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CBRAM nano-ionic devices are emerging as a competitive technology solution for transistor free memory, offering low power consumption, fast switching, and non-volatility. However, due to the process by which switching is achieved in these devices, namely stochastic growth of a conductive filament bridging the two electrodes within the amorphous material between the electrodes, they suffer from reliability problems. In this work we present devices built with a nanotube structure of chalcogenide glasses to confine the growing conductive bridge. This structure is found to greatly improve device reliability and switching speed. Furthermore, the technology does not involve additional steps, is cost-effective, and is fully compatible with conventional CMOS technology. We have verified the process of conductive bridge growth with scanning electron microscopy and atom force microscopy and characterized the devices in terms of their current–voltage characteristics, memory window, endurance, and retention, all of which show excellent parameters. Their performance stability is also demonstrated at 130 °C, while multilevel switching is established by application of a variety of compliance currents.

Chalcogenide glasses are one of the most versatile materials that have been widely researched because of their flexible optical, chemical, electronic, and phase change properties. Their application is usually in the form of thin films, which work as active layers in sensors and memory devices. In this work, we investigate the formulation of nanoparticle ink of Ge–Se chalcogenide glasses and its potential applications. The process steps reported in this work describe nanoparticle ink formulation from chalcogenide glasses, its application via inkjet printing and dip-coating methods and sintering to manufacture phase change devices. We report data regarding nanoparticle production by ball milling and ultrasonication along with the essential characteristics of the formed inks, like contact angle and viscosity. The printed chalcogenide glass films were characterized by Raman spectroscopy, X-ray diffraction, energy dispersive spectroscopy and atomic force microscopy. The printed films exhibited similar compositional, structural, electronic and optical properties as the thermally evaporated thin films. The crystallization processes of the printed films are discussed compared to those obtained by vacuum thermal deposition. We demonstrate the formation of printed thin films using nanoparticle inks, low-temperature sintering and proof for the first time, their application in electronic and photonic temperature sensors utilizing their phase change property. This work adds chalcogenide glasses to the list of inkjet printable materials, thus offering an easy way to form arbitrary device structures for optical and electronic applications.

We demonstrate a novel chalcogenide glass (ChG)-capped optical fiber temperature sensor capable of operating within harsh environment. The sensor architecture utilizes the heat-induced phase change (amorphous-to-crystalline) property of ChGs, which rapidly (80–100 ns) changes the optical properties of the material. The sensor response to temperature variation around the phase change of the ChG cap at the tip of the fiber provides abrupt changes in the reflected power intensity. This temperature is indicative of the temperature at the sensing node. We present the sensing performance of six different compositions of ChGs and a method to interpret the temperature profile between 440 ∘C and 600 ∘C in real-time using an array structure. The unique radiation-hardness property of ChGs makes the devices compatible with high-temperature and high-radiation environments, such as monitoring the cladding temperature of Light Water (LWR) or Sodium-cooled Fast (SFR) reactors.

Chalcogenide glasses are the advanced materials of choice for the emerging nanoionic memory devices – conductive bridge random access memory (CBRAM). To understand the nature of the effects occurring in these devices under influence of electron-beam radiation, the interaction of blanked chalcogenide films and nanostructured films containing chalcogenide glass and silver (Ag) source are studied. Raman spectroscopy, energy-dispersive X-ray spectroscopy and X-ray diffraction are used for establishing the structural and compositional effects occurring under radiation. They have strong compositional dependence with the stoichiometric compositions being most stable showing less structural changes after radiation. These effects are associated with the availability of lone-pair electrons, their participation in the bonding configurations and the coupling of electron states in the bandgap. They are further enhanced in the bilayers by silver diffusion in the chalcogenide matrix, as a result of interaction with electrons. These effects are used to interpret the electrical performance of CBRAM devices after radiation. The devices are characterized by their resistance states, threshold voltage and endurance. Those based on selenium-rich and stoichiometric composition undergo continuous parameters changes with increase in the radiation dose while in the devices based on germanium-rich composition a counter play of the structural changes and expulsion of silver occur.

Programmable metallization cell (PMC) devices work by growing and dissolving a conducting metallic bridge across a chalcogenide glass (ChG) solid electrolyte, which changes the resistance of the cell. PMC operation relies on the incorporation of metal ions in the ChG films via photo-doping to lower the off-state resistance and stabilize resistive switching, and subsequent transport of these ions by electric fields induced from an externally applied bias. In this paper, the static on- and off-state resistance of a PMC device composed of a layered (Ag-rich/Ag-poor) Ge30Se70 ChG film with active Ag and inert Ni electrodes is characterized and modeled using three dimensional simulation code. Calibrating the model to experimental data enables the extraction of device parameters such as material bandgaps, workfunctions, density of states, carrier mobilities, dielectric constants, and affinities.

In this paper, previous work on chalcogenide-glass (ChG)-based radiation sensors is extended to include the effects of mechanical strain and temperature stress on sensors formed on a flexible polymer substrate. We demonstrate the feasibility of producing inexpensive flexible radiation sensors, which utilize radiation-induced migration of ${\rm Ag}^{+}$ ions in germanium selenide ( ${\rm Ge}_{20}{\rm Se}_{80}$ ) films to produce a decrease in resistance of several orders of magnitude between surface electrodes. This change in resistance can be related to total ionizing dose to give an instantaneous readout of radiation exposure. The ChG films are inherently flexible and this, along with an extremely simple device fabrication process at or near room temperature, allows inexpensive sensor structures to be fabricated on lightweight pliable polymeric substrates such as polyethylene napthalate (PEN). Test samples were irradiated with ionizing radiation (UV light and $^{60}$ Cobalt gamma rays). Irradiated samples were subjected to both tensile and compressive stress, and elevated operating temperatures. Stress and exposure to increased ambient temperature had little effect on device resistance. Analysis of the experimental data is supported by the results of COMSOL simulations that model radiation-induced lateral Ag diffusion in ChG.

The focus of this work is on the formation of a lithography-free redox conductive bridge memristor array, comprised of different compositions of GexSe1−x chalcogenide glasses with the aim of selecting the chalcogenide material that provides the best performance. Various memristive arrays were fabricated on a metal–chalcogenide–metal stack. This structure offers high device density with the simplest configuration and allows access to each nano redox conductive bridge device. It was found that the device stability and threshold voltage were a function of the chalcogenide glass composition, with the Ge-rich film contributing to the best device performance, which is attributed to the formation of rigid structure and the availability of Ge–Ge bonds. Additionally, these parameters were dependent on the thickness and the surface roughness of the chalcogenide glass. Application of a nonlithography method for fabricating the array structure offered excellent yield, stable ON–OFF states and good uniformity. This demonstration, along with success achieved at the single cell level, suggests that the redox conductive bridge memristor is well positioned for ultrahigh performance memory and logic applications.

This work focuses on the study of Ge rich phases in the Ge–Se chalcogenide glass system. Radiation induced effects particularly related to Ag diffusion in the glasses under the influence of different doses of γ radiation are investigated and documented. Raman spectroscopy, X-ray diffraction, energy dispersive X-ray spectroscopy, scanning electron microscopy, and atom force microscopy confirmed the occurrence of radiation-induced Ag diffusion and oxidation of the hosting chalcogenide thin films. This causes Ag surface deposition and structural reorganization of the hosting backbone, and affects the electrical performance of the films. It is suggested that the sensing ability of the thin films can be substantially influenced by the encapsulating the sensing elements to avoid the oxidation of the chalcogenide film.

Programmable metallization cells (PMCs) are emerging ReRAM devices exhibiting resistance switching due to cation transport in a solid-state electrolyte and redox reactions at the electrodes. Their non-volatility and low power requirements have led to increased interest in their development for non-volatile memory applications. Investigation of the total dose response of PMCs will contribute to our understanding of radiation induced effects in these novel memory devices as well as assess their suitability for use in ionizing radiation environments. This work investigates the impact of total ionizing dose on the switching characteristic of silver doped Ge30Se70 PMC memory devices. The results obtained show that the resistance switching characteristic of these cells which use a solid state electrolyte based on Ge30Se70 is not affected by a total dose exposure of up to 10 Mrad( Ge30Se70).

In this study we demonstrate the potential radiation sensing capabilities of a metal-chalcogenide glass (ChG) device. The lateral device senses radiation-induced migration of Ag+ ions in germanium selenide glasses by measuring changes in electrical resistance between electrodes. These devices exhibit a high-resistance `OFF-state' (~ 1012 Ω) before irradiation, but following irradiation with either 60Co gamma-rays or UV light, their resistance drops to a low-resistance `ON-state' (~ 103 Ω). The devices have exhibited cyclical recovery with room temperature annealing of Ag doped ChG, which suggests potential use in reusable radiation sensor applications. Furthermore, the mechanisms of radiation-induced Ag/Ag+ transport and reactions in ChG are modeled using a finite element device simulator. The essential reactions captured by the simulator are radiation-induced carrier generation, combined with reduction/oxidation for both ionic and neutral Ag species in the chalcogenide film. The results provide strong qualitative evidence that finite element codes can simulate ionic transport reactions in the ChG and reveal plausible mechanisms for radiation-induced metal doping.

Solid state electrolytes fabricated with chalcogenide glass (ChG) are considered viable candidates for the next generation of non-volatile memory technologies. These glasses, which are composed of group IV and/or group V elements with those of group VI chalcogens (S, Se, and Te), are excellent metal ion conductors. Because of this property, the resistance across structures composed of ChG films sandwiched between active metal (e.g., Ag) and inert metal (e.g., Ni) electrodes can be switched upon the application of sufficient bias, thereby enabling memristive action. In this paper, the effects of 60Co gamma-ray irradiations on Ag/Ge30Se70 test structures are investigated. The results show that exposure to high-energy photons can trigger the transport of Ag+ & ions from an active Ag top layer into an underlying Ge30Se70 ChG film. Post-irradiation annealing experiments also indicate that this “photo-doping” process is reversible once the radiation stress is removed. Numerical simulations which model the mechanisms of radiation-induced photo-doping and recovery are shown to agree well with the data. The results and analysis presented in this paper suggest the ChG-based memristors may be more susceptible to transient radiation effects than cumulative radiation damage.

CBRAM cells were irradiated with 14 MeV neutrons to a total fluence of 3.19×1013 n/cm2. This is the first time that the effect of displacement damage on the DC characteristics of CBRAM has been examined. The high resistance and low resistance states of the cells are shown to converge with increasing neutron fluence. After reaching a fluence of 2.93×1013 n/cm2, the CBRAM cells became irrecoverably locked into their final resistance state.

We report the results of our study on the impact of variable atomic ratio of Ge x Se 1-x on the total ionization dose (TID) influenced lateral diffusion of Ag into chalcogenide glasses (ChG) in flexible radiation detection sensors.

In this work we present data about electronic devices based on a planar structure; inert electrode/nanophase chalcogenide glass/inert electrode in close proximity with a source of silver (Ag) oriented laterally over the chalcogenide glass film. The conductivity of the devices changes with radiation and it can be measured by contacting the two inert electrodes. Spacing of the electrodes was chosen after an in-depth investigation into the electric field (E-field) and E-field energy displacement simulations with the aid of COMSOL multi-physics software. Simulations have been used to enlighten a specific device structure to perform in situ measurements. Bias voltages, inert electrode material and thickness of the films were used as standards for all different types of simulations while only varying the spacing and the geometries to affect the E-fields. It has been established from the experimental results that a 1 V bias is the most appropriate for the device performance and this is the voltage used in the simulations. The key motivation for this research is to find appropriate dimensions and geometry, which do not cause a change in conduction as a direct result of the applied E-field, but rather effectively contribute to the establishment of only the radiation induced change of the device conductivity. The process flow for the device fabrication is described and data from the device performance are presented as well. The radiation induced Ag doping is mapped in the device volume using electron dispersion X-ray spectroscopy (EDS) (© 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

The change of chemical structure resulting after X-ray and photo-induced silver diffusion into chalcogenide glass (ChG) thin films is monitored by high resolution X-ray photoelectron spectroscopy (XPS). As 40 S 60 and Ge 30 Se 70 thin films, which are based on pyramids and tetrahedral structural units, are investigated as model materials. Survey, core level (As 3d, S 2p, Ge 3d, Ge 2p, Se 3d, Ag 3d 5/2 , O 1s, C 1s) and valence band spectra have been recorded and analyzed. Reference point for the binding energy is established by the subsequent deposition of thin gold film on top of the measured samples. The chemical structure gradually changes during diffusion of silver in all the samples. The mechanism of change depends on the chemical composition, thickness of the diffused silver layer and conditions of irradiation. It is revealed that surface oxygen can play important role in the Ag photodiffusion process, leading to phase separation on the surface of the films. Photodiffusion of Ag into As 40 S 60 film leads to the formation of a uniform ternary phase and arsenic oxides on the surface. The formation of ethane-like Ge 2 (S 1/2 ) 6 units together with germanium oxidation are the main outcomes of X-ray induced Ag diffusion into Ge 30 Se 70 film.

We report our results of continuous illumination of Ge 46 S 54 chalcogenide glass films with bandgap light in air. The outcome of this process is the formation of Ge-S backbone depleted in germanium. We relate this to consumption of some of the germanium available in the initial material due to the occurrence of a photoinduced oxidation. This is proved using energy dispersion spectroscopy which shows the presence of 17.68at.% oxygen in the glass post-radiation. Raman spectra demonstrate that the initial material, shows breathing modes, characteristic for Ge 46 S 54 glass. After prolonged illumination Raman spectra reveal structure characteristic for the composition of the Ge-S backbone close to Ge 33 S 67 . The oxide forms a film on the surface and this changes the surface relief, studied by atomic force microscopy, but the oxidation is not surface-limited. The oxidation process in these glasses is discussed and the higher priority of germanium oxidation compared to the oxidation of sulphur is stated.

High-resolution X-ray photoelectron spectroscopy is used to identify the mechanism of X-ray-induced Ag diffusion into Ge30Se70 chalcogenide glass thin films, which are prepared in situ to avoid oxygen contamination. From the analysis of Ge 3d, Se 3d, and Ag 3d core levels, and valence band spectra, changes in the electronic structure are determined as Ag diffuses gradually with increasing irradiation. The ternary phase based on Ge2Se6 units, which contains homopolar Ge–Ge bonds, forms when diffusion approaches equilibrium where Ag content ∼30 at.%. The formation of a Se-rich composition is indicated in the near-surface region at the initial stage of the process, but the previously assumed Ag2Se phase is not detected.

We demonstrate how the radiation response and performance of Ag-chalcogenide glass radiation sensors fabricated on a flexible substrate can be optimized by modifications of spacing between electrodes.

The conductive bridge non-volatile memory technology is an emerging way to replace traditional charge based memory devices for future neural networks and configurable logic applications. An array of the memory devices that fulfills logic operations must be developed for implementing such architectures. A scheme to fabricate these arrays, using ion bombardment through a mask, has been suggested and advanced by us. Performance of the memory devices is studied, based on the formation of vias and damage accumulation due to the interactions of Ar+ ions with GexSe1-x (x=0.2, 0.3 and 0.4) chalcogenide glasses as a function of the ion energy and dose dependence. Blanket films and devices were created to study the structural changes, surface roughness, and device performance. Raman Spectroscopy, Atomic Force Microscopy (AFM), Energy Dispersive X-Ray Spectroscopy (EDS) and electrical measurements expound the Ar+ ions behavior on thin films of GexSe1-x system. Raman studies show that there is a decrease in area ratio between edge-shared to corner-shared structural units, revealing occurrence of structural reorganization within the system as a result of ion/film interaction. AFM results demonstrate a tendency in surface roughness improvement with increased Ge concentration, after ion bombardment. EDS results reveal a compositional change in the vias, with a clear tendency of greater interaction between ions and the Ge atoms, as evidenced by greater compositional changes in the Ge rich films.

Chalcogenide glasses (ChG) are the advanced material for the emerging nanoionic memory devices — conductive-bridging RAM (CBRAM). In order to understand the nature of the effects occurring within these devices under the influence of electron - beam radiation, we studied the interaction of blanked chalcogenide films and nanostructured films containing chalcogenide glass and Ag source. Using Raman spectroscopy, EDS and XRD we established the structural and composition effects occurring under radiation, which have strong compositional dependence, and connected them to the availability of lone-pair electrons in the systems, their participation in the bonding configurations, and the coupling of electron states in the band gap. These effects are used to interpret the electrical performance after radiation of CBRAM devices, which were characterized with their resistance states, threshold voltage and endurance.

Thermally and photoinduced diffusion of Ag in thin amorphous Ge20Se80 films are investigated with particular attention being given to the reaction kinetics and the local structure that results. The differences in the nature of the two diffusion processes with regard to the amount of the diffused silver in the films and the changes in the backbone structure of the hosting film are presented and discussed. Ag diffusion in this particular chalcogenide glass composition results in the formation of a phase separated structure formed by the Ge–Se backbone and Ag2Se or Ag nanocrystals.

We investigate the nature of thin films formed by the photodissolution of Ag into Se-rich Ge–Se glasses for use in programmable metallization cell devices. These devices rely on ion transport in the film so produced to create electrically programmable resistance states. The way in which Ag incorporates into the chalcogenide film during photodiffusion is examined using Rutherford backscattering spectroscopy analysis and Raman spectroscopy. The results suggest that an Ag-rich phase separates due to the reaction of Ag with free Se from the chalcogenide glass leaving a Ge-rich chalcogenide matrix.

The impact of varying: 1) metals used to form contact electrodes and 2) chalcogenide glass atomic ratio/chemical composition on the performance of our recently developed flexible radiation detection sensors has been investigated. For electrodes, three group 11 elements (i.e., copper, silver, and gold) were used. For chalcogenide glass film, either Ge x S1− x or Ge x Se1− x was used where the atomic ratio of the chalcogen atoms (i.e., sulfide or selenide) was varied from device to device. Selenide systems with Ag electrodes were found to be very promising, since the limit of detection of the sensors showed clear dependence on the Se atomic ratio in the chalcogenide glass film. The other selenide and sulfide systems with different group 11 metal electrodes were not as suitable for the present lateral diffusion-based design due to either their control instability or very slow diffusion caused by $\gamma $ irradiation from a 60Co source.

Two different displacement damage experiments were performed on CBRAM cells. In one experiment, conductive bridging random access memory (CBRAM) cells were exposed to 14 MeV neutrons to a total fluence of $3.19 \times 10^{13}$ n/cm2. In the second test, CBRAM cells were bombarded with 200 keV Si2+ ions. In both the experiments, the high resistance and low resistance states (LRSs) of the cells were observed to converge with increasing particle fluence. After reaching a 14 MeV neutron fluence of $2.93 \times 10^{{{13}}}$ n/cm2, the CBRAM cells became irrecoverably locked into their final resistance state. In situ testing during heavy ion exposure showed a steady decrease in the resistance state of each cell with each successive exposure to the beam. The devices eventually became locked in an LRS.

Data about gamma radiation induced effects in Ge40Se60 chalcogenide thin films and radiation induced silver diffusion within these are presented. Blanket films and devices were created to study the structural changes, diffusion products, and device performance. Raman spectroscopy, X-ray diffraction, current vs. voltage (I–V) and impedance measurements expound the behavior of Ge40Se60 glass and silver diffusion within this glass under radiation. Raman study shows that there is a decrease in the area ratio between edge shared and corner shared structural units revealing structural reorganization occurring in the glasses as a result of gamma radiation. X-ray diffraction studies revealed that with sufficiently radiation dose it is also possible to create Ag2Se in selenium-depleted systems. Oxidation of the Ge enriched chalcogenide backbone is confirmed through the electrical performance of the sensing elements based on these films. Combination of these structural and diffusion products influences the device performance. The I–V behavior is characterized by increase in current and then stabilization as a function of radiation dose. Additionally, device modeling is also presented using Silvaco software and analytical methods to shed light on the device behavior. This type of sensor design and material characterizations facilitate in improving the radiation sensing capabilities of silver containing chalcogenide glass thin films.

This study is related to fabrication and characterization of redox conductive bridge memristors (RCBM). An active region in RCBM is formed by chalcogenide glass (ChG) doped with silver (Ag). We report the application of plasma enhanced chemical vapor deposition (PECVD) method for depositing ChG films which gives the advantage of flexibility in the composition and structure not easily achieved with sputtering or thermal evaporation. The growth kinetics of the deposition process, as well as the properties of the films is investigated. Optimal deposition conditions for reliable device performance are determined. The electrical characteristics of the devices fabricated at these conditions are also tested.