Design to secure temporal invariance of triboelectric sensing signals

Triboelectric nanogenerator (TENG) has been extensively explored for use as self-powered tactile sensors, mainly focused on tactile sensitivity. However, the signal magnitude of the triboelectric sensor (TES) varies upon time even under the same mechanical stimulus. There have been little studies on how to secure the same signal magnitude at any time of mechanical contacts regardless of the contact frequency. This study systematically investigates the retention time of the charge-saturated state in TES and suggests DC charging for enhancing the retention time by filling the deep charge traps. It characterizes the potential barrier for the surface charge diffusion in a patterned triboelectric surface and finds the potential barrier is large enough to confine the generated surface charges. It also reports that the TES generates identical output signal at any time regardless of the touch frequency as long as the contact time interval is less than the retention time. This study demonstrates a TES with five patterns of different sizes, which has only two global electrodes (top and bottom). The TES generates time- and frequency-independent sensing signals so that it successfully recognizes the contact locations and the contact sequences.