MicroLED Innovations

MicroLED Fabrication: Thermal Management Challenge for High-Brightness Displays

Team MicroLED Innovations

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MicroLED Fabrication

Introduction

The microLED market is gaining traction compared to LCD and OLED displays.

Globally, the MicroLED market was at a valuation of $610.7 million in 2021. This is projected to grow at a CAGR of 80.8% from 2022 to 2030. By 2030, it can reach an estimated value of $35,470 million. 

But as we are moving ahead, there are certain challenges that need to be addressed that’s typically associated with this technology. One such issue is managing heat in the fabrication of high-brightness displays. This is because it increases power consumption and overall heat production as well. Unfortunately, usual cooling solutions, such as fans and heat sinks, are not enough for this task due to their compact size.

This article will investigate the challenges of thermal management in microLED fabrication and explore the possible solutions.

MicroLED Fabrication Thermal Management: Existing Methods and Challenges 

Below are the common thermal management methods in the MicroLED fabrication process and their existing solutions. 

Method: Heat Dissipation Enhancement in MicroLED Display Panels

  • Solution: This method uses pixel units that have driving circuits between the substrate and light-emitting elements. A metal structure is coupled to a thin-film transistor in the circuitry of the microLED units. This connection dissipates heat from the microLED, away from the substrate, and onto the metal layer.
  • Limitations: Although it improves heat dissipation, improvement is needed for high-power applications.

Method: Innovative Thermal Diffusion Technology for Uniform Lighting in MicroLED Displays

  • Solution:This innovation uses a backlight unit for displays that use mini-LEDs or microLEDs. This backlight design addresses two challenges:
    • Converting LED light for color accuracy and 
    • Achieving uniform light distribution across the display. 

It uses a color conversion sheet to adjust the LED light spectrum. Then, it uses two diffusion lens sheets with microscopic pyramid patterns to scatter the light and reduce hot spots.

  • Limitations: It does not directly address the heat generated by the microLEDs. 

Method: In-Pixel Temperature Sensing Using Off Currents in MicroLED Displays

  • Solution: This temperature sensing circuit monitors pixel temperature in high-brightness microLED displays. Within the pixel circuitry, it makes use of the temperature-dependent off currents of two distinct thin film transistors. The pixel temperature can be determined by measuring the difference in off current between the transistors.
  • Limitations: It does not actively cool the microLEDs. 

Method: MicroLED Display Module with Enhanced Luminance and Heat Dissipation

  • Solution: This display module includes luminance and heat emission for microLED fabrication. Its substrate, which is encircled by a layer that blocks light and reflects light, contains microLEDs. The reflective coating aids in rerouting light coming from the microLED’s side in a forward direction. By stopping light leakage, the light-blocking layer improves light efficiency and uses less energy. 
  • Limitations: Not suitable for high-power applications.

Proposed Solutions for MicroLED Fabrication Thermal Management

The solutions for microLED fabrication can be broadly categorized into three areas: 

  • Engineered Substrates, 
  • Thermally Optimized Device Architectures and 
  • Advanced Thermal Packaging Solutions.

Engineered Substrates

These are innovations in substrate materials that can rapidly conduct heat laterally over larger surface areas. These include:

  • Single Crystal Diamond: With unprecedented thermal conductivity, diamond substrates can reduce temperature increase in high-power density microLEDs.
  • CVD Graphene Films: Chemical vapor deposition generates atomically thin graphene sheets that are optically transparent and exhibit very high in-plane heat conductivity.
  • High Conductivity Polymer Composites: Reinforcing polymer matrixes with fillers like boron nitride or graphite nanoparticles creates composite substrates with thermal conductivities superior to metals.

Thermally Optimized Device Architectures

These are structural designs conducting heat away from the thermally sensitive p-n junction. They include:

  • Integrated Microchannel Coolant Arrays: A monolithic amalgamation of tiny heat pipes or sealed microchannels with circulating coolant fluids provides active junction cooling to minimize temperature rises.
  • High Aspect Ratio Pillar Designs: Fabricating narrow, tall LED pillars increases junction surface area, reducing thermal resistance.
  • Dual-Purpose Photonic Crystal Cavities: MicroLED fabrications with periodic photonic crystal resonant cavity patterns enhance light extraction efficiency.

Advanced Thermal Packaging Solutions

These are innovative packaging techniques for effective heat removal. They include:

  • Optimized Micro-Pinfin Heatsinks: High-density arrays of micromachined pin fins precisely tuned to match underlying heat patterns maximize thermal contact and heat transfer rate.
  • Phase Change Materials: Encapsulants with high latent heat absorb and dampen transient thermal spikes during high brightness operation, improving mean time to failure.

Experimental Results Regarding Thermal Management In MicroLED Fabrication

Here are some key findings from recent studies:

Monolithic Integration of GaN-Based Transistors and MicroLED

This study focused on the integration of microLEDs with different types of transistors, including BJT, HEMT, TFT, and MOSFET. Theoretical models were used to support and interpret experimental results, providing a framework within which experimental observations can be understood and explained.

Efficiency Boosting by Thermal Harvesting in InGaN/GaN Light-Emitting Diodes

In this work, two different LED groups were designed: Group A is two LEDs bonded together for heat transmission, and Group B is two LEDs separated from each other. 

In each group, the two LEDs were run in a vacuum chamber at one fixed and one tunable biassed voltage, respectively. An experimental and numerical analysis was conducted on the two groups’ respective efficiency. 

According to the experimental results, Group A’s optical output power can be improved by up to 15.36% when compared to Group B. 

The fundamental cause is that, in Group A, the heat transmission by the LED under a high biassed voltage causes the wall-plug efficiency of the LED with a voltage lower than photon voltage (V < ℏω/q) to be remarkably boosted by elevated temperature. Because of its lower temperature, the LED in Group A with a highly biased voltage reduces thermal droop and increases total efficiency even further. 

Device temperature measurement and numerical calculation of radiative recombination under different temperatures further support the superior performance of Group A LEDs.

End Note 

After evaluating the existing and proposed solutions for thermal management in MicroLED fabrication, engineered substrates stand out as the most promising. In particular, single-crystal diamond and CVD graphene films offer exceptional potential. Their exceptional thermal conductivity and ability to dissipate heat efficiently make them ideal for high-power applications. Future research should focus on refining these materials to further enhance their thermal properties.

Moreover, combining these advanced substrates with thermally optimized device architectures can provide a comprehensive approach to heat management. This synergistic application can significantly improve the efficiency and reliability of MicroLED displays. The use of phase change materials and optimized micro-pinfin heatsinks in thermal packaging also holds significant potential.