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Journal ArticleDOI

Film-Nanostructure-Controlled Inerasable-to-Erasable Switching Transition in ZnO-Based Transparent Memristor Devices: Sputtering-Pressure Dependency

31 Oct 2019-Vol. 1, Iss: 11, pp 2184-2189
TL;DR: This work proposes ZnO-based nonvolatile memory for invisible electronic applications and gives valuable insight into the design of WORM and rewritable memories.
Abstract: We found that the write-once-read-many-times (WORM, inerasable)-to-rewritable (erasable) transition phenomenon results from the different structures of the filament, which is determined by the grain orientations of the deposited films. The conduction mechanism of this switching transition and its impact on the synaptic behavior in various ZnO nanostructures are also discussed. Furthermore, our WORM devices have a programmable physical damage function that can be exploited for use in security systems against data theft, hacking, and unauthorized use of software/hardware. This work proposes ZnO-based nonvolatile memory for invisible electronic applications and gives valuable insight into the design of WORM and rewritable memories.
Citations
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Journal ArticleDOI
TL;DR: The neutral oxygen irradiation technique 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.
Abstract: 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.

31 citations

Journal ArticleDOI
TL;DR: In this article, the authors suggest that interfacial engineering could be considered in designing high-performance analog memristor devices, which can achieve an excellent analog behavior having a 2-bit per cell and robust epoch training.
Abstract: 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.

17 citations

Journal ArticleDOI
TL;DR: In this paper, the effect of the TiW barrier layer on the switching properties of Ga-doped ZnO (GZO) nanorods based on Electrochemical Metallization Memory is investigated.
Abstract: 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.

16 citations


Cites background from "Film-Nanostructure-Controlled Inera..."

  • ...However, switching stability is one of the significant obstacles in the realization of ZnO-based memristors; several efforts have been made to avoid this issue, such as surface oxidation [20], neutral ion irradiation [17], and adjusting deposition parameter [21], [22]....

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Journal ArticleDOI
TL;DR: In this article, a stack structure of ITO/TiO y /TiO x /TiN with high transmittance is fabricated, in which an oxygen-deficient TiO y layer between TiO x and ITO top electrode is introduced to adjust the gradual current characteristics during the SET/RESET process.
Abstract: Transparent synaptic devices remain great prospects for a future comprehensive simulation of artificial synapses with the combination of photoelectric coupling characteristics in the neuromorphic system. In this article, one type of memristors based on a stack structure of ITO/TiO y /TiO x /TiN with high transmittance ( ${T}>81$ %) is fabricated, in which an oxygen-deficient TiO y layer between TiO x and ITO top electrode is introduced to adjust the gradual current characteristics during the SET/RESET process. Furthermore, the devices with different thickness ratios (1:4, 1:2, 1:1, 2:1) of oxygen-deficient TiO y active layers are designed to realize the adjustability of the multilevel resistance state and the analog resistive switching (RS) behavior and improve electrical performances and synaptic simulation characteristics. Meantime, the device based on optimum thickness ratio (1:2) offers excellent uniformity for 1000 cycles and better nonlinearity (0.69) at a low programming power consumption, which reveals further simulation of essential synaptic functions, including paired-pulse facilitation (PPF), and spike-timing-dependent plasticity (STDP) as well as learning–relearning characteristics. In addition, oxygen concentration gradient could be regulated by controlling the thickness ratio to drive oxygen vacancy redistribution at the interfacial layer, which are also demonstrated by high-resolution transmission electron microscopy (HRTEM) and improve electronic properties and analog modulation characteristics.

9 citations

References
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Journal ArticleDOI
TL;DR: The discovery of a Ag(2)S inorganic synapse is reported, which emulates the synaptic functions of both STP and LTP characteristics through the use of input pulse repetition time and indicates a breakthrough in mimicking synaptic behaviour essential for the further creation of artificial neural systems that emulate characteristics of human memory.
Abstract: The electronic properties of inorganic devices such as memristors can be used to simulate neurological behaviour. In particular, ionic and electronic effects in a silver sulphide device are now shown to mimic short- and long-term synaptic functions. Memory is believed to occur in the human brain as a result of two types of synaptic plasticity: short-term plasticity (STP) and long-term potentiation (LTP; refs 1, 2, 3, 4). In neuromorphic engineering5,6, emulation of known neural behaviour has proven to be difficult to implement in software because of the highly complex interconnected nature of thought processes. Here we report the discovery of a Ag2S inorganic synapse, which emulates the synaptic functions of both STP and LTP characteristics through the use of input pulse repetition time. The structure known as an atomic switch7,8, operating at critical voltages, stores information as STP with a spontaneous decay of conductance level in response to intermittent input stimuli, whereas frequent stimulation results in a transition to LTP. The Ag2S inorganic synapse has interesting characteristics with analogies to an individual biological synapse, and achieves dynamic memorization in a single device without the need of external preprogramming. A psychological model related to the process of memorizing and forgetting is also demonstrated using the inorganic synapses. Our Ag2S element indicates a breakthrough in mimicking synaptic behaviour essential for the further creation of artificial neural systems that emulate characteristics of human memory.

1,404 citations

Journal ArticleDOI
01 Oct 1997-Nature
TL;DR: In this article, an invisible thin-film p-type conductor with a conductivity approaching that needed for real applications has been presented, but only now is there an invisible n-type conductor that can be used in real applications.
Abstract: Imagine the applications that invisible electronic circuits, including active components such as diodes and transistors, might have To make them, we need invisible conductors of two types _ some in which the charge carriers are electrons (n-type), and others in which they are holes (p-type) Invisible n-type conductors have been relatively easy to make, but only now is there an invisible thin-film p-type conductor with a conductivity approaching that needed for real applications

305 citations

Journal ArticleDOI
TL;DR: In this article, the impact of different top and bottom electrodes, and different doping elements, on ZrO 2 dielectric properties are described, and a roadmap of the applications of ZRO 2 thin film in future low power, nanoscale microelectronic device applications is realized from this review.

205 citations

Journal ArticleDOI
TL;DR: This review gives the concrete overview of the present status and prospects of transparent RRAM devices based on ZnO and covers the different nanostructured-based emerging resistive switching memory devices for low power scalable devices.
Abstract: In the advancement of the semiconductor device technology, ZnO could be a prospective alternative than the other metal oxides for its versatility and huge applications in different aspects. In this review, a thorough overview on ZnO for the application of resistive switching memory (RRAM) devices has been conducted. Various efforts that have been made to investigate and modulate the switching characteristics of ZnO-based switching memory devices are discussed. The use of ZnO layer in different structure, the different types of filament formation, and the different types of switching including complementary switching are reported. By considering the huge interest of transparent devices, this review gives the concrete overview of the present status and prospects of transparent RRAM devices based on ZnO. ZnO-based RRAM can be used for flexible memory devices, which is also covered here. Another challenge in ZnO-based RRAM is that the realization of ultra-thin and low power devices. Nevertheless, ZnO not only offers decent memory properties but also has a unique potential to be used as multifunctional nonvolatile memory devices. The impact of electrode materials, metal doping, stack structures, transparency, and flexibility on resistive switching properties and switching parameters of ZnO-based resistive switching memory devices are briefly compared. This review also covers the different nanostructured-based emerging resistive switching memory devices for low power scalable devices. It may give a valuable insight on developing ZnO-based RRAM and also should encourage researchers to overcome the challenges.

176 citations