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(a) Schematic diagram of the process flow for fabricating flexible OLED display by LLO. (b) The corresponding flexible OLED display fabricated by laser lift-off (LLO) based on the technology shown in (a). A 248 nm excimer KrF laser with a pulse width of 25 ns is used for the LLO. Adapted with permissions from [188]. Copyright Royal Society of Chemistry, 2014.
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Hetero-integration of functional semiconductor layers and devices has received strong research interest from both academia and industry. While conventional techniques such as pick-and-place and wafer bonding can partially address this challenge, a variety of new layer transfer and chip-scale transfer technologies have been developed. In this review...
Citations
... Apart from high-resolution deformable displays, some emerging applications, such as optogenetics [20][21][22][23][24][25][26][27][28] and smart contact lenses [29][30][31][32][33] , also drive the development of highly efficient, biocompatible light sources that can be conformally attachable to skins or implantable inside the human body for healthcare [34] . Micro-LEDs in flexible/stretchable formats are well suited for these purposes. ...
Recently, flexible/stretchable micro-scale light-emitting diodes (LEDs), with dimensions significantly smaller than conventional diodes used for illuminations, have emerged for promising applications in areas such as deformable displays, wearable devices for healthcare, etc . For such applications, these devices must have some unusual features that common inorganic LEDs do not intrinsically own, including conformability, biocompatibility, mechanical flexibility, etc . This Perspective focuses on summarizing the most recent progress in developing such flexible emitters based on inorganic semiconductors, followed by reviewing their potential applications. Finally, major challenges and future research directions of deformable micro-scale LEDs are presented.
... Semiconductor materials have provided a strong boost to the development of modern science and technology, and their development have also promoted the development of the world's industries, industries that greatly enhance the productivity of society [1][2][3]. Semiconductor materials can be divided into silicon-based semiconductors and compound semiconductors [4][5][6]. The global semiconductor chip market, dominated by silicon wafers, is expected to exceed $772.03 billion by 2030 [7]. ...
Single-crystal sapphire (α-Al2O3) has been widely used in semiconductor, optics, communication, national defense, and other fields. Before application, an ultra-smooth surface which is scratch free and subsurface damage free is essential. Furthermore, the sapphire has unique qualities such as significant rigidity and chemical stability, which make it extremely arduous to process. Chemical mechanical polishing (CMP) is recognized as the final process to reduce the roughness and eliminate surface defects of a sapphire surface. In this review, the materials and equipment used for the chemical polishing of a sapphire wafer are summarized, and the surface nanoscale changes of sapphire wafer are reviewed from the angles of regulating polishing-process parameters, composition of polishing slurry including that which is nano-abrasive, a pH regulator, a complexing agent, and other additives, as well as hybrid CMP technologies. The outlook and future applications are also summarized.
... Among various lift-off techniques such as chemical lift-off, mechanical lift-off, and ion lift-off, laser lift-off (LLO) technology offers several advantages, including high energy input efficiency, minimal device damage, equipment flexibility, and versatile application modes. As a result, LLO has become a pivotal technology for manufacturing flexible electronic devices [19][20][21][22][23]. ...
This work explores the pivotal role of laser lift-off (LLO) as a vital production process in facilitating the integration of Micro-LEDs into display modules. We specifically investigate the LLO process applied to high-performance gallium nitride (GaN)-based green Micro-LED arrays, featuring a pixel size of 20 × 38 μm on a patterned sapphire substrate (PSS). Scanning electron microscopy (SEM) observations demonstrate the preservation of the GaN film and sapphire substrate, with no discernible damage. We conduct a comprehensive analysis of the optoelectrical properties of the Micro-LEDs both before and after the LLO process, revealing significant enhancements in light output power (LOP) and external quantum efficiency (EQE). These improvements are attributed to more effective light extraction from the remaining patterns on the GaN backside surface. Furthermore, we examine the electroluminescence spectra of the Micro-LEDs under varying current conditions, revealing a slight change in peak wavelength and an approximate 10% decrease in the full width at half maximum (FWHM), indicating improved color purity. The current–voltage (I–V) curves obtained demonstrate the unchanged forward voltage at 2.17 V after the LLO process. Our findings emphasize the efficacy of LLO in optimizing the performance and color quality of Micro-LEDs, showcasing their potential for seamless integration into advanced display technologies.
... Advances have been made in transfer technologies 6 , such as the stamp method 7-10 and FSA [11][12][13][14][15][16][17][18][19][20] . However, these technologies are only suited to serve the small-volume market, with no tangible solutions to address the high-volume market. ...
MicroLED displays have been in the spotlight as the next-generation displays owing to their various advantages, including long lifetime and high brightness compared with organic light-emitting diode (OLED) displays. As a result, microLED technology1,2 is being commercialized for large-screen displays such as digital signage and active R&D programmes are being carried out for other applications, such as augmented reality³, flexible displays⁴ and biological imaging⁵. However, substantial obstacles in transfer technology, namely, high throughput, high yield and production scalability up to Generation 10+ (2,940 × 3,370 mm²) glass sizes, need to be overcome so that microLEDs can enter mainstream product markets and compete with liquid-crystal displays and OLED displays. Here we present a new transfer method based on fluidic self-assembly (FSA) technology, named magnetic-force-assisted dielectrophoretic self-assembly technology (MDSAT), which combines magnetic and dielectrophoresis (DEP) forces to achieve a simultaneous red, green and blue (RGB) LED transfer yield of 99.99% within 15 min. By embedding nickel, a ferromagnetic material, in the microLEDs, their movements were controlled by using magnets, and by applying localized DEP force centred around the receptor holes, these microLEDs were effectively captured and assembled in the receptor site. Furthermore, concurrent assembly of RGB LEDs were demonstrated through shape matching between microLEDs and receptors. Finally, a light-emitting panel was fabricated, showing damage-free transfer characteristics and uniform RGB electroluminescence emission, demonstrating our MDSAT method to be an excellent transfer technology candidate for high-volume production of mainstream commercial products.
... The epilayers are transferred to other substrates while preserving the original growth substrate. Various approaches have been reported for the separation of the epilayers, including laser lift-off [120], chemical etching of the growth substrate [121], and the use of a sacrificial layer [122,123]. These techniques have many drawbacks, such as high costs and long processing times. ...
Photoelectrochemical (PEC) water splitting is a promising approach for hydrogen production using solar energy with zero emissions. However, the solar-to-hydrogen efficiency (STH) of the practical PEC systems (∼10%) is far from the theoretical value (<25%). However, the key barrier to improving STH efficiency is the lack of high-performance and chemically stable photoelectrodes. In recent years, InGaN nanowires have emerged as a promising solution in designing efficient photoelectrodes for PEC water splitting. Their tunable band gap, excellent chemical stability, and high catalytic activity make them strong candidates for PEC applications. Yet, these systems do not yield the STH efficiencies required for commercial applications. The primary purpose of this article is to provide a comprehensive literature review of the advances in InGaN nanowires for the production of H2 via photoelectrochemical water splitting. The first sections of this article present the working principle of PEC water splitting using InGaN nanowires and the recent approaches to growing well-elongated InGaN nanowires. Then, the paper discusses strategies that can enhance the stability and efficiency of this technology, in addition to reducing the fabrication cost of InGaN NW photoelectrodes via the reuse of the growth substrate by employing the h-BN lift-off transfer technique.
... Although AR/VR microdisplays are intriguing applications for µLEDs, display manufacturers have greater financial motivations towards µLED-based flat-panel displays for televisions, smartphones and other consumer electronics. Contrary to microdisplays, flat-panel displays require lower pixel density (100-500 PPI) and a larger display area (up to 80 inches and beyond), making mass transfer the desired approach (see Supplementary Fig. 10a for illustration of process flow) 3,5 . Currently the major cost driver for these technologies is insufficient transfer yield, in particular for smaller µLEDs 3,4 . ...
... Contrary to microdisplays, flat-panel displays require lower pixel density (100-500 PPI) and a larger display area (up to 80 inches and beyond), making mass transfer the desired approach (see Supplementary Fig. 10a for illustration of process flow) 3,5 . Currently the major cost driver for these technologies is insufficient transfer yield, in particular for smaller µLEDs 3,4 . We conceived a solution using 2DLT-based mass transfer of stacked µLED chips. ...
Micro-LEDs (µLEDs) have been explored for augmented and virtual reality display applications that require extremely high pixels per inch and luminance1,2. However, conventional manufacturing processes based on the lateral assembly of red, green and blue (RGB) µLEDs have limitations in enhancing pixel density3–6. Recent demonstrations of vertical µLED displays have attempted to address this issue by stacking freestanding RGB LED membranes and fabricating top-down7–14, but minimization of the lateral dimensions of stacked µLEDs has been difficult. Here we report full-colour, vertically stacked µLEDs that achieve, to our knowledge, the highest array density (5,100 pixels per inch) and the smallest size (4 µm) reported to date. This is enabled by a two-dimensional materials-based layer transfer technique15–18 that allows the growth of RGB LEDs of near-submicron thickness on two-dimensional material-coated substrates via remote or van der Waals epitaxy, mechanical release and stacking of LEDs, followed by top-down fabrication. The smallest-ever stack height of around 9 µm is the key enabler for record high µLED array density. We also demonstrate vertical integration of blue µLEDs with silicon membrane transistors for active matrix operation. These results establish routes to creating full-colour µLED displays for augmented and virtual reality, while also offering a generalizable platform for broader classes of three-dimensional integrated devices.
... Various transfer printing techniques [19], [20], [21] undesirable printing inaccuracy issues of the inks. We also note 157 that thermal release tapes [24], [25] combined with the LLO irradiation to achieve adhesion control of the photosensitive 164 tape, which is a simple, damage-free process and can be 165 delivered to the device surface remotely. ...
Microscale light-emitting diodes (Micro-LEDs) have attracted intensive research attention due to their potential applications in high-resolution displays, wearables, and VR/AR headsets. However, their device performance can be compromised by the common Micro-LED lateral structure, usually with both two electrodes facing toward the p-side. Here, we developed printable, silicon-based vertical Micro-LEDs with two electrodes facing oppositely, which showed better heat dissipation, and were 60% brighter over conventional lateral Micro-LEDs. We further developed a novel double-tape-assisted transfer process, which allowed these vertical micro-LEDs to be transferred completely to a polyimide tape in a simple yet reliable manner. Combined with a bonding scheme based on low-melting-point-patterned indium alloys, these printed Micro-LEDs on the tape can be further integrated onto silicon backplanes with a shared p-contact. Followed by forming an individual n-electrode connected to each pixel, a novel-inverted, vertical microdisplay prototype device with individually addressing cathodes was demonstrated for the first time.
... For conventional LEDs, mechanical bending during operation induces strain and potential self-heating, causing a degradation in the device performance, which may limit the utilization of μLEDs in flexible substrates. 49,165,166 In 2020, Asad et al. demonstrated several intermediary metal bonding layers and developed a "paste-and-cut" technique to transfer GaN μLEDs from sapphire substrates to flexible platforms. They also investigated the effect of LED geometry on the performance of the flexible devices. ...
Dopant‐selective electrochemical etching (ECE) of gallium nitride (GaN) results in well‐defined porous layers with tunable refractive index, which is extremely interesting for integrating photonic components into nitride technology. Herein, the impact of nitrogen implantation with and without subsequent rapid thermal annealing (RTA) on the porosification process of highly n‐doped GaN ([Si] 3 × 10 ¹⁹ cm ⁻³ ) is investigated. Implantation is expected to compensate the donors of the n‐GaN layer to spatially suppress porosification during ECE. Optical transmission, electrochemical capacitance–voltage, and X‐Ray diffractometry of as‐grown and as‐implanted GaN suggest successful compensation of n‐dopants. Cross‐sectional scanning electron microscopy reveals the presence of mesopores (diameter 2–50 nm) after ECE of the as‐grown n‐GaN. In the case of implanted n‐GaN, it is found that ECE results in macropores (diameter > 50 nm), which can be suppressed by an intermediate RTA step. The implanted and annealed n‐GaN layers solely exhibit mesopores at the top and bottom, while the intermediate region remains unimpaired. Chronoamperometry and gravimetry provide additional insight and confirm the presence of macro‐ and mesopores in samples without and with RTA, respectively. The results demonstrate a successful implementation of etch‐resisting subsurface layers, which are required for 3D refractive index engineering in porous GaN.
