US5487032A
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Method and apparatus for reduced fatigue in ferroelectric memory elements
Assignee: Olympus Corp
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Filing: 1994-11-10
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Granted: 1996-01-23
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Expires: 2014-11-10
Abstract
Abstract A method and apparatus for programming ferroelectric memory cells which reduces fatigue effects of switching polarization of the ferroelectric devices associated with the memory cells such as ferroelectric capacitors and transistors. Alteration of the rise AC fall times associated with signals used to switch ferroelectric device polarization are shown to reduce fatigue of the ferroelectric material thereby increasing the useful life of ferroelectric memory cells. Slowing the rise and fall times as well as the rate of signal level rise and fall, (signal shape), are shown to reduce the fatigue effects of switching polarization of ferroelectric devices. Methods and apparatus for producing a triangular ("sawtooth") signal waveform, a Gaussian signal waveform, and a waveform having exponential rise and fall times are disclosed.
Inventors
- 👤 Takashi Mihara
- 👤 Hitoshi Watanabe
- 👤 Hiroyuki Yoshimori
- 👤 Carlos A. Paz de Araujo
- 👤 Larry D. McMillan
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-11-09 04:46
CPC Classifications
G; G11; G11C; G11C11/00; G11C11/21; G11C11/22
Claims Analysis
Total Claims: 22
Claim 1
Independent Claim
207 words
In a non-volatile memory device having at least one ferroelectric memory element within at least one memory cell, wherein a polarization state of said ferroelectric memory element is associated with a stored logic "1" and another polarization state of said ferroelectric memory element is associated with a stored logic "0", a method for reducing polarizability fatigue of said ferroelectric memory element comprising the steps of: receiving a request to coerce the state of polarization of said ferroelectric memory element to a desired state of polarization; generating, responsive to said request, a waveform electric field signal having a directional polarity and having a maximum amplitude sufficient to alter said state of polarization of said ferroelectric memory element, said signal having a predetermined rise time, during which the amplitude of said signal changes from a first level to said maximum amplitude, wherein said predetermined rise time is selected from the group comprising, about one half the plate rise time of said ferroelectric memory element, and about one half the sense delay time of said ferroelectric memory element; and applying, responsive to said request, said signal to said ferroelectric memory element such that the state of polarization of said ferroelectric memory element is coerced to said desired state of polarization.
Claim 2
Dependent Claim
207 words
In a non-volatile memory device having at least one ferroelectric memory element within at least one memory cell, wherein a polarization state of said ferroelectric memory element is associated with a stored logic "1" and another polarization state of said ferroelectric memory element is associated with a stored logic "0", a method for reducing polarizability fatigue of said ferroelectric memory element comprising the steps of: receiving a request to coerce the state of polarization of said ferroelectric memory element to a desired state of polarization; generating, responsive to said request, a waveform electric field signal having a directional polarity and having a maximum amplitude sufficient to alter said state of polarization of said ferroelectric memory element, said signal having a predetermined rise time, during which the amplitude of said signal changes from a first level to said maximum amplitude, wherein said predetermined rise time is selected from the group comprising, about one half the plate rise time of said ferroelectric memory element, and about one half the sense delay time of said ferroelectric memory element; and applying, responsive to said request, said signal to said ferroelectric memory element such that the state of polarization of said ferroelectric memory element is coerced to said desired state of polarization.
Claim 3
Dependent Claim
14 words
The method of claim 1 wherein said ferroelectric memory element is a ferroelectric capacitor.
Claim 4
Dependent Claim
66 words
The method of claim 1 wherein said signal has a predetermined fall time, during which the amplitude of said signal changes from said maximum amplitude back to said first level, wherein said predetermined fall time is selected from the group comprising, about one half the plate rise time of said ferroelectric memory element, and about one half the sense delay time of said ferroelectric memory element.
Claim 5
Dependent Claim
29 words
The method of claim 3 wherein said signal has a predetermined hold time of about zero, during which the amplitude of said signal is held at said maximum amplitude.
Claim 6
Dependent Claim
17 words
The method of claim 3 wherein said waveform signal is a Gaussian shape waveform electric field signal.
Claim 7
Independent Claim
27 words
The method of claim I wherein the amplitude of said waveform signal rises exponentially from said first level to said maximum amplitude over said predetermined rise time.
Claim 8
Dependent Claim
27 words
The method of claim 1 wherein the amplitude of said waveform signal falls exponentially from said maximum amplitude to said first level over said predetermined fall time.
Claim 9
Dependent Claim
185 words
A non-volatile memory device comprising at least one ferroelectric memory element within at least one memory cell wherein a polarization state of said ferroelectric memory element is associated with a stored logic "1" and another polarization state of said ferroelectric memory element is associated with a stored logic "0"; means for generating a waveform electric field signal, said signal having a directional polarity and having a maximum amplitude sufficient to alter said state of polarization of said ferroelectric memory element, said signal having a predetermined rise time, during which the amplitude of said signal changes from a first level to said maximum amplitude, wherein said predetermined rise time is selected from the group comprising, about one half the plate rise time of said ferroelectric memory element, and about one half the sense delay time of said ferroelectric memory element; and means connected to an electrode of said ferroelectric memory element and associated with said means for generating for applying said signal to said ferroelectric memory element such that the state of polarization of said ferroelectric memory element is coerced to a desired state of polarization.
Claim 10
Dependent Claim
185 words
A non-volatile memory device comprising at least one ferroelectric memory element within at least one memory cell wherein a polarization state of said ferroelectric memory element is associated with a stored logic "1" and another polarization state of said ferroelectric memory element is associated with a stored logic "0"; means for generating a waveform electric field signal, said signal having a directional polarity and having a maximum amplitude sufficient to alter said state of polarization of said ferroelectric memory element, said signal having a predetermined rise time, during which the amplitude of said signal changes from a first level to said maximum amplitude, wherein said predetermined rise time is selected from the group comprising, about one half the plate rise time of said ferroelectric memory element, and about one half the sense delay time of said ferroelectric memory element; and means connected to an electrode of said ferroelectric memory element and associated with said means for generating for applying said signal to said ferroelectric memory element such that the state of polarization of said ferroelectric memory element is coerced to a desired state of polarization.
Claim 11
Dependent Claim
15 words
The memory device of claim 8 wherein said ferroelectric memory element is a ferroelectric capacitor.
Claim 12
Dependent Claim
67 words
The memory device of claim 8 wherein said signal has a predetermined fall time, during which the amplitude of said signal changes from said maximum amplitude back to said first level, wherein said predetermined fall time is selected from the group comprising, about one half the plate rise time of said ferroelectric memory element, and about one half the sense delay time of said ferroelectric memory element.
Claim 13
Dependent Claim
30 words
The memory device of claim 10 wherein said signal has a predetermined hold time of about zero, during which the amplitude of said signal is held at said maximum amplitude.
Claim 14
Dependent Claim
18 words
The memory device of claim 10 wherein said waveform signal is a Gaussian shape waveform electric field signal.
Claim 15
Dependent Claim
28 words
The memory device of claim 8 wherein the amplitude of said waveform signal rises exponentially from said first level to said maximum amplitude over said predetermined rise time.
Claim 16
Dependent Claim
28 words
The memory device of claim 8 wherein the amplitude of said waveform signal falls exponentially from said maximum amplitude to said first level over said predetermined fall time.
Claim 17
Dependent Claim
255 words
In a non-volatile memory device having at least one ferroelectric memory element within at least one memory cell, wherein a polarization state of said ferroelectric memory element is associated with a stored logic "1" and another polarization state of said ferroelectric memory element is associated with a stored logic "0", a method for reducing polarizability fatigue of said ferroelectric memory element comprising the steps of: receiving a request to coerce the state of polarization of said ferroelectric memory element to a desired state of polarization; generating, responsive to said request, a sawtooth shaped waveform electric field signal having a directional polarity and having a maximum amplitude sufficient to alter said state of polarization of said ferroelectric memory element, said signal having a predetermined rise time, during which the amplitude of said signal changes from a first level to said maximum amplitude, wherein said predetermined rise time is selected from the group comprising, about one half the plate rise time of said ferroelectric memory element, and about one half the sense delay time of said ferroelectric memory element, said signal having a predetermined hold time, equal to about zero, during which the amplitude of said signal remains at said maximum amplitude, said signal having a predetermined fall time, during which the amplitude of said signal changes from said maximum amplitude to said first level; and applying, responsive to said request, said signal to said ferroelectric memory element such that the state of polarization of said ferroelectric memory element is coerced to said desired state of polarization.
Claim 18
Dependent Claim
255 words
In a non-volatile memory device having at least one ferroelectric memory element within at least one memory cell, wherein a polarization state of said ferroelectric memory element is associated with a stored logic "1" and another polarization state of said ferroelectric memory element is associated with a stored logic "0", a method for reducing polarizability fatigue of said ferroelectric memory element comprising the steps of: receiving a request to coerce the state of polarization of said ferroelectric memory element to a desired state of polarization; generating, responsive to said request, a sawtooth shaped waveform electric field signal having a directional polarity and having a maximum amplitude sufficient to alter said state of polarization of said ferroelectric memory element, said signal having a predetermined rise time, during which the amplitude of said signal changes from a first level to said maximum amplitude, wherein said predetermined rise time is selected from the group comprising, about one half the plate rise time of said ferroelectric memory element, and about one half the sense delay time of said ferroelectric memory element, said signal having a predetermined hold time, equal to about zero, during which the amplitude of said signal remains at said maximum amplitude, said signal having a predetermined fall time, during which the amplitude of said signal changes from said maximum amplitude to said first level; and applying, responsive to said request, said signal to said ferroelectric memory element such that the state of polarization of said ferroelectric memory element is coerced to said desired state of polarization.
Claim 19
Dependent Claim
14 words
The method of claim 15 wherein said ferroelectric memory element is a ferroelectric capacitor.
Claim 20
Dependent Claim
251 words
In a non-volatile memory device having at least one ferroelectric memory element within at least one memory cell, wherein a polarization state of said ferroelectric memory element is associated with a stored logic "1" and another polarization state of said ferroelectric memory element is associated with a stored logic "0", a method for reducing polarizability fatigue of said ferroelectric memory element comprising the steps of: receiving a request to coerce the state of polarization of said ferroelectric memory element to a desired state of polarization; generating, responsive to said request, a Gaussian shaped waveform electric field signal having a directional polarity and having a maximum amplitude sufficient to alter said state of polarization of said ferroelectric memory element, said signal having a predetermined rise time, during which the amplitude of said signal changes from a first level to said maximum amplitude, wherein said predetermined rise time is selected from the group comprising, about one half the plate rise time of said ferroelectric memory element, and about one half the sense delay time of said ferroelectric memory element, said signal having a predetermined hold time during which the amplitude of said signal remains at said maximum amplitude, said signal having a predetermined fall time, during which the amplitude of said signal changes from said maximum amplitude to said first level; and applying, responsive to said request, said signal to said ferroelectric memory element such that the state of polarization of said ferroelectric memory element is coerced to said desired state of polarization.
Claim 21
Dependent Claim
251 words
In a non-volatile memory device having at least one ferroelectric memory element within at least one memory cell, wherein a polarization state of said ferroelectric memory element is associated with a stored logic "1" and another polarization state of said ferroelectric memory element is associated with a stored logic "0", a method for reducing polarizability fatigue of said ferroelectric memory element comprising the steps of: receiving a request to coerce the state of polarization of said ferroelectric memory element to a desired state of polarization; generating, responsive to said request, a Gaussian shaped waveform electric field signal having a directional polarity and having a maximum amplitude sufficient to alter said state of polarization of said ferroelectric memory element, said signal having a predetermined rise time, during which the amplitude of said signal changes from a first level to said maximum amplitude, wherein said predetermined rise time is selected from the group comprising, about one half the plate rise time of said ferroelectric memory element, and about one half the sense delay time of said ferroelectric memory element, said signal having a predetermined hold time during which the amplitude of said signal remains at said maximum amplitude, said signal having a predetermined fall time, during which the amplitude of said signal changes from said maximum amplitude to said first level; and applying, responsive to said request, said signal to said ferroelectric memory element such that the state of polarization of said ferroelectric memory element is coerced to said desired state of polarization.
Claim 22
Dependent Claim
14 words
The method of claim 17 wherein said ferroelectric memory element is a ferroelectric capacitor.
References Cited (Backward Citations)
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