Characteristics of ferroelectric field effect transistors composed of a ferroelectric Bi₃TaTiO₉ gate stack and a single-layer MoS₂ channel

Polycrystalline Bi₃TaTiO₉ (BTTO) thin films of layered perovskite ferroelectric materials were deposited on a Pt/Ta/glass substrate via a pulsed laser deposition (PLD) method using two different PLD deposition rates of 0.03 and 0.5 nm/pulse under the same substrate temperature conditions. The BTTO thin film grown by the low PLD deposition rate exhibited a highly a-oriented crystal structure, which was confirmed by X-ray diffraction experiments. The crystallinity of the a-oriented film caused an improvement in the ferroelectric polarization and piezoelectric coefficients; at the same time, the leakage current characteristics were slightly deteriorated. Ferroelectric field effect transistors (FeFETs), made of monolayer MoS₂ channels and BTTO thin films as a gate dielectric layer, exhibited clearly different memory windows as a nonvolatile memory. In addition, the reliability of the FeFETs was confirmed by fatigue tests up to 10¹² switching cycles and retention tests up to 10⁶ s.