Multilayer redox-based HfOx/Al2O3/TiO2 memristive structures for neuromorphic computing

Abstract

Redox-based memristive devices have shown great potential for application in neuromorphic computing systems. However, the demands on the device characteristics depend on the implemented computational scheme and unifying the desired properties in one stable device is still challenging. Understanding how and to what extend the device characteristics can be tuned and stabilized is crucial for developing application specific designs. Here, we present memristive devices with a functional trilayer of HfOx/Al2O3/TiO2 tailored by the stoichiometry of HfOx (x = 1.8, 2) and the operating conditions. The device properties are experimentally analyzed, and a physics-based device model is developed to provide a microscopic interpretation and explain the role of the Al2O3 layer for a stable performance. Our results demonstrate that the resistive switching mechanism can be tuned from area type to filament type in the same device, which is well explained by the model: the Al2O3 layer stabilizes the area-type switching mechanism by controlling the formation of oxygen vacancies at the Al2O3/HfOx interface with an estimated formation energy of ≈ 1.65 ± 0.05 eV. Such stabilized area-type devices combine multi-level analog switching, linear resistance change, and long retention times (≈ 107–108 s) without external current compliance and initial electroforming cycles. This combination is a significant improvement compared to previous bilayer devices and makes the devices potentially interesting for future integration into memristive circuits for neuromorphic applications.

Energy Efficient Photonic Memory Based on Electrically Programmable Embedded III-V/Si Memristors: Switches and Filters

“…1a-c) is comprised of 300nm thick p-type Si doped at 5×10 17 cm -3 , alternating layers of HfO2/Al2O3, and 150nm thick n-type GaAs doped at 3×10 18 cm -3 . We chose a multilayer HfO2/Al2O3 stack because Mahata et al and Park et al, have shown improved resistive switching due to atomic inter-diffusion and promotion of oxygen vacancies (VO 2+ ) at the HfO2/Al2O3 (HfAlO) interface 61,62 . Fig.…”

“…This turns the high impedance capacitor into a device exhibiting a low resistance state. During the "reset" process only the interfacial filament is believed to rupture first due to Al2O3 having less VO 2+ than HfO2 61,62 , thus breaking the conductive path via a combination of Joule heating and field effect. This effectively restores the memristor in its high resistance state.…”

The Role of Vacancy Dynamics in Two‐Dimensional Memristive Devices

“…[ 3 ] Currently, most reported memristors are vertical two‐terminal metal‐insulator‐metal structures. [ 3–5 ] They have been intensively investigated for neuromorphic computing [ 6,7 ] and were used in nonvolatile memory architectures, frequently referred to as resistive random‐access memory (rRAM) or memristive random‐access memory (mRAM). [ 8 ]…”

“…[3] Currently, most reported memristors are vertical two-terminal metalinsulator-metal structures. [3][4][5] They have been intensively investigated for neuromorphic computing [6,7] and were used in nonvolatile memory architectures, frequently referred to as resistive randomaccess memory (rRAM) or memristive random-access memory (mRAM). [8] A novel class of memristive materials is 2D and quasi-2D layered transition metal dichalcogenides (TMDCs) such as MoS 2 , MoSe 2 , WS 2 , and WSe 2 .…”

Correlation between Electronic Structure, Microstructure, and Switching Mode in Valence Change Mechanism Al2O3/TiOx‐Based Memristive Devices

“…[14][15][16] Both mechanisms give a spatially uniform contribution to the total current leading to an area-dependent switching hysteresis often characterized by low device-to-device and low cycle-to-cycle variation. Interfacial switching has been reported for different perovskite materials, such as SrTiO 3 [17] and (Pr,Ca)MnO 3 [18] but also for oxygen-deficient transition metal oxides like TaO x , [19][20][21][22] NbO x , [23,24] WO x , [25,26] HfO x , [27,28] and TiO x [29,30] in combination with different tunneling barriers, mostly Al 2 O 3 . Some material stacks enable operation in either abrupt filamentary or gradual area-dependent switching mode controlled by the operation conditions.…”