Resistive Switching Device Technology Based on Silicon Oxide for Improved ON-OFF Ratio--Part II: Select Devices

The cross-point architecture for memory arrays is widely considered as one of the most attractive solutions for storage and memory circuits thanks to simplicity, scalability, small cell size, and consequently high density and low cost. Cost-scalable vertical 3-D cross-point architectures, in particular, offer the opportunity to challenge Flash memory with comparable density and cost. To develop scalable cross-point arrays, however, select devices with sufficient ON-OFF ratio, current capability, and endurance must be available. This paper presents a select device technology based on volatile resistive switching with Cu and Ag top electrode and silicon oxide (SiOₓ) switching materials. The select device displays ultrahigh resistance window and good current capability exceeding 2 MAcm⁻². Retention study shows a stochastic voltage-dependent ON-OFF transition time in the 10 μs-1 ms range, which needs to be further optimized for fast memory operation in storage class memory arrays

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

Bipolar switching in chalcogenide phase change memory

Phase change materials based on chalcogenides are key enabling technologies for optical storage, such as rewritable CD and DVD, and recently also electrical nonvolatile memory, named phase change memory (PCM). In a PCM, the amorphous or crystalline phase affects the material band structure, hence the device resistance. Although phase transformation is extremely fast and repeatable, the amorphous phase suffers structural relaxation and crystallization at relatively low temperatures, which may affect the temperature stability of PCM state. To improve the time/temperature stability of the PCM, novel operation modes of the device should be identified. Here, we present bipolar switching operation of PCM, which is interpreted by ion migration in the solid state induced by elevated temperature and electric field similar to the bipolar switching in metal oxides. The temperature stability of the high resistance state is demonstrated and explained based on the local depletion of chemical species from the electrode region

Clinical Features, Cardiovascular Risk Profile, and Therapeutic Trajectories of Patients with Type 2 Diabetes Candidate for Oral Semaglutide Therapy in the Italian Specialist Care

Introduction: This study aimed to address therapeutic inertia in the management of type 2 diabetes (T2D) by investigating the potential of early treatment with oral semaglutide. Methods: A cross-sectional survey was conducted between October 2021 and April 2022 among specialists treating individuals with T2D. A scientific committee designed a data collection form covering demographics, cardiovascular risk, glucose control metrics, ongoing therapies, and physician judgments on treatment appropriateness. Participants completed anonymous patient questionnaires reflecting routine clinical encounters. The preferred therapeutic regimen for each patient was also identified. Results: The analysis was conducted on 4449 patients initiating oral semaglutide. The population had a relatively short disease duration (42%  60% of patients, and more often than sitagliptin or empagliflozin. Conclusion: The study supports the potential of early implementation of oral semaglutide as a strategy to overcome therapeutic inertia and enhance T2D management

SiOx-based resistive switching memory (RRAM) for crossbar storage/select elements with high on/off ratio

Resistive switching memory (RRAM) is among the most promising technologies for storage class memory (SCM) and embedded nonvolatile memory (eNVM). Feasibility of RRAM as SCM and/or embedded memory requires large on/off ratio, good endurance, high retention, and the availability of a robust select element for crossbar array integration. This work presents Ti/SiOx RRAM with high on/off ratio (>104), good endurance (>107), high uniformity and strong retention (260°C for 1 hour), thanks to the high SiOx band gap. Ag/SiOx devices show volatile switching with high on/off ratio (> 107) and bidirectional operation applicable to select devices in crossbar arrays

Impact of thermoelectric effects on phase change memory characteristics

Joule heating in phase change memory (PCM) controls programming characteristics, read disturb, and programming disturb. To optimize the energy consumption and reliability of PCM, a thorough understanding of Joule heating as a function of the electrical operation of the device is thus strongly required. This paper presents a comprehensive characterization of thermoelectric (TE) effects in PCM operated at positive and negative voltage polarity. The impact of polarity was studied for all major temperature-dependent properties of the PCM device, namely, melting, crystallization, ion migration, threshold switching, and holding. It was demonstrated that heating is less efficient under negative voltage, compared with positive voltage. It was also shown that the positive and negative voltages needed to induce all above phenomena display a universal correlation. We propose a unified finite-element model for the PCM, which correctly accounts for the observed polarity-dependent heating and the universal voltage characteristics. The impact of isotropic scaling on TE is finally addressed

Resistive switching synapses for unsupervised learning in feed-forward and recurrent neural networks

Milo V, Pedretti G, Laudato M, et al. Resistive switching synapses for unsupervised learning in feed-forward and recurrent neural networks. In: 2018 IEEE International Symposium on Circuits and Systems (ISCAS). IEEE; 2018: 1-5