No abstract

Topological quad-domain textures in ferroelectric nanoislands have been considered as enablers for nanoelectric devices. However, the fabrication of ordered arrays of ferroelectric islands exhibiting this domain structure is a challenge. By using substrate patterning to create nucleation sites, highly ordered quad-domain ferroelectric polarization configurations were achieved in BiFeO3 nanoisland arrays. Reversible switching of the quad-domain between the center divergent state with highly conductive domain walls and the center convergent state with insulating domain walls can be realized, resulting in a resistance change with a large on/off ratio. This templated growth strategy enables the controllable fabrication of exotic topological domains and sheds light on their applications for configurable electronic devices.

Nanoscale tantalum nitride–aluminum oxide–silicon nitride–silicon oxide–silicon (TANOS) memory devices utilizing a recess region were investigated to improve device performance and reduce cell-to-cell interference. The dependence of electrical properties on the depth of the recess region in the TANOS flash memory devices was simulated by using Synopsys TCAD Sentaurus. The cell-to-cell interference characteristics of the TANOS flash memory devices dependent on the recess region were investigated. The drain current at an on-state in the TANOS flash memory devices increased with increasing depth of the recess region owing to the existence of the fringe field generated from the recess region. The coupling ratio of the TANOS flash memory increased with increasing depth of the recess region. The simulation results showed that the cell-to-cell interference in the TANOS flash memory devices decreased with increasing depth of the recess region.

Among electromagnetic wave spectrum, infrared region has many attractive applications such as a LiDAR, optical communication, telecommunications, thermography, bioimaging, photovoltaics, and night visions. However, the expensive cost of epitaxial III-V semiconductors and the fabrication process hinders the widespread of the infrared technology beyond the silicon absorption range. Colloidal quantum dots have a great potential as an alternative materials for infrared detection. Lead chalcogenide QDs not only have tunable bandgap in infrared region but also have process compatibility with conventional Si ROIC in the device fabrication process, which remarkably reduces fabrication costs. The performance of photodetectors incorporating the lead chalcogenide QDs, however, is suboptimal and needs further improvement. One of the main factors limiting the performance of QD-based photodetectors is a high density of surface defects. QDs inherently have large surface-to-volume ratios and dangling bonds on the surface acted as trap sites. Various methods to reduce surface defects, such as thermal and ligand treatment, have been introduced; however, even after these treatments, QD-based photodetectors still show the relatively low detectivity (D*). In this work, we demonstrate the various approaches to improve the performance of infrared photodetectors and their results. We focused on the reducing the trap density by the surface treatment of QDs using thermal annealing and chemical treatment in order to improve the device performance. We developed the chemical treatment method for reducing trap states with maintaining the existing ligands. Thermal annealing also can reduce the trap density; however, it sintered QDs by atomic diffusion. We found optimal condition for reducing the surface traps with suppressing sintering. The effects of these treatments were evaluated by the device performance and trap characterization. These approaches improve the bandwidth and the responsivity compared to reference devices. Moreover, we treated the surface of QD layers to show the interfacial effect on the QD devices.