technology because of its higher brightness, lower power consumption, and faster response than OLED and LCD technologies. [1-5] They are expected to be suited for many applications in the brightnesssensitive or power-sensitive environments such as wearable devices, optogenetics, outdoor displays, and AR/VR. [6-13] Despite these attractive advantages, fabricating high-resolution micro-LED displays is proven to be very challenging because accurately assembling millions of micro-LEDs onto a driving circuit requires complicated transfer and bonding process. [3,14] A scalable active-driven micro-LED display device is primarily composed of two major parts: a micro-LED array, and a driver backplane. [14-20] In order to generate any display pattern, the micro-LED array must be electrically connected to the pads on the driver backplane. This is most commonly achieved by flip-chip bonding technologies such as bump bonding and anisotropic conductive film (ACF) bonding, [13] whereas in some cases it can be done using via filling or metal wiring technology. [3,4,21] The latter technology is not preferred, because for high-resolution display, both metal wires and vias occupy extra space. In the course of bonding, the small chip size may incur serious registration/alignment errors, resulting in forming display defects. Therefore, the fabrication of a micro-LED display device involves two challenging processes: i) assembling millions of micro-LED chips in a fast, accurate, and low-cost manner, and ii) reliably bonding the micro-LEDs onto the driver circuit with minimized displacement. Micro-LED arrays can be made in a monolithic manner, without using tedious pick-and-place technology. [12] In a monolithic approach, an array of micropixels is formed simultaneously on the same native substrate using only a lithography process, and all these pixels on the same substrate are then integrated onto a driver backplane via one-time flip-chip bonding. Optionally, the sapphire can be taken off by laser liftoff (LLO), [21,22] in order to suppress the optical crosstalk and beam divergence induced by the thick substrate. [23,24] Flip-chip bonding is a proven technology which is fast and compatible with wafer-level bonding. Furthermore, it can improve the light-emitting efficiency because of less light absorption caused The development of micro-sized light emitting diode (LED) displays has driven the research of micro-LED mass-transfer technology. To date, various transfer technologies are proposed, but ample room for improvements in the transfer yield and transfer accuracy still remains. Furthermore, whether these techniques are suited for the subsequent bonding process is not well investigated, which is essential for achieving a good electric connection between micro-LEDs and driver electronics. Here a systematical solution, termed as "tape-assisted laser transfer," which is not only suited for high-yield micro-LED transfer but also well compatible with subsequent bonding process, is developed. Using a low-cost adhesive tape as the support s...
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.
In this work, we performed a systematic study of the physical properties of amorphous Indium–Gallium–Zinc Oxide (a-IGZO) films prepared under various deposition pressures, O2/(Ar+O2) flow ratios, and annealing temperatures. X-ray reflectivity (XRR) and microwave photoconductivity decay (μ-PCD) measurements were conducted to evaluate the quality of a-IGZO films. The results showed that the process conditions have a substantial impact on the film densities and defect states, which in turn affect the performance of the final thin-film transistors (TFT) device. By optimizing the IGZO film deposition conditions, high-performance TFT was able to be demonstrated, with a saturation mobility of 8.4 cm2/Vs, a threshold voltage of 0.9 V, and a subthreshold swing of 0.16 V/dec.
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