Vertically Stacked Light Emitting Diodes for High Density Illumination
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Solution Overview
Problem
Current light emitting diodes (LEDs) face limitations in increasing light output per unit area and efficient operation under AC power supply, with challenges in light extraction efficiency and reverse current issues when connected directly to AC power.
Innovation Solution
A light emitting device with vertically stacked LEDs, featuring a specific semiconductor layer structure and electrode configuration, allowing for improved light output and AC power operation by interposing active layers and cladding layers, and using codoped layers to enhance crystal quality and efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If the chip area is increased to obtain necessary light output per unit chip, then the light output is improved, but the manufacturing costs per chip increase
Solution Approach 1:
The patent transitions from two-dimensional planar LED arrays to three-dimensional vertically stacked LED structures. Multiple active layers are stacked in the vertical direction on a single chip substrate, enabling multiple light-emitting elements to occupy the same footprint area. This dimensional transition allows increased light output per unit chip area without proportionally increasing chip size or manufacturing complexity
Solution Approach 2:
The patent implements a nested structure where multiple active layers are integrated within a single chip substrate. The vertically stacked configuration allows one LED structure to be nested within the spatial envelope of another, with shared substrate and electrode structures. This nesting approach enables multiple light-emitting functions to be achieved within a single chip unit, improving light output without linearly increasing manufacturing costs
2Adaptability or versatility
If LED arrays are two-dimensionally connected in series on an insulating substrate to form AC-driven devices, then AC power operation is enabled, but the light output is considerably limited compared to simultaneous operation
Solution Approach 1:
The patent resolves the limitation of sequential operation by stacking multiple active layers vertically, allowing simultaneous conduction of current through all layers. The vertical stacking configuration with interleaved electrode connections enables all LEDs to operate at the same time rather than alternating sequentially, thereby achieving both AC power compatibility and high light output
Solution Approach 2:
The patent combines multiple active layers into a single integrated chip structure with unified electrode connections. By merging the electrical pathways and optical outputs of multiple LEDs into one device, the system achieves simultaneous operation of all layers when connected to AC power, rather than requiring separate sequential operation of individual LEDs or arrays
3Adaptability or versatility
If light emitting diodes are connected directly to AC power supply, then power supply compatibility is improved, but the LED may be easily damaged due to reverse current
Solution Approach 1:
The patent divides the single chip into multiple independently connected active layers with separate electrode pathways. This segmentation allows the device to be connected to AC power in a way that directs current through different layers during different half-cycles, preventing reverse current damage to any single LED while maintaining continuous light output
Solution Approach 2:
The patent inverts the conventional approach by connecting multiple LEDs in a configuration where the polarity alternates across different layers rather than requiring a single LED to withstand reverse polarity. This inverted connection scheme allows AC power operation by having each layer experience only forward bias during its designated conduction period, eliminating reverse current damage while maintaining AC compatibility
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 significantly enhances light output per unit area and enables stable operation under AC power supply, offering improved efficiency and versatility in wavelength emission.
Implementation Method 1
a lower active layer which is interposed between the lower semiconductor layer of a first conductive type and the semiconductor layer of a second conductive type, and an upper active layer which is interposed between the upper semiconductor layer of a second conductive type and the upper semiconductor layer of a first conductive type
Implementation Method 2
it is most important to eliminate internal loss of light due to total internal reflection... As the surface of the N-type semiconductor layer is roughened, the extraction efficiency of light emitted to the outside through the N-type semiconductor layer can be improved
Data Source
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AI summary
Disclosed is a light emitting device having vertically stacked light emitting diodes. It comprises a lower semiconductor layer of a first conductive type positioned on a substrate, a semiconductor layer of a second conductive type on the lower semiconductor layer of a first conductive type, and an upper semiconductor layer of a first conductive type on the semi¬ conductor layer of a second conductive type. Furthermore, a lower active layer is interposed between the lower semiconductor layer of a first conductive type and the semiconductor layer of a second conductive type, and an upper active layer is interposed between the semiconductor layer of a second conductive type and the upper semiconductor layer of a first conductive type. Accordingly, there is provided a light emitting device having a structure in which a lower light emitting diode comprising the lower active layer and an upper light emitting diode comprising the upper active layer are vertically stacked. Therefore, light output per unit area of the light emitting device is enhanced as compared with a conventional light emitting device, and thus, a chip area of the light emitting device needed to obtain the same light output as the conventional light emitting device can be reduced.