Multilevel erase pulse for amorphous memory devices
AssigneeHarris Corporation
InventorsRonald G. Neale, Grady M. Wood
Life of this patent
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Abstract
The Write/Erase lifetimes of amorphous memory devices are extended by applying a multilevel erase pulse wherein the first stage has a current amplitude sufficient to heat the crystal filament to the phase change temperature but not to provide the energy for the phase change and erasure of the crystal structure and the second stage has a current amplitude sufficient to heat the filament to remove the crystal structure. Preferably the first stage current is equal to the write current and the second stage is equal to the write current times the ratio of the electrical conductivity of the amorphous conducting state to the apparent conductivity of the crystalline state.
Claims22
A method of resetting a filament-type memory device including spaced electrodes between which extend a body of generally amorphous substantially nonconductive memory semiconductor material which, when a set voltage pulse in excess of a given threshold voltage value and duration is applied to said electrodes, has formed therein a crystalline low resistance filamentous path resettable into a generally amorphous condition by application of one or more voltage pulses producing reset current pulses through said filamentous path which heat the same to a temperature which changes the phase of the crystalline filament and are of a duration which is so short that upon termination of each reset current pulse the filamentous path will be quickly quenched to leave at least portions of the filamentous path in a substantially amorphous condition, said method comprising:
- applying to said electrodes a plurality of reset voltage pulses which produce a plurality of reset current pulses each having a first stage amplitude and duration sufficient to heat the filament to the phase change temperature of the material and a second stage amplitude and duration larger than said first stages and sufficient to change the phase of the crystal structure.
A method of resetting a filament-type memory device including spaced electrodes between which extend a body of generally amorphous substantially nonconductive memory semiconductor material which, when a set voltage pulse in excess of a given threshold voltage value and duration is applied to said electrodes, has formed therein a crystalline low resistance filamentous path resettable into a generally amorphous condition by application of one or more reset voltage pulses producing reset current pulses through said filamentous path which heat the same to a temperature which changes the phase of the crystalline filament and are of a duration which is so short that upon termination of each reset current pulse the filamentous path will be quickly quenched to leave at least portions of the filamentous path in a substantially amorphous condition, said method comprising:
- applying to said electrodes a plurality of reset voltage pulses which produce a plurality of reset current pulses, each current pulse having a first stage and a second stage, said first stage having sufficient amplitude and duration to heat the filament to the phase change temperature of the material during an initial plurality of reset pulses while minimizing filament overdrive during a subsequent plurality of reset pulses when the filament switches states, and said second stage having sufficient amplitude and duration to produce a substantial complete phase change of said material from crystalline to amorphous during said reset pulses.
In a circuit having a filament-type memory device including spaced electrodes between which extend a body of generally amorphous substantially nonconductive memory semiconductor material which, when a set voltage pulse in excess of a given threshold voltage value and duration is applied to said electrodes has formed therein, a crystalline low resistance filamentous path resettable into a generally amorphous condition by application of one or more reset voltage pulses producing reset current pulses through said filamentous path which heat the same to a temperature which changes the phase of the crystalline filament and are of a duration which is so short that upon termination of each reset current pulse the filamentous path will be quickly quenched to leave at least portions of the filamentous path in a substantially amorphous condition;
- and means selectively connectable to said electrodes for applying reset voltage pulse or pulses which produces a reset current pulse or pulses which substantially completely convert the crystalline filamentous path to a substantially amorphous filamentous path, the improvement comprising said means applying reset voltage pulse or pulses which produces a reset current pulse having a first stage amplitude sufficient to heat the filament to the phase change temperature of the material and a second stage amplitude larger than said first stage amplitude and sufficient to heat the filament to change the phase of the crystal structure.
Dependencies are inferred from the claim text.