Photomemory Devices Research Articles

EFFECT OF DIFFERENT UV EXPOSURE ENERGY ON POLYIMIDE-BASED NONVOLATILE RESISTIVE PHOTOMEMORY DEVICE

Recently, many researchers pay attractive attention to organic memory technology. Polyimide film was used as the resistive switching layer of nonvolatile photomemory in this study. In order to improve the performance of the device, different wavelengths of Ultraviolet (UV) light were used to operate the device, and its impact on the polyimide film was discussed. In this paper, three different UV light bands, UVA, UVB, and UVC, are used to switch devices between low resistance state (LRS) and high resistance state (HRS). It can be seen from the results that all three kinds of energies of UV light can transform the polyimide film from HRS to LRS successfully. According to the data, after 1s of UVB irradiation, the LRS current of polyimide-based photomemory device is the largest, and the data retention ability is also the best, the second is to irradiate UVA, and the last is to irradiate UVC. The results of the optical properties and electrical properties are coincidental. Therefore, different UV energies can affect this photomemory device.

Photoinduced Nonvolatile Memory Transistor Based on Lead-Free Perovskite Incorporating Fused π-Conjugated Organic Ligands.

Perovskites field-effect transistors (PeFETs) have been intensively investigated for their application in detector and synapse. However, synapse based on PeFETs is still very difficult to integrate excellent charge carrier transporting ability, photosensitivity, and nonvolatile memory effects into one device, which is very important for developing bionic electronic devices and edge computing. Here, two-dimensional (2D) perovskites are synthesized by incorporating fused π-conjugated pyrene-O-ethyl-ammonium (POE) ligands and a systematic study is conducted to obtain enhanced performance and reliable PeFETs. The optimized (POE)2 SnI4 transistors display the hole mobility over 0.3cm2 V-1 s-1 , high repeatability, and operational stability. Meanwhile, the derived photo memory devices show remarkable photoresponse, with a switching ratio higher than 105 , high visible light responsivity (>4×104 AW-1 ), and stable storage-erase cycles, as well as competitive retention performance (104 s). The photoinduced memory behavior can be benefiting from the insulating nature of quantum-well in 2D perovskite under dark and its excellent light sensitivity. The excellent photo memory behaviors have been maintained after 40 days in a N2 atmosphere. Finally, a 2D perovskite-only transistors with a multi-level memory behavior (16 distinct states) is described by controlling incident light pulse. This work provides broader attention toward 2D perovskite and optoelectronic application.

Floating gate photo-memory devices based on van der Waals heterostructures for neuromorphic image recognition

Two-dimensional (2D) materials with reconfigurable properties show potential in neuromorphic hardware applications. However, most 2D materials-based neuromorphic hardware is volatile, which needs large energy to accomplish perception functions. Here, we report on nonvolatile floating gate photo-memory devices based on ReS2/h-BN/SnS2 van der Waals heterostructures. The devices exhibit a large memory window of ∼60 V, a high program/erase current ratio of ∼107 with excellent retention characteristics, a low off-state current of 7.4 × 10−13 A, and a high detectivity of 1.98 × 1013 cm Hz1/2 W−1, allowing for multi-bit information storage. For the multi-level storage capacity, 27 photo-memory states are obtained by pulsed laser illumination. Moreover, a neuromorphic computing network is also constructed based on the photo-memory devices with a maximum recognition accuracy of up to 90%. This work paves the way for miniaturization and high-density integration of future optoelectronics for neuromorphic hardware applications.

Concept of Photoactive Invisible Inks toward Ultralow‐Cost Fabrication of Transistor Photomemories

AbstractFinding the outperforming photoactive charge trapping materials for a new‐trending transistor photomemory application is labor intensive, costly reagents and solvents, and not to mention, inefficient energy and time consumption. In this work, costless organic‐based inks are introduced as a novel photoactive charge storage material that is inspired by high fluorescent ink of cheap invisible pens when exposed to ultraviolet light. The pure powder inks of invisible pens with bright red and greenish‐yellow emission are selected. The estimated usage costs about $0.003 cm−2, confirming its ultralow‐budget material. The pentacene‐based organic field‐effect transistor memory scheme is employed to evaluate the memory behaviors. These invisible‐ink‐based charge storage layers endow a transistor memory device with photoinduced recovery. Interestingly, by conducting the photoassisted operation on the same device, its threshold voltage shifts toward more positive direction, resulting in broaden memory window and faster device operations. On top of that, invisible‐ink‐based transistor photomemory demonstrates the well‐defined and feasible multibit memory cell for the next‐generation storage media. As a result, the employment of commercial invisible inks as a cheapest photoactive charge trapping material can favor the advancement of transistor photomemory devices and related functional applications.

Polyimide-based ultraviolet-operated nonvolatile photomemory device

Organic nonvolatile photomemory devices have drawn considerable attention in the field of optical computing. However, most organic nonvolatile photomemory devices use a charge-trap-type architecture that is complex and difficult to miniaturize. This paper proposes a nonvolatile polyimide (PI) resistive photomemory device with a simple metal–PI–metal configuration; its resistance can be altered using pulsed ultraviolet (UV) irradiation and can be maintained at the altered level even after irradiation has ceased. The resistance can also be returned to the initial state by subsequent irradiation with UV light. The memory window is around 7 order of magnitude. Fourier-transform infrared spectroscopy and UV–visible/near-infrared spectroscopy demonstrated that UV irradiation caused a high-energy-gap (Eg) aromatic form of PI to transform into low-Eg quinoid form, prompting the dominant conduction mechanism of the photomemory device to change from hopping conduction to ohmic conduction. A model characterizing the PI-based photomemory device was also developed and is discussed herein.

Carrier channeling and funneling through the C60 self-assembled monolayer/zinc oxide colloidal quantum Dot/MAPbI3 perovskite functional interfaces

We demonstrated channeling and funneling of charge carriers through functional interfaces with a configuration of C60 self-assembled monolayer (SAM)/zinc oxide (ZnO) colloidal quantum dots (CQDs)/Ag nanoparticles (NPs)/MAPbI3. The combination of the localized surface plasmon-resonance (LSPR) effect and the electron accepting capability of the C60 SAM enabled the funneling of carriers under illumination. Photoinduced charge transfer is facilitated by the presence of ZnO CQDs, through which the photoexcited carriers in MAPbI3 is channeled into the C60 SAM with a large diffusion length. This demonstrates that LSPR-induced charge retention at the interface is potentially applicable to photomemory devices.

High‐Performance Non‐Volatile Flash Photomemory via Highly Oriented Quasi‐2D Perovskite

AbstractSolution‐processable organic–inorganic hybrid perovskite materials have been applied to a variety of optoelectronic devices due to its long exciton lifetime and small binding energy. It has emerged as promising front‐runners for next‐generation non‐volatile flash photomemory devices. However, the effect of crystal orientation of perovskite on the performance of photomemory still has not fully developed. Herein, non‐volatile flash photomemory with quasi‐2D perovskite/polystyrene‐block‐poly(ethylene oxide) (PS‐b‐PEO) as photoactive floating‐gate and p‐type semiconductor poly(3‐hexylthiophene‐2,5‐diyl) (P3HT) as the chare‐transporting layer is successfully demonstrated. By adding phenylethylammonium bromide (PEABr) in formamidinium lead bromide perovskite (FAPbBr3), the crystal orientation of quasi‐2D perovskite is highly improved, which results in raised charge transfer efficiency from 76% to 90% compared to the pure FAPbBr3. Furthermore, ON/OFF current ratio of 104, low photo‐programming time of 5 ms under light intensity of 0.85 mW cm−2, charge transfer rate of 0.063 ns−1, and data storage capacity of over 7 bits (128 levels) in one cell can be achieved. In addition, the correlation between photo‐responsive current and photoluminescence (PL) is first examined by in operando PL measurement, which provides a new platform to explore the charge transfer process in photomemory.

Liquid Crystalline Rylenediimides with Highly Order Smectic Layer Structure as a Floating Gate for Multiband Photoresponding Photonic Transistor Memory

AbstractWith the growing demands of light fidelity technology, photonic transistor memory has gained considerable attention for next‐generation optoelectronic devices. In this work, alkylated rylenediimides of 2,9‐diphenethylanthra[2,1,9‐def:6,5,10‐d“e”f]diisoquinoline‐1,3,8,10(2H,9H)‐tetraone (C8‐PDI) and 2,7‐dioctylbenzo[lmn][3,8]phenanthroline‐1,3,6,8(2H,7H)‐tetraone (C8‐NDI), and pyromellitic diimide of 2,6‐dioctylpyrrolo[3,4‐f]isoindole‐1,3,5,7(2H,6H)‐tetraone (C8‐PMDI) have been used as floating gate electrets in the photonic field‐effect transistor‐type memory. The structure‐optics‐performance relationship of these rod‐like molecules has been systematically studied, and the memory device exhibited a decent response to photowriting and electrical erasing processes, owing to the 3D ordered smectic layer structure and brickwork stacking. Therefore, an evenly distributed photogating moiety, efficient exciton dissociation associated with decent carrier tunneling and charge trapping can be obtained. Among them, the sought‐after C8‐NDI presents favorable energy level alignment, multiband photoresponding, and an optimal block ratio. The fabricated photonic memory with C8‐NDI electret presented a remarkable memory switchability with a memory ratio of 104 and a stable memory ratio of 105 over 10,000 s. To the best of knowledge, this is the first work to utilize rylenediimides based liquid crystals as an efficient charge blocking electret, and these findings open an avenue for designing rod‐like molecules with highly ordered liquid crystalline properties in the ultrafast photomemory devices.

Improving the performance of photonic transistor memory devices using conjugated block copolymers as a floating gate

We report the synthesis, morphology and photo-memory device applications of a block copolymer (BCP) consisting of poly(9,9-dioctylfluorene) (PFO) and polystyrene (PS).

Nonvolatile Multilevel Photomemory Based on Lead-Free Double Perovskite Cs2AgBiBr6 Nanocrystals Wrapped Within SiO2 as a Charge Trapping Layer.

Floating gate transistor photomemory (FGTPM) has been regarded as one of the most prospective nonvolatile photomemory devices because of its compatibility with transistor-based circuits, nondestructive reading, and multilevel storage. Until now, owing to the excellent photoelectric properties, lead-based perovskite nanocrystals (PNCs) have been applied in most of the perovskite-based FGTPM devices and embedded in the polymer matrix as the charge trapping layer. However, the polymer matrix and its solvent would degrade the structure of the PNCs, resulting in the loss of their unique photoresponse ability. In addition, lead-based perovskites have environmental unfriendliness and poor stability. Hence, a novel nonvolatile FGTPM based on oligomeric silica (OS) wrapped lead-free double perovskite Cs2AgBiBr6 NCs was demonstrated for the first time. Acting synchronously as the protection layer for the discrete Cs2AgBiBr6 NCs and charge tunneling layer for the FGTPM device, the OS layer can achieve controllable thickness by adjusting the process parameters, leading to an adjustment of storage properties with a larger memory window (58 V). Owing to the excellent photoresponse ability of the Cs2AgBiBr6@OS composite layer, the FGTPM device exhibited high-performance with repeatable multilevel nonvolatile photomemory and precise photoresponse ability of wavelength/time/power-dependent photoirradiation without extra gate biasing.

Two-Dimensional Cs2Pb(SCN)2Br2-Based Photomemory Devices Showing a Photoinduced Recovery Behavior and an Unusual Fully Optically Driven Memory Behavior

The rapid development of Internet of Things and big data has made the conventional storage devices face the need of reforming. Rather than using electrical pulses to store data in one of two states, photomemory exploiting optical stimulation to store light information emerges as a revolutionary candidate for the optoelectronic community. However, fully optically-driven photomemory with fast data transmission speed and outstanding energy saving capability suffers from less exploration. Herein, a transistor-type photomemory using a 2D Cs2Pb(SCN)2Br2/polymer hybrid floating gate is explored and three host polymers, polystyrene (PS), poly(4-vinylphenol) (PVPh), and polyvinylpyrrolidone (PVP), are investigated to understand the relationship between polymer matrix selection and memory performance. All devices show a photo-induced recovery memory behavior but with two distinctly different photomemory behaviors. Besides the demonstration of a regular non-volatile photomemory showing a high on/off ratio of > 106 over 104 s, an unusual fully optically-driven memory behavior is intriguingly accomplished in the Cs2Pb(SCN)2Br2/PVP photomemory. Using white light serving as the driver of programming and blue laser acting as the main performer of erasing, this device can be switched between two distinguishable states and possesses acceptable data discriminability as evidenced by its fully optically-driven writing (programing)-reading-erasing-reading (WRER) switching function that shows an on/off current ratio of 103. This study not only presents the first 2D perovskite-based photomemory but also shows a novel fully optically-driven memory that has been rarely reported in the literature.

Artificial visual memory device based on a photo-memorizing composite and one-step manufacturing

A new way of thinking about the physical behavior of polymers is demonstrated to design a multi-functional material for artificial photo memory devices, realizing light perception and memory itself instead of integrating distinct electronic elements.

An in situ rewritable electrically-erasable photo-memory device for terahertz waves.

A terahertz read-only in situ electrically-erasable rewritable photo-memory device based on a perovskite:Ag (perovskite with Ag nanoparticles added)/SnO2/PEDOT:PSS hetero-junction structure is reported. Under low optical excitation, considerable terahertz amplitude modulation in a perovskite:Ag/PEDOT:PSS hybrid structure was achieved. When a SnO2 nanoparticle film was inserted between the perovskite and PEDOT:PSS layer, the attenuation of the terahertz signal was weaker than that of the perovskite:Ag/PEDOT:PSS hybrid structure; however, the SnO2 nanoparticle film considerably prolonged the recovery time of the modulated terahertz wave in air after photo-excitation was stopped. In addition, when bias voltages were applied to the perovskite:Ag/PEDOT:PSS and perovskite:Ag/SnO2/PEDOT:PSS hybrid structures, respectively, the terahertz signals recovered rapidly for both structures. Consequently, the photo-memory functionality was achieved based on a perovskite:Ag/SnO2/PEDOT:PSS hybrid structure with an in situ method for erasing stored information.

Nonvolatile Rewritable Photomemory Arrays Based on Reversible Phase‐Change Perovskite for Optical Information Storage

AbstractThe high transmission speed of optical signals and their application in optical computation have created a growing demand for photon‐programmed memory devices. Rather than using electrical pulses to store data in one of two states, the photomemory (PM) devices exploit the optical stimulation to store the light information. In this work, the application of a nonvolatile rewritable PM array using the photochromic inorganic perovskite CsPbIBr2 grown by a vapor‐deposition process is demonstrated. Reversible phase transitions between orthorhombic (δ) and cubic (α) phases are achieved in CsPbIBr2 films through laser‐induced heat and moisture exposure. The PM pixels in an optically absorbing perovskite phase exhibit ≈50‐fold photoresponsivity as large as those in a transparent‐colored non‐perovskite phase. Storing optical data are achieved by heating pixels through a near‐infrared laser, while moisture exposure is used to erase the stored information. The nonvolatile PM array exhibits great write‐read‐erase cycle endurance and data retention capability without obvious performance degradation after storage in air for one week. This work demonstrates the promising application of vapor‐deposited inorganic perovskite for optical information storage and the unique potential of them for use in optical switches, tunable metasurfaces, and many other applications.

Microfluidics-Assisted Synthesis of Cross-Linked Colloidosomes with Multisensitive Behaviors: A Potential Platform for Photo Memory Device and Blue-Light-Triggered Release Vehicle

Uniformly sized and cross-linked colloidosomes were prepared via microfluidic emulsification combined with a post-cross-linking reaction between NH2/ruthenium dual-functionalized microgels and poly(N-isopropylacrylamide)-r-(N-acryloxysuccinimide)-based polymers. When mixed with catalyst-free Belousov–Zhabotinsky reaction substrates, the colloidosomes first experienced decrease in size and then exhibited mechanical oscillations. In addition, the colloidosome behavior can be regulated using different types of light, which then displayed reversible deswelling/swelling cycles under alternating white light on/off stimuli, but only expanded and even ruptured under the stimulus of continuous blue light illumination. These multisensitive colloidosomes could be potentially applied in the fields of photo memory devices and blue light-triggered release vehicles.

Influence of polymeric electrets on the performance of derived hybrid perovskite-based photo-memory devices.

Organic-inorganic hybrid perovskite has become one of the most important photoactive materials owing to its intense light-harvesting property as well as its facile solution processability. Besides its photovoltaic applications, a novel photo-programmed transistor memory was recently developed based on the device architecture of a floating-gate transistor memory using a polymer/perovskite blend as the gate dielectric with the non-volatile memory characteristics of decent light response, applicable On/Off current ratio, and long retention time. In this study, we further clarify the influence of polymer matrix selection on the photo-response and memory properties of derived hybrid perovskite-based photo-memory devices. Four different host polymers, polystyrene (PS), poly(4-vinylphenol) (PVPh), poly(methyl methacrylate) (PMMA), and poly(methacrylic acid) (PMAA), were systematically investigated for comparison herein. This revealed that dissimilar chemical interactions existed between the host polymers and perovskite, resulting in the distinct memory behavior of the derived photo-memory devices, attributable to the different morphologies of the hybrid dielectric layers and the different sizes of the distributed perovskite nanoparticles (NPs). The photo-response behavior and the resultant On/Off current ratio increased as the size of the embedded perovskite NPs decreased, due to the enhanced photo-induced charge transfer across the dielectric/pentacene interface, benefiting from the better confinement effect of perovskite NPs in the polymer matrix. These results demonstrate the influence of perovskite NP aggregation at the dielectric/pentacene interface on the resultant memory behavior of the newly developed photo-memory device.

Photomodulated Hysteresis Behaviors in Perovskite Phototransistors with Ultra-Low Operating Voltage

Hysteresis behaviors in the current curves of perovskite-based devices have been widely observed and directly affect the device performances. Phototransistors with a channel material of CH3NH3PbI3 were fabricated, and they showed ambipolar transport characteristics with anticlockwise hysteresis hoops. Electric field and monochromatic light can narrow the wide hysteresis window from 2.1 V in the dark to only 0.5 V under the illumination. A photoexcited high-field-effect carrier mobility of 1.05 cm2 V–1 s–1 was achieved at a low-operating voltage. The responsivity and photosensitivity of the phototransistor were calculated to be 1 AW–1 and 18 000%, respectively. The modulation effect of voltage bias and monochromatic lights on such hysteresis behaviors has been demonstrated. By investigating the photo-sensitive carrier-transport characteristics in perovskite channel, the origin of hysteresis can be attributed to the charge-trapping process. This work also provides an effective approach to achieve a photocontrolled temporary erasing process as a data protection mechanism in future photomemory devices.

Modulating the Photochemistry of Bipyridylic Compounds by Symmetric Substitutions

A quantum electronic study of the effect of substituents on (2,2'-bipyridyl)-3,3'-diol and (2,2'-bipyridyl)-3,3'-diamine is presented. A large difference in the photochemical behavior between the original and the substituted selected systems is expected. For the sake of simplicity, the study is restricted to the symmetrically bi-substituted compounds: fluorine, the more electronegative atom and thus a strong σ-acceptor but also a weak π-donor group, and NO(2), a strong π-acceptor substituent. Among the large set of compounds studied, two receive special attention: 5,5'-dinitro-(2,2'-bipyridyl)-3,3'-diamine and 6,6'-difluoro-(2,2'-bipyridyl)-3,3'-diol. While in the former case the nitro substitution transforms (2,2'-bipyridyl)-3,3'-diamine, previously suggested to behave as a photomemory material, into a simple fluorescent species, the latter substitution turns (2,2'-bipyridyl)-3,3'-diol into a fresh new candidate for a photomemory device.

Bipyridyl Derivatives as Photomemory Devices: A Comparative Electronic‐Structure Study

The two isoelectronic bipyridyl derivatives [2,2'-bipyridyl]-3,3'-diamine (BP(NH(2))(2)) and [2,2'-bipyridyl]-3,3'-diol (BP(OH)(2)) are experimentally known to undergo very different excited-state double proton transfer processes that result in fluorescence quantum yields that differ by four orders of magnitude. Such differences have been theoretically explained in terms of topographical features in the potential energy surface and the likely presence of conical intersections. The hypothetical hybrid compound [2,2'-bipyridyl]-3-amin-3'-ol (BP(OH)(NH(2))) presents intermediate photochemical features of its "ancestors". In this report we analyze the photochemical properties of a whole family of "dark" (not fluorescent) states that can be accessed from each bipyridyl derivative upon irradiation of light of a given wavelength and their potential application as photomemory devices. In the light of our density functional theory (DFT), time-dependent DFT (TDDFT), and complete active space self-consistent field (CASSCF) calculations, BP(NH(2))(2) is the more likely candidate to become a photomemory device.

Development of Flexible Photo Sensor and Memory Devices Based on Organic Photo FET

ABSTRACTThe photo FET having a photosensitive insulator layer showed excellent photo-switching properties upon illuminating the gate dielectric layer, because the gate capacitor was rapidly charged up by providing a large amount of photo-generated charges in the dielectric layer to the gate capacitor. In this study, we have tried to give a memory function to the photo FET. Further, we have tried to fabricate flexible photo FETs by using only solution processes in order to utilize the photo FET as flexible photo sensor and photo memory devices. As a result, we have succeeded in observing the memory effect of the photo FET and the photo-switching behavior of the flexible photo FETs