30 research outputs found
Nanoscale imaging of He-ion irradiation effects on amorphous TaO toward electroforming-free neuromorphic functions
Resistive switching in thin films has been widely studied in a broad range of
materials. Yet the mechanisms behind electroresistive switching have been
persistently difficult to decipher and control, in part due to their
non-equilibrium nature. Here, we demonstrate new experimental approaches that
can probe resistive switching phenomena, utilizing amorphous TaO as a model
material system. Specifically, we apply Scanning Microwave Impedance Microscopy
(sMIM) and cathodoluminescence (CL) microscopy as direct probes of conductance
and electronic structure, respectively. These methods provide direct evidence
of the electronic state of TaO despite its amorphous nature. For example CL
identifies characteristic impurity levels in TaO, in agreement with first
principles calculations. We applied these methods to investigate He-ion-beam
irradiation as a path to activate conductivity of materials and enable
electroforming-free control over resistive switching. However, we find that
even though He-ions begin to modify the nature of bonds even at the lowest
doses, the films conductive properties exhibit remarkable stability with large
displacement damage and they are driven to metallic states only at the limit of
structural decomposition. Finally, we show that electroforming in a nanoscale
junction can be carried out with a dissipated power of < 20 nW, a much smaller
value compared to earlier studies and one that minimizes irreversible
structural modifications of the films. The multimodal approach described here
provides a new framework toward the theory/experiment guided design and
optimization of electroresistive materials
FilamentāFree Bulk Resistive Memory Enables Deterministic Analogue Switching
Digital computing is nearing its physical limits as computing needs and energy consumption rapidly increase. Analogueāmemoryābased neuromorphic computing can be orders of magnitude more energy efficient at dataāintensive tasks like deep neural networks, but has been limited by the inaccurate and unpredictable switching of analogue resistive memory. Filamentary resistive random access memory (RRAM) suffers from stochastic switching due to the random kinetic motion of discrete defects in the nanometerāsized filament. In this work, this stochasticity is overcome by incorporating a solid electrolyte interlayer, in this case, yttriaāstabilized zirconia (YSZ), toward eliminating filaments. Filamentāfree, bulkāRRAM cells instead store analogue states using the bulk point defect concentration, yielding predictable switching because the statistical ensemble behavior of oxygen vacancy defects is deterministic even when individual defects are stochastic. Both experiments and modeling show bulkāRRAM devices using TiO2āX switching layers and YSZ electrolytes yield deterministic and linear analogue switching for efficient inference and training. BulkāRRAM solves many outstanding issues with memristor unpredictability that have inhibited commercialization, and can, therefore, enable unprecedented new applications for energyāefficient neuromorphic computing. Beyond RRAM, this work shows how harnessing bulk point defects in ionic materials can be used to engineer deterministic nanoelectronic materials and devices.A resistive memory cell based on the electrochemical migration of oxygen vacancies for ināmemory neuromorphic computing is presented. By using the average statistical behavior of all oxygen vacancies to store analogue information states, this cell overcomes the stochastic and unpredictable switching plaguing filamentāforming memristors, and instead achieves linear, predictable, and deterministic switching.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/163547/3/adma202003984_am.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/163547/2/adma202003984-sup-0001-SuppMat.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/163547/1/adma202003984.pd
High-Speed CMOS-Free Purely Spintronic Asynchronous Recurrent Neural Network
Neuromorphic computing systems overcome the limitations of traditional von
Neumann computing architectures. These computing systems can be further
improved upon by using emerging technologies that are more efficient than CMOS
for neural computation. Recent research has demonstrated memristors and
spintronic devices in various neural network designs boost efficiency and
speed. This paper presents a biologically inspired fully spintronic neuron used
in a fully spintronic Hopfield RNN. The network is used to solve tasks, and the
results are compared against those of current Hopfield neuromorphic
architectures which use emerging technologies