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Epitaxy, a process for growing single-crystalline overlayers on wafers, has advanced the commercial deployment of high-quality heterostructured electronic and optoelectronic devices. Recent increasing demand for multifunctional, high-performance devices on a single chip has driven a technological shift from miniaturization towards high-density hetero-integration. This transition has catalyzed the evolution of stamping-printing and transfer-assembly techniques [1]. One strategy for heterogeneous integration utilizes transfer-based assembly methods, which entail the delamination of epi-layers fabricated through various batches and procedures. This approach grapples with two significant technical challenges in achieving high-density integration of high-performance devices (i.e., fabrication of micro-LED displays for AR applications). First, traditional epitaxial growth methods result in epi-layer devices strongly bonded to the substrate, complicating their separation without the use of high-power laser irradiation or chemical etchants. These separation techniques, known to inflict damage to both the substrate and epi-layers, impose strict constraints that limit enhanced device performance and productivity [2]. Second, during the transfer and assembly process, different functional devices must be segmented into tiny chips prior to their accurate transfer and assembly onto the target surface (or substrate). Even small misalignment during chip bonding to backplane circuits can disrupt device interconnects with the underlying layouts, thereby increasing the manufacturing costs of micro-LED displays. Additionally, the fabrication of higher-density vertical stack devices poses a formidable challenge, relevant not only for high-resolution display production (such as augmented reality (AR) and metaverse devices) but also for hetero-integrated electronics. In this presentation, we explore innovative epitaxy techniques (i.e., remote and van der Waals epitaxy) that eliminate chemical bonds between the epi-layer and the wafer [3-5]. This approach provides a potential solution via the straightforward delamination of epi-layers and their subsequent stacking, enhanced by meticulous photolithographic patterning procedures [4]. We will highlight our recent work on high-density, heterogeneously integrated vertical R/G/B micro-LEDs and flexible devices, leveraging these novel epitaxy methods, and emphasize potential applications in AR [6]. The remote epitaxy of spatially isolated micro-crystal LEDs has facilitated the fabrication of deformable lighting devices [7]. This emergent bond-free epitaxy could be readily adopted to extend the reach of semiconductor manufacturing, potentially leading to a heterogeneous system on a chip for comprehensive electronic and optoelectronic solutions.
References
[1] J. A. Rogers et al., Science 327, 1603 (2010).
[2] H. Kum et al., Nat. Electron. 2, 439 (2019).
[3] H. Kim et al., Nat. Rev. Methods Primers 2, 40 (2022).
[4] Y. Kim et al., Nature 544, 340 (2017).
[5] Y. J. Hong et al., Nano Lett. 12, 1431 (2012); Y. J. Hong and T. Fukui, ACS Nano 5, 7576 (2011).
[6] J. Shin et al., Nature 614, 81 (2023).
[7] J. Jeong et al., Sci. Adv. eaaz5180 (2020); J. Jeong et al., Nano Energy 86, 106075 (2021).
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