Wenxu Xianyu

2-stack 1D-1R Cross-point Structure with Oxide Diodes as Switch Elements for High Density Resistance RAM Applications

We have successfully integrated a 2-stack 8times8 array 1D- lR (one diode-one resistor) structure with 0.5 mumtimes0.5 mum cells in order to demonstrate the feasibility of high density stacked RRAM. p-CuOx/n-InZnOx heterojunction thin film was used for the first time as a oxide diode which shows increased current density of two orders over our previous p-NiOx/n-TiOx oxide diode. And Ti-doped NiO was used for the storage node. No limitation to the number of stacks has been observed from our results. Cell and device properties of our cross-point structure 8times8 array are reported. In addition, all fabrication processes were done at room temperature without other dedicated facilities or processes allowing for compatibility with current CMOS technology. Bi-stable switching for 1D-1R memory was demonstrated for our 2-stack cross-point structures showing excellent behavior for both diode and storage nodes. The forward current density for p-CuOx/n-IZOx diodes was over 104A/cm2, and the operation voltage for the storage node with diode attached was around 3 V.

Electromigration effect of Ni electrodes on the resistive switching characteristics of NiO thin films

The effects of Ni and Ni0.83Pt0.17 alloy electrodes on the resistance switching of the dc-sputtered polycrystalline NiO thin films were investigated. The initial off-state resistances of the films were similar to that of Pt∕NiO∕Pt film. However, after the first cycle of switching, the off-state resistance significantly decreased in the films with Ni in the electrode. It can be attributed to the migration of Ni from electrodes to the NiO films. The improvement in data dispersion of switching parameters is explained in terms of the decrease of the effective thickness of the films resulting from the migration of Ni.

Comparative structural and electrical analysis of NiO and Ti doped NiO as materials for resistance random access memory

In order to investigate the mechanism behind bistable resistance switching in NiO thin films, we have done detailed x-ray photon spectroscopy (XPS) and x-ray diffraction Analysis (XRD) on NiO and Ti doped NiO samples fabricated under various conditions. We discovered that a high initial resistivity was required for samples to undergo bistable resistance switching, and the presence of metallic Ni content in these samples was determined by XPS. XRD data also showed that NiO grown with a relative (200) orientation was preferred over those grown with relative (111) orientation.

Scalable 3-D Fin-Like Poly-Si TFT and Its Nonvolatile Memory Application

In this paper, we extensively investigated the structure and electrical characteristics of an n-type poly-Si thin-film transistor with a novel 3D fin-like channel. Further, owing to the high-quality thin film in the channel, an experimental device with a nonvolatile (NV) memory structure for system integration on panel or embedded memory applications is successfully demonstrated for the first time. By following the previously reported method and by improving the process conditions, the final fin-like channel shows a real 3D profile and a maximum aspect ratio of 3.5:1 with a minimum average width equal to 135 nm after an excimer laser annealing on a unique prepatterned amorphous silicon channel. The high-level dc characteristics, such as carriers field-effect mobility up to 289 cm2 /V.s, subthreshold slope below 190 mV/dec, ON-OFF current ratio greater than 5 x 106, etc., reveal the effect of film quality and the advantage of the gate-all-around structure on the devices performance; moreover, it also indicates one potential scaling method for this technology. By applying a special program/erase (P/E) mode with electron injection/expulsion from the backside gate electrode, the NV memory structure in this channel demonstrates reasonable P/E characteristics, threshold voltage shifting of 1.41 V at | Vg \ = 12 V, pulse time = 1 ms, and acceptable reliability.

Defect-induced degradation of rectification properties of aged Pt∕n-InxZn1−xOy Schottky diodes

In this study, Pt/IZO (InxZn1−xOy) Schottky diodes were fabricated and the degradation phenomenon was investigated. The Pt/IZO Schottky diodes showed a rectifying ratio of 105, however, the electrical properties were degraded with aging. An increase in defect and carrier concentrations was observed from capacitance-voltage analysis and photoluminescence in the aged Pt/IZO Schottky diode. The degradation of the rectifying properties of the aged diodes originates possibly from the electron tunneling due to the increased defect concentrations.

Advanced poly-Si TFT with fin-like channels by ELA

The advanced low-temperature polysilicon (poly-Si) thin-film transistor with three-dimensional channels of fin-like profile has been demonstrated using excimer laser annealing and unique undercut structure without any additional patterning process. This approach provides a very narrow fin-like channel in devices with high ratio of film thickness to the width as well as a high-quality poly-Si film in channels with better crystallinity for the effect of columnar-like grain growth following the shrinkage of silicon stripe after laser irradiation. Due to that and the stronger electrical stress on the channel by the multigate, the new device with a fin-like channel structure shows good characteristics of the highest mobility up to 395 cm/sup 2//V/spl middot/s, a subthreshold voltage slope below 400 mV/dec, and an ON-OFF current ratio higher than 10/sup 6/.

Tensile-Strained Single-Crystal Si Film on Insulator by Epitaxially Seeded and Laser-Induced Lateral Crystallization

Tensile-strained single-crystal silicon films on insulator islands have been grown from Si wafer substrates by a process combining selective epitaxial growth (SEG) and pulsed laser crystallization. An amorphous Si film on an insulator island is completely melted by a single excimer laser pulse, leading to the solidification of the molten Si seeded from epitaxially grown single-crystal Si regions. Analyses of the resulting microstructures reveal that the laterally crystallized film is single-crystalline. A tensile strain of up to 8.8×10-3 within the crystallized region was measured by Raman spectroscopy. The tensile-strained Si film has potential applications in high-performance devices for three-dimensionally stacked integrated circuits.

Excimer Laser Annealing of PbZr0.4Ti0.6O3 Thin Film at Low Temperature

PbZr 0.4 Ti 0.6 O 3 (PZT) thin films with high crystallinity and high remanant polarization (P r ) have been fabricated by sol-gel deposition with pulsed excimer (XeCl) laser annealing at low process temperatures. The amorphous PZT films were prepared on Pt/Ti/SiO 2 /Si substrates by a sol-gel method. The deposited amorphous PZT films were annealed at 550°C for 10min. to initiate the nucleation of the PZT perovskite phase, and then annealed with an UV pulsed excimer laser (308 nm) heating at 400°C. X-ray diffraction (XRD) patterns show that 150-230 mJ/cm 2 range multi-shot excimer laser irradiation drastically improved the crystallinity of the PZT perovskite phase. Field emission SEM (FE SEM) image show that the PZT thin film has uniform-sized crystal grains. The ferroelectric properties were found to depend on the laser energy density and shot number.

33.2: Investigation of the Fin-Like TFT Structure in LTPS Devices

LTPS TFTs realized with 3D Fin-like multiple-channels exhibit better electrical characteristics than those of conventional planar TFTs, due to their novel structure and the higher film quality in their device channels obtained through an ELC (Exicmer Laser Crystallization) process. The processes developed to form high TSi/WSi ratio Si fins serve to provide a larger ELC process window without involving additional patterning steps.

Degradation by water vapor of hydrogenated amorphous silicon oxynitride films grown at low temperature

We report on the degradation process by water vapor of hydrogenated amorphous silicon oxynitride (SiON:H) films deposited by plasma-enhanced chemical vapor deposition at low temperature. The stability of the films was investigated as a function of the oxygen content and deposition temperature. Degradation by defects such as pinholes was not observed with transmission electron microscopy. However, we observed that SiON:H film degrades by reacting with water vapor through only interstitial paths and nano-defects. To monitor the degradation process, the atomic composition, mass density, and fully oxidized thickness were measured by using high-resolution Rutherford backscattering spectroscopy and X-ray reflectometry. The film rapidly degraded above an oxygen composition of ~27 at%, below a deposition temperature of ~150 °C, and below an mass density of ~2.15 g/cm3. This trend can be explained by the extents of porosity and percolation channel based on the ring model of the network structure. In the case of a high oxygen composition or low temperature, the SiON:H film becomes more porous because the film consists of network channels of rings with a low energy barrier.