Monolithic Multi-Chip LED for UV Current Spreading
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Solution Overview
Problem
High-power UV LEDs face challenges with current spreading and light extraction efficiency due to large chip size, leading to increased voltage requirements and light loss, particularly in UVC LEDs with high Al-content n-AlGaN structures that are not suitable for spreading current over large areas.
Innovation Solution
A monolithic multi-chip collective light-emitting diode design featuring multiple mini chips with n-type and p-type structures, where each mini chip has a mini n-contact and p-ohmic contact, and an n-bridge metal connecting the mini n-contacts to an n-bonding pad, forming a network to enhance current spreading and light extraction efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If large chip size is used for high-power UV LEDs, then current injection capability is improved, but current spreading becomes difficult and voltage increases
Solution Approach 1:
The patent divides a large chip into multiple smaller mini-chips (e.g., 9 mini-chips arranged in a 3x3 array). Each mini-chip has its own n-contact and p-contact, allowing current to be injected and spread independently across each small region. This segmentation resolves the contradiction by enabling high total current injection while maintaining good current spreading within each mini-chip, avoiding the voltage increase that would occur in a single large chip.
2Power
If large chip size is used for high-power UV LEDs, then power handling is improved, but light extraction efficiency deteriorates
Solution Approach 1:
By segmenting the large chip into multiple small mini-chips, the patent reduces the lateral propagation distance for light within each mini-chip. This shorter propagation path minimizes absorption losses and improves light extraction efficiency for each mini-chip. The overall power handling capability is maintained through the collective output of all mini-chips working together.
3Illumination intensity
If high Al-content n-AlGaN structure is used for UVC LEDs, then UV light emission is improved, but current spreading capability deteriorates
Solution Approach 1:
The patent uses high Al-content n-AlGaN structures in each mini-chip to achieve strong UVC emission, while the segmentation into multiple small mini-chips allows each to maintain good current spreading independently. The n-bridge metals connecting adjacent n-contacts further assist current distribution across the entire array, resolving the contradiction between high UV emission and current spreading capability.
Solution Approach 2:
The n-bridge metals serve as intermediary elements that connect the n-contacts of adjacent mini-chips. These bridges facilitate current redistribution from regions of high current density to regions of lower current density, enhancing overall current spreading capability while allowing each mini-chip to utilize high Al-content structures for optimal UVC emission.
4Ease of operation
If multiple mini-chips are monolithically integrated, then current spreading and light extraction are improved, but device complexity increases
Solution Approach 1:
The patent employs segmentation to create multiple mini-chips with standardized structures, each containing n-contact, p-contact, and active region. This modular approach improves current spreading and light extraction while managing complexity through repetition of proven design units. The regular array arrangement (e.g., 3x3 grid) and systematic interconnection patterns further simplify fabrication and design.
Solution Approach 2:
The patent merges multiple mini-chips into a single monolithic device structure, sharing common substrates and epitaxial layers. This combining approach achieves the benefits of improved current spreading and light extraction from multiple small chips while reducing overall device complexity compared to assembling separate chips, as the mini-chips are integrated during the epitaxial growth process rather than being joined afterward.
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 design improves current spreading and light extraction efficiency, reducing voltage requirements and increasing the light output power of high-power UV LEDs by distributing current uniformly across the chip, thereby enhancing their performance and yield.
Implementation Method 1
The n-AlGaN and p-AlGaN structures respectively inject electrons and holes into MQW active-region for light-generation
Implementation Method 2
an n-bridge metal electrically connecting the mini n-contact of each of the mini chips to an n-bonding pad
Implementation Method 3
Nitride compound semiconductors such as InN, GaN, AlN, and their ternary and quaternary alloys depending on alloy composition enable ultraviolet (UV) emissions ranging from 410 nm approximately to 200 nm
Data Source
AI summary
A high-power light-emitting diode is made by monolithically integrating multiple miniature light-emitting chips for improved operation voltage, light extraction efficiency and device yield. The light emitting diode includes a plurality of monolithically integrated mini chips, each of the mini chips has a mini n-contact formed on an n-type structure, a mini p-ohmic contact formed on a p-type structure, and a mini light emitting area defined by the mini p-ohmic contact. An n-bridge metal electrically connecting the mini n-contact of the mini chips to an n-bonding pad, the n-bridge metal is formed on the p-type structure and on sidewall of an opening in the p-type structure and on the active-region.