Polarity-dependent reversible resistance switching in Ge–Sb–Te phase-change thin films

In this paper, we demonstrate reversible resistance switching in a capacitorlike cell using a Ge–Sb–Te film that does not rely on amorphous-crystalline phase change. The polarity of the applied electric field switches the cell resistance between lower- and higher-resistance states, as was observed in current-voltage characteristics. Moreover, voltage pulses less than 1.25 V showed this switching within time scales of microseconds with more than 40% contrast between the resistance states. The latter are found to be nonvolatile for months. The switching could also be achieved at nanoscales with atomic force microscopy with a better resistance contrast of three orders of magnitude.

Clonal Selection and Population Dynamics of Vγ2/Vδ2 T Cells in Macaca Fascicularis

HIV infection increases the susceptibility to new M. tuberculosis (Mtb) infections, the risk of reactivating latent infections and the risk of rapid TB progression. γδ T cells, in particular the Vγ2Jγ1.2 subset, are thought to be part of the innate immune response to both HIV and Mtb. Importantly, both HIV and Mtb perturb gd T cells homeostasis, causing a profound and highly specific depletion of the Vγ2Jγ1.2 subset

Stress-Induced Crystallization of Ge-Doped Sb Phase-Change Thin Films

<p>The large effects of moderate stresses on the crystal growth rate in Ge-doped Sb phase-change thin films are demonstrated using direct optical imaging. For Ge6Sb94 and Ge7Sb93 phase-change films, a large increase in crystallization temperature is found when using a polycarbonate substrate instead of a glass substrate. This increase is attributed to the tensile thermal stress induced in the phase-change film due to a difference in thermal expansion coefficient between the film and the polycarbonate substrate. By applying a uniaxial compressive stress to a phase-change film, we show and explain that isotropic crystal growth becomes unidirectional (perpendicular to the uniaxial stress) with a strongly enhanced growth rate. This is a direct proof that modest stresses can have large consequences for the amorphous phase stability and for the crystal growth rates, and these stresses are thus highly relevant for memories based on phase-change materials.</p>

Ultra high density scanning electrical probe phase-change memory for archival storage

The potential for using probe-based phase-change memories for the future archival storage at densities of around 1 Tbit/in.² is investigated using a recording medium comprising a Si/TiN/DLC/GeSbTe/diamond-like carbon (DLC) stack together with a conductive PtSi tip for writing and reading. Both experimental and computational simulation results are presented. The simulations include a physically-realistic threshold switching model, as well as the effects of thermal boundary resistance and electrical contact resistance. The simulated bit size and shape correspond closely to that written experimentally

In situ transmission electron microscopy study of the crystallization of fast-growth doped SbxTe alloy films

Crystallization of amorphous thin films composed of doped SbxTe with x = 3.0, 3.6, and 4.2 and constant dopant level was studied by in situ heating in a transmission electron microscopy. Magnetron sputtering was used to deposit 20-nm-thick films sandwiched between two types of 3-nm-thick dielectric layers on 25-nm-thick silicon-nitride membranes. One type of dielectric layer consists of ZnS–SiO2 (ZSO), the other of GeCrN (GCN). Crystallization was studied for temperatures in-between 150 and 190 °C. The type of dielectric layer turned out to strongly influence the crystallization process. Not only did the nucleation rate appear to depend sensitively on the dielectric layer type, but also the growth rate. The velocity of the crystalline/amorphous interface is about 5 times higher for the x = 4.2 film than for the x = 3.0 film if ZSO is used. In case of GCN, the interface velocity is about 2 times higher for the x = 4.2 film than for the x = 3.0 film. The activation energy for crystal growth is not significantly dependent on the Sb/Te ratio but is clearly different for ZSO and GCN—2.9 eV and 2.0 eV, respectively. The incubation time for the crystal nuclei formation is longer for ZSO than for GCN. Although the effects of the Sb/Te ratio and the dielectric layer type on the growth rates are strong, their effects on the nucleation rate are even more pronounced. A higher Sb/Te ratio results in a lower nucleation rate and the use of GCN instead of ZSO leads to higher nucleation rates.