Light emitting diodes, LEDs, historically have been used for indicators and produced low amounts of heat. The introduction of high brightness LEDs with white light and monochromatic colors have led to a movement towards general illumination. The increased electrical currents used to drive the LEDs have focused more attention on the thermal paths in the developments of LED power packaging. The luminous efficiency of LEDs is soon expected to reach over 80 lumens/W, this is approximately 6 times the efficiency of a conventional incandescent tungsten bulb. Thermal management for the solid-state lighting applications is a key design parameter for both package and system level. Package and system level thermal management is discussed in separate sections. Effect of chip packages on junction to board thermal resistance was compared for both SiC and Sapphire chips. The higher thermal conductivity of the SiC chip provided about 2 times better thermal performance than the latter, while the under-filled Sapphire chip package can only catch the SiC chip performance. Later, system level thermal management was studied based on established numerical models for a conceptual solid-state lighting system. A conceptual LED illumination system was chosen and CFD models were created to determine the availability and limitations of passive air-cooling.

Thermal management of LEDs: Package to system

Flexible electronics have become an important trend under the environment of informational society. As a result, the utilization of conventional metals and inorganic semiconductors are restricted in the flexible devices...

https://pubs.rsc.org/en/content/articlepdf/2023/ma/d2ma00940d

A review on polymers and their composites for flexible electronics

The distributions of the electroluminescence of AlGaInP-based flip-chip red light-emitting diodes with a size of <inline-formula> <tex-math notation="LaTeX">$100\,\,\mu \text{m}\,\,\times 200\,\,\mu \text{m}$ </tex-math></inline-formula> have been obtained via microscopic hyperspectral imaging by capturing spatially resolved light emission from the side of a transparent substrate. As the injected DC current exceeds the current corresponding to the maximum external quantum efficiency, the light emission from the current crowding region decreases due to the self-heating effect, whereas the emission of the region corresponding to the anode becomes dominant due to the low heat resistance.

Effect of Current on the Inhomogeneous Light Emission From AlGaInP-Based Flip-Chip Red Mini-LEDs

In this paper, we demonstrate that nitride-based R/G/B micro-LEDs allow temperature sensing through a forward voltage response on both temperature and display devices. In temperature sensing, micro...

R/G/B Micro-LEDs for In-Pixel Integrated Arrays and Temperature Sensing

In order to investigate the photoelectric characteristics of 80 × 120 µm2 mini-light-emitting-diodes (mini-LEDs) with sidewall passivation by atomic layer deposition (ALD), this paper uses the techniques of spectrometer-based spectroradiometer and microscopic hyperspectral imaging (µ-HSI). The temperature-dependent electroluminescence is measured using a spectrometer-based spectroradiometer. By analyzing the rising parts of external quantum efficiency at room temperature with a two-level model, the difference of physical mechanisms between mini-LEDs with ALD and without ALD are determined. In addition, the thermal quenching indicates that the ALD sidewall passivation can enhance the temperature stability of the mini-LEDs. The ALD sidewall passivation also enhances the light extraction efficiency according to the theoretical calculation of transmittance. Moreover, the µ-HSI technique is used to evaluate different local areas of mini-LEDs. The obtained results reveal the optimization on lateral distribution of current density within the chip after sidewall passivation.

The impacts of sidewall passivation via atomic layer deposition on GaN-based flip-chip blue mini-LEDs

P-108: Stable Thermal Distribution of Flexible Transparent InGaN/GaN Multiple Quantum Wells Micro-LED Arrays

Temperature-dependent Forward Voltage of AlGaInP-based Red Micro-LEDs

We present studies of the color uniformity and thermal stability of a flexible and transparent ${32}\times {32}$ mini-LED array on polyethylene terephthalate (PET) substrate up to a brightness rating of 5000 nits at room temperature, whose brightness is required for outdoor display applications. Surprisingly, even at 5000 nits, the temperature variation on the surface of the LED array is less than 9 °C, despite the relatively low thermal diffusivity of the polymer substrates. The average surface temperature was 33 °C. This indicates that the heat dissipation of the fabricated LED array is superior with even a polymer substrate. Further, the narrow electroluminescent (EL) emissions from the mini-LED array help to realize wider color gamut than Rec. 2020 color gamut in display applications. The color differences from the EL spectra were calculated at three different brightness. The calculated values are far less than the color discrimination threshold of the human eye corresponding to 0.005 at all testing brightness and meet the display industry requirement for color difference.

Color Difference and Thermal Stability of Flexible Transparent InGaN/GaN Multiple Quantum Wells Mini-LED Arrays

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Papers

P-108: Stable Thermal Distribution of Flexible Transparent InGaN/GaN Multiple Quantum Wells Micro-LED Arrays

Temperature-dependent Forward Voltage of AlGaInP-based Red Micro-LEDs

Color Difference and Thermal Stability of Flexible Transparent InGaN/GaN Multiple Quantum Wells Mini-LED Arrays