Fig. 4: Stretchable LPTHE with gradient stiffness and strain isolation.

a Schematics showing that strain isolation induced by gradient stiffness (blue region) protects chips from open circuits and short circuits. For textiles without strain isolation, wires easily detach from chip terminals, and the lateral expansion of wires narrows the spacing between adjacent chip terminals. b FEA results showing the effect of gradient stiffness on strain distributions of textiles with an SOT-23-5 footprint. The LPT with only soft regions programmed cannot isolate strain and thus exhibits visible deformation at the chip footprint. For comparison, the LPT with gradient stiffness exhibits strain isolation, showing negligible strain in the same area. c, d Photos of SOT-23-5 chips and LM wires on textiles (c) without and (d) with gradient stiffness. Both images are rendered using false colors. e, f (e) Resistance variations and (f) their enlarged view of an LPTHE resistor under cyclic stretching. g Resistance variations of the LPTHE resistor under gradually increased strain until failure. h Photos of a LPTHE screen containing 25 LED chips, 20 VIAs, and 16 VIBs. VIA, vertical interconnect access. i FEA results showing strain distributions of the substrate of the LPTHE screen. j Photos of the LPTHE screen displaying five different patterns when being stretched or bent.