Bistable Devices Research Articles

A bistable electromagnetic micro-power generator using FR4-based folded arm cantilever

This paper discusses a wideband, bistable vibrational micro-power generator using a folded cantilever beam. At an acceleration of 0.5g (35Hz frequency) the device generated a peak power of 22μW across an optimum resistive load of 1kΩ. The half-power bandwidth of the nonlinear bistable device was increased by 5Hz (15% of the peak power frequency) with respect to the linear counterpart. The choice of FR4 as the structural material and the utilization of a folded cantilever design are aimed at achieving a low operational frequency within a relatively small footprint. The bistable mechanism which is introduced into the system by means of a magnetic force between a pair of repulsively positioned NdFeB permanent magnets was analytically modelled, numerically simulated and successfully validated with experimental results. The wideband frequency response is further experimentally modified by adjusting the gap between the repulsive magnets. The effect of the depth of the bistable potential well on the performance of the vibration energy harvester at low to medium accelerations is also validated numerically and experimentally.

TOP-electrode-eliminated organic bi-stable devices and their two switching modes in different atmospheres

An OBD device fabrication method without top electrode deposition is presented to investigate organic bi-stable mechanisms, showing that the bi-stable phenomenon can appear without penetration of metal atoms into the organic layer. Two switch modes, unipolar switch usually present in organic devices and bipolar switch usually present in both organic and inorganic devices, were found in the same organic device when measured in nitrogen and air atmospheres, respectively. It has been observed that pre-bias of the opposite polarity promotes the switch in air atmosphere. Atomic force microscopy showed protrusions could form at the anode/organic interface. A possible mechanism relating needle-tip formation to atmospheres is proposed, which could unify both organic and inorganic memory behaviors.

Various projective synchronization phenomena in two different variable time-delayed systems related to optical bistable devices

We analytically and numerically analyze the existence of various projective (projective-anticipatory, projective and projective-lag) synchronization between two different modulated time-delayed chaotic systems in this paper. The innovation of our work is that we report on projective-anticipatory and projective-lag synchronization of two different variable time-delayed chaotic systems, while other existing work only mentioned projective synchronization in such systems. Based on the theory of Krasovskii–Lyapunov stability, we derive the sufficient stability condition through theoretical analysis. Mackey–Glass and Ikeda models related to optical bistable or hybrid optical bistable devices are taken for examples to verify the validity and effectiveness of the proposed method.

Electrical bistable devices using composites of zinc sulfide nanoparticles and poly-(N-vinylcarbazole)**Project supported by the National Natural Science Foundation of China (Grant No. 61377028), the Natural Science Funds for Distinguished Young Scholar, China (Grant No. 61125505), and the Fundamental Research Funds for the Central Universities, China (Grant No. 2014JBZ009).

N-dodecanethiol capped zinc sulfide (ZnS) nanocrystals were synthesized by the one-pot approach and blended with poly (N-vinylcarbazole) (PVK) to fabricate electrical bistable devices. The corresponding devices did exhibit electrical bistability and negative differential resistance (NDR) effects. A large ON/OFF current ratio of 104 at negative voltages was obtained by applying different amplitudes of sweeping voltage. The observed conductance switching and the negative differential resistance are attributed to the electric-field-induced charge transfer between the nanocrystals and the polymer, and the charge trapping/detrapping in the nanocrystals.

Organic memristive devices based on DNA embedded in silver nanoparticles layer

Two-terminal electrical bistable device is fabricated with structure “Al/deoxyribonucleic acid-cetyltrimethylam- monium bromide/silver nanoparticles/deoxyribonucleic acid-cetyltrimethylammonium bromide/indium tin oxide”, and I-V curves are measured. The results show that the conductivity and the memristive characteristics are significantly improved by the embedding Ag nanoparticles layer. The optimal particle diameters are in a range of 15 - 20 nm, and the maximum on/off current ratio can reach 103. It is also found that I-V characteristic of the device depends on the sweeping voltage amplitude VA. As VA increases, switching voltages (VSET, VRESET) and the on/off current ratio ION/IOFF increase. Furthermore, the transition between high-and low-resistance-state depends on the direction of the applied electric field, which shows that the device possesses polarity.

Controllable optical bistability and multistability in asymmetric double quantum wells via spontaneously generated coherence

We investigate the nonlinear optical phenomena of the optical bistability and multistability via spontaneously generated coherence in an asymmetric double quantum well structure coupled by a weak probe field and a controlling field. It is shown that the threshold and hysteresis cycle of the optical bistability can be conveniently controlled only by adjusting the intensity of the SGC or the controlling field. Moreover, switching between optical bistability and multistability can be achieved. These studies may have practical significance for the preparation of optical bistable switching device.

Electrical bistable properties of hybrid device based on SiO2 modified-ZnO nanoparticles embedded in poly-4-vinyl-phenol

Abstract An electrical bistable device was fabricated by using SiO2 modified-ZnO nanoparticles (NPs) embedded in poly-vinyl-phenol (PVP) polymer as the charge storage medium. Compared to the reference devices with PVP or ZnO NPs embedded in PVP, the proposed device showed improved reproducible electrical bistability. The time maintenance for On/Off states reached 10 4 s , revealing the better environmental stability. The carrier transport mechanism was interpreted by the space-charge-limited-current (SCLC), thermionic emission (TE) and ohmic conduction models. The charge trapping and de-trapping process of ZnO NPs were described based on the energy-band diagram of the device.

Observation and Control of Hot Atom Damage in Ferroelectric Devices

Ferroelectric materials are the most common example of a Landau structure, defined as a system having an atom/mass moving in a double-well energy landscape. These materials have applications in memories, actuators, low power logic transistors, and so on. For a bipolar ac signal typical in most of the applications, one suspects that the repeated roller coaster shuttling of the moving atoms located microscopically at the domain walls could lead to bond dissociation, suggesting a new channel for defect generation with no classical counterpart. Here, we demonstrate that once the bipolar pulses initiate transfer of atoms between the energy pockets, the transient overshoot away from their equilibrium positions (hot atoms) leads to significant increase in defect generation. We interpret the degradation theoretically and demonstrate a set of soft-switching schemes to control the hot atom damage and to improve the device lifetime dramatically. The damage mechanism should be generic in other Landau structures, such as microelectromechanical systems, nonvolatile memories, and analogous control strategies should improve the lifetime of all such bistable devices.

Tri-Stable Polarization Switching of Fluorescent Light Using Photo-Luminescent Cholesteric Liquid Crystals

Using a photo-luminescent cholesteric liquid crystal (PL-CLC) cell, tri-stable electro-optic switching behaviour was demonstrated. Stable planar, uniformly lying helix (ULH), and focal conic states were obtained at an electric field of zero after applying proper electric signals corresponding to each state. When a PL-CLC cell was placed on a ultraviolet (UV) back-light, the cell emitted fluorescent light with different types of polarization corresponding to the liquid crystal (LC) state: the planar, ULH, and focal conic states emitted circularly polarized light, linearly polarized light, and un-polarized light, respectively. Hence, the proposed PL-CLC cell worked as a tri-stable polarization-switching light source. We also demonstrated that the PL-CLC cell can be used to fabricate a bistable fluorescent LC device.

Charge trapping models of resistance switching in organic bistable devices with embedded nanoparticles

We discuss three different models of switching between the high conductivity and low conductivity state in organic bistable devices (OBD) with embedded nanoparticles. All models assume the same basic mechanism: charge trapping and de-trapping in metal nanoparticles. We show trapped charges can both induce an increase or a reduction of the total current depending on device configurations. The influence of energy disorder is investigated.

All-optical proteretic (reversed-hysteretic) bi-stable device

In this paper, we report for the first time a design and simulation (via VPIphotonics) of an all-optical proteretic bi-stable device. The proteresis is a reversed hysteresis with an interesting characteristic which increases the oscillation frequency of a feed-back system with a relaxation dynamics by reducing the feed-back delay. The calculation of the bi-stable device parameters, a simulation of the theoretical device, and a simulation of the all-optical device are given. Applications of the proteretic device in ultra-high speed oscillations are also discussed.

Order reconstruction phenomena and temperature-driven dynamics in a 3D zenithally bistable device

We model the zenithally bistable device (ZBD) in three dimensions (3D), within the Landau-de Gennes theory, and find three stable static states in 3D without an applied field: the vertically aligned nematic (VAN) state, the hybrid aligned nematic (HAN) state and a third, high-tilt state, which we call the THAN state, with an interior and a surface defect. We recover the order reconstruction (OR) phenomenon around the defects in the HAN and THAN states and the 3D THAN and HAN solutions exhibit stable biaxial cylinders connecting defects on opposite faces of the ZBD device. We demonstrate a two-way temperature-driven switching between high-tilt and low-tilt states through controlled heating and cooling procedures in two dimensions (2D), with no applied fields.

Cavity-enabled self-electro-optic bistability in silicon photonics.

We propose a new type of bistable device for silicon photonics, using the self-electro-optic effect within an optical cavity. Since the bistability does not depend on the intrinsic optical nonlinearity of the material, but is instead engineered by means of optoelectronic feedback, it appears at low optical powers. This bistable device satisfies all the basic criteria required in an optical switch to build a scalable digital optical computing system.

Optical bistability based on Fano resonances in single- and double-layer nonlinear slab waveguide gratings

In this paper, we numerically investigate all-optical bistable switching at low input intensity based on Fano resonances available in nonlinear slab waveguide gratings with narrow slits. Fano resonances with various quality factors (Q-factors) in the single- and double-layer slab waveguide gratings are designed and their characteristics are studied by the finite-difference time-domain method. Dependencies on wavelengths of operation, various switching intensities, contrast, and bandwidth of all-optical bistabilities are observed. Comparing nonlinear characteristics of single- and double-layer grating configurations, the latter provides more bistable efficiency with the low input intensities needed and high contrast with high Q-factors at certain operating wavelengths. Both grating configurations in this work provide interesting venues for highly efficient Fano resonance-based all-optical bistable switching devices.

Enhancement of memory margins for stable organic bistable devices based on graphene-oxide layers due to embedded CuInS2 quantum dots

Current–voltage (I–V) curves for Al/CuInS2 (CIS) quantum dots (QDs) embedded in graphene-oxide layer/indium-tin-oxide devices at 300K showed a current bistability with a maximum high conductivity (ON)/low conductivity (OFF) ratio of 1×104, which was 100 times larger than the ON/OFF ratio of the device without CIS QDs. I–V curves and write-read-erase-read voltage cycles demonstrated the rewritable nonvolatile memory properties of the organic bistable devices (OBDs) with ON and OFF current states at the same voltage. The retention time was above 1×105s, indicative of the memory stability of the OBDs. I–V curve at lower voltages up to 0.05V was attributed to the thermionic emission mechanism, and the curve in the applied voltage range from 0.06 to 0.17V was related to an ohmic mechanism. The I–V characteristics in the applied voltage above 0.18V dominantly followed the space-charge-limited-current behaviors.

A low-power all-optical bistable device based on a liquid crystal layer embedded in thin gold films

An all-optical bistable (AOB) resonator device composed of a 430-nm-thick liquid crystal (LC) layer embedded in two thin gold films (MLM) is reported in this paper. This device allows the use of the incident illumination at normal incidence, whereas the previous AOB devices based on twisted nematic (TN)-LC function only for illumination at oblique incidence. The fastest switching time was measured to be 1.8 ms, which is significantly faster than that of TN-LC. Because the MLM device operates free from electronic circuits, it is promising for two-dimensional optical data processing, random access optical memories, and spatial light modulators.

Negative differential resistance and carrier transport of electrically bistable devices based on poly(N-vinylcarbazole)-silver sulfide composites

An electrically bistable device has been fabricated based on poly(N-vinylcarbazole) (PVK)-silver sulfide (Ag2S) composite films using a simple spin-coating method. Current–voltage (I-V) characteristics of the as-fabricated devices exhibit a typical electrical bistability and negative differential resistance (NDR) effect. The NDR effect can be tuned by varying the positive charging voltage and the charging time. The maximum current ratio between the high-conducting state (ON state) and low-conducting state (OFF state) can reach up to 104. The carrier transport mechanisms in the OFF and ON states are described by using different models on the basis of the experimental result.

Energy Harvester Synthesis Via Coupled Linear-Bistable System With Multistable Dynamics

In this research we study the dynamics of a coupled linear oscillator-bistable energy harvester system. The method of harmonic balance and perturbation analysis are used to predict the existence and stability of the bistable device interwell vibration. The influences of important parameters on tailoring the coupled system response are investigated to determine strategies for improved energy harvesting performance. We demonstrate analytically that for excitation frequencies in a bandwidth less than the natural frequency of the uncoupled linear oscillator having net mass that is the combination of the bistable and linear bodies, the bistable harvester dynamics may be substantially intensified as compared to a single (individual) bistable harvester. In addition, the linear-bistable coupled system may introduce a stable out-of-phase dynamic around the natural frequency of the uncoupled linear oscillator, enhancing the performance of the harvester by providing a second interwell response not possible when using a single bistable harvester. Key analytical findings are confirmed through numerical simulations and experiments, validating the predicted trends and demonstrating the advantages of the coupled system for energy harvesting.

Design methodology for all-optical bistable switches based on a plasmonic resonator sandwiched between dielectric waveguides

We present a bistable device consisting of a Bragg grating resonator with a Kerr medium sandwiched between two dielectric slab waveguides. The resonator is situated in a nanometer-scaled metal–insulator–metal plasmonic waveguide. Due to the dimensional confinement from the dielectric waveguide to the nanoscaled plasmonic waveguide, electric fields are enhanced greatly, which will further reduce the threshold value. Moreover, a semi-analytic method, based on the impedance theory and the transfer matrix method, is developed to study the transmission and reflection spectra as well as the bistability loop of such a switch. Our method is fast and accurate, as confirmed by the finite-difference time-domain simulation.

Bias-dependent interface roughening and its effect on electric bistability of organic devices

Atomic force microscopy (AFM), field-emission scanning electron microscopy, and energy dispersive X-Ray spectroscopy are used to study morphological and compositional variations of metal-organic interfaces in organic bistable devices. The results show that bias voltage causes rougher interfaces with new protrusions, and the switching phenomena origins from the evolution of these protrusions under external electric field. In order to exclude other possible factors, three types of bistable devices are designed and examined. In addition, metal-coated AFM probes are utilized to simulate the switching process, which yields similar results and corroborates our conclusion.