Micropatterned elastic ionic polyacrylamide hydrogel for low-voltage capacitive and organic thin-film transistor pressure sensors

Electronic skins (E-skins) have attracted great research interest because of their promising applications in stretchable optoelectronics, soft robotics, and personalized healthcare devices. However, it remains a great challenge to fabricate E-skin devices that meet strict practical requirements such as high sensitivity, low-power operation and noise-proof ability. Here, we developed a novel elastic ionic polyacrylamide hydrogel (EIPH) with a high capacitance for the development of low-voltage organic thin-film transistor (OTFT) pressure sensors. The EIPH was prepared by photopolymerization of an acrylamide monomer in an aqueous solution of poly (acrylic acid) and CaCl ₂ and was then in situ micropatterned on an indium-tin oxide electrode. The fabricated capacitive sensor with 10-µm-wide EIPH micropillar structures achieved a high sensitivity of 2.33 kPa ⁻¹ with a capacitance sensitivity of 103.8 nF/kPa. This capacitance sensitivity is more than 100 times higher than that of conventional capacitive pressure sensors due to the formation of an electrical double layer. The micropatterned EIPH was adopted as a dielectric layer in the fabrication of the OTFT-based pressure sensors. Such an EIPH-based OTFT pressure sensor not only greatly enhanced the sensitivity, i.e., 7.7 times higher than its capacitive counterparts, but also largely reduced the operation voltage to 2 V.