Moisture-Resistant PL Barrier Layer for CSP LED Color Stability
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Solution Overview
Problem
Current light-emitting devices (LEDs) face challenges in maintaining the optical properties of moisture-sensitive photoluminescent materials due to exposure to oxygen and moisture, which leads to degradation, especially in compact chip scale packaging (CSP) LEDs where size constraints limit effective barrier solutions.
Innovation Solution
A light-emitting device with a layer-by-layer photoluminescent structure comprising a less-moisture-sensitive photoluminescent material as a barrier layer and a moisture-sensitive material, along with a reflective structure and encapsulation layer, to prevent oxygen and moisture penetration, while maintaining a compact form factor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If moisture-sensitive photoluminescent materials are used to achieve narrow FWHM and high color purity, then color rendering and color gamut are improved, but the materials degrade due to oxidation from oxygen and moisture exposure
Solution Approach 1:
A moisture-resistant photoluminescent material is introduced as an intermediary barrier layer between the moisture-sensitive photoluminescent material and the external environment. This intermediary layer allows the moisture-sensitive material to maintain its narrow FWHM and high color purity while protecting it from oxidation by oxygen and moisture, thus resolving the contradiction between color performance and material stability
Solution Approach 2:
The patent creates a composite photoluminescent structure combining a moisture-resistant photoluminescent material with a moisture-sensitive photoluminescent material. The moisture-resistant material serves as both a functional light-converting layer and a protective barrier, while the moisture-sensitive material provides enhanced color purity. This composite structure allows both materials to coexist with the moisture-resistant material protecting the sensitive one from degradation
2Reliability
If encapsulation layers are added to protect photoluminescent materials from moisture, then material degradation is reduced, but device complexity and fabrication cost increase
Solution Approach 1:
The moisture-resistant photoluminescent material is designed to perform multiple functions simultaneously: it converts light from the LED chip to a specific wavelength range and serves as a moisture barrier protecting the moisture-sensitive photoluminescent material. By combining protective and functional roles in a single layer, the patent reduces structural complexity and eliminates the need for separate encapsulation layers
Solution Approach 2:
The patent merges the protective barrier function with the photoluminescent conversion function into a single integrated layer. Instead of having separate encapsulation layers and functional photoluminescent layers, the moisture-resistant photoluminescent material combines both roles, simplifying the overall device structure and reducing fabrication complexity
3Reliability
If encapsulation layers are added to prevent moisture penetration, then material degradation is reduced, but light conversion efficiency decreases
Solution Approach 1:
The moisture-resistant photoluminescent material serves dual purposes as both a protective barrier and an active light-converting element. Unlike traditional encapsulation layers that merely protect but do not contribute to light conversion, this material maintains high photoluminescent efficiency while providing moisture resistance, thus avoiding the energy loss associated with separate encapsulation structures
Solution Approach 2:
The patent employs a composite photoluminescent system where the moisture-resistant material is specifically selected to have both high moisture barrier properties and high photoluminescent quantum efficiency. This ensures that the protective layer does not act as a passive barrier that blocks light, but rather as an active participant in the light conversion process, minimizing energy loss
4Volume of moving object
If chip scale packaging is used to maintain compact form factor, then device size is reduced, but effective barrier solutions against moisture are limited
Solution Approach 1:
The patent applies local quality by using a moisture-resistant photoluminescent material specifically in the region where moisture protection is most critical - the layer directly contacting the moisture-sensitive photoluminescent material. This localized approach provides effective moisture barrier protection in the compact CSP structure without requiring extensive encapsulation throughout the entire device, maintaining small form factor while ensuring reliability
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 reduces the degradation of moisture-sensitive photoluminescent materials by acting as both a light conversion and protective barrier layer, extending the operational lifetime without increasing the package size, thus meeting the requirements of compact LEDs.
Implementation Method 1
The first photoluminescent layer comprises a first photoluminescent material dispersed within a first polymer matrix material... the first photoluminescent layer functions as a barrier layer protecting the underneath second photoluminescent layer from the ambient oxygen and moisture
Data Source
AI summary
A chip scale packaging (CSP) light-emitting device including a light-emitting semiconductor die and a layer-by-layer photoluminescent (PL) structure disposed on the light-emitting semiconductor die is disclosed. The PL structure includes a second PL layer and a first PL layer disposed over the second PL layer, wherein the first PL layer functions as a photoluminescent layer and a barrier layer protecting the second PL from ambient oxygen and moisture. The first PL layer includes a less-moisture-sensitive PL material dispersed within a first polymer matrix material, whereas the second PL layer includes a moisture-sensitive PL material dispersed within a second polymer material. With these arrangements, the outermost first PL layer comprising the less-moisture-sensitive photoluminescent material functions as a wavelength-conversion layer and also serves as a barrier layer protecting the inner second PL layer comprising the moisture-sensitive photoluminescent material from ambient oxygen and moisture. Thus degradation of moisture-sensitive PL material can be reduced.