Size-controlled resistive switching performance and regulation mechanism of SnO<sub>2</sub> QDs

Abstract

As a non-volatile memory, zero-dimensional quantum dot resistive random access memory (RRAM) has shown broad application prospects in the field of intelligent electronic devices due to its advantages of simple structure, low switching voltage, fast response speed, high storage density, and low power consumption. Tin dioxide quantum dots (SnO<sub>2</sub> QDs) are a good option for resistive functional materials with excellent physical and chemical stabilities, high electron mobilities, and adjustable energy band structures. In this paper, the SnO<sub>2</sub> QDs with sizes of 2.51 nm, 2.96 nm and 3.53 nm are prepared by the solvothermal method, and the quantum size effect is observed in a small size range and the effective regulation of resistive switching voltage is achieved based on its quantum size effect, which is the unique advantage of quantum dot material in comparison with that of bulk material. Research result shows that as the size of SnO<sub>2</sub> QD increases, the SET/RESET voltage gradually decreases from –3.18 V/4.35 V to –2.02 V/3.08 V. The 3.53 nm SnO<sub>2</sub> QDs have lower SET/RESET voltage (–2.02 V/3.08 V) and larger resistive switching ratio (> 10<sup>4</sup>), and the resistive switching performance of the device has changed less than 5% after having experienced durability tests 2 × 10<sup>4</sup> times, showing good stability and retention. Besides, according to the fitting of charge transport mechanism, SnO<sub>2</sub> QD RRAM exhibits Ohmic conduction under LRS, while Ohmic conduction, thermionic emission and space charge limit current work together during HRS. The resistive switching effect of SnO<sub>2</sub> QDs is controlled by trap filled limit current and interface Schottky Barrier modulation; the trapping/de-trapping behavior of internal defect potential well of SnO<sub>2</sub> QDs on electrons dominates the HRS/LRS switching, while the effective control of ITO/SnO<sub>2</sub> QDs and SnO<sub>2</sub> QDs/Au interface Schottky barrier is the key to accurately regulating the switching voltage. The reason why SnO<sub>2</sub> QD RRAM exhibits good size-switching voltage dependence is that the larger SnO<sub>2</sub> QD has lower Fermi level and interface Schottky barrier height, so the junction resistance voltage division is reduced, and the SET/RESET voltage decrease accordingly. This work reveals the huge application potential and commercial application value of SnO<sub>2</sub> QDs in the field of resistive switching memory, and provides a new option for the development of RRAM.