Thickness effect of ultra-thin Ta2O5 resistance switching layer in 28 nm-diameter memory cell

Abstract

Resistance switching (RS) devices with ultra-thin Ta2O5 switching layer (0.5–2.0 nm) with a cell diameter of 28 nm were fabricated. The performance of the devices was tested by voltage-driven current—voltage (I-V) sweep and closed-loop pulse switching (CLPS) tests. A Ta layer was placed beneath the Ta2O5 switching layer to act as an oxygen vacancy reservoir. The device with the smallest Ta2O5 thickness (0.5 nm) showed normal switching properties with gradual change in resistance in I-V sweep or CLPS and high reliability. By contrast, other devices with higher Ta2O5 thickness (1.0–2.0 nm) showed abrupt switching with several abnormal behaviours, degraded resistance distribution, especially in high resistance state, and much lower reliability performance. A single conical or hour-glass shaped double conical conducting filament shape was conceived to explain these behavioural differences that depended on the Ta2O5 switching layer thickness. Loss of oxygen via lateral diffusion to the encapsulating Si3N4/SiO2 layer was suggested as the main degradation mechanism for reliability, and a method to improve reliability was also proposed.

Cross-Point Resistive Switching Memory and Urea Sensing by Using Annealed GdOxFilm in IrOx/GdOx/W Structure for Biomedical Applications

“…The vacancy density in the CF at CC of 10 μA is slightly varied for cycle-to-cycle, which can be avoided by using resistance verification circuit. 39 Enhanced performance and resistive switching mechanism of the cross-point memories have been explained below.…”

Resistive Random Access Memory (RRAM): an Overview of Materials, Switching Mechanism, Performance, Multilevel Cell (mlc) Storage, Modeling, and Applications

“…Physical electro-thermal model was developed by Kim et al [135] and implemented with tantalum pentoxide (Ta 2 O 5 ) -based bilayer RRAM [136][137][138] . This physical model solves the differential equations based on finite element solving method.…”

The Over-Reset Phenomenon in Ta2O5 RRAM Device Investigated by the RTN-Based Defect Probing Technique

“…During alternate reset and set operations, the filament ruptures and restores repeatedly, leading to the high resistance state and low resistance state, respectively (HRS/LRS). It has been observed in RRAMs with various oxides such as HfO 2 and Ta 2 O 5 [12,13] that once V reset increases beyond a certain level, R HRS will start to decrease instead of further increase; it is difficult to recover from the consequent window reduction [12,13]. This over-reset phenomenon will therefore limit the achievable RW by using a higher V reset .…”

“…The over-reset phenomenon has been explained by the migration of defects near the bottom electrode (BE) moving back into the constriction region of the filament at higher reset voltages, which re-connects the defect-rich filamentary regions near the top electrode (TE) and BE. This effect leads to a reduced resistance at HRS [12]. An alternative explanation is by the horizontal out-diffusion of defects from the filament into the surrounding dielectrics which forms additional conduction paths, hence the higher conduction current and lower resistance [13].…”