Figure 20.

2D/3D heterojunctions for memory devices. (a) 3D schematic of a FGFETs device based on MOCVD-grown monolayer ${\text{MoS}}_2$. (b) Transfer characteristic of the FGFET acquired for two different gate voltage sweep directions, showing a memory window of 10.6 V when observing at 1 nA constant current. (c) Simplified band diagrams of ${\text{MoS}}_2$ FGFETs for both programming (left panel) and erasing (right panel). Reproduced with permission from ref 374. Copyright 2020 Springer Nature. (d) Schematic view of a $\text{AlScN}/{\text{MoS}}_2$ FE-FET. (e) Transfer characteristic of the $\text{AlScN}/{\text{MoS}}_2$ FE-FET acquired for two different gate voltage sweep directions, showing a memory window more than 4 MV/cm. (f) Retention measurement on $\text{AlScN}/{\text{MoS}}_2$ FE-FET by monitoring the drain current for varying time intervals up to 10⁵ s. (g) Calculated ratio of depolarization field over coercive field in three different ${\text{MoS}}_2$ FE-FET cases: (1) $\text{AlScN}/{\text{MoS}}_2$; (2) ${\text{HfO}}_2/{\text{MoS}}_2$; (3) $\text{PZT}/{\text{MoS}}_2$. Reproduced with permission from ref 375. Copyright 2020 American Chemical Society. (h) Polarization charges distribution (left) and band diagram (right) in a FeS-FET in polarization down and polarization up states. (i) The demonstrated FeS-FETs showed a high on/off ratio of over 10⁸ and a large memory window of over 1 MV/cm. Reproduced with permission from ref 376. Copyright 2019 Springer Nature. (j) Illustration of an atomristor consisting of a mono or few layer TMD or h-BN sandwiched between conducting electrodes. The structure can produce nonvolatile memory effect. Reproduced with permission from ref 377. Copyright 2019 Springer Nature.