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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

I-Vswitching characteristics. Typical current-voltage characteristics of the 8-μm devices with a 2-nm-thick Al2O3 film at a CC of 500 μA. A low formation voltage of 1.65 V is observed.
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Fig5: I-Vswitching characteristics. Typical current-voltage characteristics of the 8-μm devices with a 2-nm-thick Al2O3 film at a CC of 500 μA. A low formation voltage of 1.65 V is observed.

Mentions: Figure 5 shows the typical I-V curves of the 8-μm devices with a 2-nm-thick Al2O3 film and a CC of 500 μA is applied. The sweeping voltage is shown by arrows 1 to 5. A low Vform of 1.65 V is observed for this thin Al2O3 film. Cumulative probability of 50 CBRAM devices with different size and thickness of the Al2O3 films is plotted (Figure 6a). The average values of Vform are 1.7, 2.4, and 3 V for the 8-μm devices while those values are 1.85, 2.7, and 3.4 V for the 0.4-μm devices with different thicknesses of Al2O3 film of 2, 5, and 10 nm, respectively. Those values of Vform are lower than the 20-nm-thick Al2O3 films (Figure 3a). For the 2-nm-thick Al2O3 films, tight distribution of Vform is found to be 1.6 to 1.75 V and 1.75 to 2.1 V for the 8- and 0.4-μm devices, respectively. Figure 6b shows cumulative probability of the leakage currents for the 8- and 0.4-μm devices with thicknesses of the Al2O3 films of 2, 5, and 10 nm. The leakage currents at 50% probability are found to be 3.4 μA, 60 pA, and 1.7 pA for the 8-μm devices while those values are found to be 39 nA, 22 pA, and 2.1 pA for the 0.4-μm devices with thicknesses of the Al2O3 films of 2, 5, and 10 nm, respectively. The 10-nm-thick Al2O3 films show device size-independent leakage currents, which is due to the limit of current measurement by our probe station. It is found that the variation of formation voltage is directly proportional to the switching material thickness and inversely proportional to the device size area. On the other hand, the leakage current shows the opposite nature of the formation voltage. It varies directly proportional to the device size and inversely proportional to the switching materials' thickness. It happens because the reduction in device size causes the decrement of defects inside the switching material which in turns increases its insulation property. This causes the leakage current lower, and so, the required voltage to change its resistance state is more. The reduction in switching material thickness causes the higher possibility of electron tunneling through the insulator layer which causes the enhancement in leakage current. It is observed that the 2-nm-thick Al2O3 films show better uniformity of the formation voltages as well as the leakage currents. Both the RESET current (IRESET) and voltage (VRESET) at first cycle are found to be approximately 2 mA and -0.45 V, respectively (Figure 5). The SET voltages VSET, VRESET, and IRESET at the second cycle are lower 0.5 V, -0.3 V, and approximately 540 μA than those of the values that are observed in the first cycle, respectively. The IRESET is slightly higher than the current compliance because of thinner (2 nm) Al2O3 film. To dissolve more length of the Cu filaments or to increase high resistance state (HRS), higher negative voltage of -0.8 V is required. I-V curves imply that the RESET is happened through a slow deterioration process of the existing metallic filaments in its weak point by reduction due to the negative bias on the TE. A resistance ratio (HRS/LRS) at a Vread of 0.1 V is found to be 16, which is acceptable for application.Figure 5


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)

I-Vswitching characteristics. Typical current-voltage characteristics of the 8-μm devices with a 2-nm-thick Al2O3 film at a CC of 500 μA. A low formation voltage of 1.65 V is observed.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4494016&req=5

Fig5: I-Vswitching characteristics. Typical current-voltage characteristics of the 8-μm devices with a 2-nm-thick Al2O3 film at a CC of 500 μA. A low formation voltage of 1.65 V is observed.
Mentions: Figure 5 shows the typical I-V curves of the 8-μm devices with a 2-nm-thick Al2O3 film and a CC of 500 μA is applied. The sweeping voltage is shown by arrows 1 to 5. A low Vform of 1.65 V is observed for this thin Al2O3 film. Cumulative probability of 50 CBRAM devices with different size and thickness of the Al2O3 films is plotted (Figure 6a). The average values of Vform are 1.7, 2.4, and 3 V for the 8-μm devices while those values are 1.85, 2.7, and 3.4 V for the 0.4-μm devices with different thicknesses of Al2O3 film of 2, 5, and 10 nm, respectively. Those values of Vform are lower than the 20-nm-thick Al2O3 films (Figure 3a). For the 2-nm-thick Al2O3 films, tight distribution of Vform is found to be 1.6 to 1.75 V and 1.75 to 2.1 V for the 8- and 0.4-μm devices, respectively. Figure 6b shows cumulative probability of the leakage currents for the 8- and 0.4-μm devices with thicknesses of the Al2O3 films of 2, 5, and 10 nm. The leakage currents at 50% probability are found to be 3.4 μA, 60 pA, and 1.7 pA for the 8-μm devices while those values are found to be 39 nA, 22 pA, and 2.1 pA for the 0.4-μm devices with thicknesses of the Al2O3 films of 2, 5, and 10 nm, respectively. The 10-nm-thick Al2O3 films show device size-independent leakage currents, which is due to the limit of current measurement by our probe station. It is found that the variation of formation voltage is directly proportional to the switching material thickness and inversely proportional to the device size area. On the other hand, the leakage current shows the opposite nature of the formation voltage. It varies directly proportional to the device size and inversely proportional to the switching materials' thickness. It happens because the reduction in device size causes the decrement of defects inside the switching material which in turns increases its insulation property. This causes the leakage current lower, and so, the required voltage to change its resistance state is more. The reduction in switching material thickness causes the higher possibility of electron tunneling through the insulator layer which causes the enhancement in leakage current. It is observed that the 2-nm-thick Al2O3 films show better uniformity of the formation voltages as well as the leakage currents. Both the RESET current (IRESET) and voltage (VRESET) at first cycle are found to be approximately 2 mA and -0.45 V, respectively (Figure 5). The SET voltages VSET, VRESET, and IRESET at the second cycle are lower 0.5 V, -0.3 V, and approximately 540 μA than those of the values that are observed in the first cycle, respectively. The IRESET is slightly higher than the current compliance because of thinner (2 nm) Al2O3 film. To dissolve more length of the Cu filaments or to increase high resistance state (HRS), higher negative voltage of -0.8 V is required. I-V curves imply that the RESET is happened through a slow deterioration process of the existing metallic filaments in its weak point by reduction due to the negative bias on the TE. A resistance ratio (HRS/LRS) at a Vread of 0.1 V is found to be 16, which is acceptable for application.Figure 5

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