Metasurfaces Based on Phase-Change Material as a Reconfigurable Platform for Multifunctional Devices

Integration of phase-change materials (PCMs) into electrical/optical circuits has initiated extensive innovation for applications of metamaterials (MMs) including rewritable optical data storage, metasurfaces, and optoelectronic devices. PCMs have been studied deeply due to their reversible phase transition, high endurance, switching speed, and data retention. Germanium-antimony-tellurium (GST) is a PCM that has amorphous and crystalline phases with distinct properties, is bistable and nonvolatile, and undergoes a reliable and reproducible phase transition in response to an optical or electrical stimulus; GST may therefore have applications in tunable photonic devices and optoelectronic circuits. In this progress article, we outline recent studies of GST and discuss its advantages and possible applications in reconfigurable metadevices. We also discuss outlooks for integration of GST in active nanophotonic metadevices.1115sciescopu

Dual-Functional Nanoscale Devices Using Phase-Change Materials: A Reconfigurable Perfect Absorber with Nonvolatile Resistance-Change Memory Characteristics

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.11Nsciescopu

High on/off ratio carbon quantum dot–chitosan biomemristors with coplanar nanogap electrodes

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

Solution-Processed Flexible Biomemristor Based on Gold-Decorated Chitosan

The main requirements for skin-attachable memory devices are flexibility and biocompatibility. We represent a flexible, transparent, and biocompatible resistive switching random access memory (ReRAM) based on gold-decorated chitosan for future flexible and wearable electronics. The device with an Ag/Au-chitosan/Au cross-bar structure shows nonvolatile ReRAM properties. This fabricated Au-chitosan-based biocompatible ReRAM (bioReRAM) shows reliable bipolar memory performance with mechanical flexibility. The device shows essential memory characterizations including long data retention and hundreds of switching cycles. The origin of the resistance switching properties is related to trap-assisted space-charge-limited conduction in the high-resistance state and formation/annihilation of a conductive filament in the low-resistance state. This transparent bioReRAM is a viable candidate for flexible and biodegradable nanoelectronic devices.11Nsciescopu

Investigation of Switching Mechanism in a Bio-Memristor using Conductive Atomic Force Microscopy (C-AFM)

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Biocompatible and Flexible Chitosan-Based Resistive Switching Memory with Magnesium Electrodes

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.116637sciescopu

Controlling the Resistive Switching Behavior in Starch-Based Flexible Biomemristors

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.113319sciescopu

Metasurfaces Based on Phase-Change Material as a Reconfigurable Platform for Multifunctional Devices

Integration of phase-change materials (PCMs) into electrical/optical circuits has initiated extensive innovation for applications of metamaterials (MMs) including rewritable optical data storage, metasurfaces, and optoelectronic devices. PCMs have been studied deeply due to their reversible phase transition, high endurance, switching speed, and data retention. Germanium-antimony-tellurium (GST) is a PCM that has amorphous and crystalline phases with distinct properties, is bistable and nonvolatile, and undergoes a reliable and reproducible phase transition in response to an optical or electrical stimulus; GST may therefore have applications in tunable photonic devices and optoelectronic circuits. In this progress article, we outline recent studies of GST and discuss its advantages and possible applications in reconfigurable metadevices. We also discuss outlooks for integration of GST in active nanophotonic metadevices