Self-rectifying memristor has no need for selector devices, but possess the one-way transmission behavior and multi-level non-volatile memory characteristics, which makes it promising candidate for electronic synapse. In this letter, we propose a novel self-rectifying memristor based on Pt/Hf_0.5Zr_0.5O₂/TiN structure. The devices show large memory window (10⁴) and high rectifying ratio (10⁴), which can block the sneak current in passive crossbar array without any additional hardware overhead. Moreover, the devices demonstrate excellent multi-level states modulation capability, low power consumption, high endurance and long retention. The final benchmark demonstrates that the proposed Pt/Hf_0.5Zr_0.5O₂/TiN self-rectifying memristor is a promising candidate for electronic synapse application.

Introduction: Due to the simple structure, multi-level operation and non-volatile memory capacity, memristor has been considered as a potential synapse device for constructing brain-inspired computing systems, which is expected to break the von Neumann bottleneck in traditional computing system [1,2]. Nonetheless, the sneak current, flowing through unselected cells in passive crossbar array, will lead to read-out errors and failure of program operations. Though additional selectors (i.e. transistors or diodes) in serial can solve the sneak path issues, they will lower the integration density due to their larger size. The self-rectifying memristor cell, whose nonlinear and asymmetric current-voltage characteristics can greatly suppress the sneak current flowing through the unselected cells, is attracting significant attention because of their simple two-terminal structure and 3D integration ability [3,4]. However, most current type self-rectifying memristors suffer from relatively small memory window and high-power consumption. Thus, new self-rectifying memristor is needed for being a promising candidate in electronic synapse applications.

In this letter, by using the amorphous high-k Zr-doped hafnium oxide as resistive switching material, we propose a novel self-rectifying memristor based on Pt/Hf_0.5Zr_0.5O₂/TiN structure. Experimental results demonstrate the as-fabricated device has high rectifying ration (10⁴) and large memory window (10⁴), which is sufficient to suppress sneak path issue in Mb-level passive crossbar array. Moreover, the devices possess excellent multi-level states, endurance (10⁶) and non-volatility (10³ s) capability. The excellent resistive switching performance can be ascribed to the trap-controlled space charge limited current (SCLC) effect in Hf_0.5Zr_0.5O₂ films. The final benchmark demonstrates the outstanding self-rectifying performance with previous reported devices.

Devices and experiments: The proposed self-rectifying memristors were fabricated with a 10-nm-thick Hf_0.5Zr_0.5O₂ (HZO) layer sandwiched between TiN top electrode and Pt bottom electrode, as shown in Fig. 1a . The vertical lines of Pt/Ti (25/5 nm) were deposited on the SiO₂/Si substrate as bottom electrode by e-beam evaporation after the first lithography process. Then a 10-nm-thick HZO layer was deposited on the Pt bottom electrode at a stage temperature of 280 °C. The Hf[N(C₂H₅)CH₃]₄, Zr[N(C₂H₅)CH₃]₄and H₂O were used as hafnium precursor, Zr precursor and oxygen source, respectively. The hafnium/zirconium ratio was controlled by alternate deposition of one HfO₂ cycle and one ZrO₂ cycles. Finally, the horizontal lines of TiN (30 nm) were deposited by magnetron sputtering. The cell areas of the devices range from 9 μm² (3 µm×3 µm) to 2500 µm² (50 µm×50 µm). During the electrical measurement, the voltage was applied to the Pt bottom electrode and the TiN top electrodes were grounded.