Sapphire has become an important material in modern technology due to its unique properties and versatile applications. One of its primary uses is in the manufacturing of blue laser diodes (LD) and light-emitting diodes (LEDs). Additionally, sapphire is utilized as a wafer substrate for silicon deposition to produce silicon-on-sapphire (SOS) semiconductors. These applications have driven a significant increase in the demand for sapphire in recent years.
How is Sapphire used in LED Manufacturing?
In LED production, sapphire serves as the substrate, where gallium nitride (GaN) layers are epitaxially grown. GaN is the active layer that emits light, while sapphire provides the structural support and thermal stability required during manufacturing. The high thermal conductivity and excellent optical transparency of sapphire make it an ideal base for LEDs, ensuring efficient heat dissipation and optimal light transmission.
Sapphire also contributes to the overall durability of LEDs. On one hand, its hardness (9), which is very close to that of diamond, protects the LED structure from mechanical damage. On the other hand, its chemical stability ensures resistance to environmental degradation. As the demand for LEDs in applications like displays, automotive lighting, and general illumination continues to grow, sapphire remains a critical material for enabling these innovations.
What is Sapphire Made Of?
Sapphire is a crystalline form of aluminum oxide (Al₂O₃), also known as alumina. It often contains trace amounts of impurity elements like iron and titanium, which give sapphire its characteristic blue color. At the core of sapphire production is high-purity alumina (HPA), a refined form of aluminum oxide with a purity level of 99.99% or higher. HPA is the starting material for the manufacturing of synthetic sapphire crystals through methods such as the Verneuil or Czochralski process.
From High Purity Alumina Powder to Sapphire Substrate
Making high-quality sapphire wafer substrates from HPA powder involves several steps. First, the HPA powder is processed to achieve the right particle size and purity. Next, the powder is used in crystal growth furnaces, where it is melted and solidified into single-crystal sapphire ingots. These ingots are then sliced into wafers, polished, and further processed to create the substrates used in LED manufacturing.
Why is High Purity Alumina Important for Sapphire Substrate Production?
Starting with a high-purity material is key to achieving the desired quality in sapphire substrates, and HPA’s exceptional purity makes it the ideal choice for this process. The high purity of HPA ensures that sapphire crystals grown from it are of the highest quality, free from defects that could affect performance. As a result, the sapphire produced boasts excellent optical and mechanical properties, which are crucial for applications in LEDs and laser diodes.
Another standout property of sapphire, derived from HPA, is its excellent thermal and chemical stability. LEDs operate at high temperatures and often in challenging chemical environments, making sapphire an ideal material for their substrates. The stability provided by HPA ensures that the sapphire can withstand these conditions without degrading, thus maintaining the performance of the LEDs over time.
In addition to its role in sapphire production, HPA is also valued for its environmentally conscious production methods, contributing to more sustainable manufacturing practices. Check more details on our previous blog, “Can High Purity Alumina Be Produced Sustainably?“.
Where else can High Purity Alumina be Used in LED Manufacturing aside from Substrate Fabrication?
High-purity alumina (HPA) is used in several key areas of LED manufacturing beyond substrate fabrication, contributing to improved performance and sustainability:
HPA as Fillers in Thermal Interface Materials for Heat Dissipation in LED Packages
Thermal interface materials (TIMs) are important for transferring heat between the LED base-plate and cooling system, with thermal conductivity being key to effective heat dissipation. HPA is an ideal filler for TIMs due to its excellent thermal conductivity and flow properties. By improving heat dissipation, HPA enhances the sustainability of LED technology, helping maintain optimal temperatures, peak performance, and extending lifespan to about 30,000 hours—equivalent to 12 years of daily use.
HPA as LED Encapsulant
LED encapsulation protects and packages LED chips to enhance their performance and longevity. Common types include epoxy encapsulants, which are cost-effective and transparent but have limited thermal conductivity and may yellow over time; silicone encapsulants, known for their excellent thermal stability and UV resistance but at a higher cost and slightly reduced transparency; and ceramic, offering superior thermal conductivity and mechanical strength, ideal for high-performance LEDs.
Among ceramic options, high purity alumina is particularly effective, providing exceptional thermal conductivity, mechanical strength, and chemical stability. HPA ensures efficient heat dissipation, preventing degradation and yellowing, making it ideal for high-power LED applications that require enhanced thermal management and reliability.
HPA as Coatings for Phosphors in LEDs
Phosphor is a substance that emits light when exposed to radiation, often used in LEDs to convert blue or ultraviolet light into white or specific colors. In LED lighting, phosphors are typically applied to the LED chip to create the desired light spectrum, enabling color tuning and enhancing brightness. High purity alumina is often used to coat phosphor particles, enhancing their stability and protecting them from moisture and chemicals. Its thermal stability ensures phosphors can withstand high temperatures without degradation, while its refractive properties improve light dispersion, resulting in more uniform and consistent lighting.
High Purity Alumina Grades for LED Manufacturing
The purity of alumina used in LED production should be 99.99% (equivalent to Grade 4N) or higher. This exceptionally high purity is important, as even trace impurities can greatly affect the performance and lifespan of LEDs.
| Grade (Purity) | Na | Mg | Si | Ca | Ti | Cu | Cr | Fe | K |
| 3N (99.9%) | <150 | <20 | <50 | <50 | <20 | <10 | <5 | <50 | <20 |
| 4N(99.99%) | <30 | <5 | <10 | <10 | <5 | <5 | <5 | <20 | <10 |
| 5N(99.999%) | <4 | <1 | <3 | <3 | <0.5 | <0.5 | <1 | <1 | <0.5 |
As technology advances, Polar Performance Materials’ finely-tuned high purity alumina products, such as HPA-SDF advanced 5N HPA, with high crystallinity and controlled specific surface area, will play a vital role in emerging optical applications like mini-LED and micro-LED displays.
By integrating the superior performance of 4N and 5N high purity alumina into nanoscale structures or coatings, the miniaturization of optical devices becomes possible. This integration also facilitates compatibility with other technologies, enabling the development of compact, multi-functional LED lighting solutions.
Ready to enhance your LED technology with optimized HPA grades? CAPLINQ can help. Our team specializes in customized solutions to improve performance and efficiency. Reach out today to boost your LED devices!
