Evaluating charge-type of polyelectrolyte as dielectric layer in memristor and synapse emulation.

Based on credible advantages, organic materials have received more and more attention in memristor and synapse emulation. In particular, an implementation of the ionic pathway as a dielectric layer is essential for organic materials used as building blocks of memristor and artificial synaptic devices. Herein, we describe an evaluation of the use of positive and negative polyelectrolytes as dielectric layers for a memristor with calcium ion (Ca2+) doping. The device based on a negative polyelectrolyte shows the potential to obtain an excellent resistive switching performance and synapse functionality, especially in the transformation behaviours from short-term plasticity (STP) to long-term plasticity (LTP) in both the potentiation and depression processes, which were comparable to the perfomrmance obtained with a positive polyelectrolyte. The mechanism of electrical resistance transition and synaptic function can be attributed to the migration of the doped Ca2+ and the ionic functional groups of polyelectrolyte, which result in the formation and vanishing filament-like Ca2+ flux.

Polyelectrolyte Bilayer-Based Transparent and Flexible Memristor for Emulating Synapses.

Memristors will be critical components in the next generation of digital technology and artificial synapses. Researchers are investigating innovative mechanistic understanding of the memristor devices based on low-cost, solution-processable, and organic materials as promising candidates. Here, we demonstrate a novel polyelectrolyte-based memristor device, which is simply prepared by spin-coating poly(acrylic acid) (PAA) and polyethylenimine (PEI) on an indium tin oxide (ITO) substrate followed by a magnetron sputtering of the ITO as the top electrode. The device has a potential to achieve excellent resistive switching (RS) performance and synapse functionality as well as greater flexibility and transmittance when compared to the oxide-based memories. An on/off resistance ratio of 50 can be maintained without degradation for up to 20 000 cycles (flat state) and over 4000 cycles (bending to a 2 mm radius 10 000 times) in the DC sweep mode. Moreover, the device performs various synaptic functions, including spike-timing-dependent plasticity, pulse pair plasticity, and short-term and long-term plasticity in the potentiation and depression processes. The counterions and two oppositely charged polyelectrolyte chains can move in and out of each other depending on the applied electrical potential (pulse), resulting in a change in the potential drop at the interface of the polyelectrolyte bilayer and its electrodes, which can be attributed to the RS mechanism and various synaptic functions. This insight may accelerate the technological deployment of the organic resistive memories.

Area-Type Electronic Bipolar Switching Al/TiO1.7/TiO2/Al Memory with Linear Potentiation and Depression Characteristics.

In electronic bipolar resistive switching (eBRS), the electron trapping and detrapping at the defect sites within the switching layer, such as the highly defective TiO1.7 in this study, constitute the switching mechanism. It is an appealing candidate solution to the nonuniformity issue of resistive switching memory. However, TiO1.7-based eBRS has suffered from a lack of endurance and retention. In this study, a 7 nm-thick stoichiometric TiO2 layer is interposed between an Al bottom electrode and a 50 nm-thick TiO1.7 layer, which is in contact with an Al top electrode. Despite the minimal structural modification, improvements in the electrical performance were substantial. The off-to-on state resistance ratio of 20 and the resistance values could be retained up to 30 000 direct current sweep cycles and 106 alternating current pulse switching cycles. Data retention also significantly improves. Moreover, the device is electroforming-free and shows fully area-type switching characteristics. Such notable improvements are attributed to the favorable energy band structure of the Al/TiO1.7/TiO2/Al structure. The device shows almost linear potentiation and depression characteristics after the repeated pulse voltage applications, which significantly improves the accuracy of the neural network, the synapses of which are composed of the Al/TiO1.7/TiO2/Al memory cells.

Electroforming-Free, Flexible, and Reliable Resistive Random-Access Memory Based on an Ultrathin TaOx Film.

A flexible resistive switching (RS) memory was fabricated on a Ta/TaOx/Pt/polyimide (PI) structure with various TaOx thicknesses (5, 10, and 15 nm). The oxygen vacancy (VO) concentrations in the TaOx films were also adjusted by controlling the oxygen partial pressure during TaOx deposition to obtain different electroforming (EF) behaviors. When the devices of Ta/TaOx/Pt/PI showed the EF-free characteristic, the reliability and endurance performance were greatly improved compared to those of devices with EF behavior. The resistive crossbar array using the thinnest (5 nm) TaOx film showed high uniformity and endurance performance up to 108 switching cycles even after bending to a 2 mm radius 10 000 times. However, for the EF samples, the endurance performance was much lower and involved the reset failure, even with the 5 nm TaOx film.

Intravenous lidocaine infusion for pain control after laparoscopic cholecystectomy: A meta-analysis of randomized controlled trials.

BACKGROUND: This meta-analysis aimed to assess the efficiency and safety of intravenous infusion of lidocaine for pain management after laparoscopic cholecystectomy (LC). METHODS: A systematic search was performed in PubMed (August 1966-2017), Medline (August 1966-2017), Embase (August 1980-2017), ScienceDirect (August 1985-2017), and the Cochrane Library. Only randomized controlled trials (RCTs) were included. Fixed/random effect model was used according to the heterogeneity tested by I2 statistic. Meta-analysis was performed using Stata.11.0 software. RESULTS: A total of 5 RCTs were retrieved involving 274 patients. The present meta-analysis indicated that there were significant differences between groups in terms of visual analog scale scores at 12hours (weighted mean difference [WMD]=-0.743, 95% CI: -1.246 to -0.240, P = .004), 24hours (WMD=-0.712, 95% CI: -1.239 to -0.184, P = .008), and 48hours (WMD=-0.600, 95% CI: -0.972 to -0.229, P = .002) after LC. Significant differences were found regarding opioid consumption at 12hours (WMD=-3.136, 95% CI: -5.591 to -0.680, P = .012), 24hours (WMD=-4.739, 95% CI: -8.291 to -1.188, P = .009), and 48hours (WMD=-3.408, 95% CI: -5.489 to -1.326, P = .001) after LC. CONCLUSION: Intravenous lidocaine infusion significantly reduced postoperative pain scores and opioid consumption after LC. In addition, there were fewer adverse effects in the lidocaine groups. Higher quality RCTs are still required for further research.

Thin TiOx layer as a voltage divider layer located at the quasi-Ohmic junction in the Pt/Ta2O5/Ta resistance switching memory.

Ta2O5 has been an appealing contender for the resistance switching random access memory (ReRAM). The resistance switching (RS) in this material is induced by the repeated formation and rupture of the conducting filaments (CFs) in the oxide layer, which are accompanied by the almost inevitable randomness of the switching parameters. In this work, a 1 to 2 nm-thick Ti layer was deposited on the 10 nm-thick Ta2O5 RS layer, which greatly improved the RS performances, including the much-improved switching uniformity. The Ti metal layer was naturally oxidized to TiOx (x < 2) and played the role of a series resistor, whose resistance value was comparable to the on-state resistance of the Ta2O5 RS layer. The series resistor TiOx efficiently suppressed the adverse effects of the voltage (or current) overshooting at the moment of switching by the appropriate voltage partake effect, which increased the controllability of the CF formation and rupture. The switching cycle endurance was increased by two orders of magnitude even during the severe current-voltage sweep tests compared with the samples without the thin TiOx layer. The Ti deposition did not induce any significant overhead to the fabrication process, making the process highly promising for the mass production of a reliable ReRAM.

A study of the transition between the non-polar and bipolar resistance switching mechanisms in the TiN/TiO2/Al memory.

Thermochemical and electronic trapping/detrapping mechanism-based resistance switching in TiO2 is one of the most extensively researched topics in the field of resistance-switching random access memory (ReRAM). In this study, the subtle correlation between the formation and rupture of the Magnéli-based conducting filament (CF), which is the mechanism of non-polar thermochemical-reaction-based switching, and the electron trapping/detrapping at the defect centers, which is the mechanism of bipolar electronic switching, is examined in detail. The chemical interaction between the TiN top electrode and the TiO2 layer generates a stable and immobile electron trapping layer, which is called a "switching layer", whereas the thin region between the just-mentioned switching layer and the remaining Magnéli CF after the thermochemical reset comprises a non-switching layer. The seemingly very complicated switching behavior with respect to the bias polarity, compliance current, and detailed biasing sequence could be reasonably explained by the phenomenological model based on the combined motions of the CF, switching layer, and non-switching layer. Light-induced detrapping experiments further supplement the suggested switching model.

Electronic resistance switching in the Al/TiO(x)/Al structure for forming-free and area-scalable memory.

Electronic bipolar resistance switching (eBRS) in an Al/TiOx/Al structure, where the TiOx layer was reactively sputter-deposited, was examined in conjunction with a structural analysis using transmission electron microscopy. A thin (3-5 nm) insulating Al(Ti)Ox layer was formed at the bottom Al electrode interface, which provided the necessary asymmetric potential barrier for the eBRS to emerge, whereas the top Al electrode interface appeared to have provided the fluent carrier (electron) injection. The set and reset switching were related to the trapping and detrapping of the carriers at the trap centers, the characteristic energy of which was ∼0.86 eV, across the entire electrode area. The general features of this material system as the feasible RS memory were insufficient: endurance cycle, <∼8000, and retention time at 85 °C, 10(6) s. However, the detailed analysis of the switching behavior based on the space-charge limited current conduction mechanism, and its variation with the switching cycles, provided useful information on the general features of the eBRS, which could also be applicable to other binary (or even ternary) metal-oxide RS systems based on the electronic switching mechanism.