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Micromachines
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Micro-Light Emitting Diode: From Chips to Applications
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Micro-Light Emitting Diode: From Chips to Applications

A special issue of Micromachines (ISSN 2072-666X). This special issue belongs to the section "D1: Semiconductor Devices".

Deadline for manuscript submissions: closed (30 May 2023) | Viewed by 15576

Special Issue Editor

Prof. Dr. Meng-Chyi Wu

E-Mail Website
Guest Editor
Institute of Electronics Engineering, National Tsing Hua University, Hsinchu 30013, Taiwan
Interests: MicroLED; high-frequency LED; power HEMT and RF HEMT; miniaturized near-infrared spectroscopic modules

Special Issue Information

Dear Colleagues,

MicroLEDs have been considered the most promising technique for next-generation displays due to their fast response, high resolution, high brightness level, high contrast ratio, long lifetime, and low power consumption compared to traditional displays, such as liquid crystal display (LCD) and organic light-emitting diode (OLED) display. MicroLEDs can be widely applied in wearable devices, head-mounted devices, pico-projectors, near-to-eye (such as augmented reality (AR) and virtual reality (VR)) microdisplays, and visible light communication. Recently, MicroLEDs have been in the spotlight for future biomedical devices, such as biosensors, pulse oximetry (SpO2) sensors, and optogenetic stimulators. Accordingly, this Special Issue seeks to showcase research papers and review articles that focus on novel technique developments in MicroLED chips, single color/full color microdisplays, and related applications.

We look forward to receiving your submissions!

Prof. Dr. Meng-Chyi Wu
Guest Editor

Manuscript Submission Information

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Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2600 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • MicroLED
  • MicroLED display
  • high pixel density array
  • active matrix
  • full color display
  • colloidal quantum dots
  • monolithic integration
  • flip-chip bonding
  • transfer technology
  • MicroLED applications

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Published Papers (5 papers)

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Research

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12 pages, 4649 KiB  
Article
The Size-Dependent Photonic Characteristics of Colloidal-Quantum-Dot-Enhanced Micro-LEDs
by Kai-Ling Liang, Wei-Hung Kuo, Chien-Chung Lin and Yen-Hsiang Fang
Micromachines 2023, 14(3), 589; https://doi.org/10.3390/mi14030589 - 28 Feb 2023
Cited by 1 | Viewed by 2348
Abstract
Colloidal CdSe/ZnS quantum dots (QD) enhanced micro-LEDs with sizes varying from 10 to 100 μm were fabricated and measured. The direct photolithography of quantum-dot-contained photoresists can place this color conversion layer on the top of an InGaN-based micro-LED and have a high throughput [...] Read more.
Colloidal CdSe/ZnS quantum dots (QD) enhanced micro-LEDs with sizes varying from 10 to 100 μm were fabricated and measured. The direct photolithography of quantum-dot-contained photoresists can place this color conversion layer on the top of an InGaN-based micro-LED and have a high throughput and semiconductor-grade precision. Both the uncoated and coated devices were characterized, and we determined that much higher brightness of a QD-enhanced micro-LED under the same current level was observed when compared to its AlGaInP counterpart. The color stability across the device sizes and injection currents were also examined. QD LEDs show low redshift of emission wavelength, which was recorded within 1 nm in some devices, with increasing current density from 1 to 300 A/cm2. On the other hand, the light conversion efficiency (LCE) of QD-enhanced micro-LEDs was detected to decrease under the high current density or when the device is small. The angular intensities of QD-enhanced micro-LEDs were measured and compared with blue devices. With the help of the black matrix and omnidirectional light emission of colloidal QD, we observed that the angular intensities of the red and blue colors are close to Lambertian distribution, which can lead to a low color shift in all angles. From our study, the QD-enhanced micro-LEDs can effectively increase the brightness, the color stability, and the angular color match, and thus play a promising role in future micro-display technology. Full article
(This article belongs to the Special Issue Micro-Light Emitting Diode: From Chips to Applications)
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11 pages, 10661 KiB  
Article
Investigations of Sidewall Passivation Using the Sol-Gel Method on the Optoelectronic Performance for Blue InGaN Micro-LEDs
by Wenjun Huang, Xiangyu Miao and Zhaojun Liu
Micromachines 2023, 14(3), 566; https://doi.org/10.3390/mi14030566 - 27 Feb 2023
Cited by 4 | Viewed by 2380
Abstract
The optoelectronic effects of sidewall passivation on micro-light-emitting diodes (Micro-LEDs) were investigated using sol-gel chemical synthesis. Blue InGaN/GaN multi-quantum well (MQW) Micro-LEDs, ranging in size from 20 × 20 μm to 100 × 100 μm and with high EQE, were fabricated and distinguished [...] Read more.
The optoelectronic effects of sidewall passivation on micro-light-emitting diodes (Micro-LEDs) were investigated using sol-gel chemical synthesis. Blue InGaN/GaN multi-quantum well (MQW) Micro-LEDs, ranging in size from 20 × 20 μm to 100 × 100 μm and with high EQE, were fabricated and distinguished by the passivation method used, including no passivation, sol-gel SiO2, and plasma-enhanced chemical vapor deposition (PECVD) SiO2. Impressively, the sol-gel method is advantageous in improving the optoelectronic performance of Micro-LEDs. The fabricated 20 × 20 μm Micro-LEDs showed an EQE of 27.7% with sol-gel passivation, which was a 14% improvement compared to devices without sidewall passivation. Sol-gel sidewall passivation allows Micro-LEDs to effectively achieve sharper edge emission, superior surface luminous uniformity, and intensity, providing the possibility for the fabrication of low-cost and high-efficiency Micro-LEDs. Full article
(This article belongs to the Special Issue Micro-Light Emitting Diode: From Chips to Applications)
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15 pages, 4809 KiB  
Article
Comprehensive Investigation of Electrical and Optical Characteristics of InGaN-Based Flip-Chip Micro-Light-Emitting Diodes
by Chang-Cheng Lee, Chun-Wei Huang, Po-Hsiang Liao, Yu-Hsin Huang, Ching-Liang Huang, Kuan-Heng Lin and Chung-Chih Wu
Micromachines 2023, 14(1), 9; https://doi.org/10.3390/mi14010009 - 21 Dec 2022
Cited by 2 | Viewed by 2580
Abstract
Micro-light-emitting diodes (micro-LEDs) have been regarded as the important next-generation display technology, and a comprehensive and reliable modeling method for the design and optimization of characteristics of the micro-LED is of great use. In this work, by integrating the electrical simulation with the [...] Read more.
Micro-light-emitting diodes (micro-LEDs) have been regarded as the important next-generation display technology, and a comprehensive and reliable modeling method for the design and optimization of characteristics of the micro-LED is of great use. In this work, by integrating the electrical simulation with the optical simulation, we conduct comprehensive simulation studies on electrical and optical/emission properties of real InGaN-based flip-chip micro-LED devices. The integrated simulation adopting the output of the electrical simulation (e.g., the non-uniform spontaneous emission distribution) as the input of the optical simulation (e.g., the emission source distribution) can provide more comprehensive and detailed characteristics and mechanisms of the micro-LED operation than the simulation by simply assuming a simple uniform emission source distribution. The simulated electrical and emission properties of the micro-LED were well corroborated by the measured properties, validating the effectiveness of the simulation. The reliable and practical modeling/simulation methodology reported here shall be useful to thoroughly investigate the physical mechanisms and operation of micro-LED devices. Full article
(This article belongs to the Special Issue Micro-Light Emitting Diode: From Chips to Applications)
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9 pages, 2805 KiB  
Article
3200 ppi Matrix-Addressable Blue MicroLED Display
by Meng-Chyi Wu, Ming-Che Chung and Cheng-Yeu Wu
Micromachines 2022, 13(8), 1350; https://doi.org/10.3390/mi13081350 - 19 Aug 2022
Cited by 14 | Viewed by 3531
Abstract
In this article, an active matrix (AM) micro light-emitting diode (MicroLED) display with a resolution of 1920 × 1080 and a high pixel density of 3200 pixels per inch (ppi) is reported. The single pixel with a diameter of 5 μm on the [...] Read more.
In this article, an active matrix (AM) micro light-emitting diode (MicroLED) display with a resolution of 1920 × 1080 and a high pixel density of 3200 pixels per inch (ppi) is reported. The single pixel with a diameter of 5 μm on the MicroLED array exhibits excellent characteristics, including a forward voltage of 2.8 V at 4.4 μA, an ideality factor of 1.7 in the forward bias of 2–3 V, an extremely low leakage current of 131 fA at −10 V, an external quantum efficiency of 6.5%, and a wall-plug efficiency of 6.6% at 10.2 A/cm2, a light output power of 28.3 μW and brightness of 1.6 × 105 cd/m2 (nits) at 1 mA. The observed blue shift in the electroluminent peak wavelength is only 6.6 nm from 441.2 nm to 434.6 nm with increasing the current from 5 μA to 1 mA (from 10 to 5 × 103 A/cm2). Through flip-chip bonding technology, the 1920 × 1080 bottom-emitting MicroLED display through the backside of a sapphire substrate can demonstrate high-resolution graphic images. Full article
(This article belongs to the Special Issue Micro-Light Emitting Diode: From Chips to Applications)
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Review

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21 pages, 7962 KiB  
Review
Recent Advances in Micro-LEDs Having Yellow–Green to Red Emission Wavelengths for Visible Light Communications
by Konthoujam James Singh, Wei-Ta Huang, Fu-He Hsiao, Wen-Chien Miao, Tzu-Yi Lee, Yi-Hua Pai and Hao-Chung Kuo
Micromachines 2023, 14(2), 478; https://doi.org/10.3390/mi14020478 - 18 Feb 2023
Cited by 8 | Viewed by 3491
Abstract
Visible light communication (VLC), which will primarily support high-speed internet connectivity in the contemporary world, has progressively come to be recognized as a significant alternative and reinforcement in the wireless communication area. VLC has become more popular recently because of its many advantages [...] Read more.
Visible light communication (VLC), which will primarily support high-speed internet connectivity in the contemporary world, has progressively come to be recognized as a significant alternative and reinforcement in the wireless communication area. VLC has become more popular recently because of its many advantages over conventional radio frequencies, including a higher transmission rate, high bandwidth, low power consumption, fewer health risks, and reduced interference. Due to its high-bandwidth characteristics and potential to be used for both illumination and communications, micro-light-emitting diodes (micro-LEDs) have drawn a lot of attention for their use in VLC applications. In this review, a detailed overview of micro-LEDs that have long emission wavelengths for VLC is presented, along with their related challenges and future prospects. The VLC performance of micro-LEDs is influenced by a number of factors, including the quantum-confined Stark effect (QCSE), size-dependent effect, and droop effect, which are discussed in the following sections. When these elements are combined, it has a major impact on the performance of micro-LEDs in terms of their modulation bandwidth, wavelength shift, full-width at half maximum (FWHM), light output power, and efficiency. The possible challenges faced in the use of micro-LEDs were analyzed through a simulation conducted using Crosslight Apsys software and the results were compared with the previous reported results. We also provide a brief overview of the phenomena, underlying theories, and potential possible solutions to these issues. Furthermore, we provide a brief discussion regarding micro-LEDs that have emission wavelengths ranging from yellow–green to red colors. We highlight the notable bandwidth enhancement for this paradigm and anticipate some exciting new research directions. Overall, this review paper provides a brief overview of the performance of VLC-based systems based on micro-LEDs and some of their possible applications. Full article
(This article belongs to the Special Issue Micro-Light Emitting Diode: From Chips to Applications)
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