Thin film design of amorphous hafnium oxide nanocomposites enabling strong interfacial resistive switching uniformity

Abstract

A design concept of phase-separated amorphous nanocomposite thin films is presented that realizes interfacial resistive switching (RS) in hafnium oxide–based devices. The films are formed by incorporating an average of 7% Ba into hafnium oxide during pulsed laser deposition at temperatures ≤400°C. The added Ba prevents the films from crystallizing and leads to ∼20-nm-thin films consisting of an amorphous HfO x host matrix interspersed with ∼2-nm-wide, ∼5-to-10-nm-pitch Ba-rich amorphous nanocolumns penetrating approximately two-thirds through the films. This restricts the RS to an interfacial Schottky-like energy barrier whose magnitude is tuned by ionic migration under an applied electric field. Resulting devices achieve stable cycle-to-cycle, device-to-device, and sample-to-sample reproducibility with a measured switching endurance of ≥10 4 cycles for a memory window ≥10 at switching voltages of ±2 V. Each device can be set to multiple intermediate resistance states, which enables synaptic spike-timing–dependent plasticity. The presented concept unlocks additional design variables for RS devices.

Improved Switching Uniformity of SCLC-RRAM Using the Vertically Formed Nanoscale 2DEG Electrode and Control of Oxygen Vacancy Distribution

“…However, it can be interpreted that the 400 °C annealed sample had an interface-type switching mechanism because the Schottky barrier lowering by the electric field occurred before the electrons filled all V o traps in large amounts. The I-RRAM is known to gradually transition between the HRS and LRS in the DC I – V sweep, as demonstrated by the results in Figure d. − Because the 400 °C annealed sample of the I-RRAM had a resistive switching mechanism by Schottky barrier modulation rather than by formation and rupture of V o CF, which requires an electrical forming process, it also did not exhibit an overshoot current. Consequently, it exhibited a better switching uniformity, as shown in Figure d.…”

“…In this case, V o functioned as an electron trap, similar to that in the 300 °C annealed sample. However, the electric field modulated the Schottky barrier before the trap-filling switching, demonstrating an interface-type switching behavior. − Although the I-RRAM can achieve superior switching uniformity compared with the F-RRAM, it remains limited in terms of a lower on/off ratio.…”

“…Many strategies have been suggested to address this problem, including doping the oxide layer to promote desired filament pathways, using multilayer oxide for CF confinement, and scaling cell area to limit possible CF formation sites. − However, these methods have achieved limited success, owing to the intrinsic randomness of CF creation and rupture. Therefore, researchers have shifted their attention to other types of RRAM, such as interface-type RRAM (I-RRAM) − and space charge limited current (SCLC) switching-based RRAM (S-RRAM), − which employ completely different resistive switching mechanisms.…”

Electrolyte Influence on Properties of Ultra-Thin Anodic Memristors on Titanium

“…Following the TEM analysis, a hybrid interfacial resistive switching mechanism is proposed, where only partial filaments are formed. The crystalline protrusions observable in the figure act as preferential paths for the partial filament formation [42,43]. They do not reach all the way through the oxide, so there is no full filamentary switching.…”

“…The partial filaments, therefore, simulate an effective bottom electrode. Interfacial memristors exhibit resistive switching due to O species migration, including ions and vacancies, that are distributed through the entire interface [13,36,42,43]. This switching mechanism is based on the Schottky-like barrier formation, which can be modulated by varying the O species concentration [36,44].…”