A site-selective integration strategy for microdevices on conformable substrates

Microdevices can be integrated on conformable substrates to create high-performance and multifunctional human–machine interfaces. However, existing integration schemes often use unpatterned, thick and rigid adhesive layers that can increase the flexural rigidity and compromise mechanical compliance. Here we report the site-selective and anisotropically conductive integration of microdevices on conformable substrates. An adhesive precursor is selectively deposited on high-density arrays of microdevices using a velocity-controlled dip-transfer coating method. This technique suppresses capillary action and unwanted coating between devices, thereby minimizing the extent of bonding areas that degrade the inherent compliance of polymeric substrates. Ferromagnetic particles in the adhesives are magnetically self-assembled into well-defined anisotropic chains, resulting in a low contact resistance without electrical interference between fine-pitch terminals. We use the approach to additively integrate multiscale, die-level microdevices on various flexible and stretchable substrates. We show that it can be used to assemble microscale light-emitting diodes and a microcontroller die on a flexible circuit to create a skin-attachable device capable of detecting and displaying temperature. High-density device arrays can be integrated on flexible substrates using a dip-transfer coating method that suppresses adhesive layers from forming between closely spaced devices and uses magnetically self-assembled particles to increase the anisotropic conductivity.