Chang-Bum Lee

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.

Effects of metal electrodes on the resistive memory switching property of NiO thin films

The effects of various metal electrodes on the resistive switching of NiO thin films were investigated. Contrary to the belief that Pt is used for its high work function, which enables Ohmic contact to p-type NiO, resistive switching was observed in films with Ta or Al electrodes with a low work function in the as-deposited state. The resistive switching of films with a Ag or Cu top electrode with a low work function and high free energy of oxidation shows the importance of the formation of an oxide layer at the metal/NiO interface.

Stack friendly all-oxide 3D RRAM using GaInZnO peripheral TFT realized over glass substrates

This paper reports on new concept consisting of all-oxide-based device component for future high density non-volatile data storage with stackable structure. We demonstrate a GaInZnO (GIZO) thin film transistors (TFTs) integrated with 1D (CuO/InZnO)-1R (NiO) (one diode-one resistor) structure oxide memory node element. RRAM (Resistance Random Access Memory) has provided advantages in fabrication which have made these works possible. Therefore we also suggest methods and techniques for improving the distribution in bi-stable resistance characteristics of the NiO memory node. In order to fabricate stack structures, all device fabrication steps must be possible at low temperatures. The benefits provided by low temperature processes are demonstrated by our devices fabricated over glass substrates. Our paper shows the device characteristics of each individual component as well as the characteristics of combined select transistor with 1D-1R cell. XPS analysis of NiO RRAM resistance layer deposited by ALD confirms similar conclusions to previous reports of the importance of metallic Ni content in sputtered NiO for bistable resistance switching. Also we herein propose a generalized stacked-memory structure to minimize on-chip real estate to maximize integrated density.

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.

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.