SSL Devices with Interlayer CTE Management
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Solution Overview
Problem
Conventional solid state lighting (SSL) devices face issues due to differences in thermal expansion coefficients of their elements, leading to delamination and defects during manufacturing and use, which affect performance and reliability.
Innovation Solution
The implementation of SSL devices with specifically selected thermal expansion coefficients and surface characteristics, including off-cut angles for substrates and interlayer structures, to align crystal structures and reduce defects, and the use of buffer and interlayer materials to manage thermal expansion and stress between layers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional SSL devices are manufactured with standard substrate and layer structures, then manufacturing process is simple, but thermal expansion differences cause delamination and defects
Solution Approach 1:
An intermediate layer is introduced between the substrate and the SSL device layers to act as a buffer that accommodates thermal expansion differences. This intermediary layer prevents direct thermal stress transmission between mismatched materials, thereby preventing delamination and improving device reliability without fundamentally changing the manufacturing process complexity.
Solution Approach 2:
The thermal expansion coefficient parameter is modified by selecting specific substrate orientations (off-cut angles) and materials. By changing the crystallographic orientation of the substrate, the effective thermal expansion coefficient is adjusted to better match the SSL device layers, reducing thermal stress and preventing delamination while maintaining a relatively simple device structure.
2Manufacturing precision
If substrate off-cut angles are optimized to align crystal structures, then manufacturing precision and device performance improve, but manufacturing process complexity increases
Solution Approach 1:
The substrate orientation parameter (off-cut angle) is optimized to specific values that align the crystal structures of the substrate and SSL device layers. This parameter change improves manufacturing precision by ensuring better lattice matching and reducing dislocation density, while the change itself is a straightforward process modification rather than a complex procedural addition.
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 approach enhances the uniformity and alignment of crystal structures, reduces defects, and improves the reliability and efficiency of SSL devices by controlling thermal expansion and stress, thereby improving the overall performance and manufacturability of the devices.
Implementation Method 1
the various elements of the SSL devices typically have different coefficients of thermal expansion (CTE). During temperature excursions that occur in manufacturing processes and/or during use, the difference in CTEs of the device elements may cause the elements to delaminate.
Implementation Method 2
several elements of the SSL device are grown epitaxially on the substrate 20
Data Source
Figure 1A~1B
Figure 2A~2B
Figure 2C
AI summary
Solid state lighting devices with selected thermal expansion and/or surface characteristics, and associated methods are disclosed. A method in accordance with a particular embodiment includes forming an SSL (solid state lighting) formation structure having a formation structure coefficient of thermal expansion (CTE), selecting a first material of an interlayer structure to have a first material CTE greater than the substrate CTE, and selecting a second material of the interlayer structure based at least in part on the second material having a second material CTE less than the first material CTE. The method can further include forming the interlayer structure over the SSL formation structure by disposing (at least) a first layer of the first material over the SSL formation structure, a portion of the second material over the first material, and a second layer of the first material over the second material. The SSL formation structure supports an SSL emitter material, and the method further includes counteracting a force placed on the formation structure by the first material, by virtue of the difference between the second material CTE and the first material CTE. In other embodiments, the SSL formation structure can have an off-cut angle with a non-zero value of up to about 4.5 degrees.