Electromechanical sorting method for improving the sensitivity of micropyramid carbon nanotube film flexible force sensor

Abstract As one of the most concerned sensitive materials, carbon nanotubes (CNTs) are widely used in flexible sensors for wearable electronic devices. Here, we present an electromechanical sorting method that applies to micropyramid single-walled CNT (SWNT)-film flexible force sensor to further enhance its sensitivity. The principles of the method are as follows. When the micropyramid structure is under pressure, stress concentration will occur at its tip, and the resistivity of the SWNT film coated on the surface of the micropyramid structure will change remarkably, which leads to changes in the resistance of the SWNTs. The resistance of quasimetallic SWNTs increases greatly under pressure, whereas that of metallic SWNTs increases minimally (band theory). Therefore, when the threshold voltage was applied to SWNTs, the metallic SWNTs exposed in the air were oxidized and failed when the current induced defects in the graphite layer, whereas the quasimetallic SWNTs with a high gauge factor remained functional. The experimental results showed that the sensitivity of the sorted SWNTs flexible force sensor was 3.4891 kPa−1, which denotes an improvement of 56.86% compared with the initial unsorted devices. In addition, the flexible force sensor exhibited low power consumption, which is less than a microwatt, and good repeatability and stability. Finally, the sensor was successfully used in the knuckles of a person's fingers to monitor finger motions.