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ON/OFF ratio as a function of the bending condition (the substrate distance and the bending radius). (b) ON/OFF ratio as a function of the number of bendings.
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(Figure Presented) Organic nonvolatile memory devices fabricated on flexible substrates showed rewritable and nearly consistent switching characteristics, regardless of the bending circumstances. This stable memory performance with bending stress is a promising property for the practical memory devices in future flexible electronics.
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Context 1
... investigated the ON/OFF ratio as a function of the degree of bending. As shown in Figure 3 a, the ON/OFF ratios of the memory device remained over 10 4 even when bending was increased. Also, the deviations of the ON/OFF ratios were insignifi cant at all the bending condi- tions shown in the plot. ...
Context 2
... addition, the stability of the memory performance during repetitive bending conditions is also a critical factor for realizing practical fl exible memory devices. To test this, the ON/OFF ratios were monitored with increasing bending cycles, as shown in Figure 3 b. The ON/OFF ratios were measured when the device was at the maximum bending con- dition (bending radius of 9 mm). ...
Citations
... In an effort to find suitable materials for fabricating artificial synapses, a wide variety of materials have come into the field of researchers, such as metal oxide materials [21], inorganic materials [22,23], chalcogenides [24], perovskites [25][26][27][28][29], and 2D materials [30,31]. Most of the materials reported in the literature are complex to prepare and incompatible with organisms [32][33][34], making them difficult to use due to a lack of environmentally friendly disposal methods and for posing potential threats to the environment. Therefore, to produce biocompatible devices at a low cost, new materials must meet these requirements, using readily available natural compounds. ...
... Moreover, egg albumen is a protein material with variable electrical conductivity, which is similar to the neuroplasticity of biological synapses and can simulate the synaptic connections between biological neurons. Therefore, egg albumen has been used as an active or dielectric layer in fabricating high-performance resistive switching devices [36] and thin-film transistors [34]. However, in-depth research on biomaterialrelated synaptic bionics and neuromorphic computing remains incomplete. ...
As artificial synapse devices, memristors have attracted widespread attention in the field of neuromorphic computing. In this paper, Al/polymethyl methacrylate (PMMA)/egg albumen (EA)–graphene quantum dots (GQDs)/PMMA/indium tin oxide (ITO) electrically/optically tunable biomemristors were fabricated using the egg protein as a dielectric layer. The electrons in the GQDs were injected from the quantum dots into the dielectric layer or into the adjacent quantum dots under the excitation of light, and the EA–GQDs dielectric layer formed a pathway composed of GQDs for electronic transmission. The device successfully performed nine brain synaptic functions: excitatory postsynaptic current (EPSC), paired-pulse facilitation (PPF), short-term potentiation (STP), short-term depression (STD), the transition from short-term plasticity to long-term plasticity, spike-timing-dependent plasticity (STDP), spike-rate-dependent plasticity (SRDP), the process of learning, forgetting, and relearning, and Pavlov associative memory under UV light stimulation. The successful simulation of the synaptic behavior of this device provides the possibility for biomaterials to realize neuromorphic computing.
... These resistive memory devices are becoming a good alternative to traditional memory devices due to their ease of fabrication and the possibility for more complex and denser crossbar array configurations, their good operability, and lower power consumption [3][4][5][6]. Moreover, it is less difficult to obtain flexible devices simply by changing a rigid substrate to a flexible one because of the nature of the organic materials used as the active layers [7][8][9]. Several organic materials such as polymers [5,6], polymer ? nanoparticles composites [6], graphene [10], or graphene oxide [11,12] have been used for the fabrication of resistive organic memories, among them the most interesting are the carbon nanostructures [10][11][12][13][14][15][16][17]. ...
Non-volatile organic memory devices were fabricated using polystyrene sulfonate (PSS) + nitrogen-doped multi-walled carbon nanotubes (NCNTs) composites on glass and PET substrates. The organic memory devices showed different electrical properties depending on the NCNTs concentrations in the PSS matrix and the bottom electrode material. The Al/PSS + NCNTs/Al devices presented WORM-like behavior at low NCNTs concentrations (0.3 wt%). If the NCNTs concentration is 1 wt%, the devices showed rewritable memory behavior. This memory behavior is based on charge trapping/detrapping processes. While with a 3 wt% of NCNTs concentration, their rewritable behavior is related to the generation of oxygen vacancies (VO) in the thin layer of native Al oxide (AlOx) on the bottom electrode during the first voltage sweep. The ITO/PSS + NCNTs/Al devices with NCNTs concentrations ≤ 1 wt% showed a rewritable behavior, whose electrical bistability is based on the charge trapping/detrapping mechanism; while those fabricated with 3 wt% NCNTs concentration presented an ohmic behavior. The memory devices with Al as the bottom electrode can show physical deformations (bubbles) on the top electrode, when oxygen vacancies are generated due to electro-reduction of the AlOx layer, while devices with ITO as the bottom electrode did not show these bubbles. Thus, the charge trapping/detrapping processes and the VO creations can coexist in the Al/AlOx/PSS + NCNTs/Al memory devices, and one of them becomes preponderant, depending on the NCNTs concentration.
... Conventional memristors were metal-insulator-metal (MIM)-structured two-terminal devices [12]. Metals (Al [13], Cu [14], Au [15], Ag [16], etc.) are often applied as electrode layer of the memristor and the active layer of memristor is usually made of metal oxides (HfO 2 [17], TaO x [18], Al 2 O 3 [19], TiO 2 [20], etc.). However, memristors with pure metal electrode structure or metal oxide active layer structure require a large forming voltage [21] and generate a large turn-on current [22], which results in high power consumption and greatly limits the integration and practical application. ...
A memristor is a promising candidate of new electronic synaptic devices for neuromorphic computing. However, conventional memristors often exhibit complex device structures, cumbersome manufacturing processes, and high energy consumption. Graphene-based materials show great potential as the building materials of memristors. With direct laser writing technology, this paper proposes a lateral memristor with reduced graphene oxide (rGO) and Pt as electrodes and graphene oxide (GO) as function material. This Pt/GO/rGO memristor with a facile lateral structure can be easily fabricated and demonstrates an ultra-low energy consumption of 200 nW. Typical synaptic behaviors are successfully emulated. Meanwhile, the Pt/GO/rGO memristor array is applied in the reservoir computing network, performing the digital recognition with a high accuracy of 95.74%. This work provides a simple and low-cost preparation method for the massive production of artificial synapses with low energy consumption, which will greatly facilitate the development of neural network computing hardware platforms.
... because of their high ionic transport and stability characteristics [18][19][20][21]. Owing to its higher ionic conductivity, mechanical flexibility, good film forming ability and compatibility with various substrates, polyethylene oxide (PEO) can be used as an active material for humidity sensing device [22][23][24][25]. Recently, the structural characteristics of polymer thin films have been considered as an essential factor for ionic transport behavior. ...
Manipulation of ionic transport in the self-assembled polymer thin films using nanoarchitectonics approach can open the door for the development of novel electronic devices with ultrafast operation and low-power consumption. Here, we demonstrate a highly sensitive and ultrafast responsive flexible humidity sensor for human respiration monitoring. Humidity sensing behavior of the polymerbased planar devices, in which a polyethylene oxide-phosphotungstic acid (PEO-PWA) thin film is placed between an opposing inert electrodes, have been investigated by optimizing the device configuration and PWA salt concentration in the PEO matrix. The ultrafast response (~50 ms) and recovery (~52 ms) of the humidity sensor enabled us to study the real-time human respiration monitoring. Using morphological analysis, it is proposed that the ultrafast response-recovery time for this sensor is ascribed to their self-assembled lamellar-like structures of the PEO-PWA matrix polymer, which provides long-range continuous proton transport path in the polymer interface.
... Comprehension and manipulation of electric polarization in polymers is a major requisite of organic ferroelectrics due to their potential applicability in bendable memory and sensor devices [1][2][3][4]. The existence of spontaneous polarization down to few monolayers in ferroelectric polymers has revised the organic non-volatile memory, photo-voltaic, piezo sensor device studies [5][6][7][8][9][10][11]. Amid polar polymers, polyvinyledene fluoride (PVDF) and its co-polymers PVDF-TrFE, PVDF-HFP caught considerable attention owing to their easy stabilization of polar phase along with comparable dielectric constants w.r.t. ...
The local ferroelectric domain structure of interconnected PVDF nano-dots with applied DC voltages of ± 10 V to ± 100 V is evaluated using various Piezo force microscopy (PFM) methods such as conventional PFM and Dynamic contact electrostatic force microscopy (DC-EFM). The self-assembled PVDF nano-dots are fabricated by using a spin coater method with 2 wt% of PVDF-DMSO solution. The polar gamma phase is found to be induced by the microstructural confinement of PVDF monomers and also reveals a strong ferroelectric nature after poling at different DC bias voltages. Poling with altered directions of the voltages renders a 180° phase reversal of PVDF domains. The local domain study depicts that each nano-dot is functioning as a single domain and switches as a whole. The single nano-dot switching signifies the potential of using the nano-dots for organic ferroelectric memory devices.
... Many types of materials have been used as the active layer in RRAM devices, such as transition metal oxide, perovskite complex oxide, solid electrolyte, and polymer. [5][6][7][8][9]. Among various materials, metal oxides such as InGaZnO, HfO 2 , ZrO 2 , NiO, and Al 2 O 3 stands out and they are extensively studied to continuously improve the memory performance in RRAM devices for nonvolatile memory applications [3][4][5][6][10][11][12][13]. ...
In this work, a resistive switching memory device with Ag/(NiO/Al2O3)3/fluorine-doped SnO2 structure was fabricated with solution-based process including spin-coating of triple-layered NiO/Al2O3 films and ink-jet printing of Ag electrodes. Bipolar resistive switching characteristic was observed in such a structure, with the resistance ratio between high and low resistance states over two orders and good cycling stability in voltage sweeping measurements. More importantly, the SET/RESET voltages, which were in the range of 0.8‒2.4 V and − 0.7 to − 2.8 V, respectively, showed significant improvement in voltage distribution (78.4% and 71.2% narrower) as compared to devices solely based on Al2O3 film. It is believed that the narrow distribution of SET and RESET voltages results from the reduced randomness of the formation and rupture of conductive filaments under applied voltages, since NiO and Al2O3 have different dielectric constants and the distribution of electric field in the multilayers can be varied to facilitate the formation and rupture of conductive filaments. Moreover, electroforming process was not required to activate the device based on triple-layered NiO/Al2O3 films. The characterization results especially the narrow SET/RESET voltage distribution and forming-free property make devices based on multilayered NiO/Al2O3 thin films promising for thin film-based nonvolatile memory applications.
... It is also important that there are organic memristive structures that could be fabricated on flexible biocompatible substrates, used for neuroprosthetics and so-called "wearable" electronic devices 5,11,12 . Stable operation of flexible memristive devices was shown at rather small bending radii (down to 9 mm) and longitudinal twisting up to 30 degrees 13,14 . Moreover, resistance in this case can be tuned in the window between R on and R off according to the rules similar to those in biological neural networks 5 , in particular, the so-called "spike-timing-dependent plasticity" (STDP) first implemented for inorganic memristive structures 15 . ...
In this paper, the resistive switching and neuromorphic behaviour of memristive devices based on parylene, a polymer both low-cost and safe for the human body, is comprehensively studied. The Metal/Parylene/ITO sandwich structures were prepared by means of the standard gas phase surface polymerization method with different top active metal electrodes (Ag, Al, Cu or Ti of ~500 nm thickness). These organic memristive devices exhibit excellent performance: low switching voltage (down to 1 V), large OFF/ON resistance ratio (up to 104), retention (≥104 s) and high multilevel resistance switching (at least 16 stable resistive states in the case of Cu electrodes). We have experimentally shown that parylene-based memristive elements can be trained by a biologically inspired spike-timing-dependent plasticity (STDP) mechanism. The obtained results have been used to implement a simple neuromorphic network model of classical conditioning. The described advantages allow considering parylene-based organic memristors as prospective devices for hardware realization of spiking artificial neuron networks capable of supervised and unsupervised learning and suitable for biomedical applications.
... The resistive bi-stability switching in oxide materials show a promising way for future non-volatile memory devices in cross point structures due to their small device area 4F 2 , fast switching speed in nanoseconds, less power consumption~μW and known as Resistive Random Access Memory (ReRAM) devices [1][2][3][4]. The transport across metal oxides [5,6], chalcogenides [7][8][9], perovskite structures [3,[10][11][12][13][14][15], organic thin films [16][17][18][19][20][21][22] and semiconductors [23][24][25], revealed different resistance switching mechanisms such as unipolar, bipolar (non-volatile) and threshold (volatile). The rich electronic phases and the resultant formation of a conductive filament by metal ion or oxygen vacancy migration influences the resistive bi-stability in these junctions [3,4]. ...
The influence of compliance current and film thickness upon multi-level threshold resistive switching characteristics of amorphous BaTiO3 (am-BTO) thin films in Ag/am-BTO/Ag cross point structures have been investigated. The cross-point junctions are fabricated utilizing RF/DC magnetron sputtering technique and the thickness of am-BTO films are tuned with the sputtering time. The structural and microstructural details are probed with X-ray diffraction, Atomic force microscopy, Field effect scanning electron microscopy and X-ray photoelectron spectroscopy techniques. The current-voltage characteristics revealed a stable threshold resistive switching with maximum ION/IOFF ratios of ~ 2 × 10³ with low-threshold voltages and near zero voltage hold values are noted for 142 nm am-BTO thin film at 1 × 10⁻⁴ A compliance current. The compliance current found to affect the bi-stability or multi-level resistance switching. The contribution of oxygen vacancies to the switching is elucidated from X-ray photoelectron spectroscopy measurements. Furthermore, the thickness effect on threshold resistive switching properties along with conduction mechanisms in lower and higher resistance states are discussed.
... [13,14] Organic memory is regarded as a promising candidate device for wearable information storage application due to the lightweight, flexibility, and low cost. [15][16][17][18] Especially, organic NVMs based on organic thin-film transistor (OTFT) with a dielectric setup www.advelectronicmat.de OTFT-NVMs. ...
Organic thin film transistor nonvolatile memories (OTFT‐NVMs) with polymeric electret layers have attracted research attention for the application to emerging wearable electronics. However, it is challenging to develop low‐power flexible OTFT‐NVMs due to the lack of candidate polymers for flexible electret and blocking dielectric layer (BDL) equipped with the thickness downscalability and sufficiently strong insulating properties. Here, this study reports a low‐power, flexible OTFT‐NVM fabricated with a bilayer dielectric stack composed of a 3 nm thick polymer electret layer and a high‐performance BDL prepared via an initiated chemical vapor deposition process. Especially, a crosslinked poly(1,4‐butanediol diacrylate) film is newly synthesized as a BDL, which shows excellent insulating properties with high breakdown field (Ebreak > 8 MV cm−1 with its thickness of 21.3 nm). Coupled with a 3 nm thick polymer electret layer (poly(1,3,5‐trimethyl‐1,3,5‐trivinyl cyclotrisiloxane)), the fabricated NVMs exhibit a tunable memory window with dramatically reduced programming/erasing voltages less than 15 V and an extrapolated retention time as long as 108 s. Moreover, the device maintains their memory performance up to 1.6% of applied tensile strain. The OTFT‐NVMs with the ultrathin dielectric stack can serve as a promising dielectric for stable data storage in various future wearable electronics. An ultrathin polymer electret layer with extreme downscalability is developed for low‐power, nonvolatile memory via initiated chemical vapor deposition process. By combining a newly synthesized high‐performance, flexible blocking dielectric with the ultrathin (3 nm) polymer electret, the devices exhibit excellent memory characteristics with low‐power consumption and superb mechanical flexibility, presenting an important milestone for developing a low‐power, flexible nonvolatile memory.
... [5][6][7] Stable operation of flexible memristive devices was shown at rather small bending radii (down to 9 mm) and longitudinal twisting up to 30 degrees. 8,9 Moreover, resistance in this case can be tuned in the window between R on and R off according to the rules similar to those in biological neural networks, 5 in particular, the so-called "spike-timing-dependent plasticity" (STDP) first implemented for inorganic memristive structures. 10 The presence of memristive properties was found in structures based on inorganic oxides (TiO x , HfO x , SiO x , etc.), [11][12][13][14] organic (polyaniline, polythiophene) [15][16][17] and hybrid 18 materials. ...
In this paper, the resistive switching and neuromorphic behavior of memristive devices based on parylene, a biocompatible and low-cost polymer, is comprehensively studied. The Metal/Parylene/ITO sandwich structures were prepared by means of the standard gas phase surface polymerization method with different top active metal electrodes (Ag, Al, Cu or Ti of ~ 500 nm thickness). These organic memristive devices exhibit excellent performance: low switching voltage (down to 1 V), large OFF/ON resistance ratio (~ 10^3), retention (greater than 10^4 s) and high multilevel resistance switching (at least 16 stable resistive states in the case of Cu electrodes). We have experimentally shown that parylene-based memristive elements can be trained by a biologically inspired spike-timing-dependent plasticity (STDP) mechanism. The obtained results have been used to implement a simple neuromorphic network model of classical conditioning. The described advantages allow considering parylene-based organic memristors as prospective devices for hardware realization of spiking artificial networks capable of supervised and unsupervised learning.
