Phase Change Memory (PCM) is regarded as one of the most promising candidates for the next-generation nonvolatile memory. Its storage medium, phase change material, has attracted continuous exploration. Sb<sub>2</sub>Te<sub>3</sub> is a high-speed phase change material matrix with low crystallization temperature. Cr-doped Sb<sub>2</sub>Te<sub>3</sub> (CST) films with suitable composition have been studied and proved to be a promising novel phase change material with high speed and good thermal stability. In this paper, detailed R<sub>s</sub>-T characteristics and Hall characteristics of the CST films are studied. We find that, when more parts of the film crystallizes into the ordered structure, the activation energy for electrical conduction (Eσ) decreases, indicating that the semiconductor property is weakened. And with the increase of Cr-dopants, Eσ of the As-deposited (<i>As-de</i>) amorphous CST films decreases, thus the thermal stability of resistance is improved. Hall results show that Sb<sub>2</sub>Te<sub>3</sub> and CST films are all in P-type. For <i>As-de </i>amorphous films, with the increase of Cr-dopants, the carrier mobility decreases all along, while the carrier density decreases at first and then increases. For the crystalline films, with the increase of Cr-dopants, the carrier mobility decreases, while the carrier density increases.
Recently, carbon-doped Ge<sub>2</sub>Sb<sub>2</sub>Te<sub>5</sub> (CGST) has been proved to be a high promising material for future phase change memory technology. In this article, reactive ion etching (RIE) of phase change material CGST films is studied using CF<sub>4</sub>/Ar gas mixture. The effects on gas-mixing ratio, RF power, gas pressure on the etch rate, etch profile and roughness of the CGST film are investigated. Conventional phase change material Ge<sub>2</sub>Sb<sub>2</sub>Te<sub>5</sub> (GST) films are simultaneously studied for comparison. Compared with GST film, 10 % more CF<sub>4</sub> is needed for high etch rate and 10% less CF<sub>4</sub> for good anisotropy of CGST due to more fluorocarbon polymer deposition during CF<sub>4</sub> etching. The trends of etch rates and roughness of CGST with varying RF power and chamber pressure are similar with those of GST. Furthermore, the etch rate of CGST are more easily to be saturated when higher RF power is applied.
Phase change random access memory (PCM) appears to be the strongest candidate for next-generation high density nonvolatile memory. The fabrication of ultrahigh density PCM depends heavily on the thin film growth technique for the phase changing chalcogenide material. In this study, TiSb<sub>2</sub>Te<sub>4</sub> (TST) thin films were deposited by thermal atomic layer deposition (ALD) method using TiCl<sub>4</sub>, SbCl<sub>3</sub>, (Et<sub>3</sub>Si)<sub>2</sub>Te as precursors. The threshold voltage for the cell based on thermal ALD-deposited TST is about 2.0 V, which is much lower than that (3.5 V) of the device based on PVD-deposited Ge2Sb2Te5 (GST) with the identical cell architecture. Tests of TST-based PCM cells have demonstrated a fast switching rate of ~100 ns. Furthermore, because of the lower melting point and thermal conductivities of TST materials, TST-based PCM cells exhibit 19% reduction of pulse voltages for Reset operation compared with GST-based PCM cells. These results show that thermal ALD is an attractive method for the preparation of phase change materials.
Proc. SPIE. 9818, 2016 International Workshop on Information Data Storage and Tenth International Symposium on Optical Storage
KEYWORDS: Diffraction, Data storage, Chemical species, Annealing, Crystals, Transmission electron microscopy, Tellurium, Crystallography, Scanning transmission electron microscopy, Temperature metrology
The crystallization process and crystal structure of the phase change material TiSbTe alloy have been successfully established, which is essential for applying this alloy in phase change memory. Specifically, transmission electron microscopy (TEM) analyses of the film annealed <i>in situ </i>were used in combination with selected-area electron diffraction (SAED) and radial distribution function (RDF) analyses to investigate the structural evolution from the amorphous phase to the polycrystalline phase. Moreover, the presence of structures with medium-range order in amorphous TST, which is beneficial to high-speed crystallization, was indicated by the structure factors S(Q)s. The crystallization temperature was determined to be approximately 170°C, and the grain size varied from several to dozens of nanometers. As the temperature increased, particularly above 200°C, the first single peak of the rG(r) curves transformed into double shoulder peaks due to the increasing impact of the Ti–Te bonds. In general, the majority of Ti atoms enter the SbTe lattice, whereas the remainder of the Ti atoms aggregate, leading to the appearance of TiTe<sub>2</sub> phase separation, as confirmed by the SAED patterns, high-angle annular dark field scanning transmission electron microscopy (HAADFSTEM) images and the corresponding energy-dispersive X-ray (EDX) mappings.
Crystallization behavior of the Ge<sub>2</sub>Te<sub>3</sub>-TiO<sub>2</sub> films prepared by the co-sputtering using Ge<sub>2</sub>Te<sub>3</sub> and TiO<sub>2</sub> targets was investigated by in situ resistance-temperature measurement and transmission electron microscopy. The crystallization kinetic parameters including rate factor and kinetics exponent were obtained by the non-isothermal change in resistance using Kissinger’s plot and Ozawa’s method. The average kinetics exponent was estimated by the nonisothermal change in resistance. Compared with other studied compositions, the composition with TiO2 concentration of 5 at.% exhibited shorter crystallization time which was calculated by the Johnson-Mehl-Avrami equation. The crystallization behavior of Ge<sub>2</sub>Te<sub>3</sub>-TiO<sub>2</sub> film was verified by the transition electron microscopy at different annealing temperature. With the short crystallization time and high crystallization temperature, the compositions with TiO2 concentration of 5-15 at.% may be one of the competing candidates for phase change memory application.
Sb-rich Sb-Te films with different composition were investigated by temperature-dependent resistance measurement, crystal structure characterization, and in situ crystallization behavior study. The results show that when the Sb content is more than 80 at.%, Sb-rich Sb-Te films cannot be used as phase change material due to their low crystallization temperature and small resistance contrast. Sb-rich Sb-Te films with the Sb content being between 80~67 at.% can be used as phase-change-material and they have similar properties because of their similar growth-dominant crystallization behaviors.
We propose a novel multicast-enable wavelength-division-multiplexed (WDM) passive-optical-network (PON)
architecture that uses two sidebands of Optical Carrier Suppressed (OCS)-DPSK signal to carry the unicast and multicast
data. The multicast wavelength control is realized through a Wavelength Selective Switch (WSS). At the optical line
terminal (OLT), for each WDM channel, a single drive Mach-Zehnder modulator (MZM) is used to generate a subcarrier
double-sideband (DSB) DPSK signal. Then, the lower-sideband signals are separated by an interleaver and subsequently
modulated to deliver the multicast data, while the remaining upper-sideband DPSK signals carry the downstream unicast
data. In the optical network units (ONUs), part of the downstream unicast signal power is re-modulated for upstream
transmission, which enables color-free ONUs. This proposed scheme is experimentally demonstrated with a 1.25Gb/s
downstream unicast and multicast data.
A critical problem of maximum a posteriori (MAP) super-resolution (SR) image reconstructed algorithms is the choice of an appropriate prior model. Instead of modeling an original image directly, this work proposes an edge-image-based approach for stable SR reconstruction of the Lorentzian distribution. Through analyzing the convex and derivative properties of the Lorentzian distribution, we demonstrate the validity and stability of the proposed method for MAP SR reconstruction. The Lorentzwidth parameter is calculated iteratively to control the general sharpness degree of the image in the SR reconstruction process. Experiments confirm the effectiveness and robustness of the proposed method, and yield both objective and subjective qualities of the reconstructed SR images significantly better than conventional methods.
For realizing wavelength routing algorithm, hierarchy management architecture is designed basing on the TMN logical layered architecture. Information model for managing different network elements and logical resources was established, comportable features should be considered for wavelength routing management.