Fig. 4: Effect of the top film thickness on the spatial resolution of the photonic skin.
a Schematic illustration of the flow of the spatial signal when the pressure distribution (Pinput) is applied to the top film of the photonic skin. The Pinput is low-pass filtered by the top film, forming contact pressure distribution between the CNN and the ETL (Pcontact). The Pcontact is linearly converted into electrical conductance distribution between the CNN and the ETL (Gcontact) by the CNN. The light intensity distribution of the QLED (LQLED) is proportional to the Gcontact. b Schematic illustration of the situation where a micropillar array presses the top thin film. In finite element analysis (FEA), we calculated the Pcontact between the top and bottom films when Pinput was applied with the micropillar array. c SEM image where 50-μm-wide PU pillars spaced by 50 μm pressed a 1-μm-thick polyimide (PI) film on a glass substrate. Scale bar, 50 μm. d FEA results showing a line profile of Pcontact when a pillar array with a 50 µm width and 50 µm gap (254 dpi) pressed the top film with different ttop values. e, f Optical photographs where the 254 dpi PU pillar array pressed photonic skins with ttop ~ 10 µm (e) and ttop ~ 1 µm (f). The right images present FEA results showing Pcontact for the corresponding ttop values. Scale bars, 500 and 100 μm. g SEM and optical images of 1016 dpi PDMS hexagonal micro-bumps. Scale bars, 5 and 20 μm. h Optical image of the device with ttop ~ 1 µm visualizing the pressure applied with the 1016 dpi hexagonal micro-bumps. Scale bar, 20 μm.
