Optoelectronic Memory Devices Research Articles

A Perspective on tellurium-based optoelectronics

Tellurium (Te) has been rediscovered as an appealing p-type van der Waals semiconductor for constructing various advanced devices. Its unique crystal structure of stacking of one-dimensional molecular chains endows it with many intriguing properties including high hole mobilities at room temperature, thickness-dependent bandgap covering short-wave infrared and mid-wave infrared region, thermoelectric properties, and considerable air stability. These attractive features encourage it to be exploited in designing a wide variety of optoelectronics, especially infrared photodetectors. In this Perspective, we highlight the important recent progress of optoelectronics enabled by Te nanostructures, which constitutes the scope of photoconductive, photovoltaic, photothermoelectric photodetectors, large-scale photodetector array, and optoelectronic memory devices. Prior to that, we give a brief overview of basic optoelectronic-related properties of Te to provide readers with the knowledge foundation and imaginative space for subsequent device design. Finally, we provide our personal insight on the challenges and future directions of this field, with the intention to inspire more revolutionary developments in Te-based optoelectronics.

Giant persistent photoconductivity of VO2 device by single-pulse femtosecond laser

The manifestation of giant persistent photoconductivity (GPPC) is demonstrated with a fs (femtosecond) Ti:sapphire laser pulse that has a duration of 40 fs and a central wavelength of 400 nm. The femtosecond laser pulse was irradiated on a two-terminal VO2 device fabricated on a corning glass substrate. Under the applied voltages of 9–12 V, the GPPC takes place within 8.6–15 μs after the laser irradiation. The photocurrent from the GPPC in the VO2 device remains stable with the current decreasing slope of ∼0.003%/minute. With one-dimensional thermal model, the temperature (TIR) of the irradiated area is estimated as a function of time, indicating that TIR is above the insulation-to-metal transition temperature of VO2 thin film prior to the onset of GPPC. The ultrafast onset of GPPC of VO2 device can be utilized for ultrafast optoelectronic switch and memory device.

2D van der Waals Heterostructure with Tellurene Floating-Gate for Wide Range and Multi-Bit Optoelectronic Memory.

Intensive research on optoelectronic memory (OEM) devices based on two-dimensional (2D) van der Waals heterostructures (vdWhs) is being conducted due to their distinctive advantages for electrical-optical writing and multilevel storage. These features make OEM a promising candidate for the logic of reconfigurable operations. However, the realization of nonvolatile OEM with broadband absorption (from visible to infrared) and a high switching ratio remains challenging. Herein, we report a nonvolatile OEM based on a heterostructure consisting of rhenium disulfide (ReS2), hexagonal boron nitride (hBN) and tellurene (2D Te). The 2D Te-based floating-gate (FG) device exhibits excellent performance metrics, including a high switching on/off ratio (∼106), significant endurance (>1000 cycles) and impressive retention (>104 s). In addition, the narrow band gap of 2D Te endows the device with broadband optical programmability from the visible to near-infrared regions at room temperature. Moreover, by applying different gate voltages, light wavelengths, and laser powers, multiple bits can be successfully generated. Additionally, the device is specifically designed to enable reconfigurable inverter logic circuits (including AND and OR gates) through controlled electrical and optical inputs. These significant findings demonstrate that the 2D vdWhs with a 2D Te FG are a valuable approach in the development of high-performance OEM devices.

Integrating ultraviolet sensing and memory functions in gallium nitride-based optoelectronic devices.

Optoelectronic devices present a promising avenue for emulating the human visual system. However, existing devices struggle to maintain optical image information after removing external stimuli, preventing the integration of image perception and memory. The development of optoelectronic memory devices offers a feasible solution to bridge this gap. Simultaneously, the artificial vision for perceiving and storing ultraviolet (UV) images is particularly important because UV light carries information imperceptible to the naked eye. This study introduces a multi-level UV optoelectronic memory based on gallium nitride (GaN), seamlessly integrating UV sensing and memory functions within a single device. The embedded SiO2 side-gates around source and drain regions effectively extend the lifetime of photo-generated carriers, enabling dual-mode storage of UV signals in terms of threshold voltage and ON-state current. The optoelectronic memory demonstrates excellent robustness with the retention time exceeding 4 × 104 s and programming/erasing cycles surpassing 1 × 105. Adjusting the gate voltage achieves five distinct storage states, each characterized by excellent retention, and efficiently modulates erasure times for rapid erasure. Furthermore, the integration of the GaN optoelectronic memory array successfully captures and stably stores specific UV images for over 7 days. The study marks a significant stride in optoelectronic memories, showcasing their potential in applications requiring prolonged retention.

2D Semiconductor‐Based Optoelectronics for Artificial Vision

AbstractArtificial retina technologies aim to restore visual function by mimicking the natural processes of the eye. These biomimetic devices can convert light into electrical signals that the brain can interpret as visual information, bypassing damaged or non‐functional cells of the eye. To be effective, these devices should possess high sensitivity to light, high spatial resolution, biocompatibility, power efficiency, and so on. Recently, 2D semiconductor materials have appeared as a promising candidate for artificial retinal devices, thanks to their excellent optoelectronic properties, ultrathin body, flexible nature, and biocompatibility. Here the recent developments in the field of 2D semiconductors‐based optoelectronics for visual function recovery are reviewed and their potential applications are discussed. The photodetector, optoelectronic memory, and artificial synapse mechanisms and devices utilized in artificial systems that are based on 2D semiconductor materials are summarized. Additionally, a range of application scenarios for devices that are inspired by retinal cells and vision systems is explored. Finally, it is concluded with an overview of the critical technical challenges and strategies that must be addressed for the successful development of artificial retina technologies. It also highlights the potential for new applications in other fields, such as robotics and artificial intelligence.

Artificial visual perception neural system using a solution-processable MoS2-based in-memory light sensor

Optoelectronic devices are advantageous in in-memory light sensing for visual information processing, recognition, and storage in an energy-efficient manner. Recently, in-memory light sensors have been proposed to improve the energy, area, and time efficiencies of neuromorphic computing systems. This study is primarily focused on the development of a single sensing-storage-processing node based on a two-terminal solution-processable MoS2 metal–oxide–semiconductor (MOS) charge-trapping memory structure—the basic structure for charge-coupled devices (CCD)—and showing its suitability for in-memory light sensing and artificial visual perception. The memory window of the device increased from 2.8 V to more than 6 V when the device was irradiated with optical lights of different wavelengths during the program operation. Furthermore, the charge retention capability of the device at a high temperature (100 °C) was enhanced from 36 to 64% when exposed to a light wavelength of 400 nm. The larger shift in the threshold voltage with an increasing operating voltage confirmed that more charges were trapped at the Al2O3/MoS2 interface and in the MoS2 layer. A small convolutional neural network was proposed to measure the optical sensing and electrical programming abilities of the device. The array simulation received optical images transmitted using a blue light wavelength and performed inference computation to process and recognize the images with 91% accuracy. This study is a significant step toward the development of optoelectronic MOS memory devices for neuromorphic visual perception, adaptive parallel processing networks for in-memory light sensing, and smart CCD cameras with artificial visual perception capabilities.

Giant Switchable Persistent Photoconductivity in Soft Chemistry Reduced SrTiO3

AbstractHigh tunability of photoconductivity is highly desired for applications in optical memories, sensors, and bioelectronics. Recently, room temperature persistent photoconductivity (PPC) in SrTiO3 (STO) has been revealed and has attracted great attention. However, reversible switching of the PPC in STO with a large on/off ratio remains challenging to date. Here, a giant switchable PPC in soft chemistry reduced STO is reported. An initial insulator‐to‐metal transition with on/off ratio up to 7 orders of magnitude is observed and about 5 orders of magnitude transition is found to be reversible. Via nuclear magnetic resonance measurements, it is uncovered that such unusual PPC is driven by the generation of excess carriers accompanied with a configuration evolution of the incorporated hydrogen from hydridic HO+ to protic Hi+ upon illumination. The work demonstrates giant switchable PPC transition in soft chemistry reduced perovskite oxides, providing a new platform for pursuing high performance sensors and nonvolatile optoelectronic memory devices.

Optoelectronic memory in 2D MoS2 field effect transistor

2D layered materials with their tunable bandgap and unique crystal structures are excellent candidates for 2D optoelectronic memories. In this work, we present a simple approach for the realization of a nonvolatile optoelectronic memory device based on a MoS2 transistor with light induced charge storage capability. The MoS2 transistor shows 108 on/off current ratio and hysteresis width modulation by air pressure under normal and quiet measurement conditions. Moreover, the device shows persistent photoconductivity and exhibits excellent photo responsive memory performance with a current switching ratio of two orders of magnitude and a photocurrent that increases linearly with the incident light power. We show that a combination of gate voltage and light can be used to control the transistor current and increase the memory window by two orders of magnitude. The obtained results are a significant step toward the improvement of optoelectronic devices, showing that the combination of gate voltage and light can enable a multilevel memory device.

Organic-inorganic FAPbBr3 perovskite based flexible optoelectronic memory device for light-induced multi level resistive switching application

Herein, we report the multilevel resistive switching memory performance of the fabricated Al/FAPbBr3/ITO structure. The device exhibited bipolar RS behaviour with excellent electrical performances such as no forming process, low operating voltages, low power consumption, good stability and a high ON/OFF ratio (∼103). The device also showed the multilevel cell capability which was achieved by delicate control over compliance current and the stopping voltage. Owing to the rising demand for flexible devices, the constancy and uniformity of the RS behaviour of our fabricated device with mechanical robustness were confirmed by examining the memory performance of the device under various bending conditions. Besides, the device exhibited photo response-ability for which the RS effect can be enhanced by light irradiation. This investigation may be explored in the data encoding process with a certain wavelength of incident light. Intrinsic phenomena of RS effect have been explained by the growth and rupture of electric field-induced reproducible conducting filaments formed by halide vacancies as well as active Al atoms. This work provides a way for exploring the organic-inorganic hybrid perovskites nanocrystals for the development of next-generation low power consumption, light-assisted, flexible volatile memory devices.

Anisotropy and thermal properties in GeTe semiconductor by Raman analysis.

Low-symmetric GeTe semiconductors have attracted wide-ranging attention due to their excellent optical and thermal properties, but only a few research studies are available on their in-plane optical anisotropic nature that is crucial for their applications in optoelectronic and thermoelectric devices. Here, we investigate the optical interactions of anisotropy in GeTe using polarization-resolved Raman spectroscopy and first-principles calculations. After determining both armchair and zigzag directions in GeTe crystals by transmission electron microscopy, we found that the Raman intensity of the two main vibrational modes had a strong in-plane anisotropic nature; the one at ∼88.1 cm-1 can be used to determine the crystal orientation, and the other at ∼124.6 cm-1 can reveal a series of temperature-dependent phase transitions. These results provide a general approach for the investigation of the anisotropy of light-matter interactions in low-symmetric layered materials, benefiting the design and application of optoelectronic, anisotropic thermoelectric, and phase-transition memory devices based on bulk GeTe.

Covalent Functionalization of Black Phosphorus Nanosheets with Photochromic Polymer for Transient Optoelectronic Memory Devices

AbstractHow to erase sensitive data stored on memory devices quickly in an emergency has become a critical issue that needs to be addressed. Using BP‐BIBB as a key template for atom transfer radical polymerization, which is prepared by the reaction of p‐hydroxyphenyl‐functionalized black phosphorous nanosheets (C6H4OH‐BP) with 2‐bromoisobutyryl bromide (BIBB), a highly soluble poly[4‐(4‐(3,3,4,4,5,5‐hexafluoro‐2‐(2‐methyl‐5‐phenylthiophen‐3‐yl)cyclopent‐1‐en‐1‐yl)‐5‐methylthiophen‐2‐yl)phenyl methacrylate] (PHPM)‐covalently grafted BP derivative, hereafter abbreviated as PHPM‐g‐BP, is synthesized in situ. PHPM is a typical photochromic polymer that emits blue light under UV irradiation, while showing pale yellow under visible light illumination. By using PHPM‐g‐BP as an active layer, an as‐fabricated transient optoelectronic memory device exhibits a nonvolatile rewritable memory effect under UV irradiation, with an ON/OFF current ratio of 3.6 × 103, a turn‐on voltage of 1.60 V, and a turn‐off voltage of −1.41 V. Upon visible light illumination for 10 s, all the information stored in the device is erased quickly. The observed device current drops down from 10−3 to 10−8 A rapidly.

UV light controlled optoelectronic memory based on WSe2 and hBN encapsulated graphene heterostructures

In recent times, 2D materials-based heterostructures are extensively studied for fabricating different nanodevices. Among these materials, transition metal dichalcogenides (TMDC), hexagonal boron nitride (hBN), and graphene (Gr) are widely used in these devices. Optoelectronic memory devices based on 2D materials are among the recently studied devices for structural flexibility and device size miniaturization. In this study, a non-volatile optoelectronic memory device has been fabricated using tungsten diselenide (WSe2), and hBN-encapsulated Gr-based heterostructures. This device can be easily controlled with UV light and an electric field. Two points were focused on in this study; first, the doping state was changed partially i.e., by illuminating a part of the WSe2 layer by UV light and a p-n homo-junction was created. This phenomenon occurs due to the unique structure of Wse2/hBN and the p-n junction could be created in one layer. Secondly, Gr has been used as a floating gate to increase the retention time as Gr is acting as a charge trapping layer. The retention time is further increased due to the thickness of hBN because the defect states keep increasing the charges together.

An All-in-One Bioinspired Neural Network.

In spite of recent advancements in artificial neural networks (ANNs), the energy efficiency, multifunctionality, adaptability, and integrated nature of biological neural networks remain largely unimitated by hardware neuromorphic computing systems. Here, we exploit optoelectronic, computing, and programmable memory devices based on emerging two-dimensional (2D) layered materials such as MoS2 to demonstrate a monolithically integrated, multipixel, and "all-in-one" bioinspired neural network (BNN) capable of sensing, encoding, learning, forgetting, and inferring at minuscule energy expenditure. We also demonstrate learning adaptability and simulate learning challenges under specific synaptic conditions to mimic biological learning. Our findings highlight the potential of in-memory computing and sensing based on emerging 2D materials, devices, and integrated circuits to not only overcome the bottleneck of von Neumann computing in conventional CMOS designs but also to aid in eliminating the peripheral components necessary for competing technologies such as memristors.

High hysteresis and distinctive optoelectronic memory effect for ambipolar thin-film transistors using a conjugated polymer having donor–acceptor heterojunction

π-Conjugated p-type PBDB-T and n-type N2200 macromolecular units are alternatively bonded to generate ambipolar copolymer (i.e. P(BDBT-co-N2200)) for achieving donor-acceptor (D-A) heterojunction. From the laser confocal microscope photoluminescence (PL) spectra of the P(BDBT-co-N2200) copolymer, PL characteristic peaks of PBDB-T and N2200 are simultaneously observed at 695, 760, and 860 nm. The thin-film transistors (TFTs) using P(BDBT-co-N2200) copolymer show ambipolar transistor characteristics originating from the coexistence of p-type and n-type semiconducting macromolecular units. Interestingly, a high hysteresis is observed in the transfer and output characteristics of the TFTs because of the interface traps and near-interface bulk traps. Under light irradiation, distinctive photocurrents and hysteresis are observed, suggesting the optically mediated charge release and photogating effects caused by trap states. Charge trapping with a high hysteresis and photoconduction with the photogating effect of the P(BDBT-co-N2200)-based ambipolar TFTs induce stable and repeatable writing, reading, and erasing operations. The optoelectronic memory devices using the P(BDBT-co-N2200)-based ambipolar TFTs are realized with the merit of a long charge storage time of 40 s. The π-conjugated copolymer, P(BDBT-co-N2200) exhibiting D–A heterojunction, can be applied to multifunctional devices, such as photoresponsive ambipolar transistors and optoelectronic memory devices, for image sensing and data storage. Optoelectronic memory devices using the ambipolar thin-film transistors of π-conjugated P(BDBT-co-N2200) copolymer having donor-acceptor heterojunction are realized with the merit of a long charge storage time. • π-Conjugated p-type PBDB-T and n-type N2200 macromolecular units were alternatively bonded to generate ambipolar copolymer with donor-acceptor (D-A) heterojunction. • The P(BDBT-co-N2200)-based TFT showed photoresponsive ambipolar transistor characteristics. • The P(BDBT-co-N2200)-based ambipolar TFTs were successfully operated as optoelectronic memory devices with repeatable writing, reading, and erasing processes. • Readout current charges were constant regardless of the variation in waiting times and linearly increased with increasing light exposure time.

Controllable volatile-to-nonvolatile memristive switching in single-crystal lead-free double perovskite with ultralow switching electric field

All-inorganic lead-free double perovskite offers a potential material platform for electronic or optoelectronic memory devices owing to its ionic migration-based electrical transport, high photosensitivity, low toxicity, and environmental stability. However, the commonly used polycrystalline perovskite films severely restrict device performance. Herein, we demonstrate a high-performance memristor based on single-crystal double perovskite Cs2AgBiBr6 with an ultralow switching electric field of 6.67 × 104 V m−1 and a high current on/off ratio of 107. Remarkably, the resistive switching of Cs2AgBiBr6 is found to be thickness-dependent, which evolves from volatile threshold to nonvolatile resistance switching with the crystal thickness from 100 to 800 nm. Elemental analysis reveals that the formation of conductive channels in Cs2AgBiBr6 is associated with the migration of Br vacancies with low activation energy. In addition, the formed conductive channels can be annihilated by light illumination with controlled wavelength and intensity, which leads to the realization of optoelectronic memories with separate electrical-writing and optical-erasing processes. Our findings provide deep insights into the ionic migration in single-crystal perovskite and pave the way for its future application in electronic and optoelectronic memory devices.

Distinctive Photo‐Induced Memory Effect in Heterostructure of 2D Van Der Waals Materials and Lanthanum Aluminate

The role of interface in atomically thin two-dimensional (2D) van der Waals materials is crucial in their novel optoelectronic properties. This study reports a mixed-dimensional optoelectronic memory device based on a heterostructure comprising 2D monolayer molybdenum disulfide and bulk lanthanum aluminate. The reversible photo-induced doping process accompanying persistent photocurrent phenomena is controlled using a gate voltage which is applied across the lanthanum aluminate dielectric substrate under light illumination. The extremely low gate electric field (<2 × 103 V cm−1) and the opposite gate voltage polarity compared with the general photo-doping cases indicate that the conventional band bending mechanism cannot be applied to this optoelectronic device. This distinctive photo-induced memory concept is validated in lanthanum aluminate-based heterostructures with other 2D materials such as graphene and tungsten diselenide. It is postulated that the heterostructure of atomically thin van der Waals materials that are in contact with various functional oxides provides a novel platform for next-generation optoelectronic devices.

An insight into structural, electronic and optical characteristics of Mo1-xMxO3 (M = Zr, Y, ZrY) for the formation of conducting filaments in optoelectronic memory devices: A first principles study

In the present work, we have theoretically investigated the structural, electronic and optical characteristics of Mo1−xMxO3 (M = Zr, Y, co-doped (ZrY)) for Optoelectronic Resistive Random-Access Memory (ORRAM) devices and associated applications. Density functional theory within Heyd-Scuseria-Ernzerhof (HSE06) functional has been employed to better estimate optoelectronic parameters. The structural outcomes, findings of the energy band structure, spin resolved total density of states (TDOS), three dimensional iso-surface electron charge density, electron localization function and Bader charge analysis unveil thatMo1−x(ZrY)xO3 is comparatively more suitable composite with enhanced charge conductance for ORRAM devices. The partial density of states (PDOS) and Bader charge analysis results reveals that noticeable orbital contribution of the constituent atoms mainly in increasing conductivity through hybridization. Formation energy and phonon calculations confirmed that studied structures are stable. The photo absorption behavior shows that Mo1−x(ZrY)xO3 can absorb a broad electromagnetic radiations wavelength range from ultraviolet (UV) to infrared (IR) coherent with the charge conduction property which has been found a most fitted candidate for ORRAM and associated applications.

Organic-Inorganic Fapbbr3 Perovskite Based Flexible Optoelectronic Memory Device for Light-Induced Multi Level Resistive Switching Application

Organic-Inorganic Fapbbr3 Perovskite Based Flexible Optoelectronic Memory Device for Light-Induced Multi Level Resistive Switching Application

MemSor: Emergence of the In‐Memory Sensing Technology for the Digital Transformation

Since Moore's law is facing several bottlenecks, electron devices are currently developing toward the trend of “More than Moore” which is based on functional diversification in terms of sensing, storage, and processing of information. This multifunctionality is thought of as another form of miniaturization of the electronic devices, where noncomputing devices are merged with digital ones, leading to faster and more energy‐efficient processing of data. Complementary to the in‐memory computing and in‐sensor computing approaches, herein, the concept of in‐memory sensing is examined in which the roles of both analog sensors and digital memory devices are integrated and achieved using a single “MemSor” device. The demonstrated optoelectronic memory devices are first reviewed, which can sense and store optical signals, and next, perspectives on the potential integration of other sensing capabilities such as pressure and gas are provided. The implementation of the in‐memory sensing technology in future energy‐efficient and scaled down electronic systems is also discussed. The challenges in the field are finally analyzed and potential solutions for the implementation of the merged sensing and storage functions using advanced manufacturing technologies are presented.

Copper (II) Phthalocyanine (CuPc) Based Optoelectronic Memory Device with Multilevel Resistive Switching for Neuromorphic Application

AbstractThe 1D nanotubular organic semiconductor, copper (II) phthalocyanine (CuPc), embedded in poly‐methyl methacrylate (PMMA) is employed for the first time for multilevel resistive switching (RS) and neuromorphic applications. Single–double bonded planar CuPc tubes are synthesized via simple solvothermal methods and dispersed in the PMMA solution with different weight concentrations. The composite sample is deposited on an ITO coated transparent, flexible and conducting PET substrate to form Ag/CuPc@PMMA/ ITO device. I–V characterizations of the cell reveal a formation free, bipolar, non‐volatile, multilevel RS effect. The device shows a significantly large resistance ON/OFF ratio of 104, low threshold operating voltage (&lt;2 V), large endurance (&gt;104 cycles) and long retention time (&gt;104 s) at room temperature. The multilevel resistive states are induced by visible light illumination. Based on the experimental data, the conduction mechanism of this type of RS memory device under the optical and the electrical impulse is attributed by the charge trapping and detrapping methods. The synaptic short‐term and long‐term potentiation are also studied on the device during the identical pulse training process. The proposed RS active material is a potential candidate for future artificial neural systems that simulate characteristics of human memory.