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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.


Related in: MedlinePlus

Cumulative probability of HRS and LRS. The smaller size device shows superior uniformity than that of the larger size devices. It is observed that the 0.4-μm devices show 88% success for switching. The data read on the second switching cycle.
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Fig8: Cumulative probability of HRS and LRS. The smaller size device shows superior uniformity than that of the larger size devices. It is observed that the 0.4-μm devices show 88% success for switching. The data read on the second switching cycle.

Mentions: Figure 8 shows cumulative probability of device-to-devices. The HRS and LRS for the 8- and 0.4-μm devices with a 2-nm-thick Al2O3 film are plotted. The average values of at HRS and LRS are 5.34/4.44 kΩ and 895/407 Ω for the 8-μm devices, respectively, while those values are 10.3/12.9 kΩ and 1.07/539 kΩ for the 0.4-μm devices, respectively. The value of LRS is slightly lower for the 8-μm devices than the 0.4-μm devices, which is owing to higher diffusion rate of Cu ion into the Al2O3 film under external bias. By considering the resistance ratio of >2, the 0.4-μm devices show higher switching yield than that of the 8-μm devices (88% vs. 74%). This suggests that the 0.4-μm devices have good switching uniformity. Figure 9 shows the statistical distribution of resistance states with different current compliances of 100, 500, and 1,000 μA for the 2- and 10-nm-thick Al2O3 films. Except few devices or without proper sweeping voltage/current, there is no memory window at a CC of 100 μA. However, the value of LRS decreases and HRS remains almost the same with increasing the CCs (Figure 9a,b). The resistance ratio increases with increasing the CCs. Table 2 represents the average values of LRS, HRS, and HRS/LRS for the 8- and 0.4-μm devices with different thicknesses of Al2O3 film of 2, 5, and 10 nm. To obtain the average values, 50 CBRAM devices were measured. It is obvious that the resistance ratio is higher at CC of 1 mA as compared to the value at a CC of 500 μA because of lower LRS value. At a CC of 500 μA, a high resistance ratio of 9.6 is obtained for the 0.4-μm devices with a 2-nm-thick Al2O3 film. In this case, more switchable devices are obtained (Figure 8), which is due to better control of Cu migration under external bias. The values of LRS are decreased with increasing both the device size and thickness of the Al2O3 films at a CC of 500 μA (Table 2), which can be explained by IRESET later. Figure 10 shows cumulative probability of the RESET currents for the 8- and 0.4-μm devices with thicknesses of the Al2O3 films of 2, 5, and 10 nm at a CC of 500 μA. The average IRESET values of the 2-, 5-, and 10-nm-thick Al2O3 films are found to be 706.1, 749.4, and 1,690 μA, respectively, for the 8-μm devices, while those values are found to be 327.5, 505.4, and 1,020 μA, respectively, for the 0.4-μm devices. It is observed that the IRESET value decreases with decreasing the thickness of the Al2O3 films. Considering the thickness-dependent formation voltage (Figure 6a), the Cu ion can migrate more in the thicker Al2O3 films, resulting larger diameter of Cu filament. That is why the thicker Al2O3 film has higher RESET current. A lowest average RESET current of 327.5 μA with good uniformity is obtained for the 0.4-μm devices with a 2-nm-thick Al2O3 film (Figure 10). As mentioned above, the formation voltage of the thinner Al2O3 films is lower than that of the thicker one. Under SET, small amount of Cu will be migrated for the thinner Al2O3 films as well as thinner diameter of the Cu filaments. That is why the LRS value of the thinner Al2O3 films is larger than the thicker one. Under RESET, the total length of the Cu filaments will be dissolved for the thinner Al2O3 films because of both higher electric field and thinner filament diameter than that of the thicker one. On the other hand, interface-type switching or even no RESET is observed for the thicker Al2O3 films. Therefore, HRS value of the thinner Al2O3 films is higher than those of the thicker one. It can be concluded that thicker Al2O3 film can be used for the Cu pillars to apply in 3D cross-point memory and thinner one can be used for the nonvolatile resistive switching memory, and data retention test is shown below.Figure 8


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)

Cumulative probability of HRS and LRS. The smaller size device shows superior uniformity than that of the larger size devices. It is observed that the 0.4-μm devices show 88% success for switching. The data read on the second switching cycle.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
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Fig8: Cumulative probability of HRS and LRS. The smaller size device shows superior uniformity than that of the larger size devices. It is observed that the 0.4-μm devices show 88% success for switching. The data read on the second switching cycle.
Mentions: Figure 8 shows cumulative probability of device-to-devices. The HRS and LRS for the 8- and 0.4-μm devices with a 2-nm-thick Al2O3 film are plotted. The average values of at HRS and LRS are 5.34/4.44 kΩ and 895/407 Ω for the 8-μm devices, respectively, while those values are 10.3/12.9 kΩ and 1.07/539 kΩ for the 0.4-μm devices, respectively. The value of LRS is slightly lower for the 8-μm devices than the 0.4-μm devices, which is owing to higher diffusion rate of Cu ion into the Al2O3 film under external bias. By considering the resistance ratio of >2, the 0.4-μm devices show higher switching yield than that of the 8-μm devices (88% vs. 74%). This suggests that the 0.4-μm devices have good switching uniformity. Figure 9 shows the statistical distribution of resistance states with different current compliances of 100, 500, and 1,000 μA for the 2- and 10-nm-thick Al2O3 films. Except few devices or without proper sweeping voltage/current, there is no memory window at a CC of 100 μA. However, the value of LRS decreases and HRS remains almost the same with increasing the CCs (Figure 9a,b). The resistance ratio increases with increasing the CCs. Table 2 represents the average values of LRS, HRS, and HRS/LRS for the 8- and 0.4-μm devices with different thicknesses of Al2O3 film of 2, 5, and 10 nm. To obtain the average values, 50 CBRAM devices were measured. It is obvious that the resistance ratio is higher at CC of 1 mA as compared to the value at a CC of 500 μA because of lower LRS value. At a CC of 500 μA, a high resistance ratio of 9.6 is obtained for the 0.4-μm devices with a 2-nm-thick Al2O3 film. In this case, more switchable devices are obtained (Figure 8), which is due to better control of Cu migration under external bias. The values of LRS are decreased with increasing both the device size and thickness of the Al2O3 films at a CC of 500 μA (Table 2), which can be explained by IRESET later. Figure 10 shows cumulative probability of the RESET currents for the 8- and 0.4-μm devices with thicknesses of the Al2O3 films of 2, 5, and 10 nm at a CC of 500 μA. The average IRESET values of the 2-, 5-, and 10-nm-thick Al2O3 films are found to be 706.1, 749.4, and 1,690 μA, respectively, for the 8-μm devices, while those values are found to be 327.5, 505.4, and 1,020 μA, respectively, for the 0.4-μm devices. It is observed that the IRESET value decreases with decreasing the thickness of the Al2O3 films. Considering the thickness-dependent formation voltage (Figure 6a), the Cu ion can migrate more in the thicker Al2O3 films, resulting larger diameter of Cu filament. That is why the thicker Al2O3 film has higher RESET current. A lowest average RESET current of 327.5 μA with good uniformity is obtained for the 0.4-μm devices with a 2-nm-thick Al2O3 film (Figure 10). As mentioned above, the formation voltage of the thinner Al2O3 films is lower than that of the thicker one. Under SET, small amount of Cu will be migrated for the thinner Al2O3 films as well as thinner diameter of the Cu filaments. That is why the LRS value of the thinner Al2O3 films is larger than the thicker one. Under RESET, the total length of the Cu filaments will be dissolved for the thinner Al2O3 films because of both higher electric field and thinner filament diameter than that of the thicker one. On the other hand, interface-type switching or even no RESET is observed for the thicker Al2O3 films. Therefore, HRS value of the thinner Al2O3 films is higher than those of the thicker one. It can be concluded that thicker Al2O3 film can be used for the Cu pillars to apply in 3D cross-point memory and thinner one can be used for the nonvolatile resistive switching memory, and data retention test is shown below.Figure 8

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