieving high pixel density through the vertical stack.
Solution Approach 2:
The patent converts the potential harm of surface recombination into a benefit by using vertical stacking with larger chip areas. The larger chip area reduces the relative impact of surface recombination, and the vertical stack structure allows selective emission of light from different chips, turning the multi-chip complexity into a feature for enhanced color control and efficiency.
4Adaptability or versatility
If individual LED chips are arranged in each sub-pixel, then color display capability is achieved, but the mounting process time increases
Solution Approach 1:
Multiple LED chips are merged into vertically stacked configurations where each stack functions as an integrated unit. The bonding layers and shared electrode structures merge multiple chips into a single mountable entity, reducing the number of separate mounting operations required while maintaining the ability to display multiple colors through the stacked arrangement.
Solution Approach 2:
The patent arranges multiple LED chips vertically in the thickness direction rather than horizontally in the plane. This vertical stacking allows multiple color-emitting chips to be integrated within a single pixel footprint, reducing the total number of mounting positions required while maintaining full color display capability through the stacked configuration.
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 mounting time, and prevents current leakage due to surface recombination, thereby improving the external quantum efficiency and reliability of the LED display.
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
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.