High Uniformity of Resistive Switching Characteristics in a Cr/ZnO/Pt Device

Abstract

This study investigates the resistive switching behavior of Pt, Al, and Cr electrodes for ZnO-based resistance random access memory. Results show that the existence of oxygen ions in the electrode plays an important role in the resistive switching behavior during filament reduction and oxidization. The Cr/ZnO/Pt structure exhibited a significant improvement in resistive switching parameters such as operation voltages and resistance states. This is most likely due to the partial formation of oxidation layers, namely CrO x at the Cr/ZnO interface. These layers act as oxygen reservoir or oxygen supplier, and improve the efficiency of oxygen ion exchange near the electrode/oxide interface.Resistance random access memory (RRAM) has attracted considerable attention because of its potential as a replacement for flash memory in next-generation nonvolatile memory (NVM) applications. 1 The typical configuration of RRAM includes a metal/insulator/metal structure, and its operation is based on the switching of the high resistance state (HRS) and the low resistance state (LRS) (off and on state) under a large bias. Switching can be classified into two types based on I-V behaviors: bipolar and unipolar. 2 Bipolar resistive switching shows directional resistive switching, depending on the polarity of the applied voltage. Unipolar resistive switching depends on the amplitude of the applied voltage without polarity. The resistive switching behaviors were observed from various materials, such as binary oxides, perovskite oxides, and chalcogenide materials. [1][2][3][4][5][6][7] Zinc oxide (ZnO) has many characteristics ideally suited for optics and electronics, such as a wide bandgap of approximately 3.37 eV, adjustable electronic properties by doping with different dopants, and low synthetic temperature. 8 Recent research shows that ZnObased thin films have promising resistive switch characteristics. [9][10][11][12][13][14] The unipolar switching characteristics of ZnO usually appear in symmetric electrode structures such as Pt/ZnO/Pt, 9 ITO/ZnO/ITO, 10 and Al/ZnO/Al devices. 11 Bipolar switching characteristics have also been observed in TiN/ZnO/Pt, 12 Ag/ZnO:Mn/Pt, 13 and ITO/ZnO:Mg/FTO devices. 14 However, research into the influence of electrode material on the resistive switching behavior of ZnO films is lacking.Among the various resistive switching mechanisms, the formation of localized conductive paths (filaments) is one of the most widely accepted. However, the localized conductive paths in thin films are diverse in each switching, leading to the nonuniform distribution of switching voltages and resistance states. This in turn results in irresolvable errors during RRAM operation. Thus, effectively improving the stability of switching behavior is an essential issue for practical RRAM applications. Researchers have proposed methods to improve this problem, such as embedding Pt nanocrystals in TiO 2 films, 15 embedding thin Al layers between HfO 2 and electrode layers, 16 and Al doping in ZrO 2 films. 17 The current study in...

RRAM characteristics using a new Cr/GdOx/TiN structure

“…The work function of Cr is 4.5 eV [31], which is larger than Al of 4.28 eV [31]. Gibbs free energies of Cr 2 O 3 and Gd 2 O 3 are reported -694.88 [32, 33] and -1,730 [34] kJ/mole respectively at 300 K. Therefore, the Cr will not be oxidized easily with respect to Gd 2 O 3 switching material. This is benefited of Cr in the Cr/Gd 2 O 3 /TiN structure.…”

Structural, optical, electrical and resistive switching properties of ZnO thin films deposited by thermal and plasma-enhanced atomic layer deposition

“…Recently, ZnO thin films have been demonstrated to have good resistive switching characteristics [8], hence are very promising for the development of resistive random access memory (ReRAM). The thickness of the active layer of this type of devices is typically a few tens of nanometers.…”

“…So far, most of the ZnO films used for resistive switching devices were deposited by physical vapor-phase deposition (PVD) methods, especially by the magnetron sputtering. But these methods could not control the film thickness precisely, especially for nanometer thick films [8][9][10][11].…”

Unipolar resistive switching in Au/Cr/Mg0.84Zn0.16O2−δ /p+-Si

“…The reservoirs were insufficient to contain excessive oxygen during the measurement in these regions. As a reservoir, Cr is partially oxidized to CrO x at interface, triggering the reduction process of ZnO and providing sufficient oxygen ions to neutralize the oxygen vacancies for the RESET process and stabilizing the switching property [28].…”