A biocompatible and biodegradable memory device is presented for future medical devices and implantable electronics. J.-S. Lee and co-workers develop nonvolatile memory devices based on natural materials with simple solution processes on page 5586. The memory devices are decomposed entirely during immersion in water. The fabricated device is fully biocompatible and environmentally benign, with good programmable memory characteristics.
Abstract Conductive bridge random access memory (CBRAM) is a possible replacement for static field‐programmable gate arrays (FPGAs) based on random‐access memory. Ge 2 Sb 2 Te 5 (GST) is used in CBRAMs as a solid electrolyte due to its high diffusion properties of active ions and scalability to obtain high‐density memory devices. Here, the trade‐off between high memory window and uniformity of CBRAM based on GST is solved by introducing N atoms into the SE. Nitrogen‐incorporated GST film (N‐GST) is proposed as a replacement for the current GST‐based CBRAMs with improved performance and better opportunities for conventional FPGA technologies. A bidirectional polarity‐dependent characteristic with high I ON / I OFF ratio and satisfactory operation voltage is achieved by using N‐GST thin film in a programmable metallization cell (PMC). Integration of N atoms in the GST‐based PMC with a simple structure of Ag/ N‐GST /Pt increases the resistance ratio more than 100 times compared to an undoped one. Consistent data retention is attained in both resistance states for ≥3.5 × 10 4 s at temperature up to 85 °C.
Oxidation can strongly influence the performance of Cu nanowires (CuNWs) by decreasing their conductivity. Here, we identify and investigate a way to prevent the oxidation process of CuNWs to maintain the high conducting performance of CuNWs as transparent electrodes. CuNWs were synthesised using an aqueous method. We prepared several temperature treatments (from 0-300 °C) to represent oxidation of CuNWs in different environments, to study the oxidation process and changes in morphology in detail. Depending on the temperature, smooth and uniform CuNWs exposed to oxidation produced rough Cu2O and CuO nanowires. We then suggest a method of protecting nanowires from oxidation, using the Mayer rod coating method to apply a layer of PEDOT:PSS to a transparent conducting film of CuNWs. The result indicates that this method of protection can protect the film, and maintain a stable, and constant resistance over of time, without effecting the excellent conductivity properties of pure CuNWs.
A carbon-based natural nanocomposite material comprising carbon quantum dots (CQDs) is dispersed in a chitosan matrix. The CQD–chitosan nanocomposite serves as a solid polymer electrolyte layer of a biomemristor with a Au/CQD–chitosan/Al structure. The active layer of the CQD–chitosan nanocomposite is deposited from its solution on top of coplanar asymmetric nanogap (∼15 nm) Al–Au electrodes, patterned via adhesion lithography. The CQD–chitosan biomemristor presents a high on/off ratio (>106) and reproducible and reliable bipolar resistive switching behavior. An endurance of 160 cycles was recorded, while the high and low resistance states remained stable for more than 104 s. This study highlights the potential of both the CQD–chitosan material and nanogap electrode structures for application in nanoscale biocompatible memory devices.
Integration of metamaterial and nonvolatile memory devices with tunable characteristics is an enthusing area of research. Designing a unique nanoscale prototype to achieve a metasurface with reliable resistive switching properties is an elusive goal. We demonstrate a method to exploit the advantages of a phase-change material (PCM) as a metamaterial light absorber and a nanoscale data storage device. We designed and simulated a metamaterial perfect absorber (MPA) that can be reconfigured by adjusting the visible light properties of a chalcogenide-based PCM. The suggested perfect absorber is based on a Ge2Sb2Te5 (GST) film, and is tuned between two distinct states by heat treatment. Furthermore, we fabricated and characterized a resistive switching memory (ReRAM) device with the same features. The MPA/ReRAM device with a conventional metal/dielectric/metal structure (Ag/GST/Al2O3/Pt) consisted of arrays of Ag squares patterned on a GST thin film and an alumina-coated Pt mirror on a glass substrate. Based on the numerical data, amorphous GST showed perfect absorbance in the visible spectrum, whereas, crystalline GST showed broadband perfect absorbance. The fabricated ReRAM device exhibited uniform, bidirectional, and programmable memory characteristics with a high ON/OFF ratio for nonvolatile memory applications. The elucidated origin of the bipolar resistive switching behavior is assigned to the formation and rupture of conductive filaments.
Physically Transient Electronic Devices (PiTEDs) are building blocks of biodissolvable diagnostics and therapeutics. We fabricate a PiTED integrated with data storage and brain-inspired computing capable of data collection and decision-making in case of an emergency. It is also compatible with the physiological environment of the human body and biologically soluble and degradable after performing the required task. A flexible and transparent biomemristor with Mg/collagen/ITO structure is fabricated using a facile solution-assisted process. The flexible collagen-based biomemristor shows vital characterizations for a reproducible memristor, including extensive data retention and endurance cycles. The fish collagen-based device benefits from its biodegradability due to using dissolvable Mg electrodes and collagen from the fish scale as a naturally abundant protein. The Mg electrodes dissolved with water via hydrolysis after dropping water on the device. The electrolyte thin film is also easily water-soluble. The biomemristor shows a conductance modulation behavior of a biological synapse, including potentiation and depression. We constructed a memristive neuromorphic network to realize pattern recognition with a 92.2% accuracy. This device has potential applications in storing and analyzing top-secret information in defense services and implantable dissolvable medical systems.
A flexible and transparent resistive switching memory based on a natural organic polymer for future flexible electronics is reported. The device has a coplanar structure of Mg/Ag‐doped chitosan/Mg on plastic substrate, which shows promising nonvolatile memory characteristics for flexible memory applications. It can be easily fabricated using solution processes on flexible substrates at room temperature and indicates reliable memory operations. The elucidated origin of the bipolar resistive switching behavior is attributed to trap‐related space‐charge‐limited conduction in high resistance state and filamentary conduction in low resistance state. The fabricated devices exhibit memory characteristics such as low power operation and long data retention. The proposed biocompatible memory device with transient electrodes is based on naturally abundant materials and is a promising candidate for low‐cost memory applications. Devices with natural substrates such as chitosan and rice paper are also fabricated for fully biodegradable resistive switching memory. This work provides an important step toward developing a flexible resistive switching memory with natural polymer films for application in flexible and biodegradable nanoelectronic devices.
Abstract Neuromorphic and cognitive computing with a capability of analyzing complicated information is explored as a new paradigm of intelligent systems. An implementation of a renewable material as an essential building block of an artificial synaptic device is suggested and a flexible and transparent synaptic device based on collagen extracted from fish skin is demonstrated. This device exhibits essential synaptic behaviors including analog memory characteristics, excitatory postsynaptic current, and paired‐pulse facilitation as short‐term plasticity. The brain‐inspired electronic synapse undergoes incremental potentiation and depression when flat or bent. The device emulates spike‐timing‐dependent plasticity when stimulated by engineered pre‐ and post‐neuron spikes with the appropriate time difference between the imposed pulses. The proposed synaptic device has the advantage of being biocompatible owing to use of Mg electrodes and collagen as a naturally abundant protein. This device has a potential to be used in flexible and implantable neuromorphic systems in the future.
Implementation of biocompatible materials in resistive switching memory (ReRAM) devices provides opportunities to use them in biomedical applications. We demonstrate a robust, nonvolatile, flexible, and transparent ReRAM based on potato starch. We also introduce a biomolecular memory device that has a starch-chitosan composite layer. The ReRAM behavior can be controlled by mixing starch with chitosan in the resistive switching layer. Whereas starch-based biomemory devices which show abrupt changes in current level; the memory device with mixed biopolymers undergoes gradual changes. Both devices exhibit uniform and robust programmable memory properties for nonvolatile memory applications. The explicated source of the bipolar resistive switching behavior is assigned to formation and rupture of carbon-rich filaments. The gradual set/reset behavior in the memory device based on a starch-chitosan mixture makes it suitable for use in neuromorphic devices.
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