Ferroelectrically gated two-dimensional bismuth oxyselenides for strain-invariant flexible synaptic thin-film transistors

Two-dimensional van der Waals (2D vdW) semiconductors have proven to be of great importance for flexible thin-film transistors (TFTs) owing to their intrinsic mechanical flexibility and superior electronic properties. In particular, bismuth oxyselenide (Bi₂O₂Se), featuring ultrahigh electron mobility along with facile scalable thin-film growth methods, could offer a new option to deliver massively enhanced potential for flexible TFTs. However, it has remained a challenge to achieve nonvolatile flexible memory devices based on Bi₂O₂Se TFTs, thereby hindering the extension of Bi₂O₂Se TFTs to storage and emerging neuromorphic computing applications. Here, a flexible synaptic TFT is demonstrated through the creation of a Bi₂O₂Se-based ferroelectric field-effect transistor (FeFET) structure on the flexible mica substrate. The proposed device exhibits excellent nonvolatile memory characteristics, including a large memory window, excellent current modulation ratio, great retention, and strong endurance. Furthermore, the Bi₂O₂Se-based FeFET can be operated as a synaptic device with analog conductance-modulating behaviors. Owing to the superior mechanical flexibility of the component materials and the mica substrate, the Bi₂O₂Se-based FeFETs can retain their performance against various bending states, showing a strain-invariant electrical performance. This study marks the advancement of Bi₂O₂Se-based TFTs toward flexible nonvolatile memories and synaptic devices.