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Chalcogenide glass in the ternary Ge-Sb-Se system is inherently moldable, thus being considered as a strong candidate material for use in infrared-transmitting lens applications from the viewpoint of thermal and mechanical stability. In an effort to experimentally determine compositional region suitable for the molded lens applications, we evaluate its compositional dependence of hardness. Among the constituent atoms, Ge content turns out to exert a most conspicuous correlation with hardness. This phenomenological behavior is then explained in connection with the structural evolution that Ge brings about.

We studied GexSe1−x for the potential application in the Ovonic Threshold Switching (OTS) device. We found that, as Ge concentration increased, the thermal stability was deteriorated while the device performances were improved. In addition, using Spectroscopic Ellipsometry (SE) technique, the energy gap (Eg) and the Urbach energy (EU) were found to show non-monotonic dependences, with their minimum of about 1.0 eV of Eg for Ge0.6Se0.4 and 40 meV of EU for Ge0.5Se0.5. These changes are consistent with the changes in device characteristics, which might be explained in terms of the change in the number of Se-Se bondings.

We performed a study on the scalability of Ovonic Threshold Switching (OTS) devices using an amorphous chalcogenide material, Ge0.4Se0.6. As the cell size decreased, the maximum driving current was estimated to be over 3 × 10 7 A/cm 2 , surpassing the state of the art devices based on crystalline Si. However, the threshold voltage (VTH), the holding voltage (VH), and the holding current (IH) were observed to increase laying challenges to be resolved for developing non-destructive and low-power consuming selector devices. VTH was found to be reduced by decreasing the thickness of GeSe film until 40 nm, below which it started to saturate. This might be associated with the Schottky barrier formed at the interface between the amorphous semiconductor and the metal electrode.

The Ovonic Threshold Switch (OTS) based on an amorphous chalcogenide material has attracted much interest as a promising candidate for a high-performance thin-film switching device enabling 3D-stacking of memory devices. In this work, we studied on the electronic structure of amorphous Sb-doped Ge0.6Se0.4 (in atomic mole fraction) film and its characteristics as to OTS devices. From the optical absorption spectroscopy measurement, the band gap (E-g) was found to decrease with increasing Sb content. In addition, as Sb content increased, the activation energy (E-a) for electrical conduction was found to decrease down to about one third of E-g from a half. As to the device characteristics, we found that the threshold switching voltage (V-th) drastically decreased with the Sb content. These results, being accountable in terms of the changes in the bonding configuration of constituent atoms as well as in the electronic structure such as the energy gap and trap states, advance an effective method of compositional adjustment to modulate V-th of an OTS device for various applications.

To improve the quality of chest compression (CC), we developed the assistant-push method, whereby the second rescuer pushes the back of the chest compressor during CC. We investigated the effectiveness and feasibility of assistant push in achieving and maintaining the CC quality.This was a randomized crossover trial in which 41 subjects randomly performed both of standard CC (single-rescuer group) and CC with instructor-driven assistant push (assistant-push group) in different order. Each session of CC was performed for 2 minutes using a manikin. Subjects were also assigned to both roles of chest compressor and assistant and together performed CC with subject-driven assistant push. Depth of CC, compression to recoil ratio, duty cycle, and rate of incomplete recoil were quantified.The mean depth of CC (57.0 [56.0-59.0] vs 55.0 [49.5-57.5], P.001) was significantly deeper, and the compression force (33.8 [29.3-36.4] vs 23.3 [20.4-25.3], P.001) was stronger in the assistant-push group. The ratio of compression to recoil, duty cycle, and rate of incomplete chest recoil were comparable between the 2 groups. The CC depth in the single-rescuer group decreased significantly every 30 seconds, whereas in the assistant-push group, it was comparable at 60- and 90-second time points (P = .004). The subject assistant-push group performed CCs at a depth comparable with that of the instructor assistant-push group.The assistant-push method improved the depth of CC and attenuated its decline, eventually helping maintain adequate CC depth over time. Subjects were able to feasibly learn assistant push and performed effectively.

Switching devices based on Ovonic Threshold Switching (OTS) have been considered as a solution to overcoming limitations of Si-based electronic devices, but the reduction of switching voltage is a major challenge. Here, we investigated the effect of Bi-doping in Ge0.5Se0.5 thin films on their thermal, optical, electrical properties, as well as on the characteristics of OTS devices. As Bi increased, it was found that both of the optical energy gap (Egopt) and the depth of trap states decreased resulting in a drastic reduction of the threshold voltage (Vth) by over 50%. In addition, Egopt was found to be about three times of the conduction activation energy for each composition. These results are explained in terms of the Mott delocalization effect by doping Bi.

We investigated the effect of nitrogen (N) doping on the threshold voltage of an ovonic threshold switching device using amorphous GeSe. Using the spectroscopic ellipsometry, we found that the addition of N brought about significant changes in electronic structure of GeSe, such as the density of localized states and the band gap energy. Besides, it was observed that the characteristics of OTS devices strongly depended on the doping of N, which could be attributed to those changes in electronic structure suggesting a method to modulate the threshold voltage of the device.