Optoelectronic Memory Devices Research Articles

Optically Controlled Ferroelectric Nanodomains for Logic-in-Memory Photonic Devices With Simplified Structures

We report visible-light-induced ferroelectric nanodomain reversal in conductive van der Waals (vdW) ferroelectric $\alpha $ -In2Se3. We show its promising application in two-terminal optoelectronic memory devices. Compared to other vdW material-based optoelectronic memories, such a novel working prototype allows for the device operation confined within a single material channel bridging its two electrodes, which greatly reduces the complexities of device construction. In addition, using $\alpha $ -In2Se3 memory devices, we also demonstrate the universal OR and AND optical logic gates for logic-in-memory application. Our results provide a new avenue to design simplified structures of vdW material-based optoelectronic memories for dense device integration and next-generation computation.

SnS2/Si nanowire vertical heterostructure for high performance ultra-low power broadband photodetector with excellent detectivity

Nanoparticle–nanowire heterostructures provide a new platform for photodetection applications owing to their higher light absorption, large responsivity, and excellent separation efficiency of photogenerated electron–hole pairs. Herein, we report a SnS2/Si nanowire heterostructure photodetector with excellent optoelectronic properties. A high-quality SnS2/Si nanowire heterostructure was prepared by simply spin coating a wet chemically synthesized SnS2 on a vertically standing Si nanowire made by metal assisted chemical etching. The as-prepared SnS2/Si nanowire heterostructure exhibits a robust p–n junction with excellent photodetector characteristics. The photodetector based on the heterostructure shows a photo-responsivity of ∼3.8 A W−1, a specific detectivity up to ∼ 2 × 1014 Jones, and an on/off ratio up to ∼ 102 at 340 nm illumination wavelength with a significantly low optical power density of 53.75 nW/mm2 at zero bias (0 V). The photo-responsivity reached its maximum value of ∼102 A/W and detectivity of ∼1 × 1014 Jones at the same wavelength with an applied bias of −2 V. In addition, the heterostructure photodetector provides significantly good photodetector key parameters (responsivity ∼5.3 A/W, detectivity ∼ 7.5 × 1012 Jones, rise/decay time ∼0.4/0.4 s) at −2 V bias over a wide spectral range from 400 to 1100 nm. The Si nanowire and SnS2 nanoparticle heterostructure devices with an enhanced junction area open up an exciting field for novel non-toxic and environmental friendly broadband optical detection applications and optoelectronic memory devices with high responsivity, ultrahigh sensitivity, and self-sufficient functionality at low power consumption and low cost with ease of processing.

Heterojunction Channels in Oxide Semiconductors for Visible‐Blind Nonvolatile Optoelectronic Memories

AbstractOptoelectronic memory whose digital signals depend on electrical as well as optical sources have attracted tremendous attention recently due to their potential in applications, including optical communication systems, neural networks, and image correlation systems. In this work, metal‐oxide semiconductors for use as optical memory devices are accomplished through a heterojunction channel layer which acts as a quantum confinement architecture confining electrons to the front channel. Compared to conventional memories, which rely on electron injections that cause hot electron degradation, the proposed device is based on a floating body effect. After irradiation, photo‐excited carriers are separated under a lateral electrical field, and generated holes are left in the back channel, which facilitates data storage behavior. Beneficial characteristics include a memory window (≈4.6 V), a high on/off ratio (≈106), and low operating voltage (<20 V). Furthermore, photo‐excited carriers are only generated when irradiated by ultraviolet light, leading to a visible‐blind optical memory. A retention of more than 10 years and endurance cycle of more than 1000 cycles demonstrate its nonvolatile behaviors. This work provides a novel heterojunction channel layer architecture in disordered oxide semiconductors and provides a novel idea for a wide range of unipolar materials in future optoelectronic memory devices.

Programmable transition metal dichalcogenide homojunctions controlled by nonvolatile ferroelectric domains

Semiconductor devices based on two-dimensional (2D) transition metal dichalcogenides could help overcome the scaling limits of silicon complementary metal–oxide–semiconductor (CMOS) technology. However, the development of atomically thin devices requires approaches to control the carrier type in 2D semiconductors. Here, we show that a scanning probe can be used to control the polarization of ferroelectric polymers deposited on 2D transition metal dichalcogenides in order to define carrier injection and achieve p-type and n-type doping. The approach allows lateral p–n, n–p, n–n and p–p homojunctions to be arbitrarily formed and altered. Molybdenum ditelluride (MoTe2) p–n homojunction devices constructed using this method exhibit high current rectification ratios of 103 and good optoelectronic properties (responsivity of 1.5 A W−1). Unconventional nonvolatile memory devices are also built, such as an electrical writing and optical reading memory device, without the restrictions of physical source, drain or gate electrodes, and a quasi-nonvolatile memory with a refresh time of 100 s and a write/erase speed of 10 µs. By using a scanning probe to control the polarization of ferroelectric polymers deposited on the surface of two-dimensional transition metal dichalcogenides, optoelectronic and unconventional memory devices can be created based on lateral p–n junctions.

High-performance optoelectronic memory based on bilayer MoS2 grown by Au catalyst

We develop a high-performance nonvolatile MoS2-based optoelectronic memory device based on a MoS2 bilayer grown by a Au catalyst.

SnS2/Si vertical heterostructure for high-performance photodetection with large photocurrent and fast speed

It has attracted much research interest for the hot topic of photodetection application based on the two-dimensional (2D) heterostructures, owing to their higher light absorption and large separation efficiency of electron-hole pairs. However, the well-controlled growth with high-production and optoelectronic application of the heterostructures based on 2D materials still face great challenges. Photodetectors fabricated with the 2D SnS2/Si heterostructure have still not been well explored, although Si wafers have been proved to be an important substrate for novel optoelectronic application. Herein, the high-quality SnS2/Si heterostructure with large-size and uniform-thickness was prepared by using of a simple magnetron sputtering and post thermal annealing treatment in S atmosphere. The as-prepared SnS2/Si heterostructure exhibits the robust p-n contact and excellent diode rectification characteristic. The photodetector based on the heterostructure was then fabricated, which presents a reconfigurable switch behavior with a larger photocurrent up to 3.96 mA, a maximum detectivity of ~1011 Jones, a ultrafast response speed of 16 μs, and a broad bandwidth of 11.2 kHz. The highly crystalline and on-stoichiometry SnS2 films become a promising form factor to build the high-performance photodetectors. The SnS2/Si heterostructure devices open up an exciting field for novel optical detection application and optoelectronic memory devices.

Optically Switchable Memristors: A Route to Hierarchical Control in Artificial Intelligent Systems

Modulation of resistive switching memory by light opens the route to new optoelectronic devices that can be switched optically and read electronically. Applications include integrated circuits with memory elements switchable by light and optically reconfigurable and tunable synaptic circuits for neuromorphic computing applications and brain-inspired artificial intelligent systems. A novel polarization and wavelength-specific optoelectronic memory device is presented1 that can be controlled purely optically, electronically or by both. Optical or electronic modulation switches the device between low and high conducting states whilst modulation by both facilitates fine-tuning of the resistive memory properties and switching characteristics of the device. In biological synapses, the connection strength (plasticity) between two neurons is controlled by the ionic flow through the synaptic cleft and it is widely believed that the adaptation of synaptic weights enables biological systems to learn and function. Similarly, the conductance of a memristor depends on the history of the total charge that has travelled through it. A key feature of neuronal learning is habituation, whereby repeated stimuli strengthens the synaptic plasticity whilst a lack of stimuli results in weakening. Learning in biological systems also involves spike-timing-dependent plasticity (STDP). In STDP, learning the synaptic efficacy governing potentiation and depression is determined by the temporal order of pre-synaptic and post-synaptic spikes. Using our optical memristor device, we demonstrate optical control of synaptic potentiation and depression, optical switching between short and long-term memory and optical modulation of the synaptic efficacy via spike timing dependent plasticity. The work opens the route to dynamic patterning of memristor networks both spatially and temporally by light, thus allowing the development of new optically reconfigurable neural networks and adaptive electronic circuits.2 , 3 References Jaafar, A. H. et al. Reversible optical switching memristors with tunable STDP synaptic plasticity: a route to hierarchical control in artificial intelligent systems. Nanoscale 9, 17091 (2017).Kossifos, K. M., Antoniades, M. A., Georgiou, J., Jaafar, A. H. & Kemp, N. T. An Optically-Programmable Absorbing Metasurface. IEEE Int. Symp. Circuits Syst. (2018). doi:10.1109/ISCAS.2018.8351874Georgiou, J., Kossifos, K. M., Antoniades, M. A., Jaafar, A. H. & Kemp, N. T. Chua Mem-Components for Adaptive RF Metamaterials. IEEE Int. Symp. Circuits Syst. (2018). doi:10.1109/ISCAS.2018.8351852 Figure 1

Multilevel MoS2 Optical Memory with Photoresponsive Top Floating Gates.

Optoelectronic memory devices, whose states can be controlled using electrical optical signals, are receiving much attention for their potential applications in image sensing and parallel data transmission and processes. Here, we report MoS2-based devices with top floating gates of Au, graphene, and MoS2. Unlike conventional floating gate memory devices, our devices have the photoresponsive floating gate at the top, acting as a charge trapping layer. Stable and reliable switching with an on/off ratio of ∼106 and a retention time of >104 s is achieved by illumination with 405 nm light pulses as well as application of gate voltage pulses. However, upon illumination with 532 or 635 nm light pulses, multilevel optical memory effects are observed, which are dependent on the wavelength and the optical exposure dosage. In addition, compared to the device employing a graphene floating gate, the device with an MoS2 floating gate is more sensitive to light, suggesting that the multilevel optical memory properties originate from photoexcited carriers in the top floating gate and can be modulated by adjusting the top floating gate materials. The structure of the top floating gate may open up a new way to novel optoelectronic memory devices.

Deep UV-Vis photodetector based on ferroelectric/semiconductor heterojunction

Herein, we develop a ferroelectric/semiconducting heterostructure for deep UV-Vis photo detection as a new approach to enhance the photocurrent by introducing the polarization-dependent interfacial coupling effect. The deep UV-Vis photo detection efficiency of the heterostructure device is improved as compared with BaTiO3 and ZnO devices. The polarization-dependent interfacial coupling effect has been demonstrated by resistive switching and piezoresponse force microscopy study. The present work provides an efficient and novel way in designing highly efficient ferroelectric-based photodetector and new optoelectronic memory devices.

Synergistic effects of electrical and optical excitations on TiO2 resistive device**Project supported by the National Key Basic Research Project of China (Grant Nos. 2013CB921700 and 2016YFA0300600), the National Natural Science Foundation of China (Grant No. 11274375), and the Fund from Chinese Academy of Sciences (Grant No. KJCX2-YW-W24).

The influences of electrical and optical excitations on the conductivity characteristic are investigated in bulk and edge devices of ITO/TiO2/ITO structure. Driven by the electrical and optical stimuli independently, the conductivity relaxation behaviors of the pristine resistive state (PRS) are observed and ascribed to the electron trapping and the oxygen transport processes. For a resistive switching (RS) device, the conductance change under optical illumination is about two orders of magnitude smaller than the conductance change corresponding to the variation of background current due to the emergence of a great number of oxygen vacancies in the RS device. With the illumination being off, the conductance slowly decays, which suggests that the oxygen diffusion process dominates the conductance relaxation. The difference in conductance relaxation between the bulk and edge devices indicates that the oxygen exchange plays a critical role in the relaxation process of conductivity. The synergistic effects of both electrical and optical excitations on the RS devices could be used for novel applications in integrated optoelectronic memory devices.

Monolayer optical memory cells based on artificial trap-mediated charge storage and release

Monolayer transition metal dichalcogenides are considered to be promising candidates for flexible and transparent optoelectronics applications due to their direct bandgap and strong light-matter interactions. Although several monolayer-based photodetectors have been demonstrated, single-layered optical memory devices suitable for high-quality image sensing have received little attention. Here we report a concept for monolayer MoS2 optoelectronic memory devices using artificially-structured charge trap layers through the functionalization of the monolayer/dielectric interfaces, leading to localized electronic states that serve as a basis for electrically-induced charge trapping and optically-mediated charge release. Our devices exhibit excellent photo-responsive memory characteristics with a large linear dynamic range of ∼4,700 (73.4 dB) coupled with a low OFF-state current (<4 pA), and a long storage lifetime of over 104 s. In addition, the multi-level detection of up to 8 optical states is successfully demonstrated. These results represent a significant step toward the development of future monolayer optoelectronic memory devices.

Infrared Response and Optoelectronic Memory Device Fabrication Based on Epitaxial VO2 Film.

In this work, high-quality VO2 epitaxial films were prepared on high-conductivity n-GaN (0001) crystal substrates via an oxide molecular beam epitaxy method. By fabricating a two-terminal VO2/GaN film device, we observed that the infrared transmittance and resistance of VO2 films could be dynamically controlled by an external bias voltage. Based on the hysteretic switching effect of VO2 in infrared range, an optoelectronic memory device was achieved. This memory device was operated under the "electrical writing-optical reading" mode, which shows promising applications in VO2-based optoelectronic device in the future.

An optoelectronic resistive switching memory behavior of Ag/α-SnWO4/FTO device

It is known to all of us that the resistive switching memory behavior of metal-oxide-metal structure device is a fascinating candidate for next generation nonvolatile memories. In this work, α-SnWO4 nanoparticles were synthesized by a hydrothermal process. Further, a resistive switching memory device with Ag/α-SnWO4/FTO structure is demonstrated. The device presents an optoelectronic bipolar resistive switching memory behavior at room temperature. This study is useful for exploring multifunctional materials and their applications in optoelectronic nonvolatile memory devices.

Polarization-dependent interfacial coupling modulation of ferroelectric photovoltaic effect in PZT-ZnO heterostructures.

Recently, ferroelectric perovskite oxides have drawn much attention due to potential applications in the field of solar energy conversion. However, the power conversion efficiency of ferroelectric photovoltaic effect currently reported is far below the expectable value. One of the crucial problems lies in the two back-to-back Schottky barriers, which are formed at the ferroelectric-electrode interfaces and blocking most of photo-generated carriers to reach the outside circuit. Herein, we develop a new approach to enhance the ferroelectric photovoltaic effect by introducing the polarization-dependent interfacial coupling effect. Through inserting a semiconductor ZnO layer with spontaneous polarization into the ferroelectric ITO/PZT/Au film, a p-n junction with strong polarization-dependent interfacial coupling effect is formed. The power conversion efficiency of the heterostructure is improved by nearly two orders of magnitude and the polarization modulation ratio is increased about four times. It is demonstrated that the polarization-dependent interfacial coupling effect can give rise to a great change in band structure of the heterostructure, not only producing an aligned internal electric field but also tuning both depletion layer width and potential barrier height at PZT-ZnO interface. This work provides an efficient way in developing highly efficient ferroelectric-based solar cells and novel optoelectronic memory devices.

Silicon and germanium nanocrystals: properties and characterization.

Group-IV nanocrystals have emerged as a promising group of materials that extends the realm of application of bulk diamond, silicon, germanium and related materials beyond their traditional boundaries. Over the last two decades of research, their potential for application in areas such as optoelectronic applications and memory devices has been progressively unraveled. Nevertheless, new challenges with no parallel in the respective bulk material counterparts have arisen. In this review, we consider what has been achieved and what are the current limitations with regard to growth, characterization and modeling of silicon and germanium nanocrystals and related materials.

Control over the interface properties of carbon nanotube-based optoelectronic memory devices

Optoelectronic nonvolatile memory elements based on polymer-coated carbon nanotube devices can serve as building blocks in programmable circuits. Although essential for improving the circuit performances, the details of the charge trapping mechanism in these mixed organic/inorganic optoelectronic devices are not fully elucidated. The detailed mechanism was investigated by intercalating layers of a hydrophobic organic dielectric (parylene) at different interfaces in the device structure. A thin parylene layer separating the SiO2/nanotube interface from the photosensitive polymer coating is presented as an optimized solution in terms of charging, stability, and robustness.

High‐Speed Programming of Nanowire‐Gated Carbon‐Nanotube Memory Devices

Resistance programming of carbon-nanotube-based optoelectronic memory devices at sub-microsecond speed is demonstrated. The use of silicon nanowires as programming electrodes allows study of the scaling rules of the programming speed and the charge-retention mechanism. Such fast and nonvolatile memory elements have potential for the development of adaptive circuits.

Thermal-Actuated Optoelectronic Memory Medium Based on Carbon Nanotube− and Nickel−Poly(dimethylsiloxane) Composites

Employing the strong capability of absorbing near-infrared (NIR) light and converting the heat of single-walled carbon nanotubes (SWNTs), and the fast thermal actuation of carbon nanotube−poly(dimethylsiloxane) (PDMS) nanocomposite, in this work we proposed a novel NIR optoelectronic memory (OEM) medium based on a SWNT−PDMS/Ni−PDMS composite bilayer, which was actuated by a low-power-density NIR light illumination. The demo device has shown high performance, including a low operating NIR intensity, a high switching ratio, and a rapid photoresponse with no relaxation. In general, the performance has remarkably outperformed state-of-the-art polymer-based OEM devices. Moreover, the device can be performed reversibly using electric pulses. This study provides a new mechanism to design OEMs and other NIR optic-related devices.

Optoelectronic Switch and Memory Devices Based on Polymer‐Functionalized Carbon Nanotube Transistors

Associating carbon nanotubes with conjugated polymers or molecules has been recently recognized as an efficient way to improve performances of organic electronic devices and to achieve new functionality, in particular for optoelectronic applications. This approach maintains the main advantages of organic electronics for low cost, flexible and/or transparent applications. A particularly interesting example of such a nanotube/polymer combination consists of a carbon nanotube field effect transistor coated with a polymer thin film (1; 2). Indeed, such a device can ideally combine the very high carrier mobility of carbon nanotubes (100000 cm2/V.s) with the excellent optical properties of polymers (or molecules in general). Carbon nanotube transistors can, by themselves, emit or detect photons at wavelengths defined by the nanotube chirality. But, to extend their capabilities in optoelectronics, it is important to be able to tune these wavelengths independently of the nanotube structure. Functionalizing the nanotube with a polymer is an efficient way to achieve such a goal. In the present study (2), we demonstrate that drastic photo-induced modifications of the electrical characteristics of self-assembled (3) nanotube transistors functionalized by photo-conductive polymers can be achieved.

Large Photoresponsivity in High‐Mobility Single‐Crystal Organic Field‐Effect Phototransistors

Photons control number of mobile charge carriers: Organic field-effect transistors based on dithiophene-tetrathiafulvalene (DT-TTF) and dibenzo-tetrathiafulvalene (DB-TTF) show enhanced conductivity under illumination (see figure). A very high ratio of photocurrent to dark current of the order of ≈104 was observed for DT-TTF due to the photogeneration of mobile charge carriers (holes). These materials have the potential to be employed as light sensors or optoelectronic memory devices.