Effect of Al Concentration on Ferroelectric Properties in HfAlO_x‐Based Ferroelectric Tunnel Junction Devices for Neuroinspired Applications

Abstract

Since HfOx‐based ferroelectric tunnel junctions (FTJs) are attractive compared to perovskite‐based FTJs and other emerging memory devices, they are being actively studied recently. They have advantages such as a simple metal–insulator–metal structure, complementary metal oxide semiconductor (CMOS) compatibility, non‐destructive operation, and low power consumption. Moreover, doped HfOx‐based FTJs are in the spotlight in terms of neuromorphic engineering as a way of advancing from the von Neumann structure. In particular, Al dopant is effective for inducing ferroelectric properties due to its smaller radius than that of Hf. The optimal concentration of Al varies depending on the device materials and the annealing conditions during deposition. Therefore, in‐depth research is required for neuromorphic applications. Herein, the properties of FTJ devices according to Al doping concentrations are analyzed. Subsequently, using the device with the highest remanent polarization, neuromorphic applications are implemented, including spike‐timing‐dependent plasticity (STDP), paired‐pulse facilitation (PPF), long‐term potentiation, and depression. The characteristics in different frequency regions are also studied to satisfy the demand for fast switching. Finally, the FTJ device is used as a physical reservoir in reservoir computing for efficient processing of time‐dependent inputs.

Programmable Retention Characteristics in MoS2-Based Atomristors for Neuromorphic and Reservoir Computing Systems

“…Figure d illustrates the PPF synaptic function, which demonstrates the changes in the intensities of two synaptic stimuli over time at different intervals (Figure S12). − As the interval time increases, the magnitude of current decay increases, which is analogous to the STM effect. Various intervals ranging from 10 μs to 1 s are added between two identical programming pulses with a pulse amplitude of 2.5 V and pulse width of 7 μs.…”

Artificial Neural Network Classification Using Al-Doped HfOx-Based Ferroelectric Tunneling Junction with Self-Rectifying Behaviors

“…Additionally, its thickness cannot be easily scaled down because when it approaches a few nanometers, ferroelectricity is lost. − As a solution to these challenges, ferroelectric materials based on nanoscale HfO x have been proposed. Because of its compatibility with CMOS, scalability, and advantageous bandgap, HfO x is widely used. − After the ferroelectric characteristics of doped HfO x films were initially revealed in 2011, investigations have recently been conducted to accelerate the development of the orthorhombic phase (o-phase) (space group: Pca2 1 ) (o-phase), employing dopants such as Zr, Al, Si, Y, and La. − In particular, the Al dopant provides mechanical stress in HfO x to stabilize the o-phase because Al has a smaller atomic radius than Hf. , Various structures of FTJs have been studied, including metal-ferroelectric-metal (MFM), metal-ferroelectric-insulator–metal (MFIM), metal-ferroelectric-silicon (MFS), and metal-ferroelectric-insulator-silicon (MFIS). − Notably, using silicon as a bottom electrode in the MFS configuration offers advantages such as self-rectification and a larger TER compared with MFM FTJs, which are attributed to the depletion region of the semiconductor. ,, …”