Performance‐Enhancing Selector via Symmetrical Multilayer Design

Abstract

Two-terminal selectors with high nonlinearity, based on bidirectional threshold switching (TS) behaviors, are considered as a crucial element of crossbar integration for emerging nonvolatile memory and neuromorphic network. Although great efforts have been made to obtain various selectors, existing selectors cannot fully satisfy the rigorous standard of assorted memristive elements and it is in great demand to enhance the performance. Here, a new type of Ag/TaO x /TaO y /TaO x /Ag (x < y) selector based on homogeneous trilayered oxides is developed to attain the required parameters including bidirectional TS operation, a large selectivity of ≈10 10 , a high compliance current up to 1 mA, and ultralow switching voltages under 0.2 V. Tunable operation voltages can be realized by modulating the thickness of inserted TaO y . All-TaO x -based integrated 1S1R (one selector and one memristor) cells, prepared completely by magnetron sputtering and no need of a middle electrode, exhibit a nonlinear feature, which is quite characteristic for the crossbar devices, avoiding undesired crosstalk current issues. The tantalum-oxidebased homojunctions offer high insulation, low ion mobility, and rich interfaces, which is responsible for the modulation of Ag conductive filaments and corresponding high-performance cation-based selector. These findings might advance practical implementation of two-terminal selectors in emerging memories, especially resistive random access memories.tile memory and neuromorphic computing applications. [1] These applications are generally based on the crossbar array structure, where crosstalk current issues notoriously impede the read-write operations. [2] A great deal of efforts have been made to address the critical issue, and the two-terminal selector stands out for their simple structure and no need to compromise the scalability from numerous solutions. [3] Figure 1a illustrates the configuration of 1S1R (one selector and one memristor) integrated crossbar arrays. Recently, various selector elements have been introduced, including Schottky diodes, [4] metal-insulator transition, [5] fieldassisted superlinear threshold, [6] mixedionic-electronic conduction, [7] thermionic/ tunneling emission, [8] and electrochemical-metallization-based (ECM) threshold switching (TS). [9] One Schottky diode cascaded with one memristor (namely, 1D1R) is confined only to unipolar RRAM due to the unilateral conductivity of diodes. Selectors based on transport of ions and electrons are applicable to both unipolar and bipolar RRAM, but the gradually varied voltage-current (I-V) curves predestinates the moderate nonlinearity, [3b] which is not sufficient for the application of RRAM crossbar arrays.The ECM-based selector, which is based on the formation/ diffusion and Rayleigh instability of conductive filaments Nonvolatile MemoryThe ORCID identification number(s) for the author(s) of this article can be found under https://doi.

Analog Switching and Artificial Synaptic Behavior of Ag/SiOx:Ag/TiOx/p++-Si Memristor Device

“…It is the low ion mobility and low redox reaction rate of titanium oxide that controls the migration and accumulation of Ag atoms and Ag ion across the interfacial layer [36]. These two facts, as mentioned above, can cause the formation of nano-coneshaped filament from TE to BE [37]. The concentrated metallic region in the form of effective confinement of filament growth in the form of nano-cone from TE to BE can offer control of resistance states during the cyclic operation [38].…”

High‐Uniformity Threshold Switching HfO2‐Based Selectors with Patterned Ag Nanodots

“…Among them, threshold switching (TS) selectors based on electrochemical metallization (ECM) filaments have attracted considerable attention due to their potential advantages, such as simple structure, large on/off ratio, and low leakage current. [29][30][31][32][33][34][35][36] In the fabrication of TS selectors, Ag or Cu is commonly used as the active metal ions to form conductive filaments in dielectric. [29,[35][36][37] HfO 2 , as a typical transition-metal oxide, is usually used as the active switching dielectric because of its high dielectric constant, excellent chemical and thermal stability, and complementary metal-oxide-semiconductor (CMOS) compatibility.…”

Effect of Ag Concentration Dispersed in HfOx Thin Films on Threshold Switching

“…To realize a one selector-one resistive memory (1S1R), a selector requires a low OFF current to suppress the leakage current and a high ON current corresponding to the reset current of the resistive memory [21,22]. To fulfill such I-V nonlinear characteristics, we confirmed the nonlinearity (NL) and selectivity (S) of our devices and those of TS selectors previously reported to evaluate their performance as selectors [14,18,[21][22][23]. Here, we define NL and S using Eqs.…”

“…b TS behavior without the EF process maintaining a low OFF current and high NL is difficult to spontaneously rupture compared with the thin and unstable filament formed at a lower I cc [26,27]. Therefore, various methods, such as a multilayer structure (Ag/TaO x /TaO y /TaO x /Ag) and Ag nanodots templated in the dielectric, have been suggested to obtain reliable TS characteristics at a higher I cc [21,22].…”

“…There are many types of selector devices with nonlinear current-voltage (I-V) characteristics being introduced, such as Schottky diodes, metal-insulator transitions (MITs), ovonic threshold switches (OTSs), tunnel barrier selectors, and diffusive selectors (also termed diffusive memristors) [9][10][11][12][13][14][15]. Among them, a diffusive selector based on metal species (Ag or Cu) diffusive dynamics inside the dielectrics has attracted considerable interest because of its simple structure and superior performance, such as its extremely high nonlinearity [14][15][16][17][18][19][20][21][22]. The diffusive selector features a volatile threshold switch (TS) based on the formation and self-rupture of metallic filaments.…”