Ultrasensitive and robust two-dimensional indium selenide flexible electronics and sensors for human motion detection

To accurately detect human motion, a sensing material/device must be flexible, ultrasensitive to strain, and electrically and mechanically robust. However, existing electronics and sensors, which are either not flexible enough, or not ultrasensitive to strain, or suffering from poor on/off ratio and low charge mobility, do not meet these stringent requirements. Here, we demonstrate a flexible and ultrasensitive three-terminal strain sensor based on two-dimensional (2D) InSe for detecting human-motion activities. The 2D InSe exhibits a tunable bandgap and a large piezoresistive effect via strain engineering. Through electrostatic gating effect, the gauge factor of the sensor can be enhanced by 8-fold and 7-fold for a low tensile and compressive strain of only +/- 0.25%, respectively. Remarkably, the fabricated 2D InSe-based transistor achieves both a record high on/off ratio of similar to 10(8) and an electron mobility of similar to 383 cm(2)/V s, superior to all existing ones. Furthermore, flexible InSe logic inverters with a high voltage gain of similar to 10 and a large noise margin of similar to 0.7 x V-DD (supply voltage) are realized under various strain conditions. This work paves the way to enable simultaneous integration of high-performance flexible sensors and electronics based on a common 2D InSe material platform towards achieving a fully integrated sensing system.