Fabrication Of Nonvolatile Memory Devices Research Articles

Nonvolatile Memory Device Based on Copper Polyphthalocyanine Thin Films.

In this work, we report the fabrication of nonvolatile memory devices based on chemical vapor deposition-grown copper polyphthalocyanine (CuPPc) thin films. The high polymerization degree and crystallinity of the as-obtained films were confirmed by transmission electron microscopy, X-ray photoelectron spectroscopy, and UV–vis studies. It was found that the device with Au/CuPPc/indium tin oxide sandwich structure exhibits good nonvolatile memory performance with a large ON/OFF current ratio of 103 and long retention time of 1.2 × 103 s.

Ferroelastic-strain-induced multiple nonvolatile resistance states in GeTe/Pb(Mg1/3Nb2/3)O3-PbTiO3 heterostructures

We prepared 300-nm GeTe thin films on (111)-oriented and piezoelectrically active 0.71 Pb(Mg1/3Nb2/3)O3-0.29PbTiO3 (PMN-0.29 PT) single-crystal substrates by the pulsed laser deposition and investigated the effects of in situ electric-field-controllable non-180° ferroelastic domain switching of the PMN-0.29 PT on the electronic properties of the GeTe films. The in-plane strain of the PMN-0.29 PT could be modulated continuously and reversibly by electric fields in a nonvolatile manner and could be effectively transferred to the GeTe films. Based on this, we realized reversible and nonvolatile resistance switching and obtained multilevel stable nonvolatile resistance states with good stability and endurance at T = 300 K by applying appropriate asymmetrical bipolar electric fields to the PMN-0.29 PT(111) substrates along the thickness direction. Such heterostructures may be used for multilevel data storage that allows each unit to store multiple bits of information and thus improve the memory density. Our investigation would be beneficial for the fabrication of nonvolatile memory devices using PMN-xPT-based heterostructures.

Synthesis of Gold Nanoparticles Capped with Quaterthiophene for Transistor and Resistor Memory Devices

Recently, the fabrication of nonvolatile memory devices based on gold nanoparticles has been intensively investigated. In this work, we report on the design and synthesis of new semiconducting quaterthiophene incorporating hexyl thiol group (4TT). Gold nanoparticles capped with4TT(4TTG) were prepared in a two-phase liquid-liquid system. These nanoparticles have diameters in the range 2–6 nm and are well dispersed in the poly(3-hexylthiophene) (P3HT) host matrix. The intermolecular interaction between4TTand P3HT could enhance the charge-transport between gold nanoparticles and P3HT. Transfer curve of transistor memory device made of4TTG/P3HT hybrid film exhibited significant current hysteresis, probably arising from the energy level barrier at4TTG/P3HT interface. Additionally, the polymer memory resistor structure with an active layer consisting of4TTGand P3HT displayed a remarkable electrical bistable behavior.

Graphene oxide (GO)/reduced-GO and their composite with conducting polymer nanostructure thin films for non-volatile memory device

Graphene oxide (GO) was prepared by the conventional Hummer’s method and subsequently reduced (rGO) by the reduction process using hydrazine hydrate. Further, GO/rGO’s based composite with poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT-PSS) conducting polymer (CP) was prepared. The GO/rGO and CP-GO/rGO thin films were deposited on silicon substrate by drop-casting followed by air drying. Raman Spectroscopy, voltage–current (I–V) and polarization–electric field (P–E) measurements have been carried out to study the micro-structural, electrical and ferroelectric behaviors of GO/rGO and CP-GO/rGO thin films to understand the possibility of fabrication of non-volatile memory device. The linear voltage–current (I–V) relationship shows that the GO thin film behaves as semiconducting whereas rGO thin film behaves like conducting materials that are consistence with the results obtained from Raman spectroscopy measurement. The synthesized GO shows the symmetric log J–V curve with good hysteresis loop; whereas rGO shows similar symmetric curve with very small hysteresis loop. The CP-GO/rGO shows symmetric log J–V curve with very small hysteresis loop on the positive voltage side. The polarization–electric field (P–E) measurements shows that the polarization behavior of rGO is an ideal resistor response; whereas GO and CP-GO/rGO’s have lossy capacitor response (with the combined effects of capacitor and resistor) that are consistence with I–V measurements and could be used for non-volatile memory device.

Sb-Te Phase-change Nanowires by Templated Electrodeposition

ABSTRACTPhase-change memory materials (PCMMs) are semiconductors that exhibit rapid order-disorder transition under electrical or optical pulse excitation. Currently thin-film-based PCMMs play a dominant role in fabrication of non-volatile memory devices. In contrast, phase-change nanowires (PCNWs) have the potential to overcome future challenges such as high data density and low power consumption. Among the various methods to synthesize PCNWs, the vapor-liquid-solid method has been reported previously. In this paper, we report synthesis of Sb-Te PCNWs using a templated electrochemical method. Nanoporous anodic aluminum oxide (AAO) was used as a template for the growth of nanowires. Sb-Te PCNWs with different compositions, diameters and aspect ratios were grown inside the AAO template by electrodeposition. Composition and structure of these nanowires were characterized by energy dispersive X-ray spectroscopy, X-ray diffraction, and scanning and transmission electron microscopy. It is found that electrodeposition through nanosized channels results in materials that are quite different from those electrodeposited on unrestricted surface. The mechanism of nanowire formation inside the channels of AAO template is discussed.

Recent progress in gold nanoparticle-based non-volatile memory devices

Recently, much progress has been made toward the fabrication of non-volatile memory devices based on metallic nanoparticles. Among the many kinds of nanoparticles, gold nanoparticles are some of the most widely used materials for charge trapping elements in non-volatile memory devices because they are chemically stable, easily synthesized, and have a high work function. Various synthesis methods have been applied to fabricate gold nanoparticle-based nonvolatile memory devices and recent progress indicates that gold is a very promising material for non-volatile memory applications. In this article, the recent advances in fabrication and characterization of gold nanoparticle-based nonvolatile memory devices, with an emphasis on flash memory-type memory devices, are reviewed. Detailed device fabrication, characterization, and future directions are reported based on the recent research activities and literature.

Tungsten nanocrystal memory devices improved by supercritical fluid treatment

A supercritical CO2 (SCCO2) fluid technique is proposed to improve electrical characteristics for W nanocrystal nonvolatile memory devices, since the thickness and quality of tunnel oxide are critical issues for the fabrication of nonvolatile memory devices. After SCCO2 treatments, C-V curves are restored to normal, as well as the leakage current of W nanocrystal memory devices are reduced significantly. It reveals that W nanocrystal memory devices could be formed with shorter oxidation time, moreover, dangling bonds and trapping states initially created within an incomplete oxidized film will be efficiently repaired after SCCO2 treatment.

Si nanocrystals by ultra-low energy ion implantation for non-volatile memory applications

In nanocrystal (nc) metal-oxide-semiconductor (MOS) memory structures, a fine control of nc location and population is required for pinpointing the optimal device architectures. In this work, we show how to manipulate and control the depth-position, size and surface density of two dimensional (2D) arrays of Si ncs embedded in thin (<10 nm) SiO 2 layers, fabricated by ultra-low energy (typically 1 keV) ion implantation and subsequent annealing. The influence of implantation and annealing conditions on the nc characteristics (e.g. size, density) and the charge storage properties of associated MOS structures is reported with particular emphasis upon the effect of annealing in N 2-diluted–O 2 gas mixture. The latter annealing conditions restore the integrity of the oxide and allow for the fabrication of non-volatile memory devices operating at low-gate voltages. Annealing in diluted oxygen has also an effect on the population of silicon ncs. Their evolution has been studied as a function of the annealing duration under N 2 + O 2 at 900 °C. An extended spherical Deal–Grove model for the self-limiting oxidation of embedded Si ncs has been carried out. It shows that stress effects, due to the deformation of the oxide, slows down the chemical oxidation rate and leads to a self-limiting oxide growth. The model predictions are in agreement with the experimental results.

Si nanocrystals by ultra-low-energy ion beam-synthesis for non-volatile memory applications

In this work, we show how to manipulate two-dimensional arrays of Si NCs in thin (⩽10 nm) SiO 2 layers by ultra-low-energy (⩽1 keV) ion implantation and subsequent thermal annealing. The influence of implantation parameters (dose, energy), annealing conditions (temperature, duration, ambient) and oxide thickness on the NCs characteristics (position, size, density) is reported. Particular emphasis is placed upon post-implantation thermal treatments performed in nitrogen-diluted-oxygen ambient that significantly improve the integrity of the oxide and allow for the fabrication of non-volatile memory devices operating at low-gate voltages. Thermal oxidation in N 2-diluted-O 2 of high-temperature pre-formed silicon NCs has been also examined and modeled using an extended three-dimensional Deal–Grove model. This model reveals that stress effects, due to the deformation of the oxide, slow down the chemical oxidation rate and lead to a self-limiting oxidation of NCs. The model predictions are in agreement with the experimental results.