Fig. 2: Piezoresistive characterization of CNNs.

a Structure of CNN-based pressure sensors for piezoresistive characterization. The photograph shows the fabricated pressure sensor. Scale bar, 5 mm. b Pressure response and sensitivity of the pressure sensor with the 0.9-μm-thick CNN using a 50% volume ratio ink under a bias voltage of 1 V. c Plots of current as a function of the pressure applied onto CNN-based sensors using ink with three different volume ratios (30, 40, 50% v/v). d Cyclic stability of the CNN-based pressure sensor under continuous loading and unloading cycles from 0.1 kPa to 120 kPa. e Enlarged view of the recorded data in d after 4000 cycles. f Photograph showing the experimental setup for sensing cell phone vibration. g Sensing result of cell phone vibration (160 Hz) using the pressure sensor. The current was recorded at a sampling interval of 480 μs. h Enlarged view of the part of the current plot when the cell phone vibrated. i Fast Fourier transform result of the signal in h.