Vertically Stacked Full Color Micro-LEDs via Two-Dimensional Material-Based Layer Transfer

Full color micro-light emitting diode (µLED) displays have been explored for augmented and virtual reality (AR/VR) applications that require extremely high pixels-per-inch (PPI). However, conventional manufacturing processes based on pick-and-place methods are slow and expensive, and their resolutions are insufficient to meet the required pixel densities. Recent demonstrations of vertical µLED displays attempt to address these issues by stacking freestanding red, green, and blue (RGB) LED membranes and fabricating top-down, but the absence of lift-off techniques to produce ultrathin, readily released, and low-cost layers of LEDs has delayed essential technological progress. Here, we report full color, vertically stacked µLED displays that achieve the highest pixel density (5100 PPI) and the smallest pixel size (4.5 µm) reported to date, which is uniquely enabled by two-dimensional material-based layer transfer (2DLT) techniques. 2DLT allows the growth of RGB LEDs with near-submicron thickness on 2D material-coated substrates via remote epitaxy or van der Waals epitaxy, mechanical release of LEDs from 2D materials, stacking of LEDs via adhesion layers, and top-down fabrication to yield vertical RGB pixels. The smallest ever pixel height of ~9 µm is the key enabler for µLED arrays with record high PPI. Facile mechanical release process allows high-throughput manufacturing of µLEDs, and the reusability of wafers reduces material cost. Wavelength-selective polyimide absorbers serve as adhesive interlayers as well as optical filters that prevent interference between LEDs, allowing further reduction in stack thicknesses. We also demonstrate a highly resolved transfer of µLED chips to illustrate the versatility of 2DLT for constructing large-scale µLED displays. These results not only establish routes to exceptionally high-pixel density full color µLED displays for AR/VR, but also offer a generalizable platform for broader classes of 3D-integrated systems.