Browse Prior Art Database

Sublithographic asymmetric nonvolatile memory cell comprising transition-metal oxides

IP.com Disclosure Number: IPCOM000187507D
Original Publication Date: 2009-Sep-09
Included in the Prior Art Database: 2009-Sep-09
Document File: 4 page(s) / 216K

Publishing Venue

IBM

Abstract

Nonvolatile memory devices have been provided by the use of programmable-resistance materials based on transition-metal oxides (RRAM) such as Cr-doped SrTiO3 and NiO. See, for example, US 6,815,744 and I. G. Baek et al., IEEE IEDM 2004 Tech. Dig., 23.6 (2004). Electrical pulses can switch the resistance of these programmable resistance materials reversibly and persistently between a low-resistance state and a high-resistance state. It is believed that said resistance switching is caused by drift of oxygen vacancies in the transition-metal oxide which modulates the valence of the transition-metal ion and thus the conducting state. A drawback of these nonvolatile memory cells is that a conditioning process is required. This conditioning process comprises subjecting the insulating transition-metal oxide material to an appropriate electrical signal for a sufficient period of time to generate a confined conductive region in the material. The confined conductive region is generated at an arbitrary position in the dielectric material; this leads to a large variation of the operating parameters (programming voltage, resistance state, etc).The time-consuming conditioning process and the large variations of the properties of nominally identical programmable resistors used in the memory cells and of devices comprising such memory cells are severe drawbacks for manufacturability. Further drawbacks of these nonvolatile memory cells are the limited retention time, particularly at elevated temperatures, and the limited endurance (10^6 for RRAM versus 10^15 for MRAM).

This text was extracted from a PDF file.
At least one non-text object (such as an image or picture) has been suppressed.
This is the abbreviated version, containing approximately 46% of the total text.

Page 1 of 4

Sublithographic asymmetric nonvolatile memory cell comprising transition

Sublithographic asymmetric nonvolatile memory cell comprising transitionSublithographic asymmetric nonvolatile memory cell comprising transition -

oxides

oxidesoxides

For prior-art nonvolatile memory devices comprising programmable-resistance materials based on transition-metal oxides a conditioning process is required. This conditioning process comprises subjecting an insulating transition-metal oxide such as SrTiO3, NiO, and TiO2, to an appropriate electrical signal for a sufficient period of time to generate a confined conductive region in the material. This random-shaped conductive region consists of an oxygen deficient, and therefore conducting, transition-metal oxide such as SrTiO3-d, NiO1-d, and TiO2-d. The geometry of this electrically active region is influenced by local disorder of the material, electrode asperities, material impurities, etc.

    The part of the active region where the conditioning process was initiated has generally an enhanced conductivity, for example, because the cross-section of the path is larger or due to a larger density of oxygen vacancies. Electrical pulses of opposite polarity can switch the resistance of transition-metal oxides such as SrTiO3 reversibly and persistently between a low-resistance state and a high-resistance state. The conductive region (path) is disrupted and reformed at its thinnest (

weakest) part due to

which are positively charged, in the applied electric field.

Nonvolatile memory cell by the use of programmable-resistance materials based on transition-metal oxides according to prior art.

To obtain resistance switching, the disruption of the conditioned region must occur at one end of the path only. If the conducting path closes at one end and opens at the other end, the memory cell remains in the high-resistance state. Hence, a (geometrical) asymmetry is required to switch reversibly and persistently between a low-resistance state and a high-resistance state.

1

metal

---metalmetalmetal

drift of oxygen vacancies,

[This page contains 1 picture or other non-text object]

Page 2 of 4

Programmable-resistance material and thermal microscopy: Prerequisite for resistance switching (asymmetry) and failure mechanism of prior-art memory cell (symmetry after prolonged operation).

Left panel: Resistance switching, i.e., hot-spot remains at one end of conductive path. Right panel: Endurance failure, i.e, hot-spot alternates between both ends of conductive path.

In unipolar switching memory cells based on transition-metal oxides such as NiO the conductive region (path) is disrupted and reformed at its thinnest (

weakest) part due to

dielectric breakdown and thermally driven oxygen diffusion (assisted by local heating). For this type of memory cells the statistical spread of the operating parameters dep...