Abstract
A novel idea by using copper (Cu) pillar is proposed in this study, which can replace the through-silicon-vias (TSV) technique in future three-dimensional (3D) architecture. The Cu pillar formation under external bias in an Al/Cu/Al2O3/TiN structure is simple and low cost. The Cu pillar is formed in the Al2O3 film under a small operation voltage of <5 V and a high-current-carrying conductor of >70 mA is obtained. More than 100 devices have shown tight distribution of the Cu pillars in Al2O3 film for high current compliance (CC) of 70 mA. Robust read pulse endurances of >106 cycles are observed with read voltages of −1, 1, and 4 V. However, read endurance is failed with read voltages of −1.5, −2, and −4 V. By decreasing negative read voltage, the read endurance is getting worst, which is owing to ruptured Cu pillar. Surface roughness and TiO x N y on TiN bottom electrode are observed by atomic force microscope and transmission electron microscope, respectively. The Al/Cu/Al2O3/TiN memory device shows good bipolar resistive switching behavior at a CC of 500 μA under small operating voltage of ±1 V and good data retention characteristics of >103 s with acceptable resistance ratio of >10 is also obtained. This suggests that high-current operation will help to form Cu pillar and lower-current operation will have bipolar resistive switching memory. Therefore, this new Cu/Al2O3/TiN structure will be benefited for 3D architecture in the future.
Highlights
Resistive random access memory so-called RRAM has attracted great attention to the researchers owing to its simple metal-insulator-metal (M-I-M) structure, long endurance, low-power consumption, good data retention, and excellent scalability [1,2,3,4,5]
After applying positive formation voltage (Vform) on the top electrode (TE), the device switches from Initial resistance state (IRS) to low-resistance state (LRS)
That is why the current compliance of 70 mA was used to protect the device. These devices do not show reset operation even a reset voltage of −1 V. This suggests that the strong Cu filament or pillar forms in the Al2O3 film, which we are looking at the metal interconnection for 3D memory stack
Summary
Resistive random access memory so-called RRAM has attracted great attention to the researchers owing to its simple metal-insulator-metal (M-I-M) structure, long endurance, low-power consumption, good data retention, and excellent scalability [1,2,3,4,5]. To obtain 3D stack, the chemical–mechanical-polishing (CMP) will be used after Al2O3/BE (and/or Al2O3/TE) step Due to this Cu pillar formation, the area consumed by cross-points will be lesser than that of the conventional cost-effective TSV method. To get a low-cost and high-density Cu interconnection for 3D stacks, 3D architecture with Cu pillar would be a good alternative to overcome the aforementioned TSV issue [22]. In this cross-point architecture (Figure 1), the Cu as an oxidize electrode or top electrode (TE) could be used; other inert electrodes such as tungsten (W) and titanium-nitride (TiN) or bottom electrode (BE) could be used; and Al2O3 film could be used as switching layer. This new idea of 3D RRAM using Cu pillar with Al2O3-based resistive switching memory is reported for the first time
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