Forming‐Free Grain Boundary Engineered Hafnium Oxide Resistive Random Access Memory Devices

Abstract

A model device based on an epitaxial stack combination of titanium nitride (111) and monoclinic hafnia (11true1¯) is grown onto a c‐cut Al2O3‐substrate to target the role of grain boundaries in resistive switching. The texture transfer results in 120° in‐plane rotated m‐HfO2 grains, and thus, in a defined subset of allowed grain boundary orientations of high symmetry. These engineered grain boundaries thread the whole dielectric layer, thereby providing predefined breakdown paths for electroforming‐free resistive random access memory devices. Combining X‐ray diffraction and scanning transmission electron microscopy (STEM)–based localized automated crystal orientation mapping (ACOM), a nanoscale picture of crystal growth and grain boundary orientation is obtained. High‐resolution STEM reveals low‐energy grain boundaries with facing (1¯1¯2¯) and (true1¯21) surfaces. The uniform distribution of forming voltages below 2 V—within the operation regime—and the stable switching voltages indicates reduced intra‐ and device‐to‐device variation in grain boundary engineered hafnium‐oxide‐based random access memory devices.

Electron trapping in ferroelectric HfO2

“…(a) Schematics of interface traps discharging in annealed samples during cooling down from room temperature to 77 K (the hatched area represents the density of interface traps that emit electrons into the substrate due to the Fermi level shift); (b) 100 kHz CV curves measured on the annealed HfO 2 sample at 300 and 77 K before charging, illustrating V fb shift corresponding to interface traps discharge; (c) V fb shift (with respect to the initial V fb value at room temperature) variation with temperature in annealed HfO 2 samples after charge injection at 77 K due to thermal detrapping with ( ) and without ( ) effect of interface traps recharging, and V fb shift variation in the uncharged sample representing the effect of interface traps recharging (•). undercoordinated oxygen or hafnium ions at the grain boundary [35].…”

Truly Electroforming‐Free Memristor Based on TiO2‐CoO Phase‐Separated Oxides with Extremely High Uniformity and Low Power Consumption

“…The temporal uniformity of the pso-memristor is drastically enhanced compared to those of amorphous oxide-based devices and those even after structure modification to improve switching uniformity by inserting additional oxide layer, local field enhancement by nanoparticle embedding, or filament confinement by grain boundary engineering. [11,12,14,[36][37][38][39] Since spatial variation mainly stems from the random electroforming process, the electroforming-free memristors are expected to have improved spatial uniformity. Two 4 × 4 cross-bar arrays were fabricated (see Figure S5, Supporting Information) and the set voltages of all 32 devices are plotted in Figure 3e (see Figure S6 (Supporting Information) for the method to define the set voltages of the cross-bar arrays).…”

“…<3.0 µA) have rarely been achieved in oxide-based memristors such as HfO x , TaO x , TiO x , and other metal oxides. [8,9,[11][12][13][14] High switching voltage or large current usually induces permanent damages to the selector in a 1S1R (1 selector and 1 memristor) structure, which is promising for realizing ultrahigh density memristors. [15][16][17] More importantly, device-to-device (spatial) variation as well as cycle-to-cycle (temporal) variation can be a major obstacle to the accuracy of analog computing, limiting the application to large-scale passive arrays.…”

Tailoring the Switching Dynamics in Yttrium Oxide‐Based RRAM Devices by Oxygen Engineering: From Digital to Multi‐Level Quantization toward Analog Switching

“…[ 45 ] Recently, we have demonstrated how this disadvantage can be utilized via grain boundary engineering to even improve the forming voltage distribution. [ 46 ] Overall, a relatively higher distribution of V forming in the 0.3 sccm devices when compared to the other oxygen flows does not influence the general trend of the forming voltage scaling with oxygen content.…”