Electrical/Electronics Engineering

The focus of this work is on formation of lithography free redox conductive bridge memristor arrays comprised of different compositions of GexSe1-x chalcogenide glasses with the aim of selecting the insulating material with the best performance. The memristive arrays were fabricated on a metal/chalcogenide/metal stack. This structure offers high device density with the simplest of 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 performance, which is attributed to the formation of rigid structure and of Ge-Ge bonds. Additionally, these parameters were dependent on the thickness of the chalcogenide glass and its surface roughness. Application of non-lithography method for fabricating the array structure offered excellent yield, stable ON/OFF states and good uniformity. This demonstration, along with success already achieved at the single cell level, suggests that the redox conductive bridge memristor is well positioned for ultra-high performance memory and logic applications.

In this work a scheme for fabricating a conductive bridge non-volatile memory arrays, using ion bombardment through a mask, is demonstrated. Blanket films and devices have been created to study the structural changes, surface roughness and device performance. Ar + ions interaction on thin films of Ge x Se 1-x system have been studied using Raman Spectroscopy, Atomic Force Microscopy (AFM) and Energy Dispersive X-Ray Spectroscopy (EDS). The performance of the memory devices has been analyzed based on the formation of vias and damage accumulation due to Ar + ion interactions with Ge x Se 1-x (x=0.25, 0.3 and 0.4) thin films of chalcogenide glasses (ChG). This method of devices/arrays fabrication provides a unique alternative to conventional photolithography for prototyping redox conductive bridge memory without involving any wet chemistry.

Laser-matter coupling results specific structural changes in amorphous chalcogenide semiconductor layers which originate from electron-hole excitations, defect creation or modification and subsequent atomic motions. These changes can be influenced by plasmon fields. Plasmon enhanced photo-darkening and bleaching, optical recording in thin As x Se 1 − x films have been demonstrated in this paper, specifically in As 20 Se 80 and As 2 Se 3 compositions which revealed the best effects of stimulated expansion or optical darkening respectively due to the He-Ne laser (λ = 633 nm) illumination. Gold nanoparticles deposited on the silica glass substrate and covered by an amorphous chalcogenide film satisfy the conditions of efficient surface plasmon resonance in this spectral region. These experimental results support the importance of localized electric fields in photo-structural transformations of chalcogenide glasses as well as suggest better approaches for improving the performance of these optical recording media.

Diffusion mass transfer in thin chalcogenide films under illumination by a focused Gaussian beam have been studied both experimentally and theoretically. It is demonstrated that depending on the light intensity, waist of the beam, and the film thickness, one can obtain formation of either hillocks or dips in the illuminated regions. By comparison of the kinetics of hillock or dip formation on a surface of As 20 Se 80 glass films with the results of our theoretical analysis, we have estimated the photo-induced diffusion coefficients, D, at various light intensities, I, and found D to be proportional to I (D ¼ bI), with b % 1.5 Â 10 À18 m 4 /J. V C 2011 American Institute of Physics.

Unusual profile variation of holographic surface relief gratings is detected in thin (2 μm) As20Se80 chalcogenide films under e-beam irradiation: gratings of small periods were smoothed, whereas the gratings of larger periods increased their amplitudes. Irradiation was carried out in SEM, with 20 kV voltage and 8 nA current; the profiles of the irradiated areas were analyzed both by AFM and SEM. It is found that the kinetics of both flattening and growth followed by exponential law and took place due to lateral mass transport accelerated by e-irradiation. It is shown that the profile variation is mainly caused by competition between capillary forces and “chemical” forces induced by broken and deformed atomic bonds under e-beam irradiation. The kinetics of profile variation was calculated assuming that the mechanism of e-beam induced mass transfer is volume diffusion. The diffusion coefficients were estimated from the experimental data using theoretical expressions derived.

a b s t r a c t E-beam irradiation induced mass transport in thin chalcogenide films As 20 Se 80 has been detected and investigated. After irradiation in SEM by a given fluence, the profiles of the irradiated areas were analyzed both by AFM and SEM. Line e-beam scan of the film results in formation of ridges and depressions near the ridges, both grow with the exposure time. It is demonstrated that formation of ridges and depressions is induced by e-beam accelerated lateral mass transport. This is confirmed by experiments on flattening under e-beam irradiation of surface relief gratings preliminary produced on the film surface. The lateral mass transport in this case is caused by capillary forces and mobility of the film constituents is accelerated by e-irradiation. E-beam induced diffusion coefficients have been determined from the flattening kinetics.