Memory cell with volatile and non-volatile portions having ferroelectric capacitors
AssigneeRamtron Corporation
InventorsKlaus Dimmler, S. Sheffield Eaton, Jr.
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Abstract
A memory cell includes an SRAM flip-flop cell having two nodes coupled to ferroelectric capacitors so that when the SRAM is powered down, the ferroelectric devices store data and upon power up, transfer the stored data to the SRAM cell. The ferroelectric devices can be bypassed during normal SRAM operations to reduce hysteresis fatigue.
Claims8
A method of operating a memory cell having volatile and nonvolatile portions, said non-volatile portion including first and second ferroelectric capacitors each having first and second plate electrodes, the method comprising the steps of:
- storing complementary binary data in said volatile portion, including developing high and low voltages representing the complementary data at first and second nodes of the volatile memory cell portion;
- coupling said first and second nodes to the first plate electrodes of the first and second ferroelectric capacitors;
- polarizing only one of said ferroelectric capacitors by applying a low voltage to the second plate electrode thereof while the first plate electrode of said capacitor is coupled to said first or second node, said polarizing occurring in a first direction;
- thereafter
- polarizing the second ferroelectric capacitor by raising the voltage on the second plate electrode thereof while the first plate electrode is coupled to said first or second node, said polarizing occurring in a second direction.
The method according to claim, 1 wherein a third node is coupled to the second plate electrodes of each of said first and second ferroelectric capacitors, and wherein said polarizing steps comprise sequentially applying a low voltage and then a high voltage to said third node while coupling said first and second node to the first plate electrodes of said first and second ferroelectric capacitors.
A method of operating a memory cell including first and second ferroelectric capacitors each having first and second plate electrodes, the method including volatile and nonvolatile operations and comprising the steps of:
- storing complementary binary data in a volatile manner, including developing high and low voltages representing the complementary data at first and second nodes within the memory cell;
- coupling said first and second nodes to the first plate electrodes of the first and second ferroelectric capacitors;
- polarizing only one of said ferroelectric capacitors by applying a high voltage to the second plate electrode thereof while the first plate electrode thereof is coupled to said first or second node, said polarizing occurring in a first direction;
- thereafter
- polarizing the second ferroelectric capacitor by dropping the voltage on the second plate electrode thereof while the first plate electrode is coupled to said first or second node, said polarizing occurring in a second direction.
Dependencies are inferred from the claim text.