Self-powered flexible motion sensors fabricated with InN nanowires coated with tungsten-disulfide nanosheet

Flexible motion sensors are considered to be key components of the human–machine interface (HMI) of emerging new technologies and health-care systems. The performance of conventional motion sensors, which typically require an external power supply, needs to be further improved for practical applications. In this study, we demonstrate self-powered flexible motion sensors (PMSs) fabricated with InN nanowires (NWs) coated with tungsten-disulfide (WS₂) nanosheets (WS-NShs). The WS-NShs, which have a higher work function than the InN NWs, facilitate the extraction of carriers from the NWs to the electrodes to enhance the output signal of the PMSs. The output voltage of the PMS based on InN NWs coated with the 0.6-nm-thick WS-NShs, measured to be 21.2 V without an external power supply, is 2.8 times higher than that of the device without the NShs. In addition, this output voltage is much higher than previously reported values. The PMSs were highly sensitive to the bending strain and frequency, and they performed stably as a function of the operation time, relative humidity, and cyclic bending. In a practical assessment, output signals from the PMSs were measured by attaching them to the finger, wrist, and knee, indicating that the devices proposed in this work are capable of effectively tracking human motion and hold potential for implementation in HMI systems and health-monitoring technologies.