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Impact of device size and thickness of Al2O 3 film on the Cu pillar and resistive switching characteristics for 3D cross-point memory application.

Panja R, Roy S, Jana D, Maikap S - Nanoscale Res Lett (2014)

Bottom Line: The 8-μm devices show 100% yield of Cu pillars, whereas only 74% successful is observed for the 0.4-μm devices, because smaller size devices have higher Joule heating effect and larger size devices show long read endurance of 10(5) cycles at a high read voltage of -1.5 V.On the other hand, the resistive switching memory characteristics of the 0.4-μm devices with a 2-nm-thick Al2O3 film show superior as compared to those of both the larger device sizes and thicker (10 nm) Al2O3 film, owing to higher Cu diffusion rate for the larger size and thicker Al2O3 film.This conductive bridging resistive random access memory (CBRAM) device is forming free at a current compliance (CC) of 30 μA (even at a lowest CC of 0.1 μA) and operation voltage of ±3 V at a high resistance ratio of >10(4).

View Article: PubMed Central - PubMed

Affiliation: Thin Film Nano Tech. Lab., Department of Electronic Engineering, Chang Gung University, 259 Wen-Hwa 1st Rd., Kwei-Shan, Tao-Yuan, 333, Taiwan, panjarajeswar@gmail.com.

ABSTRACT
Impact of the device size and thickness of Al2O3 film on the Cu pillars and resistive switching memory characteristics of the Al/Cu/Al2O3/TiN structures have been investigated for the first time. The memory device size and thickness of Al2O3 of 18 nm are observed by transmission electron microscope image. The 20-nm-thick Al2O3 films have been used for the Cu pillar formation (i.e., stronger Cu filaments) in the Al/Cu/Al2O3/TiN structures, which can be used for three-dimensional (3D) cross-point architecture as reported previously Nanoscale Res. Lett.9:366, 2014. Fifty randomly picked devices with sizes ranging from 8 × 8 to 0.4 × 0.4 μm(2) have been measured. The 8-μm devices show 100% yield of Cu pillars, whereas only 74% successful is observed for the 0.4-μm devices, because smaller size devices have higher Joule heating effect and larger size devices show long read endurance of 10(5) cycles at a high read voltage of -1.5 V. On the other hand, the resistive switching memory characteristics of the 0.4-μm devices with a 2-nm-thick Al2O3 film show superior as compared to those of both the larger device sizes and thicker (10 nm) Al2O3 film, owing to higher Cu diffusion rate for the larger size and thicker Al2O3 film. In consequence, higher device-to-device uniformity of 88% and lower average RESET current of approximately 328 μA are observed for the 0.4-μm devices with a 2-nm-thick Al2O3 film. Data retention capability of our memory device of >48 h makes it a promising one for future nanoscale nonvolatile application. This conductive bridging resistive random access memory (CBRAM) device is forming free at a current compliance (CC) of 30 μA (even at a lowest CC of 0.1 μA) and operation voltage of ±3 V at a high resistance ratio of >10(4).

No MeSH data available.


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Thickness-dependent Al2O3film breakdown phenomena with Cu and Al top electrodes. (a)I-V characteristics show the breakdown voltage of the Cu/Al2O3/TiN and Al/Al2O3/TiN structures. The higher breakdown voltage of Al/Al2O3/TiN than that of the Cu/Al2O3/TiN structure is owing to oxidized Al at the Al/Al2O3 interface during deposition by thermal evaporator. (b) The breakdown voltage of the Al/Cu/Al2O3/TiN structures increases with increasing the thickness of Al2O3 film.
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Fig7: Thickness-dependent Al2O3film breakdown phenomena with Cu and Al top electrodes. (a)I-V characteristics show the breakdown voltage of the Cu/Al2O3/TiN and Al/Al2O3/TiN structures. The higher breakdown voltage of Al/Al2O3/TiN than that of the Cu/Al2O3/TiN structure is owing to oxidized Al at the Al/Al2O3 interface during deposition by thermal evaporator. (b) The breakdown voltage of the Al/Cu/Al2O3/TiN structures increases with increasing the thickness of Al2O3 film.

Mentions: As we have mentioned, the switching mechanism is based on Cu filament formation/dissolution into the Al2O3 film under external bias, and this could be also understood indirectly by studying the breakdown phenomenon using two different top electrodes viz. Cu and Al, as shown in Figure 7. The thickness of the Al2O3 films is 5 nm. The average breakdown voltage (VBD) of the randomly measured ten devices of the Al/Al2O3/TiN structures is -4.99 V (i.e., -4.6 to -5.2 V) whereas this value of the Al/Cu/Al2O3/TiN structures is 3.99 V (i.e., -3.7 to -4.3 V), as shown in Figure 7a. The value of VBD is higher for the Al TE because the Al makes an additional oxide layer at the Al/Al2O3 interface. According to our previous report [36], the AlOx layer was formed at the Al/TaOx interface. It is also found that the value of VBD for the Al/Cu/Al2O3/TiN structures increases with increasing the thickness of Al2O3 layer, as shown in Figure 7b. If one can compare between the breakdown voltage and the formation voltage of the Al/Cu/Al2O3/TiN structures with a 2-nm-thick Al2O3 layer, then the average value of breakdown voltage is higher than the formation voltage (-3.2 vs. 1.85 V). The similar trend is observed for all thicknesses of the Al2O3 films, as discussed above. This result reveals that the formation takes place due to the Cu ion migration through the Al2O3 layer. Under high electric field approximately 107 V/cm before breaking the stable Al-O bonds, electrochemically active Cu ions diffuse easily through the Al2O3 layer and make a metallic path under a low positive voltage applied on the TE. The Cu ion migration as well as filament formation into different switching layers under external bias was also reported by other groups [16–18, 24]. However, the switching uniformity is important of these CBRAM devices, which have been explained below.Figure 7


Impact of device size and thickness of Al2O 3 film on the Cu pillar and resistive switching characteristics for 3D cross-point memory application.

Panja R, Roy S, Jana D, Maikap S - Nanoscale Res Lett (2014)

Thickness-dependent Al2O3film breakdown phenomena with Cu and Al top electrodes. (a)I-V characteristics show the breakdown voltage of the Cu/Al2O3/TiN and Al/Al2O3/TiN structures. The higher breakdown voltage of Al/Al2O3/TiN than that of the Cu/Al2O3/TiN structure is owing to oxidized Al at the Al/Al2O3 interface during deposition by thermal evaporator. (b) The breakdown voltage of the Al/Cu/Al2O3/TiN structures increases with increasing the thickness of Al2O3 film.
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Related In: Results  -  Collection

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Fig7: Thickness-dependent Al2O3film breakdown phenomena with Cu and Al top electrodes. (a)I-V characteristics show the breakdown voltage of the Cu/Al2O3/TiN and Al/Al2O3/TiN structures. The higher breakdown voltage of Al/Al2O3/TiN than that of the Cu/Al2O3/TiN structure is owing to oxidized Al at the Al/Al2O3 interface during deposition by thermal evaporator. (b) The breakdown voltage of the Al/Cu/Al2O3/TiN structures increases with increasing the thickness of Al2O3 film.
Mentions: As we have mentioned, the switching mechanism is based on Cu filament formation/dissolution into the Al2O3 film under external bias, and this could be also understood indirectly by studying the breakdown phenomenon using two different top electrodes viz. Cu and Al, as shown in Figure 7. The thickness of the Al2O3 films is 5 nm. The average breakdown voltage (VBD) of the randomly measured ten devices of the Al/Al2O3/TiN structures is -4.99 V (i.e., -4.6 to -5.2 V) whereas this value of the Al/Cu/Al2O3/TiN structures is 3.99 V (i.e., -3.7 to -4.3 V), as shown in Figure 7a. The value of VBD is higher for the Al TE because the Al makes an additional oxide layer at the Al/Al2O3 interface. According to our previous report [36], the AlOx layer was formed at the Al/TaOx interface. It is also found that the value of VBD for the Al/Cu/Al2O3/TiN structures increases with increasing the thickness of Al2O3 layer, as shown in Figure 7b. If one can compare between the breakdown voltage and the formation voltage of the Al/Cu/Al2O3/TiN structures with a 2-nm-thick Al2O3 layer, then the average value of breakdown voltage is higher than the formation voltage (-3.2 vs. 1.85 V). The similar trend is observed for all thicknesses of the Al2O3 films, as discussed above. This result reveals that the formation takes place due to the Cu ion migration through the Al2O3 layer. Under high electric field approximately 107 V/cm before breaking the stable Al-O bonds, electrochemically active Cu ions diffuse easily through the Al2O3 layer and make a metallic path under a low positive voltage applied on the TE. The Cu ion migration as well as filament formation into different switching layers under external bias was also reported by other groups [16–18, 24]. However, the switching uniformity is important of these CBRAM devices, which have been explained below.Figure 7

Bottom Line: The 8-μm devices show 100% yield of Cu pillars, whereas only 74% successful is observed for the 0.4-μm devices, because smaller size devices have higher Joule heating effect and larger size devices show long read endurance of 10(5) cycles at a high read voltage of -1.5 V.On the other hand, the resistive switching memory characteristics of the 0.4-μm devices with a 2-nm-thick Al2O3 film show superior as compared to those of both the larger device sizes and thicker (10 nm) Al2O3 film, owing to higher Cu diffusion rate for the larger size and thicker Al2O3 film.This conductive bridging resistive random access memory (CBRAM) device is forming free at a current compliance (CC) of 30 μA (even at a lowest CC of 0.1 μA) and operation voltage of ±3 V at a high resistance ratio of >10(4).

View Article: PubMed Central - PubMed

Affiliation: Thin Film Nano Tech. Lab., Department of Electronic Engineering, Chang Gung University, 259 Wen-Hwa 1st Rd., Kwei-Shan, Tao-Yuan, 333, Taiwan, panjarajeswar@gmail.com.

ABSTRACT
Impact of the device size and thickness of Al2O3 film on the Cu pillars and resistive switching memory characteristics of the Al/Cu/Al2O3/TiN structures have been investigated for the first time. The memory device size and thickness of Al2O3 of 18 nm are observed by transmission electron microscope image. The 20-nm-thick Al2O3 films have been used for the Cu pillar formation (i.e., stronger Cu filaments) in the Al/Cu/Al2O3/TiN structures, which can be used for three-dimensional (3D) cross-point architecture as reported previously Nanoscale Res. Lett.9:366, 2014. Fifty randomly picked devices with sizes ranging from 8 × 8 to 0.4 × 0.4 μm(2) have been measured. The 8-μm devices show 100% yield of Cu pillars, whereas only 74% successful is observed for the 0.4-μm devices, because smaller size devices have higher Joule heating effect and larger size devices show long read endurance of 10(5) cycles at a high read voltage of -1.5 V. On the other hand, the resistive switching memory characteristics of the 0.4-μm devices with a 2-nm-thick Al2O3 film show superior as compared to those of both the larger device sizes and thicker (10 nm) Al2O3 film, owing to higher Cu diffusion rate for the larger size and thicker Al2O3 film. In consequence, higher device-to-device uniformity of 88% and lower average RESET current of approximately 328 μA are observed for the 0.4-μm devices with a 2-nm-thick Al2O3 film. Data retention capability of our memory device of >48 h makes it a promising one for future nanoscale nonvolatile application. This conductive bridging resistive random access memory (CBRAM) device is forming free at a current compliance (CC) of 30 μA (even at a lowest CC of 0.1 μA) and operation voltage of ±3 V at a high resistance ratio of >10(4).

No MeSH data available.


Related in: MedlinePlus