Voltage-controlled reverse filament growth boosts resistive switching memory

Nonvolatile memory devices based on filamentary resistance switching （KS） are among the frontrunners to fuel future devices and sensors of the internet of things （IoT） era. The capability of many two distinctive resistive states in response to an external electrical stimulus has been demonstrated. Through years of selection, cells based on the drift of metal ions, namely conductive-bridge memory devices, have shown a wide range of applications with nanosecond switching speeds, nanometer scalability, high-density, and low power-consumption. However, for low （sub-10-~A） current operation, a critical challenge is still represented by programming variability and by the stability of the conductive filament over time. Here, by introducing the concept of reverse filament growth （RFG）, we managed to control the structural reconfiguration of the conductive filament inside a memory cell with significant enhancements of each of the aforementioned properties. A first-in-class Cu-based switching device is demonstrated, with a dedicated stack that enabled us to systematically trigger RFG, thus tuning the device＇s properties. Along with nanosecond switching speeds, we achieved an endurance of up to 106 cycles with a 102 read window, with outstanding disturb immunity and optimal stability of the filament over time. Furthermore, by tuning the filament＇s shape, an excellent control of multi-level bit operations was achieved. Thus, this device offers high flexibility in memory applications.

Thickness-dependent monochalcogenide GeSe-based CBRAM for memory and artificial electronic synapses

Investigating the promising chalcogenide materials for the development of memory and advanced neuromorphic computing applications is a critical step in realizing electronic memory and synaptic devices that can efficiently emulate biological synaptic functions.However,the assessment of monochalcogenide materials for the fabrication of highly scalable memory and electronic synaptic devices that can accurately mimic synaptic functions remain limited.In the present study,we investigated the thickness-dependent resistive switching(RS)behavior of conductive bridge random access memory(CBRAM)based on a monochalcogenide GeSe switching medium for its possible application in high-performance memory and electronic synapses.GeSe thin films of different thicknesses(6,13,24,35,47,and 56 nm)were deposited via sputtering to fabricate CBRAM devices with a stacking sequence of Ag/GeSe/Pt/Ti/SiO_(2).The devices exhibited compliance current(CC)-free and electroforming-free RS with highly stable endurance and retention characteristics with no major degradation.All devices with a thickness of 6 nm had a low-resistance state(LRS),which required an initial reset to ensure reliable switching cycles.The devices with a thickness of 47 nm and above exhibited the co-existence of unipolar resistive switching(U-RS)and bipolar resistive switching(B-RS)with the CC-controlled transition between the two switching behaviors.Multilevel resistance states in the 24-nm device between a high-resistance state(HRS)and an LRS were achieved by controlling the set-CC(from 5 mA to CC-free)and the reset stop voltage(from–0.5 to–1.0 V)during the set and reset processes,respectively.The analog RS behavior of the device was further investigated with appropriate pulse measurements to emulate vital synaptic functions,including long-term potentiation(LTP),long-term depression(LTD),spike-rate-dependent plasticity(SRDP),spike-timing-dependent plasticity(STDP),paired-pulse facilitation(PPF),paired-pulse depression(PPD)and post-tetanic potentiation(PTP).Overall,the detailed investigation of thickness-dependent GeSe monochalcogenide material indicates that it is a highly suitable candidate for use in highly scalable memory devices and electronic synapses for neuromorphic computing applications.

Ultralow switching voltage and power consumption of GeS_(2)thin film resistive switching memory

The coming Big Data Era requires progress in storage and computing technologies.As an emerging memory technology,Resistive RAM(RRAM)has shown its potential in the next generation high-density storage and neuromorphic computing applications,which extremely demand low switching voltage and power consumption.In this work,a 10 nm-thick amorphous GeS_(2)thin film was utilized as the functional layer of RRAM in a combination with Ag and Pt electrodes.The structure and memory performance of the GeS_(2)-based RRAM device was characterized-it presents high on/off ratio,fast switching time,ultralow switching voltage(0.15 V)and power consumption(1.0 pJ and 0.56 pJ for PROGRAM and ERASE operations,respectively).We attribute these competitive memory characteristics to Ag doping phenomena and subsequent formation of Ag nano-islands in the functional layer that occurs due to diffusion of Ag from electrode into the GeS_(2)thin film.These properties enable applications of GeS_(2)for low energy RRAM device.