ZnO-based triboelectric nanogenerator and tribotronic transistor for tactile switch and displacement sensor applications

Abstract

Tribotronics, the coupling of triboelectricity and semiconductors, is a novel field that has sparked much interest in the nanoelectronics and nanoenergy industries. This work presents the fabrication of a ZnO tribotronic transistor by combining a ZnO thin film transistor (ZnO-TFT) and a triboelectric nanogenerator (TENG) operating in vertical contact separation mode. A Si/SiO2/ZnO/Au structure was used to construct a bottom-gated ZnO-TFT. Radiofrequency (RF) magnetron sputtering was employed to deposit ZnO thin film, and the Au contact was achieved through thermal evaporation. A range of annealing temperatures was investigated, and ZnO TFT annealed at 500 °C exhibited a maximum electron mobility of 5.47 cm2/V s and a high on/off ratio of 105. We also investigated the photoresponse of this optimized ZnO-TFT using a UV LED. A vertical contact separation mode TENG was fabricated using ZnO (tribo-positive layer) and polyvinylidene difluoride (PVDF, tribo-negative layer) and combined with the ZnO TFT to fabricate a tribotronic transistor. The drain current of the tribotronic transistor dropped from 2.9 to 0.02 µA at a drain voltage of 5 V when the tribo layers were separated by 15 mm. Within the separation region of 2 mm, the device showed a 1.29 µA/mm change in drain current demonstrating its effectiveness in displacement sensing. Unlike conventional TFTs, the TENG's output could successfully control the tribotronic transistor's drain current and was innovative in such domains where conventional electrical components were constrained. Furthermore, this ZnO tribotronic device was used as an active smart tactile switch by simply touching or releasing the ZnO TENG with a finger.