Electrically Driven Random Laser Memory

The resistive switching characteristics of Pt/CeOx/TiN memory devices are investigated for potential applications in nonvolatile resistive random access memory (RRAM). The X-ray diffraction characteristics of the sputtered CeOx layer indicate the formation of nanocrystalline single-phase CeO2 with a cubic fluorite structure. The existence of oxygen vacancies in the Pt/CeOx/TiN memory device was determined by X-ray photoelectron spectroscopic studies, while the presence of an interfacial layer between CeOx and the TiN bottom electrode was investigated by X-ray diffraction and high resolution transmission electron microscopy. The TiON layer formed at the TiN/CeOx interface seems to play a key role in the resistive switching mechanism of the device. The present CeOx-based device shows excellent bipolar resistive switching characteristics, including a low operation current (100 µA), high ON/OFF resistance ratio (∼105), and good retention/stress characteristics at both room temperature and 85 °C.

Recently, NiO film of metal-oxide-metal (MOM) structure 1a has drawn much attention because it shows reproducible resistance switching phenomena applicable to next generation nonvolatile resistive random access memory (ReRAM) device. The resistance switching phenomenon, that is, a drastic change in resistance between a high-resistance state (OFFstate) and low resistance state (ON-state) in current-voltage (I-V) characteristic of MOM structure, has been observed in binary oxides such as NiO, 1 TiO2, 2 Nb2O5, 3 Cr-doped SrZrO3, 4 Pr1-xCaMnO3, 5 and chalcogenide semiconductors although exact origin was unsolved. Among these materials, the binary oxide is the first consideration for the application due to the relatively simple fabrication process. In the case of a device fabrication, the self-limiting process of atomic layer deposition (ALD) may be very important for the growth of NiO films because the expected structure of ReRAM device requires the filling process of NiO on the hole or trench-patterned 3-dimensional substrates. Therefore, it is worthwhile to find the optimal ALD process for NiO film growth by using suitable Ni precursors. In general, most of Ni compounds are in solid state at room temperature although highly volatile liquid precursor is highly desirable to obtain conformal film qualities in ALD processes. A number of nickel precursors have been synthesized and examined for preparing Ni and NiO films using metal organic chemical vapor deposition (MOCVD) and ALD during the past years. The ligands for the nickel precursors are carbonyl, 6 β-diketonates, 7 cycolpentadienyl, 8 and alkoxides, 9 N,N'-dialkyl

Resistance switching characteristics, observed in metal oxide thin films, has recently attracted a great deal of attention to develop next generation low power, low cost, high speed, rugged and nonvolatile resistive random access memory (RRAM) devices. The memory effect in these materials is realized through the switching of the resistance of their thin films between two states of high and low resistances. Amongst the known metal oxides currently being explored for the development of RRAM, ZnO has been demonstrated to be a potential candidate. ZnO is an n‐type wide bandgap semiconductor and is highly transparent in the visible spectral region. Moreover its conductivity can be tailored in a broad range from metal like to insulator like by suitable impurity doping. Therefore it is possible to develop a fully transparent RRAM entirely based on ZnO. In this paper we report growth of a novel transparent RRAM devices based on ZnO and its variants. We studied the resistive switching characteristics of these devices and associated conduction mechanisms responsible for the switching. The details of this study will be presented in the paper (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

In this study, we demonstrated the integration of black phosphorus (BP) nanoflakes in a resistive random access memory (RRAM) with a facile and complementary metal-oxide-semiconductor-compatible process. The solution-processed BP nanoflakes embedded in polystyrene (PS) as an active layer were sandwiched between aluminum electrodes (Al/BP:PS/Al). The device shows a figure of merit with typical bipolar behavior and forming-free characteristics as well as excellent memory performances such as nonvolatile, low operation voltage (1.75 V) and high ON/OFF ratio (>102) as well as the long retention time (>1500 s). The improved device performances were attributed to the formation of effective trap sites from the hybrid structure of the active layer (BP:PS), especially the BP nanoflakes and the partly oxidized species (PxOy). Moreover, the extrinsic aluminum oxide layer was observed after the device operation. The mechanism of switching behavior was further unveiled through the carrier transport models, which confirms the conductive mechanisms of space-charge-limited current and Ohmic conductance at high resistance state (HRS) and low resistance state, respectively. Additionally, in the high electric field at HRS, the transfer curve was well fitted with the Poole–Frenkel emission model, which could be attributed to the formation of the aluminum oxide layer. Accordingly, both the trapping/de-trapping of carriers and the formation/rupture of conductive filaments were introduced as transport mechanisms in our devices. Although the partial PxOy species on BP were inevitable during the liquid phase exfoliation process, which was regarded as the disadvantages for various applications, it turns to a key point for improving performances in memory devices. The proposed approach to integrating BP nanoflakes in the active layer of the RRAM device could pave the way for next-generation memory devices.

The as-fabricated Al/BP–PAN/ITO device exhibits excellent nonvolatile rewritable memory performance, with a high ON/OFF current ratio exceeding 104 and a small switch-on voltage of −1.45 V.

Graph algorithms such as graph traversal have been gaining ever-increasing importance in the era of big data. However, graph processing on traditional architectures issues many random and irregular memory accesses, leading to a huge number of data movements and the consumption of very large amounts of energy. To minimize the waste of memory bandwidth, we investigate utilizing processing-in-memory (PIM), combined with non-volatile metal-oxide resistive random access memory (ReRAM), to improve both computation and I/O performance. We propose a new ReRAM-based processing-in-memory architecture called RPBFS, in which graph data can be persistently stored and processed in place. We study the problem of graph traversal, and we design an efficient graph traversal algorithm in RPBFS. Benefiting from low data movement overhead and high bank-level parallel computation, RPBFS shows a significant performance improvement compared with both the CPU-based and the GPU-based BFS implementations. On a suite of real-world graphs, our architecture yields a speedup in graph traversal performance of up to 33.8×, and achieves a reduction in energy over conventional systems of up to 142.8×.

We have carried out microscopic resistance profile measurements by scanning probe microscopy (SPM) and model analyses on a symmetric thin-film electrical pulse induced resistance change (EPIR) device having a Pr0.7Ca0.3MnO3(PCMO) active layer. The film morphology and surface potential distribution has been examined by atomic force microscopy (AFM) and surface scanning Kelvin probe microscopy (SKPM). Resistance distribution profiles across the device indicate contribution to the resistance switching from three parts of the device: the two PCMO interface regions within ∼1–3 μ m around the metal electrode/PCMO contacts, and the bulk PCMO material. Such an EPIR device showed a symmetric resistance switching behavior under electric pulsing at room temperature. This research indicates that the EPIR device may be used as a nonvolatile resistive random access memory (RRAM) device with different operation modes by controlling electric pulse voltage. The result is also important for understanding the resistance switching behavior in the EPIR device.

To enhance the system integrity of FPGA-based embedded systems on hardware design, we propose a hardware security scheme for nonvolatile resistive random access memory (RRAM) based FPGA, in which internal block RAM (BRAMs) are used for configuration and temporary data storage. The proposed scheme loads obfuscated configurations into nonvolatile BRAMs to protect design data from physical attacks and utilizes Chip DNA to enable logic function.

Application of ion-implantation for improved non-volatile resistive random access memory (ReRAM)

The mechanism of forming-free bipolar resistive switching in a Zr/CeOx/Pt device was investigated. High-resolution transmission electron microscopy and energy-dispersive spectroscopy analysis indicated the formation of a ZrOy layer at the Zr/CeOx interface. X-ray diffraction studies of CeOx films revealed that they consist of nano-polycrystals embedded in a disordered lattice. The observed resistive switching was suggested to be linked with the formation and rupture of conductive filaments constituted by oxygen vacancies in the CeOx film and in the nonstoichiometric ZrOy interfacial layer. X-ray photoelectron spectroscopy study confirmed the presence of oxygen vacancies in both of the said regions. In the low-resistance ON state, the electrical conduction was found to be of ohmic nature, while the high-resistance OFF state was governed by trap-controlled space charge-limited mechanism. The stable resistive switching behavior and long retention times with an acceptable resistance ratio enable the device for its application in future nonvolatile resistive random access memory (RRAM).

The present work explores the white light controlled resistive switching functionality of MoS2 nanorods (NRs) by fabricating a metal-insulator-metal stack configuration. The Cu/MoS2 NRs/Pt/Si device demonstrates the reproducible two-state bipolar resistive switching characteristics under both dark and light environments. In the dark condition, the resistive switching behavior of the NR device could be attributed to the metallic path formation/rupture between top and bottom electrodes. Whereas the applied white light causes the lowering of SET and RESET voltages by inducing conducting path formation/rupture via electron trapping/detrapping in sulfur vacancies across the MoS2 NRs. The formation of a conducting path under dark and light illumination conditions is well explained by proposing a conceptual model and analyzing the resistance vs temperature measurements. It is observed that the white light acts as an external tool to modulate the resistive switching behavior of the fabricated NR device. The correlation between the applied light intensity and the SET voltage is also demonstrated. The NR structure of the MoS2 device provides good endurance of 1500 cycles and a long retention time of 103 s at room temperature under light illumination because of straight conducting path formation through NRs. These results demonstrate that the optically active MoS2 NR based devices have potential for next generation tunable nonvolatile resistive random access memory applications with additional functionality such as photosensors and optoelectronic switches.

The data storage requirement in the digital world is increasing day by day with the advancement of the internet of things. In this respect, nonvolatile resistive random-access memory is an option that provides high density and low power data storage capabilities. In this work, zero-dimensional colloidal CdS quantum dots and a polymer composite at an appropriate ratio were used to fabricate a memristive device. Comparison with a pristine CdS quantum dot-based device reveals that a surrounding matrix around the quantum dots is needed for observing memristive behavior. The quantum dots embedded in the polymer matrix device showed extremely stable electrical switching behavior that can be operated for more than 300 cycles and 60 000 seconds. Moreover, the device needs extremely low power to operate at a very high speed. The smooth surface morphology dictates a charge trapping mechanism for the switching phenomenon; however, an interplay between different charge transport mechanisms leads to the fast switching and high on-off ratio of the device.

Resistance switching and memory effects have been observed in a heterostructure consisting of BiFeO3 (BFO) on a LaNiO3 (LNO) conducting oxide bottom electrode fabricated by chemical solution deposition on quartz substrates. The phase purity and lattice strain of monodispersed thin film nanostructures were confirmed by XRD. Bipolar switching with a resistance switching ratio of one order of magnitude at small bias voltages of +1.3 V and −0.7 V for positive and negative bias respectively has been estimated from the I–V traces measured over a span of more than 6 h. Excellent retention behavior of the BFO–LNO device is confirmed for its possible use as a non-volatile resistance random access memory device. The modeling of the I–V data suggests that in the low resistance state (on) Ohmic conduction is well fitted, whereas in the high resistance state (off) the trap-controlled space-charge-limited current mechanism dominates. The observed resistive switching (RS) is attributed to formation of a metallic filament and its rupture under electric stress conditions. The valence states of Fe ions in the fabricated device structures indicate that oxygen vacancies could also lead to RS in the device.

The many distinct advantages of random lasers focused efforts on developing a breakthrough from optical pumping to electrical pumping. However, progress in these is limited due to high optical loss and low gain. In this work, we demonstrate an electrically pumped quantum dot (QD) random laser with visible emission based on a previously unexplored paradigm named coherent Förster resonance energy transfer (CFRET). In the CFRET process, when a coherent photonic mode is formed because of multiple scattering of the emitted light traveling in mixed donor and acceptor QDs, the donor QDs not only serve as scattering centers but are also enable coherent energy transfer to acceptor QDs. Therefore, the laser action can be easily achieved, and the lasing threshold is greatly reduced. Our approach of electrically pumped QD-based random lasers represents a substantial step toward a full-spectrum random laser for practical applications.

Coherent random lasing behavior in low-dimensional active weakly scattering random systems