Stretchable Active Matrix Inorganic LED Display Enabled by Overlay-Aligned Roll-Transfer Printing

Journal: Advanced Functional Material

Publication date: 2017. 03

Summarized by Sejin Kim


– Roll-Transfer of Inorganic Components on Arbitrary Substrates


v. The three steps of transfer process

  1. Transfer of the Si-TFTs from the bulk SOI wafer to a carrying substrate
  2. Transfer of the LEDs from an AlInGaP wafer to a carrying substrate
  3. Integration of the display, followed by transfer from the carrying substrate to rubber or plastic substrate


Fig. 1


– TFT Fabrication for Printing Process

v. Picking step


Fig. 2


Fig. 3

  1. Conventional TFT fabrication
  2. Etching BOX with the ribbon pattern of PR mask
  3. Etching of the exposed bulk Si by inductively coupled plasma RIE

v. Placing step

  1. Printing of TFT onto the prepared PMMA/glass substrate




– Integration of Si-TFT and μ-LED on a Temporary Substrate Using Roll Transfer


Fig. 5

  1. Undercutting of μ-LED by selectively eliminating the sacrificial layer (AlAs)
  2. Picking of the μ-LED with automated roll-to-plate printing machine with two mounted microscopes


Fig. 6


– Transfer Printing on Elastomer Substrate

Fig. 7

  1. Reactive-ion etching of the epoxy layers and NOA (with O2 for 40 min)
  2. The exposed PMMA sacrificial layer was dissolved
  3. Transfer of the device from glass to PDMS substrate (the PDMS substrate was baked at 70 °C for making a strong bond between the device and the PDMS substrate)


– Stretchable LED Display with Si Backplane TFTs

Fig. 8

v. The elastic interconnects are composed of polymeric encapsulated metals with a sandwiched structure and are located in the neutral plane



Fig. 9

v. Most of the strain occurs on the serpentine-shaped bridge region; the strain on the island region is negligible.