The stochastic nature of conductive filament formation and dissolution always leads to large fluctuations of key device parameters that hinder the practical applications of resistive random-access memories (RRAMs). Here, we report a simple bilayer oxide-based device structure of Al/TiOx/TiOy/FTO (x < y) employed to address this variability issue and improve the overall performance of the memory device. The bipolar resistive switching performance remarkably improved in these bilayer devices with lower forming voltage (~1 V), set/reset voltages of 0.4/-0.6 V, a programming current of 10 mA, an enlarged ON/ OFF ratio (>103), longer retention (>103 s), and better uniformity as compared to the control Al/TiOy/FTO device. Moreover, the modulation of TiOx layer thickness enables tunability of switching voltages, cur- rents, and the resistance window. In addition, reliable and reproducible multiple resistance states, more specifically different low resistance states, can be achieved in bilayer devices by controlling the pro- gramming current down to 10 mA, which is in contrast to the binary states of the control devices. These improved switching parameters with multilevel storage capability in bilayer devices are attributed to the incorporation of an oxygen vacancy-rich interfacial layer, namely TiOx, which serves as an oxygen va- cancy reservoir and facilitates effective conductive filament formation inside the switching layer. Furthermore, the thermodynamics involving the dielectric constant and Gibb's free energy of oxide formation at the Al/TiOx and TiOx/TiOy interfaces play a pivotal role in the associated switching mech- anism. The spatial variability of the operating voltage across these devices is found to be as low as 8%. These findings pave the way for low power, low cost, and high density data storage applications.
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The stochastic nature of conductive filament formation and dissolution always leads to large fluctuations of key device parameters that hinder the practical applications of resistive random-access memories (RRAMs). Here, we report a simple bilayer oxide-based device structure of Al/TiOx/TiOy/FTO (x < y) employed to address this variability issue and improve the overall performance of the memory device. The bipolar resistive switching performance remarkably improved in these bilayer devices with lower forming voltage (~1 V), set/reset voltages of 0.4/-0.6 V, a programming current of 10 mA, an enlarged ON/ OFF ratio (>103), longer retention (>103 s), and better uniformity as compared to the control Al/TiOy/FTO device. Moreover, the modulation of TiOx layer thickness enables tunability of switching voltages, cur- rents, and the resistance window. In addition, reliable and reproducible multiple resistance states, more specifically different low resistance states, can be achieved in bilayer devices by controlling the pro- gramming current down to 10 mA, which is in contrast to the binary states of the control devices. These improved switching parameters with multilevel storage capability in bilayer devices are attributed to the incorporation of an oxygen vacancy-rich interfacial layer, namely TiOx, which serves as an oxygen va- cancy reservoir and facilitates effective conductive filament formation inside the switching layer. Furthermore, the thermodynamics involving the dielectric constant and Gibb's free energy of oxide formation at the Al/TiOx and TiOx/TiOy interfaces play a pivotal role in the associated switching mech- anism. The spatial variability of the operating voltage across these devices is found to be as low as 8%. These findings pave the way for low power, low cost, and high density data storage applications.
