The microLED substrate is the foundational layer that directly impacts the quality, scalability, and cost of microLED displays—critical factors for manufacturers aiming for a wider market reach.

For example, NSC Innovation uses an advanced 200mm GaN-on-silicon solution for AR and VR displays. They monolithically integrated silicon CMOS with GaN LEDs at full wafer scale, enabling widespread adoption of microdisplays.

However, selecting an ideal microLED substrate remains challenging. GaN-on-Silicon and transparent glass are cost-effective substrates, but can manufacturers improve yield and reduce costs? Let’s find out.

The Role of Substrates in MicroLED Displays

MicroLED substrates ensure that each LED within a display is properly aligned, stable, and efficient in light output. Proper alignment minimizes irregularities in the image and enhances the stability of the microLEDs by reducing thermal and mechanical stress.

 A study on MicroLED display quality improvements showed that precision substrates improve pixel alignment accuracy by up to 99.9%, significantly reducing visual artifacts like moiré patterns and color banding.

Performance Impact of Substrates 

The substrate material influences three key performance aspects:

1. Light emission efficiency: The substrate must enable effective light transmission while minimizing energy loss. This helps achieve brighter displays without excessive power consumption.
2. Thermal management: Since microLEDs operate at high temperatures, substrates need to dissipate heat efficiently to ensure durability and maintain performance over time.
3. Yield and scalability: High-quality substrates reduce production defects, leading to better yield rates and scalable manufacturing processes. Reducing defect rates helps microLED displays compete with existing OLED technology.

5 Types of Cost-Effective MicroLED Substrates

Here are the major types of substrates that offer unique benefits and challenges for cost-effective and scalable display manufacturing:

1. Glass

Glass substrates are affordable, transparent, and easy to work with. They are ideal for large microLED displays.

• Widely available and compatible with many existing display technologies
• Less durable than other materials for high-performance applications

For example, X-Celeprint uses glass as a target substrate for micro-transfer printing, combining different, non-native components on a single substrate.

2. Silicon

Silicon substrates offer excellent structural integrity. They are ideal for compact, high-resolution displays like smartwatches and VR headsets. 

Also, high-resolution microLED displays on silicon substrates achieve pixel densities exceeding 2,000 PPI, compared to OLED displays, which average around 500–700 PPI for similar applications. 

• Well-supported by an established supply chain, thereby reducing manufacturing costs
• Suitable for smaller displays due to its limited light emission efficiency
• Silicon has a high thermal conductivity of approximately 149 W/m·K, compared to 1.1 W/m·K for glass. This conductivity allows for effective heat dissipation, which is crucial in compact devices 

3. Gallium Nitride (GaN)

GaN substrates can enhance microLED performance, including high electron mobility and wide-bandgap efficiency. They are ideal for ultra-bright displays by enabling superior brightness with minimal energy loss.

Also, GaN substrates maintain stability and efficiency under high temperatures, with a thermal conductivity of about 253±8.8% W/m·K—significantly higher than materials like glass or sapphire.

• Resilient under high temperatures and stress
• Expensive and more suitable for specialized displays than broader mass-market use

4. GaN-on-Silicon Substrate

GaN-on-Silicon substrate is a cost-effective alternative to GaN microLED displays. This hybrid substrate combines the high performance of GaN while being affordable and scalable. 

It also aligns with existing semiconductor production methods so you can scale production more efficiently.

• Durable and possesses excellent thermal stability
• Suitable for high-performance displays in outdoor environments

Companies like Porotech are mass-producing microLEDs on 200-mm gallium nitride (GaN)-on-silicon for consumer display applications.

Each microLED substrate offers a distinct balance between performance and cost, with unique strengths and limitations. Weigh these factors before selecting a suitable substrate for the intended application and display size. 

5. Sapphire Substrate for Performance

Sapphire substrates offer excellent durability, high thermal conductivity, and mechanical strength. They transmit light without darkening under UV radiation, making it a good choice for displays.

• Expensive but can withstand harsh environmental factors
• Supports fine pixel structures and is suitable for small form-factor displays

Some Emerging MicroLED Substrates

Besides these, researchers are exploring new substrate materials to lower costs and enhance production efficiency. 

• Materials like sulfur and transparent glass are suitable substrate options, as they are affordable and compatible with existing microelectronics manufacturing processes. 

Transparent glass allows over 90% light transmission in the visible spectrum, which is beneficial for enhancing brightness.

• Sulfur-based substrates are readily available and could contribute to energy-efficient displays. Initial studies show promising results, with sulfur-based coatings maintaining up to 85% of their light-enhancing effects after 1,000 hours of accelerated aging tests.

However, they emit less light than high-performance substrates and are only suitable for displays with lower brightness requirements.

• While sulfur substrates are still under R&D, companies like Tianma and PlayNitride have developed transparent microLED displays.
  
• Did you know Samsung also unveiled its transparent microLED display at the Consumer Electronics Show (CES) 2024 in Las Vegas? 

The display incorporates a unique transparent glass substrate that creates a nearly invisible screen, enhancing the floating effect and allowing viewers to see through it.

Latest Techniques for High-Yield Production

Advanced manufacturing techniques like epitaxial growth on transparent glass and silicon carbide substrates help reduce substrate costs. 

These techniques improve yield by minimizing material waste and maximizing production output. 

You can create high-quality microLED displays at a fraction of the traditional cost.

Innovations in material science like 3D printing, metamaterials, and nanotechnology enable cost-effective, high-performance substrates that can be produced at scale.

Scaling MicroLED Production through Substrate Innovations

There must be an increased focus on leveraging established fabrication processes to streamline microLED production. With mature mass-transfer processes, you can yield more displays at a lower cost per unit. 

Here are a few techniques:

1. LIFT

Laser Induced Forward Transfer (LIFT) technique uses an excimer laser to precisely transfer LED dies onto display panels. LIFT achieves highly accurate placement of dies smaller than 20 µm x 20 µm, making it effective for high-resolution displays. This method reduces costs while maintaining quality in microLED displays.

2. LLO

The Laser Lift Off technique separates the microLEDs from their growth substrates and transfers them to a temporary carrier for easier handling. This allows for high-volume and precision die handling. 

3. Transfer and Repair

After the dies are transferred to the panel, additional techniques, such as transfer and repair, ensure the correct placement of each die. 

By combining LLO, LIFT, and other techniques like transfer and repair, you can achieve high yields and reduced costs, making microLED technology more viable for large-scale production.

Final Note

Adopting cost-effective microLED substrates offers a competitive edge in the rapidly evolving display market. In 2023, the US microLED market reached an estimated $138.25 million, reflecting the high demand for this technology. 

Ongoing innovation will lower production costs and expand the potential applications for microLED technology, making it more accessible and versatile across a wide range of consumer electronics and industries.

As technology advances, research into new materials and manufacturing processes will likely lead to even more cost-effective, efficient, and adaptable substrates for microLED displays.