LED Stack Electrode Pad Layout for Larger Sub-Pixels
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Solution Overview
Problem
Existing LED displays face challenges in efficiently utilizing sub-pixels within a restricted area, leading to reduced brightness and increased manufacturing time due to the need for multiple LED chips per pixel, which also complicates the mounting process.
Innovation Solution
A light emitting device with a stacked structure of LED stacks, including first, second, and third LED stacks, each with transparent electrodes and electrode pads at different elevations, allowing for increased sub-pixel area without increasing pixel size, and featuring recessed transparent electrodes to protect against manufacturing damage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If multiple LED chips are arranged on a two-dimensional plane to provide blue, green, and red light for each pixel, then all necessary colors can be displayed, but the number of LED chips increases and the mounting time increases
Solution Approach 1:
The patent transitions from two-dimensional arrangement of LED chips to a three-dimensional stacked structure where multiple LED stacks are arranged vertically. Each stack contains multiple LED chips emitting different colors (blue, green, red) that are stacked in the vertical direction rather than spread out horizontally. This dimensional change reduces the number of chips per pixel from 3 to effectively 1 stack, thereby reducing mounting complexity and time while maintaining full color display capability.
2Area of stationary object
If the area of each sub-pixel is reduced to arrange sub-pixels in a restricted area, then more sub-pixels can fit in the display, but the luminous area of sub-pixels is reduced and brightness deteriorates
Solution Approach 1:
The patent utilizes the vertical dimension by stacking multiple LED chips (blue, green, red) vertically within each sub-pixel location. This allows the sub-pixel footprint on the two-dimensional display plane to remain small while accommodating multiple light-emitting elements in the third dimension. The stacked configuration increases the effective luminous area without increasing the planar sub-pixel area, thereby maintaining both high display area utilization and brightness.
Solution Approach 2:
The patent implements a nested structure where multiple LED chips are stacked vertically within each LED stack, with smaller LED chips positioned above larger ones. The LED stacks themselves are nested within the sub-pixel regions, which are nested within the overall pixel structure. This nesting arrangement maximizes the use of vertical space, allowing multiple light-emitting elements to occupy a minimal planar area while maintaining adequate luminous area for each chip.
3Reliability
If transparent electrodes are extended to the edge of semiconductor layers for electrical contact, then good electrical connection is achieved, but the electrodes are exposed and vulnerable to damage during manufacturing
Solution Approach 1:
The patent applies beforehand cushioning by extending the semiconductor layer beyond the edge of the transparent electrode, creating a protective overhang. This structural configuration protects the transparent electrode edge from damage during subsequent manufacturing processes such as dicing or handling, while the transparent electrode still maintains adequate electrical contact with the semiconductor layer through its extended coverage area.
Solution Approach 2:
The patent performs preliminary action by designing the transparent electrode to extend beyond the semiconductor layer edge before the damaging manufacturing steps occur. This pre-configured extension ensures that when dicing or other edge-affecting processes are performed, the electrode is already protected by the overlapping semiconductor material, preventing edge damage that would compromise electrical connection.
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 enhances sub-pixel area utilization, reduces manufacturing time, and improves production yield by preventing electrode damage during the manufacturing process.
Implementation Method 1
a first transparent electrode interposed between the first LED stack and the second LED stack, and being in ohmic contact with a lower surface of the first LED stack; a second transparent electrode interposed between the first LED stack and the second LED stack, and being in ohmic contact with an upper surface of the second LED stack
Data Source
AI summary
A light emitting device for a display including first, second, and third LED stacks each including a first conductivity type semiconductor layer, an active layer, and a second conductivity type semiconductor layer; first, second, and third transparent electrodes in ohmic contact with the first, second, and third LED stacks, respectively; a first electrode pad disposed on the first conductivity type semiconductor layer of the third LED stack; a lower second electrode pad disposed on the third transparent electrode; first, second, and third bump pads disposed on the first LED stack and electrically connected to the first, second, and third LED stacks, respectively; and a common bump pad commonly electrically connected to the first, second, and third LED stacks, in which a lower surface of the first electrode pad is located at a different elevation from a lower surface of the lower second electrode pad.