Conducting filament engineering by triple-layer RRAM for uniform resistive switching

Abstract

IntroductionRecently, in filament type random access memory (RRAM), variability of switching parameters is one of significant obstacles to commercialization. Thus, various approaches have been proposed to improve the variability of switching parameters. Especially, a lightning-rod effect which is a control of filament dissolution region was proposed as a simple and effective approach [1]. According to previous researches, switching uniformity of various parameters such as read resistance (R read ), set voltage (V set ), and reset current were significantly improved by decreasing reset bias (V reset ). It can be explained by narrower physical gap between an electrode and conducting filament by the decreased V reset . Since the switching non-uniformity comes from the random formation of conducting filament path in the physical gap, we can improve switching uniformity by minimizing the physical gap (lightning-rod effect). However, the resistance ratio (on/off ratio) which determines operation window is degraded due to the reduced physical gap, as shown in Fig. 1. This relation can be defined as a trade-off between the lightning-rod effect (narrower physical gap) and on/off ratio. Therefore, to improve uniformity with reasonable on/off ratio, we need to optimize both the lightning-rod effects and the resistance ratio.Based on the previous papers, inserting additional layer can improve on/off ratio [2]. Thus, we inserted additional layer into typical bi-layer structure RRAM. Moreover, TiO x layer which could lead to non-linear LRS was employed as an interlayer for non-linear resistive switching [3]. The mechanism of triple-layer RRAM was proposed by the difference of oxygen vacancy concentration and chemical potential, as shown in Fig. 2(b) and (c). The layer having high chemical potential can resolve the conducting filament faster than low chemical potential layer [4]. Based on this mechanism, maximized lightning-rod effects can be achieved by resolving the filament at only one layer.The proposed approaches are summarized in Fig. 2(a). To improve switching uniformity without on/off ratio degradation, electrical and structural optimizations such as a limited switching region (lightning-rod effect), bi-layer structure, and insertion of buffer layer were proposed.

Retracted Article: High uniformity and improved nonlinearity by embedding nanocrystals in selector-less resistive random access memory

“…An NL value of >10 has been reported for the other devices, such as TaO x /TiO x based oxide heterostructure RRAM 22 and transition metal oxide (TMO) based RRAM. 19 A very clear ξ and η scaling trend can be observed from Fig. 3d.…”

“…A simple RRAM cell with NL nature can solve this problem. 19 NL behaviour in I-V hysteresis can reduce effectively the undesired current flow through a series-parallel configuration of the crossbar array. Therefore, NL is a muchneeded parameter to obtain a better high density crossbar RRAM array operation.…”

Comprehensive analysis of electro thermally driven nanoscale insulator–metal transition SmNiO3-based selector for cross-point memory array

“…Figure 6(b) shows multiple cycles with good uniform characteristics, which are essential for cross point array application. 28,29) Again, 1.88 V was applied as V read and 0.94 V was selected as V read =2. The 1S1R device showed significant suppression of current at V read =2 compared with the 1R device [Fig.…”

Super non-linear RRAM with ultra-low power for 3D vertical nano-crossbar arrays

“…Lee et al proposed a TiO 2 /HfO 2 bilayer device with a non-linear low resistance state (LRS), which benefits from the introduction of a TiO 2 tunneling layer. 20 A non-linearity of only 5 was obtained due to the large leakage current. By incorporating metal-insulator transition (MIT) materials, such as NbO 2 , TiO x , or VO x , hybrid build-in non-linear RRAM devices with bilayer structures, [21][22][23] have successfully enhanced the non-linearity up to 100, but the leakage currents were still as high as the μA level.…”

“…The intermediate electrode can shorten the cells in the same column, leaving behind the self-selective cell (SSC) as the only choice to prohibit the sneaking current. 17 Various self-selective cells have been developed, such as self-rectifying devices, 18,19 build-in non-linear RRAM (BNR), [20][21][22][23][24][25][26] and back-to-back stacked complimentary switching devices, 27 among which the build-in non-linear RRAM is more preferable than others to configure V-RRAM arrays, owing to its lower power consumption on the unselected cells using a V/2 bias scheme.…”