Composition-Controlled Atomic Layer Deposition of Phase-Change Memories and Ovonic Threshold Switches with High Performance.

Chalcogenide compounds are the main characters in a revolution in electronic memories. These materials are used to produce ultrafast ovonic threshold switches (OTSs) with good selectivity and moderate leakage current and phase-change memories (PCMs) with excellent endurance and short read/write times when compared with state-of-the-art flash-NANDs. The combination of these two electrical elements is used to fabricate nonvolatile memory arrays with a write/access time orders of magnitude shorter than that of state-of-the-art flash-NANDs. These devices have a pivotal role for the advancement of fields such as artificial intelligence, machine learning, and big-data. Chalcogenide films, at the moment, are deposited by using physical vapor deposition (PVD) techniques that allow for fine control over the stoichiometry of solid solutions but fail in providing the conformality required for developing large-memory-capacity integrated 3D structures. Here we present conformal ALD chalcogenide films with control over the composition of germanium, antimony, and tellurium (GST). By developing a technique to grow elemental Te we demonstrate the ability to deposit conformal, smooth, composition-controlled GST films. We present a thorough physical and chemical characterization of the solids and an in-depth electrical test. We demonstrate the ability to produce both OTS and PCM materials. GeTe4 OTSs exhibit fast switching times of ∼13 ns. Ge2Sb2Te5 ALD PCMs exhibit a wide memory window exceeding two orders of magnitude, short write times (∼100 ns), and a reset current density as low as ∼107 A/cm2-performance matching or improving upon state-of-the-art PVD PCM devices.

Changes in the Prescription of Glucose-Lowering Medications in Patients With Type 2 Diabetes Mellitus After a Cardiovascular Event: A Call to Action From the DATAFILE Study.

Background Evidence accumulated that some glucose-lowering medications protect against cardiovascular events ( CVEs ) in patients with type 2 diabetes mellitus (T2DM) and established cardiovascular disease. The present study evaluated if and how glucose-lowering medication prescription pattern changes in T2DM after a CVE. Methods and Results DATAFILE (Diabetes Therapy After a Cardiovascular Event) was a retrospective multicenter study conducted at 12 diabetes mellitus specialist outpatient clinics in Italy. We identified T2DM patients with an incident CVE for whom a follow-up visit was available after the event. We selected control T2DM patients without an incident CVE , who were matched with cases for age, sex, known diabetes mellitus duration, baseline hemoglobin A1c, kidney function, and follow-up time. We extracted clinical variables and compared prescribed therapies at baseline and follow-up. We included 563 patients with and 497 matched patients without an incident CVE . As expected, patients with a subsequent CVE had a higher baseline prevalence of ischemic heart disease. After a median of 9.5 months, in patients with versus those without a CVE , there was a significant increase in the prescription of beta-blockers, loop diuretics, dual antiplatelet therapy, and, among glucose-lowering medications, a significant decrease in metformin. Hemoglobin A1c marginally declined only in the control group, whereas low-density lipoprotein cholesterol decreased only in patients with CVE . Conclusions This study highlights that occurrence of a CVE in T2DM patients did not prime the prescription of glucose-lowering medications provided with cardiovascular protective effects, even though glucose control remained poor. These data emphasize the need to optimize the therapeutic regimen of T2DM patients with established cardiovascular disease, according to updated guidelines.

Surface diffusion-limited lifetime of silver and copper nanofilaments in resistive switching devices.

Silver/copper-filament-based resistive switching memory relies on the formation and disruption of a metallic conductive filament (CF) with relatively large surface-to-volume ratio. The nanoscale CF can spontaneously break after formation, with a lifetime ranging from few microseconds to several months, or even years. Controlling and predicting the CF lifetime enables device engineering for a wide range of applications, such as non-volatile memory for data storage, tunable short/long term memory for synaptic neuromorphic computing, and fast selection devices for crosspoint arrays. However, conflictive explanations for the CF retention process are being proposed. Here we show that the CF lifetime can be described by a universal surface-limited self-diffusion mechanism of disruption of the metallic CF. The surface diffusion process provides a new perspective of ion transport mechanism at the nanoscale, explaining the broad range of reported lifetimes, and paving the way for material engineering of resistive switching device for memory and computing applications.

Impact of oxide and electrode materials on the switching characteristics of oxide ReRAM devices.

Resistive switching random-access memory (ReRAM) is one of the most promising technologies for non-volatile memories. Thanks to the low power and high speed operation, the high density CMOS-compatible integration, and the high cycling endurance, the ReRAM technology is becoming a strong candidate for high-density storage arrays and novel in-memory computing systems. However, ReRAM suffers from cycle-to-cycle switching variability and noise-induced resistance fluctuations, leading to insufficient read margin between the programmed resistive states. To overcome the existing challenges, a deep understanding of the roles of the ReRAM materials in the device characteristics is essential. To better understand the role of the switching layer material in controlling ReRAM performance and reliability, this work compares SiOx- and HfO2-based ReRAM at fixed geometry and electrode materials. Ti/HfO2/C and Ti/SiOx/C devices are compared from the point of view of the forming process, switching characteristics, resistance variability, and temperature stability of the programmed states. The results show clear similarities for the two different oxides, including a similar resistance window and stability at high temperatures, thus suggesting a common nature of the switching mechanism, highlighting the importance of the electrodes. On the other hand, the oxide materials play a clear role in the forming, breakdown, and variability characteristics. The discrimination between the role of the oxide and the electrode materials in the ReRAM allows ReRAM optimization via materials engineering to be better explored for future memory and computing applications.

Errors in insulin treatment management and risk of lipohypertrophy.

AIMS: Lipohypertrophy (LH) represents the most common skin-related complication associated with insulin therapy. Our aim is to estimate the prevalence of LH among insulin-treated patients, to identify its association with errors in insulin injection technique and storage, and the correlation between LH, risk of hypoglycemia, and glycemic control. METHODS: Consecutive patients with T1DM or T2DM, attending a diabetes clinic for a routine visit, were administered an anonymous questionnaire investigating the modalities of insulin injection, the correct use of pen device, insulin storage, and reported frequency of hypoglycemic episodes. The presence of LH was assessed by inspection and palpation of injection sites. RESULTS: Overall, 352 patients were enrolled (mean age 68 ± 12 years, 43.2% males, 88.9% with T2DM, mean duration of insulin therapy 9.1 ± 8.6 years). The prevalence of LH was 42.9%. At multivariate analysis, the strongest correlates of LH were not spacing injections (OR 20.4; 95% CI 10.5-39.6) and not rotating the site of injection (OR 2.01; 95% CI 1.08-3.75). Increasing doses of insulin and longer duration of insulin therapy also increased the risk of LH. The presence of LH was associated with a 2.7 times higher risk of severe hypoglycemia. Higher daily insulin doses, lack of rotation of injection sites, and keeping insulin in use in the refrigerator were independent correlates of higher HbA1c levels. CONCLUSIONS: Insulin injection technique is suboptimal in many patients, highlighting the need for improved patient education. Increasing the awareness of the importance of preventing lipohypertrophy and insulin injection errors represents an important tool to reduce the clinical, social, and economic burden of diabetes.

Unsupervised Learning by Spike Timing Dependent Plasticity in Phase Change Memory (PCM) Synapses.

We present a novel one-transistor/one-resistor (1T1R) synapse for neuromorphic networks, based on phase change memory (PCM) technology. The synapse is capable of spike-timing dependent plasticity (STDP), where gradual potentiation relies on set transition, namely crystallization, in the PCM, while depression is achieved via reset or amorphization of a chalcogenide active volume. STDP characteristics are demonstrated by experiments under variable initial conditions and number of pulses. Finally, we support the applicability of the 1T1R synapse for learning and recognition of visual patterns by simulations of fully connected neuromorphic networks with 2 or 3 layers with high recognition efficiency. The proposed scheme provides a feasible low-power solution for on-line unsupervised machine learning in smart reconfigurable sensors.