Study of a charge transition-driven resistive switching mechanism in TiO2-based random access memory via density functional theory.

The nature of the conducting filament (CF) with a high concentration of oxygen vacancies (VOs) in oxide thin film-based resistive random access memory (RRAM) remains unclear. The VOs in the CF have been assumed to be positively charged (VO2+) to explain the field-driven switching of RRAM, but VO2+ clusters in high concentration encounter Coulomb repulsion, rendering the CF unstable. Therefore, this study examined the oxidation state of VOs in the CF and their effects on the switching behavior via density functional theory calculations using a Pt/TiO2/Ti model system. It was concluded that the VOs in the CF are in a low oxidation state but are transformed to VO2+ immediately after release from the CF. In addition, the short-range interactions between VOs were confirmed to facilitate the rupture and rejuvenation of the CF by reducing the required activation energy. Finally, an improved switching model was proposed by considering the charge transition of VOs, providing a plausible explanation for the reported coexistence of two opposite bipolar switching polarities: the eight-wise and the counter-eight-wise polarities.

Atomic Layer Deposition of Sb2 Te3 /GeTe Superlattice Film and Its Melt-Quenching-Free Phase-Transition Mechanism for Phase-Change Memory.

Atomic layer deposition (ALD) of Sb2 Te3 /GeTe superlattice (SL) film on planar and vertical sidewall areas containing TiN metal and SiO2 insulator is demonstrated. The peculiar chemical affinity of the ALD precursor to the substrate surface and the 2D nature of the Sb2 Te3 enable the growth of an in situ crystallized SL film with a preferred orientation. The SL film shows a reduced reset current of ≈1/7 of the randomly oriented Ge2 Sb2 Te5 alloy. The reset switching is induced by the transition from the SL to the (111)-oriented face-centered-cubic (FCC) Ge2 Sb2 Te5 alloy and subsequent melt-quenching-free amorphization. The in-plane compressive stress, induced by the SL-to-FCC structural transition, enhances the electromigration of Ge along the [111] direction of FCC structure, which enables such a significant improvement. Set operation switches the amorphous to the (111)-oriented FCC structure.

Differential impact of serum total bilirubin level on cerebral atherosclerosis and cerebral small vessel disease.

BACKGROUND: A low serum total bilirubin (T-bil) level is associated with an increased risk of atherosclerosis. However, the differential impact of the serum T-bil level on cerebral atherosclerosis and cerebral small vessel disease (SVD) is still unclear. METHODS: We evaluated serum T-bil levels from 1,128 neurologically healthy subjects. Indices of cerebral atherosclerosis (extracranial arterial stenosis [ECAS] and intracranial arterial stenosis [ICAS]), and indices of SVD (silent lacunar infarct [SLI], and moderate-to-severe white matter hyperintensities [msWMH]) were evaluated by the use of brain magnetic resonance imaging (MRI) and MR angiography. RESULTS: In logistic regression analysis after adjusting for confounding variables, subjects within middle T-bil (odds ratio [OR]: 0.63; 95% CI: 0.41-0.97) and high T-bil tertiles (OR: 0.54; 95% CI: 0.33-0.86) showed a lower prevalence of ECAS than those in a low T-bil tertile. Although subjects with a high T-bil tertile had a lower prevalence of ICAS than those with a low T-bil tertile, the statistical significance was marginal after adjusting for confounding variables. There were no significant differences in the proportions of subjects with SLI and msWMH across serum T-bil tertile groups. CONCLUSIONS: The serum T-bil level is negatively associated with cerebral atherosclerosis, especially extracranial atherosclerosis, but not with SVD.

Effect of lightly doped drain structure on P-channel metal induced lateral crystallization thin film transistors.

A Lightly Doped Drain (LDD) structure is known to be very effective in preventing hot electrons in modern NMOS transistors. In this work, the lightly doped region was formed in poly TFT by using a separate LDD mask aligned to a gate mask. The misalignment can be calculated to be about 1.5 microm, and depending on the location of the V(d) application between the source and drain, an LDD or Lightly Doped Source (LDS) structure can be realized on the same TFT. In this way, we can make a perfect comparison between these two structures. It turned out that the LDD is mainly responsible for the low leakage current, and no more than 0.5 microm of the lightly doped region is necessary to lower the leakage current down to less than 5 x 10(-11) amps at V(d) = 10 volts. Typically, the on-current of MILC TFT is more than 10(-4) amps, but 2.5 microm LDS decreases it to below 10(-7) amps.