Preparation of Remote Plasma Atomic Layer-Deposited HfO2 Thin Films with High Charge Trapping Densities and Their Application in Nonvolatile Memory Devices.

Optimization of equipment structure and process conditions is essential to obtain thin films with the required properties, such as film thickness, trapped charge density, leakage current, and memory characteristics, that ensure reliability of the corresponding device. In this study, we fabricated metal-insulator-semiconductor (MIS) structure capacitors using HfO2 thin films separately deposited by remote plasma (RP) atomic layer deposition (ALD) and direct-plasma (DP) ALD and determined the optimal process temperature by measuring the leakage current and breakdown strength as functions of process temperature. Additionally, we analyzed the effects of the plasma application method on the charge trapping properties of HfO2 thin films and properties of the interface between Si and HfO2. Subsequently, we synthesized charge-trapping memory (CTM) devices utilizing the deposited thin films as charge-trapping layers (CTLs) and evaluated their memory properties. The results indicated excellent memory window characteristics of the RP-HfO2 MIS capacitors compared to those of the DP-HfO2 MIS capacitors. Moreover, the memory characteristics of the RP-HfO2 CTM devices were outstanding as compared to those of the DP-HfO2 CTM devices. In conclusion, the methodology proposed herein can be useful for future implementations of multiple levels of charge-storage nonvolatile memories or synaptic devices that require many states.

Characteristics of Hf0.5Zr0.5O2 Thin Films Prepared by Direct and Remote Plasma Atomic Layer Deposition for Application to Ferroelectric Memory.

Hf0.5Zr0.5O2 (HZO) thin film exhibits ferroelectric properties and is presumed to be suitable for use in next-generation memory devices because of its compatibility with the complementary metal-oxide-semiconductor (CMOS) process. This study examined the physical and electrical properties of HZO thin films deposited by two plasma-enhanced atomic layer deposition (PEALD) methods- direct plasma atomic layer deposition (DPALD) and remote plasma atomic layer deposition (RPALD)-and the effects of plasma application on the properties of HZO thin films. The initial conditions for HZO thin film deposition, depending on the RPALD deposition temperature, were established based on previous research on HZO thin films deposited by the DPALD method. The results show that as the measurement temperature increases, the electric properties of DPALD HZO quickly deteriorate; however, the RPALD HZO thin film exhibited excellent fatigue endurance at a measurement temperature of 60 °C or less. HZO thin films deposited by the DPALD and RPALD methods exhibited relatively good remanent polarization and fatigue endurance, respectively. These results confirm the applicability of the HZO thin films deposited by the RPALD method as ferroelectric memory devices.

Atom Probe Tomographic Imaging of PbS Quantum Dot Formation on Neodymium Clusters in Silicate Glasses.

The first 3-D direct observation of clusters of Nd oxide inside silicate glasses was achieved using atom probe tomography. Three-dimensional elemental maps of major chemical elements in glasses such as Si, Al, Zn and O showed no evidence of regions that had concentrations higher than the average values, whereas the Nd aggregated into regions of high concentration. Elemental maps of Nd and Pb recorded from the glasses containing PbS QDs showed highly-concentrated areas of both elements at the same locations; this result indicates that PbS QDs formation started in association with the Nd clusters.

Antisense RNA-based High-Throughput Screen System for Directed Evolution of Quorum Quenching Enzymes.

Quorum quenching (QQ) enzymes, which disrupt the quorum sensing signaling process, have attracted considerable attention as new antimicrobial agents. However, their low catalytic efficiency for quorum sensing molecules remains a challenge. Herein, we present an antisense RNA-based high-throughput screen system for directed evolution of a quorum quenching enzyme. The screening system was constructed by incorporating an antisense RNA (RyhB) into a synthetic module to quantitatively regulate the expression of a reporter gene fused with a sense RNA (sodB). To control the expression of a reporter gene in response to the catalytic activity of a quorum quenching enzyme, the region of interaction and mode between a pair of antisense (RyhB) and sense (sodB) RNAs was designed and optimized through the prediction of the secondary structure of the RNA pair. The screening system constructed was shown to lead to a significant reduction in the false-positive rate (average 42%) in the screening of N-acyl-homoserine lactonase (AiiA) with increased catalytic activity, resulting in a true-positive frequency of up to 76%. The utility and efficiency of the screening system were demonstrated by selecting an AiiA with 31-fold higher catalytic efficiency than the wild-type in three rounds of directed evolution. The present approach can be widely used for the screening of quorum quenching enzymes with the desired catalytic property, as well as for a synthetic network for a stringent regulation of the gene expression.

Over-expression of recombinant proteins with N-terminal His-tag via subcellular uneven distribution in Escherichia coli.

Specific tags with defined amino acid residues are widely used to purify or probe target proteins. Interestingly, the tagging system occasionally results in an increase of the recombinant protein expression in vivo. Here, we systematically examined this phenomenon using a poly-histidine (His)-tag fused to N- or C-terminal region of green, red, and blue fluorescent proteins by quantification and uneven distribution in cytoplasm of Escherichia coli. This effect was further supported by the distinct over-expression of several unrelated proteins, such as esterase, neopullulanase, and chloramphenicol acetyltransferase, tagging with the same tag. These results suggest that a poly-His-tag placed at N-terminal region can induce over-expression of recombinant protein via subcellular uneven distribution in vivo.