Stacked Micro LED Pillar Layout Without Through Vias
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Solution Overview
Problem
The challenge in developing micro LEDs for display applications, such as augmented reality, is the reduction in light emitting area due to the use of through vias, which increases non-radiative surface recombination and lowers external quantum efficiency, especially as the size of the LEDs decreases, making it difficult to reduce via size proportionally with the LEDs.
Innovation Solution
A stacked light emitting device with a novel electrical connection structure using pillars instead of through vias to connect the LEDs, allowing for independent driving of each LED stack and alleviating the reduction in light emitting area, thereby reducing non-radiative surface recombination and enhancing quantum efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If through vias are used to connect LEDs to pads, then electrical connection is achieved, but light emitting area is reduced and non-radiative surface recombination increases
Solution Approach 1:
The patent extracts the harmful through vias from the LED structure and replaces them with side surface connection structures. The connection structures are positioned on the side surfaces of the LED stacks rather than penetrating through the light emitting region, thereby removing the source of non-radiative recombination while maintaining electrical connectivity.
Solution Approach 2:
The patent transitions from a vertical through-via connection approach to a lateral side-surface connection approach. By moving the connection structures from the vertical dimension (through the LED) to the lateral dimension (on the side surfaces), the light emitting area is preserved while electrical connection is maintained.
2Area of moving object
If via size is reduced proportionally with LED size reduction, then light emitting area is preserved, but manufacturing precision limitations prevent further via size reduction
Solution Approach 1:
The patent removes the via structures entirely from the manufacturing process and replaces them with side surface connection structures. This eliminates the manufacturing precision constraints associated with via formation while maintaining the goal of preserving light emitting area in miniaturized LEDs.
3Productivity
If stacked LED structure is used to reduce number of chips, then mounting process time is reduced, but complex electrical connection structure is required
Solution Approach 1:
The patent combines multiple LED stacks vertically into a single integrated structure with shared connection infrastructure. The first, second, and third LED stacks are connected to common pads through shared connection structures, reducing the overall number of discrete components and simplifying the mounting process while maintaining individual control capability.
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
This solution effectively increases the light emitting area and reduces non-radiative surface recombination, improving the external quantum efficiency of micro LEDs, even at smaller sizes, such as 5 μm×5 μm or less, by eliminating the need for through vias and allowing for independent control of each LED stack.
Implementation Method 1
Light emitting diodes have been used in various fields including displays... Light emitting devices used in such LED displays are often referred to as micro LEDs
Implementation Method 2
the effect of non-radiative surface recombination may be increased, thereby lowering an external quantum efficiency of the LED
Data Source
AI summary
A light emitting device including an insulation unit, a light emitting region including first, second, and third LED stacks each including first and second conductivity type semiconductor layers, a first pillar electrically connected to the first conductivity type semiconductor layers of the first, second, and third LED stacks, and a second pillar, a third pillar, and a fourth pillar electrically connected to the second conductivity type semiconductor layers of the first, second, and third LED stacks, respectively, an intermediate first connector and a lower first connector respectively electrically connecting the first conductivity type semiconductor layers of the second LED stack and the third LED stack to the first pillar, in which the insulation unit have four corners, and the first, second, third, and fourth pillars are disposed near the four corners covering a side surface of the insulation unit, respectively.