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(a) Schematic diagram of the micro-LED array, illustrating the metal lines running across the " sloped sidewalls. " (b) Optical microphotograph (x1000 magnification) showing a fabricated device.
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Matrix-addressable arrays of InGaN micro-light-emitting diodes with 128 × 96 pixels and a resolution of 1200 dpi have been fabricated using a novel "sloped sidewall" process. The devices have been fabricated on InGaN blue and green wafers, emitting light at the wavelengths of 468 and 508 nm, respectively. A simple circuit, which enables the display...
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... surface of each individual pixel is subsequently ex- posed for contact formation by liftoff. The remaining masking steps are for metal deposition of the current-spreading layer (Ni-Au, 30/30 nm, thermally evaporated), p-region intercon- nect metal lines (Au, 200 nm, sputtered), and n-region bonding pads (Ti-Al, 20/200 nm, thermally evaporated). Fig. 1(a) de- picts the Au metal lines running conformally across the sloped sidewall columns. The contacts were subjected to rapid thermal annealing at 500 for 5 min in air after deposition of the cur- rent spreading layer, and again in N for 30 s at 500 at the completion of device fabrication. Fig. 1(b) shows a microphoto- graph (at a ...
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... pads (Ti-Al, 20/200 nm, thermally evaporated). Fig. 1(a) de- picts the Au metal lines running conformally across the sloped sidewall columns. The contacts were subjected to rapid thermal annealing at 500 for 5 min in air after deposition of the cur- rent spreading layer, and again in N for 30 s at 500 at the completion of device fabrication. Fig. 1(b) shows a microphoto- graph (at a magnification of 1000 x) of a region of a fabricated ...
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... The size of lightemitting units can be reduced to the micron scale through rational process design. Kansas State University and the University of Strathclyde are two of the pioneers of research on micro-LEDs [95][96][97][98][99]. HR color technologies endow devices with micron-scaled colorful LED pixel arrays and allow for the manufacture of HR color displays [100][101][102][103]. ...
... Then, the sub-strate covered with the developed photoresist film is ion-etched to obtain the designed pattern, after which the remaining photoresist is removed [81][82][83][84][85]. Fig. 2b shows a flow diagram of a typical micro-LED fabrication process based on photolithography and dry-etching. Micro-LED displays developed before 2010 were monochromatic, with the highest resolution of 128 × 96 (fabricated by Choi et al. [97] in 2004), the smallest pixel size of 8 μm, and the highest pixel density of 1295 dots per inch (DPI) [86][87][88][89][90][91][92][93][95][96][97][98][99]. As the manufacturing level developed, Ou et al. [42] from Hong Kong Beida Jade Bird Display Limited fabricated a monochromatic active-matrix (AM) micro-LED display (Fig. 2c) with a pixel density of 5080 DPI and a resolution of 2560 × 1920 in 2018. ...
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... Microdisplays featuring high resolution and aperture ratios of emitting pixels have the potential to revolutionize the near-to-eye applications ranging from healthcare and military to personal entertainment [1][2][3][4][5][6]. The first commercial microdisplay, which combined inorganic light-emitting diode backlights and liquid crystal displays [7][8][9], had a relatively low field angle and a relatively small field of view, making them unsuitable for various applications. ...
The effective reflective anode remains a highly desirable component for the fabrication of reliable top-emitting organic light-emitting diodes (TE-OLEDs) which have the potential to be integrated with complementary metal-oxide-semiconductor (CMOS) circuits for microdisplays. This work demonstrates a novel laminated anode consisting of a Cr/Al/Cr multilayer stack. Furthermore, we implement an ultra-thin titanium nitride (TiN) layer as a protective layer on the top of the Cr/Al/Cr composite anode, which creates a considerably reflective surface in the visible range, and meanwhile improves the chemical stability of the electrode against the atmosphere or alkali environment. Based on [2-(2-pyridinyl-N)phenyl-C](acetylacetonate)iridium(III) as green emitter and Mg/Ag as transparent cathode, our TE-OLED using the TiN-coated anode achieves the maximum current efficiency of 71.2 cd/A and the maximum power efficiency of 66.7 lm/W, which are 81% and 90% higher than those of the reference device without TiN, respectively. The good device performance shows that the Cr/Al/Cr/TiN could function as a promising reflective anode for the high-resolution microdisplays on CMOS circuits.
... For example, the spacing and pitch of the transferred objects can be tuned based on an individual user's need. An example of applications that require programmable assembly is the microscale light-emitting diode (Micro-LED) display 7,22,24,29,34,35 , which has received intense research interest from the display industry, because of its high brightness, low power consumption, and fast switching speed. For this particular application, millions of Micro-LED chips with size down to a few tens of microns must be prepared densely on source wafers for cost savings and then transfer and printed onto a driven backplane with desired layouts in a relatively sparse form. ...
Large-area, programmable assembly of diverse micro-objects onto arbitrary substrates is a fundamental yet challenging task. Herein a simple wafer-level micro-assembly technique based on the light-triggered change in both surface topography and interfacial adhesion of a soft photo-sensitive polymer is proposed. In particular, the light-regulated polymer growth creates locally indented and elevated zones on the stamp surface. The light-mediated adhesion reduction, on the other hand, facilitates the inks to be released from the polymer. The interplay of these two effects makes it feasible for the programmable assembly of ultra-small components onto various substrates coated with supplementary adhesive layers. The fidelity of this technique is validated by assembling diverse materials and functional devices, with the printing size up to 4-inch. This work provides a rational strategy for large-scale and programmable assembly of diverse delicate micro-objects, bypassing the common issues of some existing techniques such as poor transfer uniformity, small printing area, and high cost.
... Le développement des procédés technologiques pour fabriquer et reporter les micro-LEDs sur des circuits CMOS ont permis de démontrer que les micro-écrans nitrures peuvent atteindre des luminances bien supérieures aux LCDs et OLEDs tout en maintenant de très bonnes performances sur de larges gammes de température [36]. En 2004, Choi et al. [58] ont développé des matrices adressables monolithiques bleue et verte de 128 x 96 micro-LEDs, avec des performances de luminosité améliorées par rapport aux LEDs organiques. Très récemment, Yadavalli et al. [59] ont fait la démonstration d'un micro-écran full-color basé sur l'intégration monolithique de micro-LEDs de 5 à 10 µm sur un circuit CMOS. ...
Cette thèse est consacrée à l’épitaxie sélective en phase vapeur aux organométalliques de multipuits quantiques InGaN/GaN pour la fabrication de micro-écrans émissifs. Les LEDs InGaN/GaN sont un candidat idéal pour cette application, notamment en raison de leur forte luminosité et leur grande fiabilité qui permet un haut rendement avec une faible consommation.A ce jour, le grand défi des écrans émissifs est la réalisation d'un dispositif intégrant des pixels rouge, vert et bleu avec un pas inférieur à 10 µm. L’objectif de cette thèse est de développer des structures à multipuits quantiques InGaN/GaN émettant à différentes longueurs d’onde en utilisant l'épitaxie sélective en phase vapeur aux organométalliques. Cette technique consiste à masquer partiellement la surface du substrat avec une couche de matériau amorphe. Lors de la croissance, les espèces en phase gazeuse ne se déposent pas sur le diélectrique et migrent vers les ouvertures définies en amont dans le masque. Il est ainsi possible d'obtenir lors d'une même croissance des puits InGaN présentant des épaisseurs différentes, et donc des émissions de différentes couleurs.L’étude présentée dans ce manuscrit s'articule autour de la croissance, la modélisation numérique basée sur la diffusion de particules en phase vapeur et en surface, et la caractérisation des empilements épitaxiés sélectivement. Nous étudions en premier lieu le dépôt du composé binaire GaN et de l’alliage InGaN avec un masque diélectrique afin de définir les conditions de croissances autorisant une bonne sélectivité.Dans un second temps, nous étudions la croissance localisée de multipuits quantiques InGaN/GaN, et en particulier l’influence des effets de la croissance sélective sur les propriétés des structures en fonction des paramètres de croissance et de la géométrie du masque utilisé. Nous démontrons notamment une modulation étendue de la longueur d’onde d’émission mesurée par photoluminescence, de 405 à 608 nm dans des zones de recroissance de 3 µm obtenue en une seule croissance localisée à 805 °C, permettant d’envisager l’utilisation de cette technique dans la fabrication d’écrans émissifs.
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... 微型发光二极管(MicroLED, μLED)是将传统LED 的像素点从毫米级降低至微米级, 并在单个芯片上将 驱动电路与像素点高度集成的新一代无机自发光显示 技术 [1] , 其像素尺寸通常不超过100 μm或50 μm, 每一 个像素都能独立定址和单独发光. MicroLED的概念最 早由Jiang等人 [ 2 ] 提出, 相比LCD与OLED显示器, MicroLED具有分辨率更高、功耗更低、寿命更长、 响应快速和高可靠性等优势 [3] , 在高分辨率显示 [4] 、可 穿戴/可植入光电设备 [5] 、光通信 [6] 、生物医学检测 [7] 等许多领域具有广泛的应用前景. ...
... The typical GaN LED structure, consisting of a p-n junction with multi-quantum wells (MQWs) in between, can potentially be a very versatile platform apart from serving the function of a plain monochromatic LED emitter. Using a variety of top-down processes without involving re-growth, devices of other functionalities can be fabricated on that same wafer, including microdisplays [7], microdisk lasers [8] as well as phosphor-free broadband and white-light LEDs [9]. Subsequently, the monolithic integration of two or more of such devices have also been demonstrated, including the integration of LEDs and photodetectors for on-chip visible light communication [10] and the integration of waveguides with microdisk lasers to facilitate mode out-coupling [8]. ...
... For rapid prototyping, the emitter region is patterned by nanosphere lithography while the dimensions of the other regions are retained. Nanosphere lithography has been proven to be a versatile way of fabricating nanostructured devices as demonstrated by our previous studies [7,9]. With an array of sparsely-packed nanopillars serving as the emitter, the conduction area can be significantly reduced. ...
... Finally, the nanostructured emitter is planarized with spin-on glass (SOG) followed by an etch-back by reactive ion etching (RIE), as demonstrated in figure 4(d), so as to prepare the surface for contact deposition. This has been demonstrated as an effective way for fabricating contacts on nanopillars based on our previous studies [7,9]. The base region is then etched followed by deposition of contact metals as shown in figures 4(e) and (f). ...
The light-emitting bipolar transistor (LEBJT) has been developed in response to aspirations for on-chip electronics with GaN-based light-emitting diode (LED) devices. The design utilizes the existing p-n junction of an LED structure to construct a PNP bipolar junction transistor comprising two back-to-back p-n junctions, saving the need for customized structures or epitaxial regrowth. Two designs of monolithic GaN LEBJTs have been demonstrated in this work - an LEBJT with a larger emitter area size for conversion of electronic to optical signal, as well as an LEBJT with reduced emitter area for boosting of current gain. Employing an emitter comprising an array of nanopillars patterned by nanosphere lithography, the LEBJT exhibits an average current gain of 20 and a bandwidth of 180 MHz.
... During the past few decades, InGaN/GaN based light-emitting diodes (LEDs) have been extensively studied to improve the external quantum efficiency (EQE) and optical output power (Shuji et al., 1991;Tan et al., 2012;Ji et al., 2013;Zhang et al., 2013). Owing to the high efficiency, long lifetime, and versatile packaging flexibility, III-nitride based LEDs have been widely used as the backlighting for smartphones and flat-panel displays, and are very promising for applications such as visible light communication and micro-displays (Choi et al., 2004a;McKendry et al., 2010;McKendry et al., 2012). All these applications require small LED chips, which have superior properties including high current density, high power density and high response speed. ...
Strain-reduced micro-LEDs in 50 μm × 50 μm, 100 μm × 100 μm, 200 μm × 200 μm, 500 μm × 500 μm, and 1,000 μm × 1,000 μm sizes were grown on a patterned c-plane sapphire substrate using partitioned growth with the metal-organic chemical-vapor deposition (MOCVD) technique. The size effect on the optical properties and the indium concentration for the quantum wells were studied experimentally. Here, we revealed that the optical properties can be improved by decreasing the chip size (from 1,000 to 100 µm), which can correspondingly reduce the in-plane compressive stress. However, when the chip size is further reduced to 50 μm × 50 μm, the benefit of strain release is overridden by additional defects induced by the higher indium incorporation in the quantum wells and the efficiency of the device decreases. The underlying mechanisms of the changing output power are uncovered based on different methods of characterization. This work shows the rules of thumb to achieve optimal power performance for strain-reduced micro-LEDs through the proposed partitioned growth process.
... Light-emitting diode (LED) displays (1)(2)(3)(4)(5) are transforming the landscape of display technology for higher dynamic range, improved readability under various illumination conditions, and unprecedented form factors applicable to surface-mountable electronics (6,7), biomedical devices (8,9), and transportation vehicles. The application-driven development of LEDs requires achieving high-performance and costeffective manufacturing. ...
There have been rapidly increasing demands for flexible lighting apparatus, and micrometer-scale light-emitting diodes (LEDs) are regarded as one of the promising lighting sources for deformable device applications. Herein, we demonstrate a method of creating a deformable LED, based on remote heteroepitaxy of GaN microrod (MR) p - n junction arrays on c -Al 2 O 3 wafer across graphene. The use of graphene allows the transfer of MR LED arrays onto a copper plate, and spatially separate MR arrays offer ideal device geometry suitable for deformable LED in various shapes without serious device performance degradation. Moreover, remote heteroepitaxy also allows the wafer to be reused, allowing reproducible production of MR LEDs using a single substrate without noticeable device degradation. The remote heteroepitaxial relation is determined by high-resolution scanning transmission electron microscopy, and the density functional theory simulations clarify how the remote heteroepitaxy is made possible through graphene.
... Early generations of LED displays such as alphanumeric indicators and dot-matrix displays were fabricated in a passive-matrix format, requiring continuous line-scanning for the display of arbitrary patterns. While impressive demonstrations are still being made with such devices today, including e.g. a 1000 fps single-pixel camera [19], there are clear scalability issues, with traditional displays starting to experience flicker-issues when going beyond 0.01 Megapixels [20]. Addressing pixels in an array with direct, individual contacts, with separate electronic drivers, is even more limiting as the space requirements of the metal tracks make it difficult to create arrays larger than 10 × 10 [21]. ...
Gallium nitride-based light-emitting diodes (LEDs) have revolutionized the lighting industry with their efficient generation of blue and green light. While broad-area (square millimetre) devices have become the dominant LED lighting technology, fabricating LEDs into micro-scale pixels (micro-LEDs) yields further advantages for optical wireless communications (OWC), and for the development of smart-lighting applications such as tracking and imaging. The smaller active areas of micro-LEDs result in high current density operation, providing high modulation bandwidths and increased optical power density. Fabricating micro-LEDs in array formats allows device layouts to be tailored for target applications and provides additional degrees of freedom for OWC systems. Temporal and spatial control is crucial to use the full potential of these micro-scale sources, and is achieved by bonding arrays to pitch-matched complementary metal-oxide-semiconductor control electronics. These compact, integrated chips operate as digital-to-light converters, providing optical signals from digital inputs. Applying the devices as projection systems allows structured light patterns to be used for tracking and self-location, while simultaneously providing space-division multiple access communication links. The high-speed nature of micro-LED array devices, combined with spatial and temporal control, allows many modes of operation for OWC providing complex functionality with chip-scale devices.
This article is part of the theme issue ‘Optical wireless communication’.
