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Atomic View of Filament Growth in Electrochemical Memristive Elements.

Lv H, Xu X, Sun P, Liu H, Luo Q, Liu Q, Banerjee W, Sun H, Long S, Li L, Liu M - Sci Rep (2015)

Bottom Line: The physical nature of the formed filament was characterized by high resolution transmission electron microscopy.Copper rich conical filament with decreasing concentration from center to edge was identified.Based on these results, a clear picture of filament growth from atomic view could be drawn to account for the resistance modulation of oxide electrolyte based electrochemical memristive elements.

View Article: PubMed Central - PubMed

Affiliation: Key Laboratory of Microelectronics Devices and Integrated Technology, Institute of Microelectronics, Chinese Academy of Sciences, Beijing, 100029, China.

ABSTRACT
Memristive devices, with a fusion of memory and logic functions, provide good opportunities for configuring new concepts computing. However, progress towards paradigm evolution has been delayed due to the limited understanding of the underlying operating mechanism. The stochastic nature and fast growth of localized conductive filament bring difficulties to capture the detailed information on its growth kinetics. In this work, refined programming scheme with real-time current regulation was proposed to study the detailed information on the filament growth. By such, discrete tunneling and quantized conduction were observed. The filament was found to grow with a unit length, matching with the hopping conduction of Cu ions between interstitial sites of HfO2 lattice. The physical nature of the formed filament was characterized by high resolution transmission electron microscopy. Copper rich conical filament with decreasing concentration from center to edge was identified. Based on these results, a clear picture of filament growth from atomic view could be drawn to account for the resistance modulation of oxide electrolyte based electrochemical memristive elements.

No MeSH data available.


Description of the discrete resistance change using direct tunneling.(a) The gap length vs. the VG curve fitted by the low voltage tunnel equation. The barrier height is 2.0 eV and the size of the filament tip is 2.5 nm in calculation. (b) Histogram of the tunnel gap lengths obtained from the resistance data in Fig. 2(b). (c–e) Schematic diagrams of filament growth.
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f4: Description of the discrete resistance change using direct tunneling.(a) The gap length vs. the VG curve fitted by the low voltage tunnel equation. The barrier height is 2.0 eV and the size of the filament tip is 2.5 nm in calculation. (b) Histogram of the tunnel gap lengths obtained from the resistance data in Fig. 2(b). (c–e) Schematic diagrams of filament growth.

Mentions: Based on the tunneling conduction during filament growth, the filament length can be easily correlated with the measured resistance by a simple low voltage direct tunnel equation (the programming voltage was generally less than 0.5 V, as shown in Figure S6). This tunneling system had three components (the filament tip, tunnel gap and counter electrode) and three key parameters (the tip size, barrier height and barrier width). The barrier height for electron transmission was assigned to 2.0 eV, which was estimated from the I-V curve of a fresh device with a known barrier width of 3 nm (Figure S7). Although the real situation is more complex than the fresh state, the value of the barrier height was reasonable and comparable with the reported results373839. Another parameter related to tunnel resistance is the area of the filament tip. Most studies have assumed the tip size to be 1 to 4 nm2740. After establishing the two critical parameters, the cell resistance can then be regenerated by calculating the tunnel resistance with the variable gap length or barrier width. The modeling data are shown in Figure S8. The relationship between R and VG, as shown in Fig. 2a, can be converted to the gap length vs. VG, as shown in Fig. 4a. Discrete tunneling corresponds to discrete increase of the filament. Interestingly, the increment of filament was found with a feature of basic unit (0.2 nm and 0.27 nm from the above modeling parameters). Moreover, this unit length was nearly independent of the size of filament tip, as shown in Figure S9. Figure 4b shows the histogram of the tunnel gap lengths corresponding to the data in Fig. 2b. The difference between two neighboring peaks of the gap length was either 0.2 nm or 0.27 nm.


Atomic View of Filament Growth in Electrochemical Memristive Elements.

Lv H, Xu X, Sun P, Liu H, Luo Q, Liu Q, Banerjee W, Sun H, Long S, Li L, Liu M - Sci Rep (2015)

Description of the discrete resistance change using direct tunneling.(a) The gap length vs. the VG curve fitted by the low voltage tunnel equation. The barrier height is 2.0 eV and the size of the filament tip is 2.5 nm in calculation. (b) Histogram of the tunnel gap lengths obtained from the resistance data in Fig. 2(b). (c–e) Schematic diagrams of filament growth.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4543950&req=5

f4: Description of the discrete resistance change using direct tunneling.(a) The gap length vs. the VG curve fitted by the low voltage tunnel equation. The barrier height is 2.0 eV and the size of the filament tip is 2.5 nm in calculation. (b) Histogram of the tunnel gap lengths obtained from the resistance data in Fig. 2(b). (c–e) Schematic diagrams of filament growth.
Mentions: Based on the tunneling conduction during filament growth, the filament length can be easily correlated with the measured resistance by a simple low voltage direct tunnel equation (the programming voltage was generally less than 0.5 V, as shown in Figure S6). This tunneling system had three components (the filament tip, tunnel gap and counter electrode) and three key parameters (the tip size, barrier height and barrier width). The barrier height for electron transmission was assigned to 2.0 eV, which was estimated from the I-V curve of a fresh device with a known barrier width of 3 nm (Figure S7). Although the real situation is more complex than the fresh state, the value of the barrier height was reasonable and comparable with the reported results373839. Another parameter related to tunnel resistance is the area of the filament tip. Most studies have assumed the tip size to be 1 to 4 nm2740. After establishing the two critical parameters, the cell resistance can then be regenerated by calculating the tunnel resistance with the variable gap length or barrier width. The modeling data are shown in Figure S8. The relationship between R and VG, as shown in Fig. 2a, can be converted to the gap length vs. VG, as shown in Fig. 4a. Discrete tunneling corresponds to discrete increase of the filament. Interestingly, the increment of filament was found with a feature of basic unit (0.2 nm and 0.27 nm from the above modeling parameters). Moreover, this unit length was nearly independent of the size of filament tip, as shown in Figure S9. Figure 4b shows the histogram of the tunnel gap lengths corresponding to the data in Fig. 2b. The difference between two neighboring peaks of the gap length was either 0.2 nm or 0.27 nm.

Bottom Line: The physical nature of the formed filament was characterized by high resolution transmission electron microscopy.Copper rich conical filament with decreasing concentration from center to edge was identified.Based on these results, a clear picture of filament growth from atomic view could be drawn to account for the resistance modulation of oxide electrolyte based electrochemical memristive elements.

View Article: PubMed Central - PubMed

Affiliation: Key Laboratory of Microelectronics Devices and Integrated Technology, Institute of Microelectronics, Chinese Academy of Sciences, Beijing, 100029, China.

ABSTRACT
Memristive devices, with a fusion of memory and logic functions, provide good opportunities for configuring new concepts computing. However, progress towards paradigm evolution has been delayed due to the limited understanding of the underlying operating mechanism. The stochastic nature and fast growth of localized conductive filament bring difficulties to capture the detailed information on its growth kinetics. In this work, refined programming scheme with real-time current regulation was proposed to study the detailed information on the filament growth. By such, discrete tunneling and quantized conduction were observed. The filament was found to grow with a unit length, matching with the hopping conduction of Cu ions between interstitial sites of HfO2 lattice. The physical nature of the formed filament was characterized by high resolution transmission electron microscopy. Copper rich conical filament with decreasing concentration from center to edge was identified. Based on these results, a clear picture of filament growth from atomic view could be drawn to account for the resistance modulation of oxide electrolyte based electrochemical memristive elements.

No MeSH data available.