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.

One important technical hurdle that has to be overcome for using organic transistors in radio-frequency identification tags is for these devices to operate at rf frequencies (typically 13.56MHz) in the front end. It was long thought that organic transistors are too slow for this. In this letter we show that organic transistor based full-wave rectifier circuits utilizing pentacene, a p-channel organic semiconductor, can operate at this frequency with a useful efficiency. In order to achieve such high-frequency operation, we make use of the nonquasistatic state of the transistors.

Reversible addition‐fragmentation chain transfer (RAFT) polymerization was used to produce poly(methyl acrylate) (pMA) loops grafted onto silica nanoparticles using doubly anchored bifunctional RAFT agents 1,4‐bis(3′‐trimethoxysilylpropyltrithiocarbonylmethyl)benzene (Z‐group approach) and 1,6‐bis(o,p‐2′‐trimethoxysilylethylbenzyltrithiocarbonyl)hexane (R‐group approach) as mediators. In both cases, molecular weights of the resulting surface‐confined polymer loops increased with monomer conversion, whereas the grafting density was significantly higher in the case of the R‐group supported RAFT polymerization due to mechanistic differences of the RAFT process at the surface. This result was evident from thermogravimetric analysis and supported by scanning electron microscopy. Polymer loops with molecular weights up to 53,000 g mol−1 were accessible with polydispersities of about 2.0 without and 1.5 with the addition of free RAFT agent. UV signals of the detached pMA loops measured via size exclusion chromatography were shifted to higher molecular weights compared with the corresponding RI signals, indicating branching reactions caused by the close proximity of growing radicals and polymer at the surface of the silica nanoparticles. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 7656–7666, 2008

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The present study introduces the silica-anchored azo-initiator 4,4′-azobis(4-cyano-N-(3″-triethoxysilylpropyl)-valeric amide) (ACTA) for the surface-initiated polymerization of methyl acrylate (MA) with and without additional grafted reversible addition–fragmentation chain transfer (RAFT) agents 1,4-bis(3′-trimethoxysilylpropyltrithiocarbonylmethyl)benzene and 1,6-bis(o,p-2′-trimethoxysilylethylbenzyltrithiocarbonyl)hexane. While the sole use of silica-linked ACTA produced grafted poly(methyl acrylate) (pMA) of high molecular weight, due to a 2D Trommsdorff effect, the polymerization in combination with the fixed RAFT agents exhibited living behaviour with increasing molecular weights during polymerization. Silica-pMA hybrids were further analyzed via thermogravimetric analysis and scanning electron microscopy, which revealed significant differences between the three approaches.

Summary: Reversible addition‐fragmentation chain transfer (RAFT) polymerization with benzyl(3‐trimethoxylsilylpropyl)trithiocarbonate (BTPT) and 1,4‐bis(3′‐trimethoxysilylpropyltrithiocarbonylmethyl)benzene (TPTB) as mediators was performed to produce branched poly(methyl acrylate) (pMA). The deviation of the experimental number average molecular weights towards higher values and the size exclusion chromatography (SEC) traces measured at distinct time instants after polymerization indicated a coupling of the trimethoxysilyl end‐groups to form terminal‐linked pMA of high molecular weight. The trimethoxysilyl moieties also caused the unusual creation of doubly ionized pMA chains in electrospray ionization mass spectrometry (ESI‐MS). BTPT was furthermore anchored onto fumed silica to carry out a RAFT graft polymerization with benzylpropyltrithiocarbonate as additional RAFT agent in solution to afford well‐defined pMA chains fixed to silica nanoparticles. A block copolymerization of the living anchored pMA chains with styrene (Sty) produced grafted pMA‐b‐pSty chains with good agreement between experimental and theoretical molecular weights.

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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