Size-controlled resistive switching performance and regulation mechanism of SnO₂ 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.

Research Process of Carbon Dots in Memristors

“…[26,98] In the Coulomb blockade effect, the system energy rises after the injected electrons reaching CDs, which may block other electrons along the conducting paths until the trapped electrons escape from CDs, realizing the storage and release of electrons in memristors. [27][28][29] Compared with semiconductor quantum dots, such as perovskite quantum dots and chalcogenide quantum dots, CDs have better eco-environmental protection characteristic and physicochemical stability, which can avoid the problems of toxicity and moisture exposure. [32,99] CDs are generally considered to have four types, including graphene quantum dots (GQDs), carbon quantum dots (CQDs), carbon nanodots (CNDs), and carbonized polymer dots (CPDs).…”

“…The quantum effects of CDs, such as quantum confinement effect and Coulomb blockade effect, are very likely to refine the memristance of CDMs in different ways. [26][27][28][29][30] The quantum confinement effect plays a vital role in quantizing electron energy levels when the size of CDs and their Bohr radius of excitons are in the same order of magnitude, which can act on band gap, energy level alignment, and interfacial potential barrier of memristors. [26,98] In the Coulomb blockade effect, the system energy rises after the injected electrons reaching CDs, which may block other electrons along the conducting paths until the trapped electrons escape from CDs, realizing the storage and release of electrons in memristors.…”

“…[1,2] excellent solution processing, high conductivity, biocompatibility, and specific quantum effects, which can provide memristors with distinguished memristive performances. [24][25][26][27][28][29][30] The key performance parameters of a majority of CDs-based memristors (CDMs) have been summarized in Table 1, from which it can be found that nearly half of the reported threshold voltages are lower than 1.0 V, while the threshold voltages of other memristors based on metal oxides, perovskites, and organic materials are above 1.0 V as a whole. [31][32][33] The low threshold voltage is beneficial to modulate memristance and reduce energy consumption.…”