Large quantities of microscopic red, green, and blue light-emitting diodes (LEDs) made of crystalline inorganic semiconductor materials micro-transfer printed in large quantities onto rigid or flexible substrates form monochrome and color displays having a wide range of sizes and interesting properties. Transfer-printed micro-LED displays promise excellent environmental robustness, brightness, spatial resolution, and efficiency. Passive-matrix and active-matrix inorganic LED displays were constructed, operated, and their attributes measured. Tests demonstrate that inorganic micro-LED displays have outstanding color, viewing angle, and transparency. Yield improvement techniques include redundancy, physical repair, and electronic correction. Micro-transfer printing enables revolutionary manufacturing strategies in which microscale LEDs are first assembled into miniaturized micro-system "light engines," and then micro-transfer printed and interconnected directly to metallized large-format panels. This paper reviews micro-transfer printing technology for micro-LED displays. FIGURE 3 -(A) Schematic illustration of a micro-transfer stamp that is rigid in horizontal directions and compliant in the vertical dimension. (B) Photograph of a stamp on a 225 × 225 mm glass back. (C) SEM of the stamp posts.FIGURE 4 -Photograph of a 50 × 50 mm stamp silicon master (A) and elastomer stamp (B). The stamp has an array of 250 by 250 posts on a 200-micron pitch with 62,500 posts. Journal of the SID 25/10, 2017 591 FIGURE 9 -Micrographs of an array of microscopic inorganic light-emitting diodes microtransfer printed to a metal-coated substrate (left) and emitting red light (right). The anodes are connected in common with a transparent aluminum zinc oxide anode.

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Displays that use direct light emission from microscale inorganic light emitting diodes (ILEDs) have the potential to be very bright and also very power efficient. High-throughput assembly technologies that accurately and cost-effectively deposit large arrays of ILEDs onto display substrates with high yield are key enablers for ILED displays. Transfer-printing with elastomer stamps is a candidate assembly technology for making ILED displays. A variety of passive matrix ILED displays have been designed and fabricated using transfer-printed microscale ILEDs.

Major advances in flat panel displays can come from the pixel‐level integration of high performance microscale components fabricated on semiconductor wafers and transferred by advanced assembly methods onto large‐area substrates. Displays that use direct light emission from tiny inorganic light emitting diodes (µILEDs) have the potential to be very bright and power efficient. Transfer‐printing with elastomer stamps is a candidate assembly technology for making µILED displays, serving as the metaphorical bridge between the LED wafer and the display panel. This paper presents simple demonstrations of displays made from red, green, and blue µILEDs fabricated on gallium arsenide, silicon, and sapphire wafers, transferred to glass and plastic display substrates by transfer‐printing. The demonstrator displays exhibit interesting characteristics, including transparency, flexibility, repair‐ability, wide color gamut, and pulse‐width modulated active matrix driving schemes facilitated by transfer‐printed micro‐scale driver circuits.

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