Flexible Memory Research Articles

Brain network dynamics during working memory are modulated by dopamine and diminished in schizophrenia

Dynamical brain state transitions are critical for flexible working memory but the network mechanisms are incompletely understood. Here, we show that working memory performance entails brain-wide switching between activity states using a combination of functional magnetic resonance imaging in healthy controls and individuals with schizophrenia, pharmacological fMRI, genetic analyses and network control theory. The stability of states relates to dopamine D1 receptor gene expression while state transitions are influenced by D2 receptor expression and pharmacological modulation. Individuals with schizophrenia show altered network control properties, including a more diverse energy landscape and decreased stability of working memory representations. Our results demonstrate the relevance of dopamine signaling for the steering of whole-brain network dynamics during working memory and link these processes to schizophrenia pathophysiology.

Multilevel Photonic Transistor Memory Devices Based on 1D Electrospun Semiconducting Polymer /Perovskite Composite Nanofibers

AbstractPhotonic field‐effect transistor (FET) memory devices offer unique advantages over conventional voltage‐driven memory devices, such as noncontact programming capability, rapid data transmission, and low power consumption. In this article, the first example of a nanofiber‐only photonic FET memory device is reported. Perovskite nanocrystal (βNC)‐embedded polythiophenes are employed as 1D semiconducting channels of the nanofiber matrix. A decent On/Off current ratio of ≈103 is reached for the best device with a prolonged data retention of over 104 s, attributing to the favorable energy level alignment and molecular packing of conjugated polymers in nanofibers. The composite nanofiber system exhibits superior photoresponsivity and charge retention, outperforming its film‐based counterpart owing to its regular 1D confined structure, and well‐dispersed βNCs. Collectively, the structurally fine‐tuned conjugated polymer and the 1D confined structure in the nanofiber promise good data discriminability and a highly fault‐tolerant photonic memory device. In addition, the fiber‐based flexible memory device exhibits excellent photonic memory performance, indicating its integrity for application in wearable electronics. The current system represents the first application of 1D perovskite nanocrystal/conjugated polymer composite nanofibers for high‐performance photonic memory devices, which reveals their potential to make composite nanostructures for novel pioneering photonic applications.

Dual Adaptation of a Flexible Shape Memory Polymer Adhesive.

A shape memory polymer (SMP) adhesive forms a conformal and hermetic contact with a target surface at the soft, rubbery state and provides a high-strength dry adhesion at the rigid, glassy state. In particular, recent SMP adhesive studies show SMP's ability to adhere to various rough and even underwater yet rigid surfaces. However, achieving and retaining the strong adhesion on flexible target surfaces such as common fabrics has not been reported since a flexible target surface would easily be peeled off from an SMP adhesive, which is too rigid to accommodate the target surface flexing. Here, we introduce the dual adaptation of an SMP adhesive composed of a thin SMP layer and a backing fabric, which involves the shape adaptation to make a strong adhesive contact and the flexure adaptation to tolerate a target surface flexing. To discover the criteria for optimizing both shape and flexure adaptations, we present the theoretical rationale as well as the computational and experimental studies in this work. Based on the findings here, we design a thin SMP adhesive and demonstrate its dry and underwater adhesive performances on common clothes to highlight its potential applications.

Highly Flexible Artificial Synapses from SiO2-Based Conductive Bridge Memristors and Pt Nanoparticles through a Crack Suppression Technique

The growth of flexible memory devices with intrinsic neuromorphic properties is attracting tremendous attention due to the wide spread of wearable electronics. The fabrication of robust artificial synaptic structures that will have the ability to remain operational after various strain loads and perform artificial synaptic weight modulation procedures is considered the cornerstone for the development of wearable neuromorphic computing systems. Along these lines, a low-temperature Ag/SiO2/TiN memristive device is demonstrated on a polyethylene naphthalate substrate decorated with Pt nanoparticles (NPs) with a 5 nm average diameter. The memory devices are completely forming-free, operate at a low voltage of 500 mV, and exhibit great stability after bending numerous times under a record high mechanical strain of 4.16% without any severe degradation of the pulse endurance and retention capabilities. Concrete pieces of evidence regarding the crack suppression effect induced by the layer of Pt NPs on the robust memory performance are also provided. Moreover, a thorough analysis of the neuromorphic properties of our prototypes is presented, including the implementation of short-term plasticity effects, such as paired-pulsed facilitation and paired-pulse depression, which are of great importance for the rehearsal procedures of neurons during the learning function as well as for the linear distribution of the conductance pattern during synaptic potentiation and depression tasks. Additionally, Hebbian spike-time-dependent-plasticity responses were also recorded.

Polarization Stability: Robust Polarization Stability in a Self‐Assembled Ultrathin Organic Ferroelectric Nano Lamellae (Adv. Electron. Mater. 6/2021)

In article number 2001085, Pamarti Viswanath and co-workers demonstrate highly robust polarization stability in an ultrathin PVDF polymer self-assembled on a monolayer graphene oxide film. This selfassembly approach is a promising technique to fabricate highly oriented and stable ferroelectric polarization polymer systems for realizing next-generation flexible electronic memory devices.

Evidence for a gradient within the medial temporal lobes for flexible retrieval under hierarchical task rules.

A fundamental question in memory research is how the hippocampus processes contextual cues to retrieve distinct mnemonic associations. Prior research has emphasized the importance of hippocampal-prefrontal interactions for context-dependent memory. Our fMRI study examined the human medial temporal lobes (MTL) and their prefrontal interactions when retrieving memories associated with hierarchically organized task contexts. Participants learned virtual object-location associations governed by subordinate and superordinate task rules, which could be independently cued to change. On each fMRI trial, participants retrieved the correct object for convergent rule and location contextual information. Results demonstrated that hippocampal activity and hippocampal-prefrontal functional interconnectivity distinguished retrieval under different levels of hierarchically organized task rules. In explicit contrast to the hippocampal tail, anterior (body and head) regions were recruited specifically for superordinate changes in the contextual hierarchy. The hippocampal body also differed in its functional connectivity with the prefrontal cortex for superordinate versus subordinate changes. Our findings demonstrate a gradient in MTL for associative retrieval under changing task rules, and advance understanding of hippocampal-prefrontal interactions that support flexible contextual memory.

Flexible multi-level quasi-volatile memory based on organic vertical transistor

Driven by important megatrends such as cloud computing, artificial intelligence, and the Internet of Things, as a device used to store programs and data in computing systems, memory is struggling to catch up with the explosive growth of data and bandwidth requirements in the system. However, the “storage wall” between non-volatile memory and volatile memory retards the further improvement of modern memory computing systems. Herein, a quasi-volatile transistor memory based on organic polymer/perovskite quantum dot blend was fabricated using the vertical transistor configuration. Contributing to vertical structure and appropriate doping ratio of blend film, the quasi-volatile memory device displayed 1,560 times longer data retention time (> 100 s) with respect to the dynamic random access memory and fast data programming speed (20 µs) in which was far more quickly than that of other organic non-volatile memories to fill the gap between volatile and non-volatile memories. Moreover, the device retention characteristics could be further promoted under the photoelectric synergistic stimulation, which also provided the possibility to reduce electric writing condition. Furthermore, the quasi-volatile memory device showed good electrical performance under bending conditions. This work provides a simple solution to fabricate multi-level quasi-volatile memory, which opens up a whole new avenue of “universal memory” and lays a solid foundation for low power and flexible random access memory devices.

Improved resistive switching characteristics of Ag/Al:HfO x /ITO/PET ReRAM for flexible electronics application

The Al-doped HfO x flexible resistive random access memory (ReRAM) device with Ag top electrode (TE) is fabricated on indium tin oxide (ITO) coated polyethylene terephthalate (PET) with low thermal budget process. The oxygen vacancies created by Al doping may assist Ag inclusion to create/rupture the filament at lower operating voltages (V SET ≈ 0.46 V and V RESET ≈ −0.93 V) and SET/RESET currents (I SET ≈ 2 × 10−5 A and I RESET ≈ 8 × 10−5 A). The Ag/Al:HfO x /ITO/PET ReRAM exhibits highly stable resistive switching (RS) behaviour with lower switching power (P SET ≈ 9.2 µW and P RESET ≈ 74.4 µW). The stable switching parameters like SET/RESET voltages, resistances in high resistance states (HRS) and low resistance states (LRS) are observed even at higher temperature (100 °C) and in flexible condition (i.e. 5 mm dia). The current conduction mechanism in HRS is dominated by space charge limited conduction whereas LRS is not completely Ohmic in nature. The RS mechanism has been explained by the formation of the combined effect of Ag atoms and oxygen vacancies. Considering the improved performance of the ReRAM device fabricated at low-temperature process, it may provide a promising candidate for the low power flexible electronics applications.

Comprehensive Non-volatile Photo-programming Transistor Memory via a Dual-Functional Perovskite-Based Floating Gate.

Photonic transistor memory has received increasing attention as next-generation optoelectronic devices for light fidelity (Li-Fi) application due to the attractive advantages of ultra-speed, high security, and low power consumption. However, most transistor-type photonic memories developed to date still rely on electrical bias for operation, imposing certain limits on data transmission efficiency and energy consumption. In this study, the dual manipulation of "photo-writing" and "photo-erasing" of a novel photonic transistor memory is successfully realized by cleverly utilizing the complementary light absorption between the photoactive material, n-type BPE-PTCDI, in the active channel and the hybrid floating gate, CH3NH3PbBr3/poly(2-vinylpyridine). The fabricated device not only can be operated under the full spectrum but also shows stable switching cycles of photo-writing (PW)-reading (R)-photo-erasing (PE)-reading (R) (PW-R-PE-R) with a high memory ratio of ∼104, and the memory characteristics possess a stable long-term retention of >104 s. Notably, photo-erasing only requires 1 s light illumination. Due to the fully optical functionality, the rigid gate electrode is removed and a novel two-terminal flexible photonic memory is fabricated. The device not only exhibits stable electrical performance after 1000 bending cycles but also manifests a multilevel functional behavior, demonstrating a promising potential for the future development of photoactive electronic devices.

Strain history of 3D printed bilayer structure with flexible elastomer and shape memory polymer filaments during thermal tensile test

This study aimed to investigate the strain history of a 3D-printed shape-memory polymer (SMP) and elastomer bilayer specimen under thermal tensile load. First, printing conditions for producing single-layer and bilayer specimens using a fused deposition modeling 3D printer were determined. Tensile tests under thermal effects were then conducted on both specimens. A 1 kg weight was used as a constant tensile load, and temperature cycles ranging from 25 to 65 °C were implemented to determine the thermal effects. The strain history was measured using a strain gauge attached to the specimen during the tests. An initial bending deformation caused by the shrinkage of the elastomer layer was observed in the bilayer specimen immediately after printing. This initial bending was then removed from the bilayer specimen via uniform heating. Strain relaxation was observed in the strain history of the single-layer SMP specimen. Mismatch strain between the two layers of the bilayer specimens was also confirmed from the thermal tensile test results. Analyses and discussions on the strain history data are provided in this paper. In general, this study determined the empirical deformation characteristics of a 3D-printed SMP–elastomer bilayer structure under combined thermal and tensile loading conditions. The results can be used to comprehend the deformation of bilayer SMP–elastomer structures and will be useful for designing a bilayer structure made of 3D-printed SMP material.

Flexible On-Line Reconfiguration of Multi-Core Neuromorphic Platforms

Neuromorphic architectures are emerging not only for real-time simulation of brain-scale biological neural networks but also to support innovative brain-inspired computational paradigms. In both domains there is an increasing demand for flexibility in terms of network configuration and runtime redesign of network parameters and simulated neurons models. Due to the intrinsically high parallelism of these architectures and complexity of the interconnect, broadcasting updates to the cores is time consuming. Hence, static solutions where the network is reloaded from an external host instead of being reconfigured are highly inefficient. To address these requirements, we designed an Application Command Protocol (ACP). The proposed protocol provides a mechanism to remotely trigger the execution of high-level op-codes by the cores and manage their application memory, and supports a more flexible computational model and memory management. We worked on SpiNNaker, a multi-core globally-asynchronous locally-synchronous platform running Spiking Neural Networks (SNNs) simulations. We demonstrated ACP in two SNN applications: i) SNN configuration, where simulation data are efficiently generated through ACP in the memory of computing nodes and ii) SNN reconfiguration, where ACP is used to change SNN network parameters at runtime and to easily switch from learning to test phase in a SNN classification application.

Epigenetically regulated digital signaling defines epithelial innate immunity at the tissue level

To prevent damage to the host or its commensal microbiota, epithelial tissues must match the intensity of the immune response to the severity of a biological threat. Toll-like receptors allow epithelial cells to identify microbe associated molecular patterns. However, the mechanisms that mitigate biological noise in single cells to ensure quantitatively appropriate responses remain unclear. Here we address this question using single cell and single molecule approaches in mammary epithelial cells and primary organoids. We find that epithelial tissues respond to bacterial microbe associated molecular patterns by activating a subset of cells in an all-or-nothing (i.e. digital) manner. The maximum fraction of responsive cells is regulated by a bimodal epigenetic switch that licenses the TLR2 promoter for transcription across multiple generations. This mechanism confers a flexible memory of inflammatory events as well as unique spatio-temporal control of epithelial tissue-level immune responses. We propose that epigenetic licensing in individual cells allows for long-term, quantitative fine-tuning of population-level responses.

Flexible Semantic Network Structure Supports the Production of Creative Metaphor

ABSTRACT Metaphors are a common way to express creative language, yet the cognitive basis of figurative language production remains poorly understood. Previous studies found that higher creative individuals can better comprehend novel metaphors, potentially due to a more flexible semantic memory network structure conducive to remote conceptual combination. The present study extends this domain to creative metaphor production and examined whether the ability to produce creative metaphors is related to variation in the structure of semantic memory. Participants completed a creative metaphor production task and two verbal fluency tasks. They were divided into two equal groups based on their creative metaphor production score. The semantic networks of these two groups were estimated and analyzed based on their verbal fluency responses using a computational network science approach. Results revealed that the semantic networks of high-metaphor producing individuals were more flexible, clustered, and less rigid than that of the low-metaphor producing individuals. Importantly, these results replicated across both semantic categories. The findings provide the first evidence that a flexible, clustered, and less rigid semantic memory structure relates to people’s ability to produce figurative language, extending the growing literature on the role of semantic networks in creativity to the domain of metaphor production.

Hf‐ and Ti‐Based Organic/Inorganic Hybrid Dielectrics Synthesized via Chemical Vapor Phase for Advanced Gate Stack in Flexible Electronic Devices

AbstractTo achieve the low power operation required by various high performance flexible electronics, such as switching and memory devices, advanced gate dielectrics should be ultra‐thin, flexible, with low gate leakage current. Organic–inorganic hybrid dielectrics are proposed to realize this combination of attributes, where the organic matrix contributes outstanding mechanical flexibility and the inorganic component provides the required electrical characteristics. Among candidate inorganic components, HfOx and TiOx are particularly attractive because of their high dielectric constant (high‐k) and wide/narrow energy bandgap. Flexible Hf and Ti hybrid high‐k dielectrics are synthesized in this work via an initiated chemical vapor deposition (iCVD) process, where 2‐hydroxyethyl‐methacrylate (HEMA) and tert‐butyl peroxide (TBPO) are used as monomers and initiators, respectively. The synthesized Hf hybrid dielectrics exhibit a high‐k value of 9.6, leakage currents below 1.0 × 10–6 A cm–2 at 2 MV cm–1, bandgaps of 5.9 eV, and electrical breakdown fields over 3 MV cm–1. The synthesized Ti hybrid dielectrics exhibit the highest k‐value of 13.0 and decent currents below 1.0 × 10–4 A cm–2 at 2 MV cm–1 due to its narrow bandgap of 3.8 eV, making it suitable for use as a charge trapping layer for flexible memory devices, rather than as a gate dielectric. n‐type and p‐type organic thin film transistors (OTFT) prepared with the Hf hybrid dielectrics exhibit typical transfer and output characteristics, even under tensile stresses as high as 2.0% strain. Under the mechanical stress condition of 2.0% tensile strain, no noticeable degradation is observed in the Hf hybrids in terms of saturation mobility (μsat), subthreshold swing (S.S.), interface trap density (Dit), threshold voltage (VT), or hysteresis. These results show that the Hf and Ti hybrid dielectrics can enhance the performance of flexible electronics.

A flexible nickel phthalocyanine resistive random access memory with multi-level data storage capability

Metal phthalocyanine is considered one of the most promising candidates for the design and fabrication of flexible resistive random access memory (RRAM) devices due to its intrinsic flexibility and excellent functionality. However, performance degradation and the lack of multi-level capability, which can directly expand the storage capacity in one memory cell without sacrificing additional layout area, are the primary obstacles to the use of metal phthalocyanine RRAMs in information storage. Here, a flexible RRAM with pristine nickel phthalocyanine (NiPc) as the resistive layer is reported for multi-level data storage. Due to its high trap-concentration, the charge transport behavior of the device agrees well with classical space charge limited conduction controlled by traps, leading to an excellent performance, including a high on-off current ratio of 107, a long-term retention of 106 s, a reproducible endurance over 6000 cycles, long-term flexibility at a bending strain of 0.6 %, a write speed of 50 ns under sequential bias pulses and the capability of multi-level data storage with reliable retention and uniformity.

Synthesis of wafer-scale ultrathin graphdiyne for flexible optoelectronic memory with over 256 storage levels

<h2>Summary</h2> Two-dimensional (2D) graphdiyne (GDY) is a promising floating-gate material for flexible optoelectronic flash memory owing to its fascinating electrical and optical properties. However, research in GDY-based flash memory is still in its infancy owing to the huge challenge in the synthesis of large-area and ultrathin GDY films with high quality and uniformity. Here, an electric double-layer-confined strategy is proposed to synthesize a wafer-scale GDY film with thickness of 1 nm. Then, a two-terminal top-floating-gated optoelectronic memory with multibit storage capability is investigated using GDY as a photoresponsive top-floating gate. Benefiting from the excellent charge storage capability and high photoresponse of GDY, this device exhibits over 256 distinct storage levels (8 bits) with signal-to-noise ratios larger than 100. Moreover, the fully 2D material and two-terminal architecture endows the device with robust bending stability for over 1,000 bending circles, paving the way to develop wearable electronics.

Low-Temperature Growth of Ferroelectric Hf0.5Zr0.5O2 Thin Films Assisted by Deep Ultraviolet Light Irradiation

Low-temperature deposition of inorganic ferroelectric (FE) thin films is highly demanded for lowering the environmental impact through lesser energy consumption. Doped HfO2-based FE thin films commonly require high crystalline temperature (>450 °C) to exhibit ferroelectricity. Here, we report that the crystallization temperature of the metastable orthorhombic (O) phase in Hf0.5Zr0.5O2 thin films can be lowered to 350 °C via a deep ultraviolet (DUV) irradiation process carried out before rapid thermal annealing (RTA). The DUV irradiation initializes a nucleation process of the crystal growth through photochemical cleavage of organic residues, followed by the densification of metal oxide films, and the subsequent RTA at 350 °C crystallizes the Hf0.5Zr0.5O2 thin film with a higher O-phase fraction. The DUV-irradiated films annealed at 350 °C exhibited FE characteristics, whereas the non-irradiated films annealed above 450 °C become FE. Our study suggests that DUV irradiation can be successfully utilized to lower the crystallization temperature of HZO thin films and can lead to the realization of flexible FE random access memories.

Synthesis of nanocomposite films based on conjugated oligomer-2D layered MoS2 as potential candidate for optoelectronic devices

In this investigation, we have analyzed the structural, electrical, and optical behaviors of pure and composite thin films which are obtained from 2D monolayer molybdenum disulfide (MoS2) flakes, conjugated oligomer (CO) 1,4-Bis(9-ethyl-3-carbazo-vinylene)-9,9-dihexyl-fluorene (BECV-DHF), and by combining CO (BECV-DHF) with MoS2 in forms of CO/MoS2 composites. All the samples are coated on SiO2/Si substrates using the spin coating procedure where a spin-coating solution has been obtained by dispersing CO and MoS2 in ethanol or toluene. The structural morphology of MoS2 films and CO/MoS2 films of various thicknesses are analyzed using field emission scanning electron microscope (FE-SEM), transmission electron microscope (TEM), and profilometer. These experimental results confirm the formation of MoS2 layer composite with oligomer nanocrystals. The optical properties of MoS2, CO, and CO/MoS2 films showed that the increased film thickness shifted the spectral peaks towards near infrared (NIR) and ultraviolet–visible (UV) regions of the electromagnetic spectrum. Moreover, devices such as solar cells, flexible memory cell and MOSFET were designed. The I-V characteristics of these devices show that CO/MoS2 composite films could serve as potential candidates for organic-inorganic nano-electronic device applications.

Multilevel resistive switching performance of TiO2-based flexible memory prepared by low-temperature sol-gel method with UV irradiation

The flexible Ag/TiO2/ITO/PET resistive switching memory is prepared by low-temperature sol-gel method with UV irradiation, and the simple method that combined the advantages of sol-gel method and low temperature can be applied to fabricate high-quality film. The flexible Ag/TiO2/ITO/PET memory device displays good resistive behavior, for instance, the narrow distributions of switching voltages, good cycle endurance, and long retention time. Meanwhile, the multilevel resistance states of the device can be realized by controlling the compliance current or reset voltages, showing the potential of applications in neural networks and high-density storge. In addition, flexibility of the Ag/TiO2/ITO/PET is studied, which exhibit good endurance and retention properties under bending condition. The I–V curves are replotted and fitted for analyzing the conductive mechanism of the device. The fitting results show that SCLC and Ohmic mechanism are main mechanisms of high resistance state and low resistance state respectively. The electrochemical and thermochemical modes are adopted to explain resistive switching behavior. Our results indicate the Ag/TiO2/ITO/PET memory has potential application in wearable and foldable electronics.

Total ionizing dose effects of 60Co-γ ray radiation on the resistive switching and its bending performance of Al-in-O/InOx-based flexible RRAM device

Flexible resistive switching random access memory (RRAM) device is one of the promising candidates for non-volatile memory used in space because of its features such as simple structure, high speed, low power consumption, durability and lightweight with reduction in thickness. Al-In-O/InOx self-mixing layer can be applied for flexible RRAM due to its low annealing temperature (i.e. temperatures<180 °C), forming-free resistive switching characteristics and low SET and RESET voltage. Herein, effects of the total ionizing dose of 60Co-γ ray radiation on the resistive switching, the bending performance of the prepared flexible RRAM devices based on the Al-In-O/InOx films were studied. The results indicated that the resistance decreases with the bias in high resistance state (HRS) and the SET voltages of the device decrease very slightly after irradiation, while the low resistance state (LRS), RESET voltage, and retention parameters are almost immune to radiation. Moreover, after irradiation, the decrease of resistance with the bias in HRS becomes more exacerbated when bended. Mechanism of bending on the RS is studied by the first-principles calculation, and the mechanism underlying the irradiation effect is studied from the viewpoint of the origin of RS.