Recent studies have argued that global warming is responsible for a wavier jet stream, thereby driving midlatitude extreme flooding and drought. Polar amplification—the relative enhancement of ...high-latitude temperatures under global warming—is argued to be the principal climate state driving midlatitude extremes. Namely, the decreased meridional temperature gradient suppresses the mean zonal winds, leading to wavier midlatitude jets. However, although observations are consistent with such a linkage, a detailed dynamical mechanism is still debated. Here, we argue that the Northern Hemisphere land–sea thermal forcing contrast that underlies zonally asymmetric forcing drives a response in the planetary geostrophic motion, which provides balanced mean fields for synoptic eddies in midlatitudes and thus for wavier jet streams. We show that when the barotropic zonal mean wind
U
is smaller than a threshold, proportional to the
β
-plane effect and dry static stability, the flow field exhibits a dramatic transition from a response confined near the surface to one reaching the upper atmosphere. As global warming enhances polar amplification, the midlatitude jet stream intensity is suppressed. The confluence of these effects leads to wavier jet streams.
Conventional computing architectures are poor suited to the unique workload demands of deep learning, which has led to a surge in interest in memory-centric computing. Herein, a trilayer (Hf
Si
O
/Al
...O
/Hf
Si
O
)-based self-rectifying resistive memory cell (SRMC) that exhibits (i) large selectivity (ca. 10
), (ii) two-bit operation, (iii) low read power (4 and 0.8 nW for low and high resistance states, respectively), (iv) read latency (<10 μs), (v) excellent non-volatility (data retention >10
s at 85 °C), and (vi) complementary metal-oxide-semiconductor compatibility (maximum supply voltage ≤5 V) is introduced, which outperforms previously reported SRMCs. These characteristics render the SRMC highly suitable for the main memory for memory-centric computing which can improve deep learning acceleration. Furthermore, the low programming power (ca. 18 nW), latency (100 μs), and endurance (>10
) highlight the energy-efficiency and highly reliable random-access memory of our SRMC. The feasible operation of individual SRMCs in passive crossbar arrays of different sizes (30 × 30, 160 × 160, and 320 × 320) is attributed to the large asymmetry and nonlinearity in the current-voltage behavior of the proposed SRMC, verifying its potential for application in large-scale and high-density non-volatile memory for memory-centric computing.
Memristor-integrated passive crossbar arrays (CAs) could potentially accelerate neural network (NN) computations, but studies on these devices are limited to software-based simulations owing to their ...poor reliability. Herein, we propose a self-rectifying memristor-based 1 kb CA as a hardware accelerator for NN computations. We conducted fully hardware-based single-layer NN classification tasks involving the Modified National Institute of Standards and Technology database using the developed passive CA, and achieved 100% classification accuracy for 1500 test sets. We also investigated the influences of the defect-tolerance capability of the CA, impact of the conductance range of the integrated memristors, and presence or absence of selection functionality in the integrated memristors on the image classification tasks. We offer valuable insights into the behavior and performance of CA devices under various conditions and provide evidence of the practicality of memristor-integrated passive CAs as hardware accelerators for NN applications.
To study the dynamical mechanism by which Arctic amplification affects extreme weather events in mid-latitude, we investigated the local and remote circulation response to pan-Arctic and regional ...Arctic thermal forcing. A comprehensive atmospheric GCM (General Circulation Model) coupled to a slab mixed-layer ocean model is used for the experiment. With the increasing thermal forcing in the pan-Arctic configuration, the mid-latitude jet tends to shift equatorward, mainly due to the southward shift of the convergence zone of eddy-heat flux and eddy-momentum flux. From the regional Arctic forced experiments, zonal mean response is similar to the response from the pan-Arctic configuration. The non-zonal response is characterized by the 300 hPa circumpolar zonal wind of wavenumber-1 structure, which establishes an enhanced wavier mid-latitude jet. In the polar region at 300 hPa, regional thermal forcing drives a distinct east–west dipole circulation pattern, in which anticyclonic circulation is located to the west of the thermal forcing, and cyclonic circulation is located to the east. The lower-level circulation shows the opposite pattern to the upper-level circulation in the polar region. While the strength of circulation increases with gradual thermal forcing, the overall dipole pattern is unchanged. In regional warming simulation, compared to the pan-Arctic warming, increasing residual heat flux in a dipole pattern causes enhanced heat advection to mid-latitude.
Abstract Although the seasonal prediction skill of climate models has improved significantly in recent decades, the prediction skill of the Arctic Oscillation (AO), the dominant climate mode over the ...Northern Hemisphere, remains poor. Additionally, the local representation of AO impacts has diverged from observations, which limits seasonal prediction skill of climate models. In this study, we attempted to improve prediction skill of surface air temperature (SAT) with two post-processing on dynamical model’s seasonal forecast: (1) correction of the AO impact on SAT pattern, and (2) correction of AO index (AOI). The first correction involved replacing the inaccurately simulated impact of AO on SAT with that observed. For the second correction, we employed a empirical prediction model of AOI based on multiple linear regression model based on three precursors: summer sea surface temperature, autumn sea-ice concentration, and autumn snow cover extent. The application of the first correction led to a decrease in prediction skills. However, a significant improvement in SAT prediction skills is achieved when both corrections are applied. The average correlation coefficients for the North America and Eurasian regions increased from 0.23 and 0.06 to 0.28 and 0.30, respectively.
The immense increase of unstructured data require novel computing systems that can process the input data with low power and parallel processing. This functionality is similar to that of human brains ...that are composed of numerous neurons, synapses, and their complex connections. To mimic the functionality of the human brain with an electronic device, the resistive switching device and crossbar array has attracted considerable attention for artificial synaptic devices and integrated systems, respectively. For this purpose, the self‐rectifying resistive switching cell based on the Si:ZrOx thin film is developed and its reliability characteristics are tested. Four achievements are highlighted in this study. 1) The retention characteristic is improved by the adoption of TaOx thin film as an oxygen reservoir layer. 2) The asymmetric electrodes can make the self‐rectifying resistive cell (SRC) have sufficient rectifying characteristic. 3) The linearity of conductance update has a dominant effect on the inference performance compared to that of the conductance range variation. 4) The device of the interface‐type resistive switching shows a high enough device yield in the crossbar array device and exhibits reliable multiply‐and‐accumulate operations in the crossbar array to mimic the human brain‐inspired computing system.
This study investigates the mimicking of the functions of the human brain with self‐rectifying resistive switching memory. Artificial synaptic devices based on Si:ZrOx are fabricated and demonstrate their ability to function as an integrated system through the crossbar array structure.
Ruthenium (Ru) thin films were grown
via
atomic layer deposition (ALD) using a novel Ru precursor with enhanced reactivity, namely Ru(η
5
-cycloheptadienyl)
2
(Ru(chd)
2
) and O
2
. Self-limiting ...growth during the Ru ALD process was achieved by varying the Ru precursor and O
2
feeding times. Metallic Ru films with a low resistivity (10-16 μΩ cm) grew at deposition temperatures between 200 and 300 °C, where the growth per cycle (GPC) during Ru ALD was 0.2 to 0.4 Å cy
−1
at 265 °C. The Ru incubation times were considerably shorter using the novel precursor (negligible on Pt and TiN, ∼22 cycles on SiO
2
) compared with those associated with Ru ALD using a high-valency Ru precursor and O
2
. The characteristics of the Ru film were influenced by the substrate. Specifically, the Pt substrate gave rise to an amorphous film, while crystalline films were grown on the TiN and SiO
2
substrates, where a high RuO
x
content resulted on the SiO
2
substrate.
The incubation cycle free ALD Ru film was deposited using an open-coordinated structured Ru(
ii
) precursor, Ru(η
5
-cycloheptadienyl)
2
.
Abstract
A Ta/TaO
x
/Pt stacked capacitor-like device for resistive switching was fabricated and examined. The tested device demonstrated stable resistive switching characteristics including uniform ...distribution of resistive switching operational parameters, highly promising endurance and retention properties. To reveal the resistive switching mechanism of the device, micro structure analysis using high-resolution transmission electron microscope (HR-TEM) was performed. From the observation results, two different phases of Ta-metal clusters of cubic α-Ta and tetragonal β-Ta were founded in the amorphous TaO
x
mother-matrix after the device was switched from high resistance state (HRS) to low resistance state (LRS) by externally applied voltage bias. The observed Ta metal clusters unveiled the origin of the electric conduction paths in the TaO
x
thin film at the LRS.
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•The GeTex-based resistive switching device shows forming-free, uniform operating distribution, and stable retention.•The mechanism of resistive switching explains the optimized ...chemical composition of the GeTex for reliable performances.•The proposed device can be the future electronic component of memory or artificial neural network applications.•The chalcogenide materials can serve the materials coherency between the memory and selector for crossbar-type device.
The suitability of thin films of the chalcogenide germanium telluride (GeTex) with various chemical compositions for use as an active medium in a conductive bridge resistive switching memory device with Cu and TiN as the active and counter electrodes, respectively, was examined. Experimental results showed that all of the tested resistive switching devices showed identical current-voltage hysteresis curves for the first and second cycles, the electroforming (EF)-free characteristic, which is favourable for achieving high operational reliability. From a comparative study of different active electrodes, we concluded that the intrinsic electronic traps and diffused Cu ions in the GeTex layer were responsible for the EF-free characteristic. Furthermore, as the Te content increased, the retention characteristics of the programmed resistance state became unstable since the short-range-ordered Te-Te clusters in the GeTex layer caused the Cu conductive filament to dissolve in Cu-Te locally. Experimental results indicated that the chalcogenide materials were good candidates for a highly reliable active layer in a conducting-bridge resistive switching memory device. This report presents various microscopic analysis results to show the superior performance of chalcogenide-based resistive switching memory devices.
“The memristive device of the electro-forming free and initial “ON-state” is introduced using a Ag-dispersed chalcogenide Ge2Se3Te5 thin film. Unlike conducting-filament-based memristive devices, the ...Ag/GST/W-structured memristive device exhibits a narrow operating distribution and highly reliable performance. The microscopic origin of the desirable device performance is presented from the viewpoint of materials and device structure.”
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•Highly reliable the Ag/GST/W-structured memristive device show good operation voltage distribution, operation current distribution, stable non-volatility, and repeatability of writing/reading processes.•The GST layer in the W/GST/W structured memristive device showed a completely amorphous structure, which revealed the diffusive nature of Ag.•The Ag/GST/W structured memristive device showed characteristics of electro-forming free and initial LRS.•Based on the synaptic behavior observed from the Ag/GST/W structured memristive device, the inference accuracy was evaluated to be 92%.
In this paper, we report a Ag-dispersive chalcogenide thin film as a resistance-switching material for memristive devices. The memristive device with Ag/Ge2Se3Te5/W showed an initial low resistance state in its pristine stage (electro-forming-free), a low power consumption of 60 nW, robust state retention in a harsh environment of 85 °C for 2 h, and reliable endurance. We used high-resolution transmission electron microscopy, X-ray photoelectron spectroscopy, Auger electron spectroscopy, and electrical conduction characteristics to determine the microscopic origin of the memristive device. Comparative studies of different electrodes and resistive switching layers indicated that the diffusive Ag atom in the chalcogenide thin film plays a crucial role in realizing distinctive memristive characteristics. Further, we highlighted that the observed favorable performance of the memristive device is possible with a chalcogenide material, which can serve as an electrolyte for high ion diffusion and desirable electronic traps. Moreover, the memristive device exhibited an analogous conductance variation in a nonvolatile manner, which can be adopted as an artificial synaptic device. Based on the observed synaptic performance, an inference accuracy of ∼92% was achieved using handwritten numbers from the Modified National Institute of Standards and Technology database.
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