Wafer-scale alignment and integration of micro-light-emitting diodes using engineered van der Waals forces

Abstract

Micro-light-emitting diodes (mu LEDs) can be used in mobile and virtual reality display applications where high efficiency, resolution, service life and image quality are necessary. However, mu LED displays require the alignment of millions of devices, and mass production methods are currently at an early stage of development. Here we report a method to rapidly align mu LED chips at the wafer scale by controlling the van der Waals force between the chips and interposer. We engineer the upper and lower surfaces of the mu LED chips to have different van der Waals forces, thus enabling their selective bonding to substrates in fluidic and drying processing conditions. The process allows single-faced and irreversible alignment of 259,200 mu LED chips with an accuracy of 100% and a transfer yield of 99.992% over 40 trials. To illustrate the capabilities of the approach, we create mu LED-based passive- and active-matrix displays by bonding the mu LED-loaded interposer to backplanes based on low-temperature polysilicon thin-film transistor. By engineering the upper and lower surfaces of micro-light-emitting-diode chips to have different van der Waals forces, hundreds and thousands of chips can be accurately aligned on substrates and used to create active-matrix displays.