Self-Assembled TaO_X/2H-TaS₂ as a van der Waals Platform of a Multilevel Memristor Circuit Integrated with a β-Ga₂O₃ Transistor.

Abstract

Two-dimensional (2D)-layered material tantalum disulfide (2H-TaS₂) is known to be a van der Waals conductor at room temperature. Here, 2D-layered TaS₂ has been partially oxidized by utraviolet-ozone (UV-O₃) annealing to form a 12-nm-thin TaO_X on conducting TaS₂, so that the TaO_X/2H-TaS₂ structure might be self-assembled. Utilizing the TaO_X/2H-TaS₂ structure as a platform, each device of a β-Ga₂O₃ channel MOSFET and a TaO_X memristor has been successfully fabricated. An insulator structure of Pt/TaO_X/2H-TaS₂ shows good a dielectric constant (<i>k</i> ∼ 21) and strength (∼3 MV/cm) of achieved TaO_X, which is enough to support a β-Ga₂O₃ transistor channel. Based on the quality of TaO_X and low trap density of the TaO_X/β-Ga₂O₃ interface, which is achieved via another UV-O₃ annealing, excellent device properties such as little hysteresis (<∼0.04 V), band-like transport, and a steep subthreshold swing of ∼85 mV/dec are achieved. With a Cu electrode on top of the TaO_X/2H-TaS₂ structure, the TaO_X acts as a memristor operating around ∼2 V for nonvolatile bipolar and unipolar mode memories. The functionalities of the TaO_X/2H-TaS₂ platform become more distinguished finally when the Cu/TaO_X/2H-TaS₂ memristor and β-Ga₂O₃ MOSFET are integrated to form a resistive memory switching circuit. The circuit nicely demonstrates the multilevel memory functions.