Light Receiving Element Bump Design for Thermal Stress
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Solution Overview
Problem
Light receiving elements face damage and size increase due to thermal stress from differing thermal expansion coefficients between the light receiving element and the substrate, which existing technologies fail to adequately address.
Innovation Solution
A light receiving element design featuring a semiconductor substrate with multiple conductivity layers, mesas, terraces, and grooves, along with larger second bumps that provide high joint strength and distribute stress, preventing detachment and size expansion, while minimizing the need for additional reinforcing bumps.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a large number of bumps are formed on the light receiving element to reduce stress, then the stress resistance is improved, but the light receiving element becomes larger in size
Solution Approach 1:
The patent applies different bump sizes at different locations: larger second bumps are placed at the outer peripheral portion where stress concentration occurs, while smaller first bumps are used at the central portion. This local differentiation allows effective stress resistance without increasing the overall element size uniformly.
Solution Approach 2:
The patent uses asymmetric bump distribution with different sizes and locations optimized for stress patterns. The larger second bumps are strategically positioned at the periphery rather than uniformly distributing all bumps, creating an asymmetric configuration that matches the stress distribution pattern and prevents element size increase.
2Area of moving object
If the light receiving element is made smaller to reduce size, then the compactness is improved, but the stress resistance deteriorates
Solution Approach 1:
The patent concentrates stress-mitigating structures (larger second bumps) at the outer peripheral portion where thermal stress is most severe, while keeping the central portion more compact with smaller first bumps. This localized reinforcement maintains stress resistance in a compact overall structure.
Solution Approach 2:
The bump structure is segmented into two types (first bumps at center, second bumps at periphery) with different functions. This segmentation allows the compact central region to maintain light-receiving functionality while the peripheral region provides stress resistance, achieving both compactness and strength.
3Measurement precision
If the light receiving element is operated at low temperature to achieve high S/N ratio, then the detection performance is improved, but the thermal stress increases due to temperature change
Solution Approach 1:
The patent pre-configures larger second bumps at the outer peripheral portion before thermal cycling occurs. These enlarged bumps provide a cushioning effect that absorbs and distributes thermal stress during temperature changes, protecting the light receiving element from damage while enabling low-temperature operation for high S/N ratio.
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 effectively prevents damage from thermal stress and maintains a smaller size for the light receiving element, ensuring reliable operation and efficient infrared light detection.
Implementation Method 1
a light absorbing layer provided on the first layer
Data Source
AI summary
A light receiving element includes: a semiconductor layer including a first layer, a light absorbing layer, a second layer, and a third layer, the semiconductor layer having a plurality of mesas, a terrace, and a groove; a first electrode provided on the mesas and electrically connected to the third layer; a first bump provided on the first electrode and electrically connected to the first electrode; a second electrode provided on a portion extending from the terrace to an inner side of the groove and electrically connected to the first layer; and a second bump larger than the first bump, is provided on the terrace, and is electrically connected to the second electrode, wherein the mesas and the terrace include the semiconductor layer, the groove extends to the first layer, and the second electrode is in contact with the first layer on an inner side of the groove.