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Gallium doped ZnO (GZO) top electrode thickness dependence of resistive switching characteristic of GZO/ZnO2/ZnO/ITO transparent valence change memory device is investigated. The thickness of the GZO top electrode modulates the resistance of the pristine device. Devices made with thicker GZO layer have higher leakage current; thus, require higher current compliance. An excessively high current compliance leads to a device breakdown upon reset process. Conversely, a very low current compliance may form a tiny conducting filament and is difficult to rejuvenate after the rupture; thus, its cycle-to-cycle characteristic shows a decaying behavior. Nevertheless, transparent valence change devices with a stable endurance and sufficient memory window that operate at a moderate level of current compliance are successfully fabricated by employing an appropriate thickness of the top electrode. We suggest that a good switch-ability of transparent valence change memory devices are strongly affected by the thickness of the top electrode.

Memristor devices that can operate at high speed with high density and nonvolatile capabilities have great potential for the development of high data storage and robust wearable devices. However, in real-time, the performance of memristors is challenged by their instability toward harsh working conditions such as high temperature, extreme humidity, photo irradiation, and mechanical bending. Herein, we introduce a TaOx/AlN-based flexible and transparent memristor device having stable endurance under extreme 2 mm bending (for more than 107 cycles) with an ON/OFF ratio of more than 2 orders of magnitude at 25 ns rapid switching. This device exhibits excellent flexibility under extreme bending conditions (bending radius of 2 mm) even with intense ultraviolet (UV) radiation. A thin AlN insertion layer having low dielectric and high thermal conductivity plays a crucial role in improving the switching stability and device flexibility. In particular, the devices exhibit excellent minimum switching fluctuations under UV irradiation, >106 s nonvolatility retention at high temperature (135 °C), various gas ambient, and damp heat test (humidity 95.5%, 83 °C) because of the indium metal drift during the switching process and high bonding energy of Ta–O. Most importantly, direct observation of indium metal strongly anchored in the TaOx switching layer during the switching process is reported for the first time via transmission electron microscopy, which provides clear insights into the switching phenomenon. Furthermore, the results of electrical and material analyses explain that our facile device design has excellent potential for wearable and aerospace applications.

In this letter, Ta 2 O 5 /WO 3 double-layer wearable memristor synapse has excellent recognition accuracy (97%) for just 12 epochs compared to the single-layer device (83%). The insertion of an ultra-thin WO 3 layer modulates the oxygen vacancy distribution in Ta 2 O 5 and induces digital-to-analog switching behavior. Excellent AC endurance of (>10 9 cycles) under 2 mm extreme bending, a rapid speed (25 ns), reliable bending endurance for 10 4 cycles with 4 mm bending, stable retention (>10 6 s) up to 200°C, and water-resistant behavior are achieved. The potentiation, and depression having outstanding nonlinearity (0.64) is obtained. The Ta 2 O 5 /WO 3 design is a promising candidate for wearable neuromorphic applications due to its wearability, flexibility, lightweight, low cost and environmental friendly fabrication.

The effect of the TiW barrier layer on the switching properties of Ga-doped ZnO (GZO) nanorods based on Electrochemical Metallization Memory is investigated. Vertically well-aligned and uniform GZO nanorods having a diameter of approximately 35 nm are hydrothermally grown on a seeding layer of ZnO deposited on indium tin oxide (ITO) coated glass substrate, to fabricate Cu/TiW/nanorods/ITO/Glass devices. The remarkable enhancement in the memory window (on/off ratio) is achieved in the 5 nm TiW barrier layer embedded device. This device exhibits endurance of more than 103 cycles and a large memory window of ∼103. The conduction mechanism at different current regions is studied, and it is found that Schottky emission is dominated in the low field region. The TiW barrier layer helps to retain the Cu ions and control the Cu ions diffusion, hence control the filament growth into the resistive layer, confirmed from the X-ray photoelectron spectroscopy (XPS) analysis. This device is suitable for the future low power non-volatile memory devices.

The synaptic plasticity of indium tin oxide (ITO)/ZnO/ITO highly transparent (more than 88%) analog switching resistive memory device is investigated. Highly stable analog switching behavior for more than 2500 cycles with a good memory window of approximately two orders makes it suitable for synapse application. The synaptic response is investigated by applying identical electrical pulses. The potentiation and depression of the device used the conventional identical single-pulse scheme to perform high nonlinearity (0.83) and decaying training epochs. However, the linearity and the training epochs are improved to 0.44 by implementing the identical double-pulse scheme. The proposed double-pulse scheme offers a broad dynamic range (200) having 320 conductance states. This invisible structure and double-pulse scheme can be highly suitable for the neuromorphic computing devices.

As sandboxing becomes more and more popular as a malware detection and prevention method, cybercriminals will come up with new ways to evade this technology. For instance, there are new strains of malware that can recognize if they are inside a sandbox. These malware infections do not execute their malicious code until they are outside of the sandbox. One of the techniques that attackers use for evading sandbox solution is Lack of User Input. This malware can analyze the level of user input for detecting a sandbox. In contrast to a sandbox, different types of user activity, such as mouse or keyboard activity frequently occur. The main aim of this chapter is to provide the security by detecting malware infections. This could be accomplished through sandboxing technology. Here the data obtained from the user activity, such as mouse and keyboard activity has been converted into text. This is achieved through heatmaps, scroll maps, attention maps, and keyloggers. Then the data has been converted into text and it is stored in the database. The obtained data has been obfuscated and given for futher process. This is achieved through an AI tool called Delphix. Also this chapter gives an overview about the recent problems that are facing by the industrial people during code testing phase and the recent version of sandboxing and data obfuscation techniques which are currently in use. This chapter also covers the details of converting the user activity into data that is frequently occurring in a real machine. Then obfuscation of data. So that it can be more challenging for the anti-malware engines to detect or analyze. This can be achieved through an AI tool called Delphix which masks the compressed data and keeps it between the multiple clones to hide it from the malware.

Surface oxidation employing neutral oxygen irradiation significantly improves the switching and synaptic performance of ZnO-based transparent memristor devices. The endurance of the as-irradiated device is increased by 100 times, and the operating current can be lowered by 10 times as compared with the as-deposited device. Moreover, the performance-enhanced device has an excellent analog behavior that can exhibit 3 bits per cell nonvolatile multistate characteristics and perform 15 stable epochs of synaptic operations with highly linear weight updates. A simulated artificial neural network comprising 1600 synapses confirms the superiority of the enhanced device in processing a 40 × 40 pixels grayscale image. The irradiation effectively decreases the concentration of oxygen vacancy donor defects and promotes oxygen interstitial acceptor defects on the surface of the ZnO films, which consequently modulate the redox process during rupture and rejuvenation of the filament. This work not only proposes the potential of ZnO-based memristor devices for high-density invisible data storage and in-memory computing application but also offers valuable insight in designing high-performance memristor devices, regardless of the oxide system used, by taking advantage of our neutral oxygen irradiation technique.

The effect of TiW metal barrier layer thickness on voltage-current characteristics of the Cu/TiW/ZrO2/TiN conductive bridge random access memory device was systematically investigated. The change of reset behavior from abrupt decrease to gradual decrease with increasing TiW thickness was observed. Electronic conduction during the forming process was also analyzed to obtain detailed information about the effect of TiW layer thickness on the nature of the conduction phenomenon. The temperature coefficient of resistance of the conductive filament confirms that an electro-chemical metallization (ECM) based conduction was observed in the devices made with a thinner TiW layer. On the other hand, valence change memory (VCM) based conduction was observed with a thick TiW layer. A conduction mechanism is proposed to explain the ECM to VCM conduction transformation phenomenon.

Artificial synapse having good linearity is crucial to achieve an efficient learning process in neuromorphic computing. It is found that the synaptic linearity can be enhanced by engineering the doping region across the switching layer. The nonlinearity of potentiation and depression of the pure device is 36% and 91%, respectively; meanwhile, the nonlinearity after doping can be suppressed to be 22% (potentiation) and 60% (depression). Henceforth, the learning accuracy of the doped device is 91% with only 13 iterations; meanwhile, the pure device is 78%. A detailed conduction mechanism to understand this phenomenon is proposed.

An excessive unintentional out-diffused In atom into the switching layer is a potential threat to the switching stability of memristor devices having indium tin oxide (ITO) as the electrode. We suggest that the physical factor (bombardment of Ar ions and bombardment-induced localized heat during ZnO deposition) and chemical factor (bonding dissociation energy, point defects, and bond length of atoms) are responsible for promoting the out-diffusion. The In atom acts as dopant in the ZnO lattice that degenerates the ZnO insulative behavior. Furthermore, the In ions take part in the conduction mechanism where they may compete with other mobile species to form and rupture the filament, and hence, deteriorate the switching performance. We propose a facile UV/O3 (UVO) treatment to mitigate such damaging effects. The device fabricated on the UVO-treated ITO substrate exhibits significant switching parameter improvement than that of the device manufactured on untreated ITO. This work delivers an insight into the damaging effect of out-diffusion and auto-doping processes on the reliability of memristor devices.

The Co dopant substitutes the Zn atomic position in the hexagonal crystal lattice and generates acceptor defects. These defects play significant role in modulating the conduction mechanism of the memristive device. The devices without Co dopant have high concentration of donor defects so that the electron can flow easily through hopping these donor defects; henceforth, only weak filaments can be formed during the set process. Meanwhile, the increase of the acceptor defects in the films enhances the film resistivity. This acceptor defects also contribute to an increase of barrier height at the electrode/dielectric interface where the electrons require higher energy to overcome this barrier and, eventually, induce the formation of strong filaments during the set process.

Oxidation of TiN is a diffusion-limited process due to the high stability of the TiN metallic state at the TiN/TiO2 junction. Hence, the TiN/TiO2/TiN device being the inability to form a suitable interfacial layer results in the exhibition of abrupt current (conductance) rise and fall during the set (potentiation) and reset (depression) processes, respectively. Interfacial engineering by depositing Ti film served as the oxygen gettering material on top of the TiO2 layer induces a spontaneous reaction to form a TiOx interfacial layer (due to the low Gibbs free energy of suboxide formation). Such an interface layer acts as an oxygen reservoir that promotes gradual oxidation and reduction during the set and reset processes. Consequently, an excellent analog behavior having a 2-bit per cell and robust epoch training can be achieved. However, a thick interfacial layer may degrade the switching behavior of the device due to the high internal resistance. This work suggests that interfacial engineering could be considered in designing high-performance analog memristor devices.

We explore the use of cubic-zinc peroxide (ZnO2) as a switching material for electrochemical metallization memory (ECM) cell. The ZnO2 was synthesized with a simple peroxide surface treatment. Devices made without surface treatment exhibits a high leakage current due to the self-doped nature of the hexagonal-ZnO material. Thus, its switching behavior can only be observed when a very high current compliance is employed. The synthetic ZnO2 layer provides a sufficient resistivity to the Cu/ZnO2/ZnO/ITO devices. The high resistivity of ZnO2 encourages the formation of a conducting bridge to activate the switching behavior at a lower operation current. Volatile and non-volatile switching behaviors with sufficient endurance and an adequate memory window are observed in the surface-treated devices. The room temperature retention of more than 104 s confirms the non-volatility behavior of the devices. In addition, our proposed device structure is able to work at a lower operation current among other reported ZnO-based ECM cells.

Hydrogen peroxide treatment induces the phase transformation of hexagonal ZnO to cubic ZnO2 on the surface of the ZnO switching memory film; this oxidation process effectively reduces the concentration of n-type donor defects (oxygen vacancies and zinc interstitials) in the switching film. The chemically oxidized ZnO2 layer not only lowers the operation current of the device but also can serve as an oxygen “bank” to improve the endurance of the memristor. The oxidation reaction of peroxide treatment can be easily controlled to achieve an analog behavior with good switching uniformity. The analog memristor device is able to perform two-bit per cell and synaptic operations. Based on the experimental synaptic data, an image processing of 7 × 9 pixels using a simulated artificial neural network comprises 63 synapses is evaluated to mimic the visual cortex function of the brain.

This paper reports the resistive switching and synaptic capability of AZO/ZnO/ITO transparent and flexiblevalence change memory device structure. The device performs stable endurance for more than 50 cycles with sufficient ON/OFF ratio of one order of magnitude; no intermediate state (data error) is observed during the cycle-to-cycle test. By exploiting the analog switching characteristic of the device and employing identical pulses to the top electrode, a synaptic behavior can be achieved. A low programming voltage of 1.5V is used to modulate the conductance during potentiation and depression which indicate that the device is a logic-compatible. The conduction mechanism during the switching processand the device performance is discussed.

This work reports the synthesis of a wide range of ferrocenyl-amino acids and other derivatives in excellent yield. Diverse amino acid containing azides were synthesized and ligated to ferrocene employing click reaction to access ferrocenyl amino acids. Chiral alcohols, esters, diols, amines containing azido group were tagged to ferrocene via click reaction to generate ferrocene derived chiral derivatives. A novel strategy for direct incorporation of ferrocene into a peptide and a new route to 1, 1′disubstituted ferrocene amino acid derivative are reported.

An engineering nanorod array in a ZnO-based electrochemical metallization device for nonvolatile memory applications was investigated. A hydrothermally synthesized nanorod layer was inserted into a Cu/ZnO/ITO device structure. Another device was fabricated without nanorods for comparison, and this device demonstrated a diode-like behavior with no switching behavior at a low current compliance (CC). The switching became clear only when the CC was increased to 75 mA. The insertion of a nanorods layer induced switching characteristics at a low operation current and improve the endurance and retention performances. The morphology of the nanorods may control the switching characteristics. A forming-free electrochemical metallization memory device having long switching cycles (>104 cycles) with a sufficient memory window (103 times) for data storage application, good switching stability and sufficient retention was successfully fabricated by adjusting the morphology and defect concentration of the inserted nanorod layer. The nanorod layer not only contributed to inducing resistive switching characteristics but also acted as both a switching layer and a cation diffusion control layer.

In this study, metal diffusion barrier-dependent switching polarity in ZrO2-based conducting-bridge random access memory was investigated. The device without the barrier layer (BL) exhibited nonpolar switching characteristics. However, inserting TiW BL resulted in positive reset failure. This phenomenon depends on the size and shape of the conducting bridge and also on the defects that contribute to the formation and rupture of the bridge. Consequently, the properties of the conducting bridge govern the device switching performance. Cu- and oxygen vacancy-based conducting bridge during N-Set for a device with and without the BL was proposed. The effect of the insertion of BL on the switching performance was also discussed. The absence of BL resulted in switching instability and poor nonvolatility. By contrast, a device with BL exhibited enhanced uniformity and nonvolatility, and the retention was more than 105 s at 200 °C.

This work reports the synthesis of a wide range of ferrocenyl-amino acids and other derivatives in excellent yield. Diverse amino acid containing azides were synthesized and ligated to ferrocene employing click reaction to access ferrocenyl amino acids. Chiral alcohols, esters, diols, amines containing azido group were tagged to ferrocene via click reaction to generate ferrocene derived chiral derivatives. A novel strategy for direct incorporation of ferrocene into a peptide and a new route to 1, 1′disubstituted ferrocene amino acid derivative are reported.

The capability of memristor devices to perform weight changes upon electrical pulses mimics the analogous firing mechanism in biological synapses. This capability delivers the potential for neuromorphic computing and pushes renewed interests in fabricating memristor with analog characteristics. Nevertheless, memristors could often exhibit digital switching, either during the set, reset, or both processes that degenerate their synaptic capability, and nanodevice engineers struggle to redesign the device to achieved analog switching. This chapter overviews some important techniques to transform the switching characteristics from digital to analog in valence change and electrochemical metallization types memristors. We cover physical dynamics involving interfacial diffusion, interfacial layer, barrier layer, deposition, and electrode engineering that can induce digital-to-analog switching transformation in memristor devices.

The effect of annealing on the switching characteristics of memristor devices cannot be overlooked because the thermal process can exhibit both positive and negative effects on the performance of the devices. We investigated the switching behavior of TaOx-based memristors (electrochemical metallization cell type, ECM) that were Ar-ambient annealed under two conditions, with and without the active electrode. We found a high concentration of metal species in the TaOx films, even in the device where the TaOx was annealed without the active top electrode. This indicates that the properties of the annealed films encourage the diffusion of metal species in the oxide. We suggest that the increase in non-lattice oxygen (by 4.1%, indicating a higher concentration of Vo defects) after the annealing process plays a role in this phenomenon. In addition, the concentration of metal species that exist prior to the switching activation as well as the structure of the conducting bridge determines the switching stability of the devices. The device that annealed before top electrode deposition shows the worst stability; conversely, the device that annealed after top electrode deposition has the best coefficient of variation of the LRS and HRS which is 4.69% and 78.8%, respectively. Electrical and materials analyses were conducted to understand this phenomenon. This study provides insight into the compatibility of ECM in CMOS post-processing.