MoS₂/BiFeO₃-based solid-ionic transistor

• Main Author: Chen, Jieqiong
• Other Authors: Liu Zheng
• Format: Thesis-Doctor of Philosophy
• Language: English
• Published: Nanyang Technological University 2022
• Subjects: Engineering::Materials
• Online Access: https://hdl.handle.net/10356/163916
• Institution: Nanyang Technological University

The development of innovative memory and sensing devices fired up the 2D-based electronics to deal with the shortcomings of the silicon-based hardware. The breakthrough mechanisms of memory devices based on 2D channels are in the appalling need to overcome the bottlenecks of current 2D-based electronics, including the high energy consumption, complex operation conditions, low sensitivity, limited memory capability, etc. Reviewed from state-of-the-art memory mechanisms, ionic memory is promising to solve the shortcomings mentioned above. Solid-ionic gating medium is preferred in terms of operation/storage safety and gating efficiency. BiFeO3 and MoS2 are selected as the material models to construct solid-ionic systems for both sensing and memory. In the first project, a coplanar-gated device is designed and proved to function as a high-performance n-type electrical FET, electrical memory unit, photodetector, and optical memory unit. The influence of the proposed oxygen-vacancy-based solid-ionic layer is in accord with expectation, which can serve as the charge storage centers and apply the electrostatic doping locally. The accomplishment of multifunctions in a single device paves the way for constructing in-memory sensing systems. The high sensitivity and memory capacitance indicate the prominence of the interfacial solid-ionic layer. Therefore, studying the fundamentals and applications of the oxygen-vacancy-based solid-ionic layer is essential in the area of 2D electronics for building up new families of sensing and memory devices. In the second project, a vertical-gated device is proposed to optimize the device performance further. Compared to the coplanar-gated device, it can be operated under low-voltage gate pulses, thus much more energy efficient. In addition, it can function well as an n-type electrical FET with much lower controlling gate voltage. However, the photoresponse of the vertical-gated device is different from the coplanar-gated device due to the different polarization directions of the as-grown films. The electrical sensing and memory characteristics are mainly focused on the MoS2/BiFeO3 interface in the scenario. Based on the characteristics of electrical memory, it is highly potential to be applied in neuromorphic systems to emulate diverse synaptic behaviors. In the third project, both coplanar-gated and vertical-gated devices were evaluated as artificial synaptic devices in aspects of different short-term and long-term plasticity. As a result, the MoS2/BFO-based solid-ionic transistor can successfully emulate different synaptic behaviors, including PPF/PPD, EPSC/IPSC, PND, and herbian learning. And the long-term PSC characteristics of both architectures were evaluated with MLP and CNN architectures for pattern recognitions, which proved to achieve high recognition accuracies among state-of-the-art artificial synaptic devices, highlighting the potential of the MoS2/BFO-based solid-ionic transistor in neuromorphic hardware. Based on the properties of the MoS2/BFO-based solid-ionic transistor, the solid-ionic memory in other material combinations can also been expected to build up a family of in-memory computing or in-memory sensing devices.