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Ultrafast laser lift-off is an important step in manufacturing flexible electronic display devices. To improve the picosecond laser lift-off transfer quality of micro light emitting diodes (micro-LEDs), the response surface methodology (RSM) is employed for the optimization of multiple laser processing parameters, including laser power, scanning speed, spot diameter, and scanning distance. Transfer yield and residual stress are chosen as the performance evaluation metrics, as well as the lifted-off device element composition and transfer quality under different process parameters are characterized. The optimized maximum transfer yield is 95.84% and the minimum residual tensile stress is 0.589 GPa, which is less than 0.5% prediction error of the optimum transfer yield (95.67–95.74%) and residual stress (0.588–0.592 GPa) for ultrafast laser lift-off of micro-LEDs based on the central composite design of RSM, indicating the reliable guidance ability of this model. It develops a new way for quality improvement of the ultrafast laser lift-off process for micro-LEDs. [ABSTRACT FROM AUTHOR]

Miniaturized pixel sizes in near-eye digital displays lead to pixel emission patterns with large divergence angles, necessitating efficient beam collimation solutions to improve the light coupling efficiency. Traditional beam collimation optics, such as lenses and cavities, are wavelength-sensitive and cannot simultaneously collimate red (R), green (G), and blue (B) light. In this work, we employed inverse design optimization and finite-difference time-domain (FDTD) simulation techniques to design a collimator comprised of nano-sized photonic structures. To alleviate the challenges of the spatial incoherence nature of micro-LED emission light, we developed a strategy called dual-task optimization. Specifically, the method models light collimation as a dual task of color routing. By optimizing a color router, which routes incident light within a small angular range to different locations based on its spectrum, we simultaneously obtained a beam collimator, which can restrict the output of the light emitted from the routing destination with a small divergence angle. We further evaluated the collimation performance for spatially incoherent RGB micro-LED light in an FDTD using a multiple-dipole simulation method, and the simulation results demonstrate that our designed collimator can increase the light coupling efficiency from approximately 30% to 60% within a divergence angle of ±20° for all R/G/B light under the spatially incoherent emission. [ABSTRACT FROM AUTHOR]

Wide color gamut and high resolution are becoming key features of the new generation of displays, and hence quantum dots pixels with high luminescence purity have been placed great expectations. However, how to facilely and rapidly fabricate electroluminescent pixels with both high pixels per inch (PPI) and high quantum efficiency has been a great challenge. Here, a one‐step, mask‐free, rapid laser writing strategy to fabricate ultra‐high resolution perovskite quantum dots (PQDs) pixels is presented. It is found that the laser‐induced reaction can convert PQDs into oxide, forming perovskite@oxide pixel arrays, replacing the complex etching and deposition processes previously used. Benefiting from the formation of the oxide layer, electrons transport can be effectively blocked in the non‐emitting region, thus reducing the charge leakage in micro quantum dots light emitting diodes (Micro‐QLED) arrays. Finally, red, green, blue Micro‐QLEDs are achieved with PPIs ranging from 2000 to 5000 and the highest external quantum efficiency of 17.24%, 21%, and 6.6% respectively. These results are record‐breaking in perovskite Micro‐QLEDs, providing the strategy for active‐matrix electroluminescent high‐resolution pixel arrays for next‐generation monochromatic displays. [ABSTRACT FROM AUTHOR]

Abstract This study fabricated 10 μm chip size μLEDs of blue-light GaN based epilayers structure with different mesa processes using dry etching and ion implantation technology. Two ion sources, As and Ar, were applied to implant into the LED structure to achieve material isolation and avoid defects on the mesa sidewall caused by the plasma process. Excellent turn-on behavior was obtained in both ion-implanted samples, which also exhibited lower leakage current compared to the sample fabricated by the dry etching process. Additionally, lower dynamic resistance (Rd) and series resistance (Rs) were obtained with Ar implantation, leading to a better wall-plug efficiency of 10.66% in this sample. Consequently, outstanding external quantum efficiency (EQE) values were also present in both implant samples, particularly in the sample implanted with Ar ions. This study proves that reducing defects on the mesa sidewall can further enhance device properties by suppressing non-radiative recombination behavior in small chip size devices. Overall, if implantation is used to replace the traditional dry etching process for mesa fabrication, the ideality factor can decrease from 11.89 to 2.2, and EQE can improve from 8.67 to 11.03%.

The most significant challenge associated with micro‐light‐emitting‐diode (micro‐LED) displays, which are anticipated to be the next generation of display technology, is the high manufacturing cost. In order to reduce manufacturing costs, it is essential to improve yield. Improving the manufacturing yield of them necessitates the evaluation of micro‐LED chips prior to their installation onto substrates. However, the microsize and large quantity of these chips renders inspection difficult with conventional inspection methods. Herein, we propose a method for inspecting micro‐LED chips by measuring the voltage generated between the anode and cathode due to the photovoltaic effect using a developed proximity capacitance image sensor. As this inspection method does not require the use of probe pins to contact LED electrodes, it enables simultaneous inspection of multiple chips in a short time without causing any damage to the electrodes. In this paper, an experimental system equipped with this sensor was developed to demonstrate the basic measurement principle. Moreover, we demonstrated that more than 50,000 micro‐LED chips with a size of 60 μm × 34 μm can be simultaneously inspected in approximately 2 s. [ABSTRACT FROM AUTHOR]

Transparent displays are crucial for various applications, particularly for their potential use as windows in future self‐driving cars. These displays require high transparency, low power consumption, and high mechanical reliability. Micro‐LEDs have emerged as ideal devices for the transparent displays. Efficient mass‐production processes are essential for the commercialization of transparent micro‐LED displays. This study presents roll‐based mass transfer to enhance the productivity of transparent micro‐LED displays. Roll transfer processes traditionally face resolution challenges in alignment repeatability and positional errors in both the transverse direction (TD) and machine direction (MD). This study proposes a roll‐to‐plate (R2P) transfer process with overlay alignment to improve the repeatability precision of the alignment. Detailed experimental analyses address positional errors in the TD and MD, attributed to initial contact errors and linear velocity asynchrony, respectively. The results demonstrate successful micro‐LED transfer onto a transparent circuit board (TCB) with a maximum positional error of 3.2 µm and a 99.75% yield. The resulting micro‐LED display achieves a transparency of 72.5% with 68 pixels per inch. This study overcomes the alignment challenges in the R2P process and contributes to the commercialization of transparent micro‐LED displays. It is expected to positively impact the manufacturing of transparent applications that involve rolling processes. [ABSTRACT FROM AUTHOR]

Naked-eye 3D micro-LED display combines the characteristics of 3D display with the advantages of micro-LED. However, the 3D micro-LED display is still at the conceptual stage, limited by its intrinsic emission properties of large divergence angle and non-coherence, as well as difficulties in achieving large viewing angles with high luminous efficiency. In this work, we propose a double-layer metasurface film integrating functions of collimation with multiple deflections, constituting a micro-LED naked-eye 3D display system. The system is characterized through numerical simulations using the 3D finite-difference time-domain method. The simulation results show that the double-layer metasurface film restricts 90% of the emitted light of the micro-LED to the vicinity of the 0° angle, improving its spatial coherence. Subsequently, a large-angle, low-crosstalk outgoing from −45° to 45° is achieved, while providing a deflection efficiency of over 80% and a pixel density of up to 605. We believe this design provides a feasible approach for realizing naked-eye 3D micro-LED displays with a large field of view, low crosstalk, and high resolution. [ABSTRACT FROM AUTHOR]

This study utilized blue-light epitaxial wafers and employed semiconductor processes such as maskless laser writing, dry etching, wet etching, passivation layer deposition, electron beam evaporation, and ion implantation to fabricate micro-light emitting diode (μLED) arrays with different pixel sizes but the same emitting area (900 μm²). The μLED arrays with single pixel sizes of 5 μm, 10 μm, and 15 μm were fabricated, with array numbers of 6×6, 3×3, and 2×2, respectively. This study proposes etching the material in the channel region while retaining a certain width for implantation, known as the sidewall ion implantation process, aiming to achieve better insulation characteristics by using ion implantation technology to insulate the sidewall regions. It involves ion bombardment of the defect areas generated after plasma etching and the use of a passivation layer for protection. The isolation characteristics of μLED arrays processed by sidewall implantation exhibited better electrical isolation than those of μLED arrays processed only by plasma. The light output power, external quantum efficiency, and wall-plug efficiency were all superior for the sidewall implantation process when the device was miniaturized to 5 μm. Overall, the sidewall implantation process combined with plasma dry etching effectively improved the light output characteristics, with the enhancement ratio increasing as the device was miniaturized.

Abstract In this study, arrays of μLEDs in four different sizes (5 × 5 μm2, 10 × 10 μm2, 25 × 25 μm2, 50 × 50 μm2) were fabricated using a flip-chip bonding process. Two passivation processes were investigated with one involving a single layer of SiO2 deposited using plasma-enhanced chemical vapor deposition (PECVD) and the other incorporating Al2O3 deposited by atomic layer deposition (ALD) beneath the SiO2 layer. Owing to superior coverage and protection, the double-layers passivation process resulted in a three-order lower leakage current of μLEDs in the 5 μm chip-sized μLED arrays. Furthermore, higher light output power of μLEDs was observed in each chip-sized μLED array with double layers passivation. Particularly, the highest EQE value 21.9% of μLEDs array with 5 μm × 5 μm chip size was achieved with the double-layers passivation. The EQE value of μLEDs array was improved by 4.4 times by introducing the double-layers passivation as compared with that of μLEDs array with single layer passivation. Finally, more uniform light emission patterns were observed in the μLEDs with 5 μm × 5 μm chip size fabricated by double-layer passivation process using ImageJ software.

Highlights Blue micro-light-emitting diodes (μLED)-integrated gas sensors were fabricated as monolithic structure by directly loading sensing materials onto the μLED. SnO2 nanoparticles are activated by blue μLED and exhibit outstanding sensitivity to NO2 at μ-Watt power levels. Noble metal (Au, Pd, Pt)-decorated SnO2 showed the tunable gas selectivity for 4 target gases under blue light illumination.

Quasi‐2D Ruddlesden–Popper perovskite (RPP) have surfaced as a promising candidate for light emitting diodes (LEDs) due to its outstanding optoelectronic properties. However, a reliable approach for patterning RPPs remains elusive due to the use of polar solvents in lithographic processes, which can damage the RPP. Here, a reliable and damage‐free dry micropatterning method of RPPs is reported, which also offers a cost/time advantage compared to conventional patterning methods. The sharp edges of high aspect ratio silicon micropillars are used to cut RPPs to a pre‐defined shape and then the cut RPPs are delaminated to obtain a patterned array of RPPs. The resultant patterned array exhibits no sign of degradation or discernable difference between adjacent pixels, achieving a ≈100% yield. The obtained array is utilized to fabricate a pixelated LED where a sharp electroluminescence (EL) spectrum peaking at 410 nm with full‐width‐at‐half‐maximum (FWHM) of 10 nm is observed. The pixelated devices demonstrate the potential to suppress EQE drops as the pixel size decreases, attributed to both the damage‐free micropatterning process and the defect tolerance of RPPs. Moreover, further improvements of the patterning method are demonstrated to avoid parasitic emission and suggest a promising strategy to fabricate pixel‐accessible micro‐LEDs. [ABSTRACT FROM AUTHOR]

This paper presents the design of a 40 × 40 micro-light-emitting (micro-LED) test array based on a 20 mm × 20 mm substrate. A study of the relationship between luminous brightness, driving current, and driving voltage revealed that the data voltages of the red, green, and blue micro-LED array from 0 to 255 grey levels are 0.31 V, 0.29 V, and 0.30 V, respectively, under the condition that the target brightness of the white field is 1000 nits and the color temperature is 9300 K. The brightness range of the red micro-LED array is 64.8–101.2%, the brightness range of the green micro-LED array is 66.5–102.8%, and the brightness range of the blue micro-LED array is 53.5–129.2%. In order to overcome the luminance nonuniformity, a grey level depth of 12 -bit is required. A 10T3C pixel driver circuit based on low-temperature polysilicon (LTPS) with a depth of 12 bits greyscale is designed and fabricated into the micro-LED display. A brightness uniformity of 84.1–97.1% can be achieved by brightness correction combined with a 12-bit greyscale depth system for micro-LED display. This provides a valuable reference point for subsequent improvements in the quality of micro-LED displays. [ABSTRACT FROM AUTHOR]

In this study, arrays of μLEDs in four different sizes (5 × 5 μm2, 10 × 10 μm2, 25 × 25 μm2, 50 × 50 μm2) were fabricated using a flip-chip bonding process. Two passivation processes were investigated with one involving a single layer of SiO2 deposited using plasma-enhanced chemical vapor deposition (PECVD) and the other incorporating Al2O3 deposited by atomic layer deposition (ALD) beneath the SiO2 layer. Owing to superior coverage and protection, the double-layers passivation process resulted in a three-order lower leakage current of μLEDs in the 5 μm chip-sized μLED arrays. Furthermore, higher light output power of μLEDs was observed in each chip-sized μLED array with double layers passivation. Particularly, the highest EQE value 21.9% of μLEDs array with 5 μm × 5 μm chip size was achieved with the double-layers passivation. The EQE value of μLEDs array was improved by 4.4 times by introducing the double-layers passivation as compared with that of μLEDs array with single layer passivation. Finally, more uniform light emission patterns were observed in the μLEDs with 5 μm × 5 μm chip size fabricated by double-layer passivation process using ImageJ software. [ABSTRACT FROM AUTHOR]

Highlights: Blue micro-light-emitting diodes (μLED)-integrated gas sensors were fabricated as monolithic structure by directly loading sensing materials onto the μLED. SnO2 nanoparticles are activated by blue μLED and exhibit outstanding sensitivity to NO2 at μ-Watt power levels. Noble metal (Au, Pd, Pt)-decorated SnO2 showed the tunable gas selectivity for 4 target gases under blue light illumination. Micro-light-emitting diodes (μLEDs) have gained significant interest as an activation source for gas sensors owing to their advantages, including room temperature operation and low power consumption. However, despite these benefits, challenges still exist such as a limited range of detectable gases and slow response. In this study, we present a blue μLED-integrated light-activated gas sensor array based on SnO2 nanoparticles (NPs) that exhibit excellent sensitivity, tunable selectivity, and rapid detection with micro-watt level power consumption. The optimal power for μLED is observed at the highest gas response, supported by finite-difference time-domain simulation. Additionally, we first report the visible light-activated selective detection of reducing gases using noble metal-decorated SnO2 NPs. The noble metals induce catalytic interaction with reducing gases, clearly distinguishing NH3, H2, and C2H5OH. Real-time gas monitoring based on a fully hardware-implemented light-activated sensing array was demonstrated, opening up new avenues for advancements in light-activated electronic nose technologies. [ABSTRACT FROM AUTHOR]

The progressive downscaling of silicon‐based microelectronic devices delivers compact and advanced integrated circuits for fast data processing and computing. Similarly, the miniaturization of conventional optoelectronics is also an important frontier of technology for emerging lighting, imaging, communication, and sensing. Herein, this study reports a miniature dual‐functional diode (DF‐diode) with both light‐emitting and light‐detecting functionalities. The proposed micro‐scale DF‐diode exhibits a record high responsivity of 300 mA W−1 at 265 nm with an ultrafast response rise time of 3.7 ns in light‐detecting mode. While operating in emitting mode, it demonstrates an extraordinarily high −3 dB optical bandwidth above 585 MHz with an enhanced external quantum efficiency performance. Significantly, the development of micro‐scale DF‐diodes has opened up a new avenue toward the realization of an effective and long‐distance solar‐blind optical communication system in the future. [ABSTRACT FROM AUTHOR]

Light‐emitting diodes and photodiodes, often acting as transmitters and receivers, are two key optical components for constructing an optical communication system. Recently, solar‐blind optical wireless communication (SB‐OWC) has emerged as a promising free‐space communication platform due to its unique advantages, including low background noise, high security, and non‐line‐of‐sight ability. However, the development of deep ultraviolet (DUV) emitters and detectors is still in its early stages with relatively low efficiency and poor detection capability, which hampers the further progress of SB‐OWC. Herein, a triangular‐shaped micro‐sized diode (T‐μ‐diode) is reported that can significantly boost its DUV emission and detection performance compared with a regular circular‐shaped micro‐diode (C‐μ‐diode) due to improved current injection and enhanced light extraction/absorption behavior. Specifically, the T‐μ‐diodes demonstrate superior light output power with a −3 dB modulation bandwidth over 566 MHz operating at an extremely high current density of 2 kA cm−2 while possessing a higher photo‐responsivity of ≈160 mA W−1 with a faster response speed of 5.1 ns, surpassing the traditional C‐μ‐diodes in both light emitting and detecting modes. Importantly, a bidirectional on‐chip data transmission system is realized by simply switching the operation mode of two T‐μ‐diodes monolithically fabricated on the same platform with boosted emission and detection functionalities. [ABSTRACT FROM AUTHOR]

The titanium (Ti) thin film is a material used in the thin-film transistor (TFT) of Micro-LED display and require partial processing during repair processes. For a suitable repair process, defects such as particles, droplets, and burrs should not be present during processing. In this study, Ti with a thickness of 100 nm was ablated by varying pulse duration and fluence with a wavelength of 1026 nm. In case of the pulse duration, it was set to 190 fs, 1 ps, 10 ps. Ablation thresholds of 0.116 J/cm² for 190 fs, 0.124 J/cm² for 1 ps, and 0.13 J/cm² for 10 ps were obtained. The Two-Temperature Model (TTM) equation was applied to simulate the ablation using COMSOL Multiphysics. Based on the simulation, it was observed that short pulse durations and low fluences near the ablation threshold can suppress burrs, particles, and droplets. Although various defects need to be addressed still exist, this foundational processing is expected to be helpful to study for Micro-LED display TFT repairing. [ABSTRACT FROM AUTHOR]

Abstract Transparent displays are crucial for various applications, particularly for their potential use as windows in future self‐driving cars. These displays require high transparency, low power consumption, and high mechanical reliability. Micro‐LEDs have emerged as ideal devices for the transparent displays. Efficient mass‐production processes are essential for the commercialization of transparent micro‐LED displays. This study presents roll‐based mass transfer to enhance the productivity of transparent micro‐LED displays. Roll transfer processes traditionally face resolution challenges in alignment repeatability and positional errors in both the transverse direction (TD) and machine direction (MD). This study proposes a roll‐to‐plate (R2P) transfer process with overlay alignment to improve the repeatability precision of the alignment. Detailed experimental analyses address positional errors in the TD and MD, attributed to initial contact errors and linear velocity asynchrony, respectively. The results demonstrate successful micro‐LED transfer onto a transparent circuit board (TCB) with a maximum positional error of 3.2 µm and a 99.75% yield. The resulting micro‐LED display achieves a transparency of 72.5% with 68 pixels per inch. This study overcomes the alignment challenges in the R2P process and contributes to the commercialization of transparent micro‐LED displays. It is expected to positively impact the manufacturing of transparent applications that involve rolling processes.

Abstract In this study, a 3 × 3 blue micro-LED array with a pixel size of 10 × 10 μm2 and a pitch of 15 μm was fabricated on an epilayer grown on a sapphire substrate using metalorganic chemical vapor deposition technology. The fabrication process involved photolithography, wet and dry etching, E-beam evaporation, and ion implantation technology. Arsenic multi-energy implantation was utilized to replace the mesa etching for electrical isolation, where the implantation depth increased with the average energy. Different ion depth profiles had varying effects on electrical properties, such as forward current and leakage currents, potentially causing damage to the n-GaN layer and increasing the series resistance of the LEDs. As the implantation depth increased, the light output power and peak external quantum efficiency of the LEDs also increased, improving from 5.33 to 9.82%. However, the efficiency droop also increased from 46.3 to 48.6%.

A full-color monolithic micro-light-emitting diode (LED) display based on InGaN quantum wells is demonstrated. We stacked red, green, and blue (RGB) light-emitting layers and selectively removed and regrew a p-type layer to create distinct areas on a single chip that emitted RGB colors. Subsequently, we fabricated a full-color monolithic micro-LED chip with a pixel pitch of 30 μm and pixel number of 96 × 96. Each color subpixel emits light with a single peak. We obtained a full-color image by driving the chip using a microcontroller. The proposed semiconductor process-based method enables the fabrication of low-cost and high-resolution microdisplays.

InGaN-based green light-emitting diodes with different pre-well numbers were grown by an organometallic vapor phase epitaxy deposition method on patterned sapphire substrates. Micro-LED chips with a size of 17 × 20 μm ^2 were fabricated, and a peak external quantum efficiency (EQE) of 39% was achieved at ultra-low current density of 0.07 A cm ^−2 . The EQE variation curves of different samples were studied under different current densities. It was confirmed that by reducing the number of pre-wells the Shockley–Read–Hall non-radiative recombination under ultra-low current density was suppressed, which ultimately results in a high EQE of micro-LEDs.

In this study, a 3 × 3 blue micro-LED array with a pixel size of 10 × 10 μm2 and a pitch of 15 μm was fabricated on an epilayer grown on a sapphire substrate using metalorganic chemical vapor deposition technology. The fabrication process involved photolithography, wet and dry etching, E-beam evaporation, and ion implantation technology. Arsenic multi-energy implantation was utilized to replace the mesa etching for electrical isolation, where the implantation depth increased with the average energy. Different ion depth profiles had varying effects on electrical properties, such as forward current and leakage currents, potentially causing damage to the n-GaN layer and increasing the series resistance of the LEDs. As the implantation depth increased, the light output power and peak external quantum efficiency of the LEDs also increased, improving from 5.33 to 9.82%. However, the efficiency droop also increased from 46.3 to 48.6%. [ABSTRACT FROM AUTHOR]

Micro-light-emitting diodes (μLEDs), with their advantages of high response speed, long lifespan, high brightness, and reliability, are widely regarded as the core of next-generation display technology. However, due to issues such as high manufacturing costs and low external quantum efficiency (EQE), μLEDs have not yet been truly commercialized. Additionally, the color conversion efficiency (CCE) of quantum dot (QD)-μLEDs is also a major obstacle to its practical application in the display industry. In this review, we systematically summarize the recent applications of nanomaterials and nanostructures in μLEDs and discuss the practical effects of these methods on enhancing the luminous efficiency of μLEDs and the color conversion efficiency of QD-μLEDs. Finally, the challenges and future prospects for the commercialization of μLEDs are proposed. [ABSTRACT FROM AUTHOR]

This paper presents an extensive literature review on Light-Emitting Diode (LED) fundamentals and discusses the historical development of LEDs, focusing on the material selection, design employed, and modifications used in increasing the light output. It traces the evolutionary trajectory of the efficiency enhancement of ultraviolet (UV), blue, green, and red LEDs. It rigorously examines the diverse applications of LEDs, spanning from solid-state lighting to cutting-edge display technology, and their emerging role in microbial deactivation. A detailed overview of current trends and prospects in lighting and display technology is presented. Using the literature, this review offers valuable insights into the application of UV LEDs for microbial and potential viral disinfection. It conducts an in-depth exploration of the various microorganism responses to UV radiation based on the existing literature. Furthermore, the review investigates UV LED-based systems for water purification and surface disinfection. A prospective design for a solar-powered UV LED disinfection system is also delineated. The primary objective of this review article is to organize and synthesize pivotal information from the literature, offering a concise and focused overview of LED applications. From our review, we can conclude that the efficiency of LEDs has continuously increased since its invention and researchers are searching for methods to increase efficiency further. The demand for LED lighting and display applications is continuously increasing. Our analysis reveals an exciting horizon in microbial disinfection, where the integration of UV LED systems with cutting-edge technologies such as sensors, solar power, Internet-of-Things (IoT) devices, and artificial intelligence algorithms promises high levels of precision and efficacy in disinfection practices. This contribution sets the stage for future research endeavors in the domain of viral disinfection using solar-powered UV LED modules for universal applications. [ABSTRACT FROM AUTHOR]

Micro-LEDs (μLEDs) have advantages in terms of brightness, power consumption, and response speed. In addition, they can also be used as micro-sensors implanted in the body via flexible electronic skin. One of the key techniques involved in the fabrication of μLED-based devices is transfer printing. Although numerous methods have been proposed for transfer printing, improving the yield of μLED arrays is still a formidable task. In this paper, we propose a novel method for improving the yield of μLED arrays transferred by the stamping method, using an innovative design of piezoelectrically driven asymmetric micro-gripper. Traditional grippers are too large to manipulate μLEDs, and therefore two micro-sized cantilevers are added at the gripper tips. A μLED manipulation system is constructed based on the micro-gripper together with a three-dimensional positioning system. Experimental results using this system show that it can be used successfully to manipulate μLED arrays. ARTICLE HIGHLIGHTS: HIGHLIGHTS • A piezoelectrically driven asymmetric micro-gripper is proposed. • A μLED manipulation system is constructed based on the micro-gripper together with a three-dimensional positioning system. • A single μLED array is manipulated by the proposed micro-gripper-based system. [ABSTRACT FROM AUTHOR]

As LEDs continue to miniaturize, in addition to the side‐wall defect effect causing a decrease in LED luminous efficiency, the reduction in LED size also leads to the emergence of downward and lateral light emission. These non‐forward emissions are prone to total internal reflection and significant refraction at interfaces between packaging layers and air, consequently diminishing forward light emission. To mitigate the loss of forward luminance and ambient light reflection, we propose a secondary‐optical design and simulate the physical model by commercial software. The simulation result shows that the loss was reduced from 40.06% to 18.51% with Hexagonal Structure, and the ambient light reflection was reduce from 25.41% to 4.78%. With the addition of microlens array, loss can be further reduced to 2.67%, and ambient light reflection was reduced to 5.34%. [ABSTRACT FROM AUTHOR]

InGaN/GaN green micro‐light‐emitting diode (micro‐LED, μLED) arrays with varying device sizes down to 4 μm are fabricated and characterized. The size effects on current‐voltage and capacitance‐voltage characteristics are analyzed showing minimal sidewall effects only at low bias. The influence of pulse modulation frequency on luminance is also characterized and the effect of diode negative capacitance is discussed. Subsequently, a universal and comprehensive compact model for μLEDs are built based on these findings, which covers the capacitance frequency dispersion and size scaling effects. This work reveals the significance of frequency in the display driving strategy and provides design enablement for μLED micro‐display applications including augmented/mixed reality (AR/MR). [ABSTRACT FROM AUTHOR]

An analog pulse‐width‐modulation (A‐PWM) Micro‐LED (μLED) pixel circuit based on low‐temperature‐polysilicon (LTPS) thin‐film transistors (TFTs) for mobile displays is proposed. The progressive‐emission mode is implemented using a single Sweep (SW) signal by in‐pixel logic operation circuits. By adjusting the emission time of the progressive‐emission mode, the μLED is biased with the maximum quantum efficiency (EQE). Consequently, the static power consumption of proposed pixels is reduced by 29.2%, compared with conventional schemes. [ABSTRACT FROM AUTHOR]

Micro‐LED is a new display technology that offers advantages such as high brightness, high contrast, and low power consumption. However, the performance of Micro‐LED is greatly affected by temperature, leading to color shift easily. To address this issue, this paper proposes a machine learning‐based approach for achieving global compensation, which exhibits advantages including high compensation accuracy, good smoothness, and strong generalization performance. Experimental validation using both measured and simulated data demonstrates that the proposed method achieves a single‐pixel single‐color(R) brightness prediction accuracy of 1% and the brightness prediction of multi‐pixel single‐color(R) also exhibits high accuracy. Consequently, the proposed method enables global brightness compensation and color shift compensation in Micro‐LED. [ABSTRACT FROM AUTHOR]

In our work, we achieved the 1.63‐inch 403‐PPI full‐color active‐matrix Micro‐LED display based on LTPS backplane, which possesses the property of >600 nits brightness, >120% NTSC, and >1,500,000:1 contrast ratio. At present, it is the highest PPI product of LTPS based Micro‐LED display in the world. [ABSTRACT FROM AUTHOR]

The objective of this paper was to investigate the quality of see‐through images on transparent MicroLED displays. Transparent displays have gained significant attention in various applications. However, evaluating the quality of see‐through images presented challenges, as there was no universal metric available for assessment. Image analysis methods were employed in this study, and common optical measurement metrics were also compared. The results showcased that CW‐SSIM exhibited higher sensitivity and aligned well with visual observations. This suggests the potential of CW‐SSIM as a universal metric for assessing the quality of see‐through images on transparent displays. [ABSTRACT FROM AUTHOR]

The biggest challenge in launching Micro‐LED displays is cost reduction. In our previous report (1), we proposed a super cost‐effective test method embedding EL and electrical testing (PEMPTM). In this paper, we report the validity of PEMPTM by comparing the external quantum efficiency (EQE) of LED emission and photodetection characteristics. [ABSTRACT FROM AUTHOR]

We propose a novel pulse width modulation (PWM) micro‐LED pixel circuit utilizing LTPO TFTs. It can compensate for VTH variation, ensuring uniform micro‐LED current pulse width and amplitude. In addition, the circuit exhibits excellent IR‐drop compensation. The fabricated LTPO pixel circuit was found to perform PWM with VTH and IR‐drop compensation. [ABSTRACT FROM AUTHOR]

Shrinking LEDs reduces Internal Quantum Efficiency (IQE) and challenges light collection[1]. This study employs LightTools® for geometric optical simulations to create a secondary optical structure with reflector and a black matrix, enhancing Micro‐LED efficiency. This approach significantly reduces light emission loss from the original 40% to 4.54%. and ambient light reflection from the original 25% to 4.85%. [ABSTRACT FROM AUTHOR]

We propose a 7T2C micro‐LED pixel circuit which uses a multimodal transistor (MMT) as driver for compact pulseamplitude and pulse‐width modulation (PAM + PWM) functionality. The LTPS circuit exploits the MMT's ability to maintain a constant drain current, controlled by its source gate, while the channel gate potential varies without interfering with the current magnitude. The MMT also affords a compact footprint and tolerance to large variations in drain‐source voltage caused by LED operating conditions or power supply I × R drops. [ABSTRACT FROM AUTHOR]

We report a photolithography‐based technology for patterning quantum dot color converters for micro‐LED displays. A patterning resolution of ~1 µm is achieved. The method can be applied to any color converter materials. Integration of perovskite quantum dots and CdSe/ZnS quantum dots is demonstrated to show the versatility of the technology. [ABSTRACT FROM AUTHOR]

This article presents an AR HUD using micro LED technology for enhanced brightness and image quality. It utilizes micro LED's high brightness to merge AR images seamlessly with external views and employs Nature 3D technology to improve the HUD's 3D depth, significantly boosting vehicle safety. [ABSTRACT FROM AUTHOR]

InGaN/GaN micro-light-emitting diodes (micro-LEDs) with a metal–insulator-semiconductor (MIS) structure on the sidewall are proposed to improve efficiency. In this MIS structure, a sidewall electrode is deposited on the insulating layer-coated sidewall of the device mesa between a cathode on the bottom and an anode on the top. Electroluminescence (EL) measurements of fabricated devices with a mesa diameter of 10 μm show that the application of negative biases on the sidewall electrode can increase the device external quantum efficiency (EQE). In contrast, the application of positive biases can decrease the EQE. The band structure analysis reveals that the EQE is impacted because the application of sidewall electric fields manipulates the local surface electron density along the mesa sidewall and thus controls surface Shockley–Read–Hall (SRH) recombination. Two suggested strategies, reducing insulator layer thickness and exploring alternative materials, can be implemented to further improve the EQE of MIS micro-LEDs in future fabrication. [ABSTRACT FROM AUTHOR]

Self‐luminous projection technologies, such as Micro‐LED chips, compared with traditional projection methods, does not require complex lighting path. So it can significantly improve light utilization rate and reduce costs. However, technical challenges in Micro‐LED chip production make it difficult to improve the chip's resolution further. Some studies have shown that compared with the original image resolution of the spatial light modulator (SLM), the projection images overlapped is an effective method to improve the resolution of the projector. In this paper, we study the working principle of the extended pixel resolution actuator and propose a self‐luminous projection resolution enhancement system based on Micro‐LED chip. It can improve the resolution of the projection images with the resolution of the Micro‐LED chip unchanged. The resolution enhancement system consists of a Micro‐LED chip, an extended pixel resolution actuator and a projection lens. According to the working principle of the extended pixel resolution actuator, the projection lens is an image‐space telecentric structure, in which modulation transfer function of projection imaging at Nyquist frequency 100 lp/mm is greater than 0.4. Finally, the tolerance analysis on the projection lens is completed. The results show that the projection lens has a high success rate in processing. This work is of great significance for improving the resolution of Micro‐LED self‐luminous projection images. [ABSTRACT FROM AUTHOR]

One of the micro‐LED direct view display major challenges is to find ways of drastically dropping the cost, for instance, by reducing the micro‐LED size, simplifying the assembly process and improving the assembly yield. In this paper, we present Aledia's GaN‐on‐Si nanowire (NW) LED technology made on standard 8 "Si wafers, scalable to 12" wafers. We will present two components using our NW technology and their use case for the manufacturing of micro‐LED direct view fine pitch display: NWs RGB three color chips obtained using quantum dot (QD) color conversion at chip level. The RGB chips can then be transferred on PCB or glass or TFT substrates for panel manufacturing.The integration within the same chip of a three color RGB chip together with its CMOS driving electronics. Those chips allow to obtain an active‐matrix architecture on any passive backplane without the use of TFT. [ABSTRACT FROM AUTHOR]

Micro‐LED is considered as the new generation of display with the long‐lifetime, high contrast and brightness, splicing capability, etc. Mass transfer is the bottleneck that limits the manufacturing of Micro‐LED display at large volume, due to factors such as laser‐ lift off, pick‐up, metal bonding, and so on. Metal bonding between the Micro‐LED chip and the substrate is one of the most important impactors to the light‐up yield. To solve the key thermal mismatch issue between the backplane and Micro‐LED donor during heating, the laser‐assisted bonding process could be a viable solution. We present a study in metallic element Au/Sn with high productivity, capability and low cost, as well as good thermal and electrical conductivity, excellent bonding strength, and low sensitivity to surface roughness. The result is presented in a 62× 78 pixels full color Micro‐LED display, with reliable metal electrical connection between microscale LED devices and the backplane that can be achieved under 250℃ without any damage to the backplane. In conclusion, the micro morphology and formation mechanism of different alloy phase compositions of welded metal elements have been thoroughly studied, and a feasible technological methodology has been developed for the upcoming mass production of Micro‐LED display modules. [ABSTRACT FROM AUTHOR]

Micro‐LED, as one of the most promising advanced display technologies, has attracted increasing research interest from academia and display industry. With the outstanding performance in brightness, lifetime, and contrast, Micro‐LED display shows tremendous potential for applications in various electronic terminals. The bonding between Micro‐LED and backplane is the key technology that affects the industrialization of Micro‐LED display at present. The common bonding technology can be classified as metal bonding and ACF bonding. Metal bonding has the advantages of low cost and high bonding strength. However, the bonding yield is affected by the difficulties of thermal mismatch and short circuit. In order to solve these difficulties, we developed a bonding process based on Non‐Conductive Paste (NCP). That is, the Micro‐LED transfer onto the backplane with a lay of NCP, then realizing the conductivity between the Micro‐LED and the backplane by thermocompression bonding. In this paper, we applied this technology in 180 × 160 pixels full‐color Micro‐LED display, and achieved more than 99.99% bonding yield by testing the NCP material characteristics, temperature and pressure. [ABSTRACT FROM AUTHOR]

Abstract InGaN/GaN micro-light-emitting diodes (micro-LEDs) with a metal–insulator-semiconductor (MIS) structure on the sidewall are proposed to improve efficiency. In this MIS structure, a sidewall electrode is deposited on the insulating layer-coated sidewall of the device mesa between a cathode on the bottom and an anode on the top. Electroluminescence (EL) measurements of fabricated devices with a mesa diameter of 10 μm show that the application of negative biases on the sidewall electrode can increase the device external quantum efficiency (EQE). In contrast, the application of positive biases can decrease the EQE. The band structure analysis reveals that the EQE is impacted because the application of sidewall electric fields manipulates the local surface electron density along the mesa sidewall and thus controls surface Shockley–Read–Hall (SRH) recombination. Two suggested strategies, reducing insulator layer thickness and exploring alternative materials, can be implemented to further improve the EQE of MIS micro-LEDs in future fabrication. Graphical Abstract

With the advent of technologies such as augmented/virtual reality (AR/VR) that are moving towards displays with high efficiency, small size, and ultrahigh resolution, the development of optoelectronic devices with scales on the order of a few microns or even smaller has attracted considerable interest. In this review article we provide an overview of some of the recent developments of visible micron-scale light emitting diodes (LEDs). The major challenges of higher surface recombination for smaller size devices, the difficulty in attaining longer emission wavelengths, and the complexity of integrating individual, full color devices into a display are discussed, along with techniques developed to address them. We then present recent work on bottom-up nanostructure-based sub-micron LEDs, highlighting their unique advantages, recent developments, and promising potential. Finally, we present perspectives for future development of micro-LEDs for higher efficiencies, better color output and more efficient integration.