Abstract
Resistive switching characteristics by using the Al2O3 interfacial layer in an Al/Cu/GdOx/Al2O3/TiN memristor have been enhanced as compared to the Al/Cu/GdOx/TiN structure owing to the insertion of Al2O3 layer for the first time. Polycrystalline grain, chemical composition, and surface roughness of defective GdOx film have been investigated by transmission electron microscope (TEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and atomic force microscopy (AFM). For bipolar resistive switching (BRS) characteristics, the conduction mechanism of high resistance state (HRS) is a space-charge limited current for the Al/Cu/GdOx/TiN device while the Al/Cu/GdOx/Al2O3/TiN device shows Schottky emission. However, both devices show Ohmic at a low resistance state (LRS). After the device has been SET, the Cu filament evidences by both TEM and elemental mapping. Oxygen-rich at the Cu/GdOx interface and Al2O3 layer are confirmed by energy dispersive X-ray spectroscopy (EDS) line profile. The Al/Cu/GdOx/Al2O3/TiN memristor has lower RESET current, higher speed operation of 100 ns, long read pulse endurance of >109 cycles, good data retention, and the memristor with a large resistance ratio of >105 is operated at a low current of 1.5 µA. The complementary resistive switching (CRS) characteristics of the Al/Cu/GdOx/Al2O3/TiN memristor show also a low current operation as compared to the Al/Cu/GdOx/TiN device (300 µA vs. 3.1 mA). The transport mechanism is the Cu ion migration and it shows Ohmic at low field and hopping at high field regions. A larger hopping distance of 1.82 nm at the Cu/GdOx interface is obtained as compared to a hopping distance of 1.14 nm in the Al2O3 layer owing to a larger Cu filament length at the Cu/GdOx interface than the Al2O3 layer. Similarly, the CRS mechanism is explained by using the schematic model. The CRS characteristics show a stable state with long endurance of >1000 cycles at a pulse width of 1 µs owing to the insertion of Al2O3 interfacial layer in the Al/Cu/GdOx/Al2O3/TiN structure.
Highlights
Increasing demands on data storage in computing and mobile electronics are pushing the development of memories that continue to overcome the limits in scalability, storage-density, operation speed, and low power consumption [1,2]
When a positive voltage is applied on the Cu top electrode (TE) (>VSET1 ), the Cu ions are generated by oxidation method (Cu◦ → Cuz+ + ze−, z = 1, 2) [5] and these Cu ions migrate towards the Al2 O3 /TiN interface through oxygen vacancy under an electric field as well as a Cu filament can be formed in the Al2 O3 layer and current increases (Figure 9b)
Improved bipolar resistive switching (BRS) and complementary resistive switching (CRS) characteristics of the Al/Cu/GdOx /Al2 O3 /TiN memristors have been reported as compared to the Al/Cu/GdOx /TiN devices, for the first time, owing to insertion of Al2 O3 interfacial layer
Summary
Increasing demands on data storage in computing and mobile electronics are pushing the development of memories that continue to overcome the limits in scalability, storage-density, operation speed, and low power consumption [1,2]. In order to mitigate those difficulties, the bi-layer concept has been introduced which leads to filament stability by controlling the Cu ion migration and reducing the RESET current [7,8,21,22]. Al/Cu/GdOx /Al2 O3 /TiN structure helps control the metallic filament formation/dissolution. This will help reduce the operation current in BRS/CRS performance as compared to the single Al2 O3 switching layer [13]. In this new structure, the GdOx is used as a Cu buffer layer, which helps the. Al/Cu/GdOx /Al2 O3 /TiN memristor, this shows excellent BRS and CRS characteristics owing to control the Cu ion migration
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