RTN in GexSe1-x OTS Selector Devices

Random telegraph noise (RTN) signals in GexSe1-x ovonic threshold switching (OTS) selector have been analyzed in this work, both before and after the first-fire (FF) operation and at on- and off-states. It is observed that RTN appears after the FF, and its absolute amplitude at the off-state is small and negligible in comparison with the RTN signals in RRAM devices. At the on-state, large RTN signals are observed, which can either partially or fully block the conduction path, supporting that a conductive filament is formed or activated by FF and then modulated during switching. Statistical analysis reveals that the relative RTN amplitude at on-state in GexSe1-x OTS selector is smaller than or equivalent to those in RRAM devices

Prothymosin alpha: a ubiquitous polypeptide with potential use in cancer diagnosis and therapy

The thymus is a central lymphoid organ with crucial role in generating T cells and maintaining homeostasis of the immune system. More than 30 peptides, initially referred to as “thymic hormones,” are produced by this gland. Although the majority of them have not been proven to be thymus-speciWc, thymic peptides comprise an eVective group of regulators, mediating important immune functions. Thymosin fraction Wve (TFV) was the Wrst thymic extract shown to stimulate lymphocyte proliferation and diVerentiation. Subsequent fractionation of TFV led to the isolation and characterization of a series of immunoactive peptides/polypeptides, members of the thymosin family. Extensive research on prothymosin (proT) and thymosin 1 (T1) showed that they are of clinical signiWcance and potential medical use. They may serve as molecular markers for cancer prognosis and/or as therapeutic agents for treating immunodeWciencies, autoimmune diseases and malignancies. Although the molecular mechanisms underlying their eVect are yet not fully elucidated proT and T1 could be considered as candidates for cancer immunotherapy. In this review, we will focus in principle on the eventual clinical utility of proT, both as a tumor biomarker and in triggering anticancer immune responses. Considering the experience acquired via the use of T1 to treat cancer patients, we will also discuss potential approaches for the future introduction of proT into the clinical setting

Impact of relaxation on the performance of GeSe true random number generator based on Ovonic threshold switching

Volatile Ovonic threshold switching (OTS) are promising not only as the selector in crossbar resistive switching memory arrays, but also as true random number generators (TRNG) by utilizing its probabilistic switching characteristics. However, investigation on the reliability of OTS-based TRNG is still lacking, which hinders its practical application. Previously, we found that switching probability is dependent on the pulse amplitude and width. In this work, we report that relaxation which happens during the time interval between pulses can cause switching probability drift. Optimizing the bit-generation waveform and modulating the pulse conditions could provide a practical solution, in addition to the impact of external bias and temperature. This work provides useful guidance for the practical design and operation of OTS-based TRNGs

Dependence of switching probability on operation conditions in GexSe1-x ovonic threshold switching selectors

Ovonic threshold switching (OTS) selector is a promising candidate to suppress the sneak current paths in resistive switching memory (RRAM) arrays. Variations in the threshold voltage (Vth), and the hold voltage (Vhd) have been reported, but a quantitative analysis of the switching probability dependence on the OTS operation conditions is still missing. A novel characterization method is developed in this work, and the time-to-switch-on/off (ton/toff) at a constant VOTS is found following the Weibull distribution, based on which the dependence of switching probability on pulse bias and time can be extracted and extrapolated, and the switching probability can be ensured with appropriately chosen operation conditions. The difference between square and triangle switching pulses is also explained. This provides a practical guidance for predicting the switching probability under different operation conditions and for designing reliable one-selector-one-RRAM (1S1R) arrays

Endurance improvement of more than five orders in Ge<inf>x</inf>Se<inf>1-x</inf> OTS selectors by using a novel refreshing program scheme

Selector device is critical in high-density cross-point resistive switching memory arrays for suppressing the sneak leakage current path. GexSe1-x based ovonic threshold switch (OTS) selectors have recently demonstrated strong performance with high on-state current, nonlinearity and endurance. Detailed study of its reliability is still lacking and the understanding on the responsible mechanisms is limited. In this work, for the first time, the endurance degradation mechanism of Ge-rich GexSe1-x OTS is identified. Accumulation of slow defects that remain delocalized at off-state and GeSe segregation/crystallization during cycling lead to the recoverable and non-recoverable leakage current, respectively. Most importantly, a refreshing program scheme is developed to recover and prevent the OTS degradation and the endurance can be therefore improved by more than five orders without adding additional material elements or process steps

A HydroDynamic Model for Trap-Assisted Tunneling Conduction in Ovonic Devices

Electrical conduction in ovonic threshold switching (OTS) devices is described by introducing a new physical model where the multiphonon trap-assisted tun-neling (TAT) is coupled to a hydrodynamic theory. Static and transient electrical responses from Ge(x)Se(1-x )experimental devices are reproduced, outlining the role played by the material properties like mobility gap and defects in tuning the OTS performances. A clear physical interpretation of the mechanisms ruling the different OTS conduction regimes (off, threshold, on) is presented. A nanoscopic picture of the processes featuring the carrier transport is also given. The impact of geometry, temperature, and material mod-ifications on device performance is discussed providing physical insight into the optimization of OTS devices