Sol-Gel Composites-Based Flexible and Transparent Amorphous Indium Gallium Zinc Oxide Thin-Film Synaptic Transistors for Wearable Intelligent Electronics

In this study, we propose the fabrication of sol-gel composite-based flexible and transparent synaptic transistors on polyimide (PI) substrates. Because a low thermal budget process is essential for the implementation of high-performance synaptic transistors on flexible PI substrates, microwave annealing (MWA) as a heat treatment process suitable for thermally vulnerable substrates was employed and compared to conventional thermal annealing (CTA). In addition, a solution-processed wide-bandgap amorphous In-Ga-Zn (2:1:1) oxide (a-IGZO) channel, an organic polymer chitosan electrolyte-based electric double layer (EDL), and a high-k Ta₂O₅ thin-film dielectric layer were applied to achieve high flexibility and transparency. The essential synaptic plasticity of the flexible and transparent synaptic transistors fabricated with the MWA process was demonstrated by single spike, paired-pulse facilitation, multi-spike facilitation excitatory post-synaptic current (EPSC), and three-cycle evaluation of potentiation and depression behaviors. Furthermore, we verified the mechanical robustness of the fabricated device through repeated bending tests and demonstrated that the electrical properties were stably maintained. As a result, the proposed sol-gel composite-based synaptic transistors are expected to serve as transparent and flexible intelligent electronic devices capable of stable neural operation.     

Engineering of tunnel barrier for highly integrated nonvolatile memory applications

In this paper, the engineered tunnel barrier technology is introduced by using the engineered tunnel barrier of VARIOT type (SiO₂/Si₃N₄/SiO₂) and CRESTED type (Si₃N₄/SiO₂/Si₃N₄) with Si₃N₄ and high-k HfO₂ layers as charge trapping layers, respectively. In addition, the high-k stacked VARIOT type of SiO₂/HfO₂/Al₂O₃ and Al₂O₃/HfO₂/Al₂O₃ are compared with O/N/O tunnel barrier memory. As a result, the engineered tunnel barrier memory device showed excellent memory characteristics compared to the single SiO₂ tunnel barrier memory device, such as very high P/E (program/erase) speed, good retention time and no degradation in endurance characteristics.     

Resistance switching properties of In2O3 nanocrystals memory device with organic and inorganic hybrid structure

A memory device with In₂O₃ nanocrystals embedded in a biphenyl-tertracarboxylic dianhydride-phenylen diamine (BPDA-PDA) polyimide layer on a ZnO layer was fabricated, and its electrical properties were evaluated. Then, the transmittance efficiency in the structure of the BPDA-PDA polyimide/In₂O₃ nanocrystals/ZnO/ITO/double polishing sapphire substrate was measured to be about 80% between 440 to 800 nm by ultraviolet-visible transmittance spectroscopy. A bipolar switching current bistability by difference resistance appeared in the sweep voltage rage from −7 to 7 V. It was considered that the bipolar behavior of current-voltage may originate from a resistance fluctuation because of the electron charging effect in In₂O₃ nanocrystals by voltage sweeping, Fowler–Nordheim tunneling, space-charge-limited current, and the migration of O²⁻ ions.