Ephemeral storage elements, circuits, and systems
First Claim
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1. A memory device on an integrated circuit adapted with ephemeral data retention capability comprising:
- an array of charge storage elements;
wherein said charge storage element is characterized by an inherent leakage current and is configurable;
to store a first amount of charge corresponding to a first unprogrammed state representing a first data value; and
to store a second amount of charge corresponding to a second programmed state representing a second data value;
a programming control circuit configured;
to set said array of charge elements to said second programmed state representing said second data value based on a first write operation;
to initiate and control a first scheduled erase operation in which all charge is removed from a selected charge storage element over a first predetermined erase period;
to initiate and control a second separate slower erase operation on said array, during which a controlled erase charge is actively removed from selected charge storage elements over second predetermined erase periods that are longer than said first determined period and in the absence of a new second write operation for such array;
wherein said programming control circuit is adapted to actively impose erase bias voltages to said array of charge storage elements during said controlled predetermined period so that said controlled erase charge is removed from such elements in addition to charge lost to leakage current by such elements.
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Abstract
An array of programmable non-volatile devices are is adapted such that their logic state is controllably altered over time by quiescent changes, slow controlled changes, scheduled changes, or some combination thereof imposed at a physical level. This allows for improved security and privacy for data to be permanently deleted. In some applications a data refresh and/or automatic backup can be implemented as well.
34 Citations
30 Claims
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1. A memory device on an integrated circuit adapted with ephemeral data retention capability comprising:
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an array of charge storage elements; wherein said charge storage element is characterized by an inherent leakage current and is configurable; to store a first amount of charge corresponding to a first unprogrammed state representing a first data value; and to store a second amount of charge corresponding to a second programmed state representing a second data value; a programming control circuit configured; to set said array of charge elements to said second programmed state representing said second data value based on a first write operation; to initiate and control a first scheduled erase operation in which all charge is removed from a selected charge storage element over a first predetermined erase period; to initiate and control a second separate slower erase operation on said array, during which a controlled erase charge is actively removed from selected charge storage elements over second predetermined erase periods that are longer than said first determined period and in the absence of a new second write operation for such array; wherein said programming control circuit is adapted to actively impose erase bias voltages to said array of charge storage elements during said controlled predetermined period so that said controlled erase charge is removed from such elements in addition to charge lost to leakage current by such elements. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13)
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14. A memory device on an integrated circuit adapted with ephemeral data retention capability comprising:
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an array of charge storage elements; wherein each charge storage element in said array is characterized by an inherent leakage current and is configurable; to store a first amount of charge corresponding to a first state corresponding to a first state representing a first data value; and to store a second amount of charge corresponding to a second state representing a second data value; a programming control circuit configured; to program said array of charge storage elements to said second data value based on a first write operation; to initiate and control a slow erase operation on said array, including at least a first mode in which a controlled erase charge is actively removed from a selected charge storage element over a controlled predetermined period and in the absence of a new second write operation for such selected charge storage element; to actively impose erase bias voltages to said array of charge storage elements during said controlled predetermined period so that said controlled erase charge is removed from such elements in addition to charge lost to leakage current by such elements; and to apply the smallest possible bias required to remove charge from the selected charge storage elements during said controlled predetermined period to achieve a target data retention time. - View Dependent Claims (15, 16, 17)
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18. A memory device on an integrated circuit adapted with ephemeral data retention capability comprising:
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an array of charge storage elements; wherein said charge storage element is characterized by an inherent leakage current and is configurable; to store a first amount of charge corresponding to a first unprogrammed state representing a first data value; and to store a second amount of charge corresponding to a second programmed state representing a second data value; a programming control circuit configured; to set said array of charge elements to said second programmed state representing said second data value based on a first write operation; to initiate and control an erase operation on said array, including at least a first mode in which a controlled erase charge is actively removed from selected charge storage elements at predetermined erase periods and in the absence of a new second write operation for such array; to actively impose erase bias voltages to said array of charge storage elements during said controlled predetermined period so that said controlled erase charge is removed from such elements in addition to charge lost to leakage current by such elements; and to cause apply the smallest possible bias required to remove charge from the selected charge storage elements during said controlled predetermined period to achieve a target data retention time. - View Dependent Claims (19, 20, 21)
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22. A memory device on an integrated circuit adapted with ephemeral data retention capability comprising:
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an array of charge storage elements; wherein each charge storage element in said array is characterized by an inherent leakage current and is configurable; to store a first amount of charge corresponding to a first state corresponding to a first state representing a first data value; and to store a second amount of charge corresponding to a second state representing a second data value; a programming control circuit configured; to program said array of charge storage elements to said second data value based on a first write operation; to initiate and control a slow erase operation on said array, including at least a first mode in which a controlled erase charge is actively removed from a selected charge storage element over a controlled predetermined period and in the absence of a new second write operation for such selected charge storage element; wherein said programming control circuit is adapted to actively impose erase bias voltages to said array of charge storage elements during said controlled predetermined period so that said controlled erase charge is removed from such elements in addition to charge lost to leakage current by such elements, by applying the smallest possible bias required to remove charge from the selected charge storage elements during said controlled predetermined period to achieve a target data retention time; further wherein a nominal data retention time capability of the selected charge storage elements is actively shortened by said slow erase operation. - View Dependent Claims (23, 24, 25, 26, 27, 28, 29)
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30. A memory device on an integrated circuit adapted with ephemeral data retention capability comprising:
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an array of charge storage elements; wherein said charge storage element is characterized by an inherent leakage current and is configurable; to store a first amount of charge corresponding to a first unprogrammed state representing a first data value; and to store a second amount of charge corresponding to a second programmed state representing a second data value; a programming control circuit configured; to set said array of charge elements to said second programmed state representing said second data value based on a first write operation; to initiate and control an erase operation on said array, including at least a first mode in which a controlled erase charge is actively removed from selected charge storage elements at predetermined erase periods and in the absence of a new second write operation for such array; wherein said programming control circuit is adapted to actively impose erase bias voltages to said array of charge storage elements during said controlled predetermined period so that said controlled erase charge is removed from such elements in addition to charge lost to leakage current by such elements; further wherein a nominal data retention time capability of the selected charge storage elements is actively shortened by said slow erase operation.
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Specification