Fig. 1

a Schematic illustration of the tactile sensitivity tester, which consisted of a micrometer and sample stage. The sample was pressed by the rod of the micrometer in the normal direction. The normal displacement of Δ h is the distance from the initial top height of the fingertip-shaped surface to the height of the pressed surface. b Schematic principle of tactile sensing by OTFT array. Electronic devices placed on a neutral strain surface are not exposed to lateral strain because the tensile and compressive strain cancel each other on the neutral strain surface [27–31]. However, the OTFTs placed on the off-neutral strain surface were exposed to lateral compressive strain due to the slight distortion of the fingertip-shaped curved surface