US5262982A — Nondestructive reading of a ferroelectric capacit…

Claim 1

Independent Claim 133 words

A method of determining a polarization state of a ferroelectric capacitor exhibiting hysteresis characteristics, comprising the steps of: applying a first electric field of a first polarity to the ferroelectric capacitor to produce a first readout signal of a first polarity and a first magnitude; applying a second electric field of a polarity different from that of the first electric field, across the ferroelectric capacitor to produce a second readout signal of a polarity different from that of the first readout signal; combining electrical charges resulting from the first and second readout signals to produce a resultant signal representative of the polarization state stored in the ferroelectric capacitor; and comparing the resultant signal with a reference voltage to produce an output digital state representative of the polarization state stored in the ferroelectric capacitor.

Claim 2

Independent Claim 133 words

A method of determining a polarization state of a ferroelectric capacitor exhibiting hysteresis characteristics, comprising the steps of: applying a first electric field of a first polarity to the ferroelectric capacitor to produce a first readout signal of a first polarity and a first magnitude; applying a second electric field of a polarity different from that of the first electric field, across the ferroelectric capacitor to produce a second readout signal of a polarity different from that of the first readout signal; combining electrical charges resulting from the first and second readout signals to produce a resultant signal representative of the polarization state stored in the ferroelectric capacitor; and comparing the resultant signal with a reference voltage to produce an output digital state representative of the polarization state stored in the ferroelectric capacitor.

Claim 3

Dependent Claim 32 words

The method of claim 1, further including summing the first readout signal with the second readout signal to produce a resultant polarity representative of the polarization state stored in the ferroelectric capacitor.

Claim 4

Dependent Claim 30 words

The method of claim 1, further including producing said first and second readout signals and storing a voltage representative of each said readout signal, and thereafter combining said stored voltages.

Claim 5

Dependent Claim 32 words

The method of claim 1, further including storing the first and second readout voltages in respective capacitances, and electrically isolating one said capacitance from the other during a predefined period of time.

Claim 6

Dependent Claim 23 words

The method of claim 4, further including connecting said capacitances in parallel during another predefined period of time to produce said resultant signal.

Claim 7

Dependent Claim 31 words

The method of claim 5, further including comparing the resultant signal with said reference voltage to produce said output digital state representative of the polarization state stored in the ferroelectric capacitor.

Claim 8

Dependent Claim 16 words

The method of claim 6, further including comparing the resultant signal with a circuit common potential.

Claim 9

Dependent Claim 33 words

The method of claim 1, further including applying electric fields each of a magnitude such that the ferroelectric capacitor does not switch said polarization state during the determination of the stored polarization state.

Claim 10

Independent Claim 145 words

A method for determining a polarization sate of a ferroelectric capacitor memory cell exhibiting a hysteresis characteristic, comprising the steps of: applying a word line signal to access the memory cell; applying a drive line voltage of a magnitude insufficient to change the polarization state to one plate of the ferroelectric capacitor of the memory cell, said drive line voltage having a first polarity pulse followed by a second pulse having a polarity different from said first polarity pulse; generating a first capacitor readout signal on a bit line in response to the first polarity pulse; generating a second capacitor readout signal on the bit line in response to the second polarity pulse; and combining the first and second readout signals together to derive a resultant signal for use in determining the polarization state of the ferroelectric capacitor memory cell without destroying the polarization state.

Claim 11

Independent Claim 145 words

A method for determining a polarization sate of a ferroelectric capacitor memory cell exhibiting a hysteresis characteristic, comprising the steps of: applying a word line signal to access the memory cell; applying a drive line voltage of a magnitude insufficient to change the polarization state to one plate of the ferroelectric capacitor of the memory cell, said drive line voltage having a first polarity pulse followed by a second pulse having a polarity different from said first polarity pulse; generating a first capacitor readout signal on a bit line in response to the first polarity pulse; generating a second capacitor readout signal on the bit line in response to the second polarity pulse; and combining the first and second readout signals together to derive a resultant signal for use in determining the polarization state of the ferroelectric capacitor memory cell without destroying the polarization state.

Claim 12

Dependent Claim 21 words

The method of claim 9, further including carrying out the combining step by adding together the first and second readout signals.

Claim 13

Dependent Claim 20 words

The method of claim 9, further including storing the first and second capacitor readout signals, each having an opposite polarity.

Claim 14

Dependent Claim 42 words

The method of claim 11, further including combining the readout signals by summing the readout signals together to produce a summer signal, and comparing the summed signal with a reference voltage to determine which of said readout signals has a greater magnitude.

Claim 15

Dependent Claim 42 words

The method of claim 9, further including writing the ferroelectric capacitor with a first polarization state by applying a first polarity voltage across the ferroelectric capacitor, and writing an opposite polarization state by applying a second polarity voltage across the ferroelectric capacitor.

Claim 16

Dependent Claim 12 words

A ferroelectric memory circuit for carrying out the method of claim 9.

Claim 17

Independent Claim 134 words

A method for determining a polarization state of a ferroelectric capacitor exhibiting hysteresis characteristics, comprising the steps of: applying an electric field across the ferroelectric capacitor of a first polarity and of such a magnitude that switching of the polarization state thereof does not occur, and producing a first readout signal; applying an electric field across the ferroelectric capacitor of a second polarity different from said first polarity and of such a magnitude that switching or a polarization state thereof does not occur, and producing a second readout signal; and determining the polarization state of the ferroelectric capacitor by combining the first readout signal having a defined magnitude and polarity with the second readout signal having a different polarity to obtain a resultant polarity, and assigning the polarization state based upon the resultant polarity.

Claim 18

Independent Claim 134 words

A method for determining a polarization state of a ferroelectric capacitor exhibiting hysteresis characteristics, comprising the steps of: applying an electric field across the ferroelectric capacitor of a first polarity and of such a magnitude that switching of the polarization state thereof does not occur, and producing a first readout signal; applying an electric field across the ferroelectric capacitor of a second polarity different from said first polarity and of such a magnitude that switching or a polarization state thereof does not occur, and producing a second readout signal; and determining the polarization state of the ferroelectric capacitor by combining the first readout signal having a defined magnitude and polarity with the second readout signal having a different polarity to obtain a resultant polarity, and assigning the polarization state based upon the resultant polarity.

Claim 19

Dependent Claim 38 words

The method of claim 15, further including generating the first readout signal in response to the electric field having the first polarity, and generating the second readout signal in response to the electric field having the second polarity.

Claim 20

Dependent Claim 28 words

The method of claim 15, further including charging a first storage capacitor with the first readout signal, and charging a second storage capacitor with the second readout signal.

Claim 21

Dependent Claim 33 words

The method of claim 17, further including connecting the storage capacitors in parallel to effectively produce a resultant summation signal having a polarity corresponding to the polarization state stored in said ferroelectric capacitor.

Claim 22

Dependent Claim 11 words

A ferroelectric memory for carrying out the method of claim 15.

Claim 23

Dependent Claim 148 words

A nonvolatile ferroelectric memory, comprising: a drive line; a bit line; at least one memory cell having a ferroelectric capacitor in series with a transistor switch, said cell being connected between said drive line and said bit line; a word line connected to said memory cell for controlling the transistor switch; a sense amplifier circuit connected to said bit line, said sense amplifier circuit including, a first storage capacitor for storing a first readout signal from said ferroelectric capacitor; a second storage capacitor for storing a second readout signal from said ferroelectric capacitor; isolation means for isolating said first and second storage capacitors from each other; and combining means for combining the charge stored in said first and second storage capacitors; and amplifier means for amplifying a signal representative of the combined charge to provide a digital output signal representative of a polarization state of the ferroelectric capacitor.

Claim 24

Dependent Claim 148 words

A nonvolatile ferroelectric memory, comprising: a drive line; a bit line; at least one memory cell having a ferroelectric capacitor in series with a transistor switch, said cell being connected between said drive line and said bit line; a word line connected to said memory cell for controlling the transistor switch; a sense amplifier circuit connected to said bit line, said sense amplifier circuit including, a first storage capacitor for storing a first readout signal from said ferroelectric capacitor; a second storage capacitor for storing a second readout signal from said ferroelectric capacitor; isolation means for isolating said first and second storage capacitors from each other; and combining means for combining the charge stored in said first and second storage capacitors; and amplifier means for amplifying a signal representative of the combined charge to provide a digital output signal representative of a polarization state of the ferroelectric capacitor.

Claim 25

Dependent Claim 38 words

The nonvolatile memory of claim 20, wherein isolation means comprises a first transistor for isolating said first storage capacitor from said bit line, and a second transistor for isolating said second storage capacitor from said first storage capacitor.

Claim 26

Dependent Claim 35 words

The nonvolatile memory of claim 21, further including a third transistor for isolating the second storage capacitor from said bit line, and a fourth transistor for isolating said second storage capacitor from said amplifier means.

Claim 27

Dependent Claim 19 words

The nonvolatile memory of claim 22, wherein each gate terminal of said second and fourth transistor is connected together.

Claim 28

Dependent Claim 40 words

The nonvolatile memory of claim 22, wherein said first and third transistors are driven into conduction at different times so that respective electrical charges can be stored sequentially in said first storage capacitor and then in said second storage capacitor.

Claim 29

Dependent Claim 33 words

The nonvolatile memory of claim 20, further including a driver for driving said drive line with a bipolar pulse applied to said ferroelectric capacitor to thereby generate said first and second readout signals.

Claim 30

Dependent Claim 45 words

The nonvolatile memory of claim 25, further including a feedback connection between said sense amplifier and said drive line driver so that a refresh voltage of desired magnitude can be applied to said ferroelectric capacitor based on said polarization state stored in said ferroelectric capacitor.

Claim 31

Dependent Claim 35 words

The nonvolatile memory of claim 20, further including a driver for driving said drive line with a voltage having a magnitude insufficient to switch said polarization state of the ferroelectric capacitor during a read operation.

Claim 32

Dependent Claim 12 words

The nonvolatile memory of claim 27 wherein said driver generates bipolar pulses.

Claim 33

Dependent Claim 36 words

The nonvolatile memory of claim 20, further including a driver for driving the drive line with bipolar pulses having a first magnitude during writing of the ferroelectric capacitor, and having a different magnitude during reading thereof.

Claim 34

Dependent Claim 38 words

The nonvolatile memory of claim 29, wherein the driver generates during read operations said bipolar pulses that have a magnitude less than a magnitude of the drive pulses that are generated during write operations of the ferroelectric capacitor.

Claim 35

Dependent Claim 17 words

The nonvolatile memory of claim 30, wherein said driver generates drive pulses for refreshing said ferroelectric capacitors.

Claim 36

Dependent Claim 34 words

The nonvolatile memory of claim 31, wherein said driver generates small amplitude bipolar pulses during memory read operations, and subsequent thereto said driver generates a higher magnitude pulse for refreshing an accessed memory cell.

Claim 37

Dependent Claim 11 words

A ferroelectric memory for carrying out the method of claim 1.

Claim 38

Dependent Claim 135 words

Apparatus for determining a polarization state of a ferroelectric capacitor memory cell exhibiting a hysteresis characteristic, comprising: means for applying a word line signal to access the cell; means for applying a drive line voltage to one plate of the ferroelectric capacitor of the memory cell, said drive line voltage having a first polarity pulse followed by a second different polarity pulse; means for generating a first ferroelectric capacitor readout signal on a bit line in response to the first polarity pulse; means for generating a second ferroelectric capacitor readout signal on the bit line in response to the second polarity pulse; and means for combining together electrical charges representative of the first and second readout signals to determine a resultant first or second polarity that corresponds to the polarization state of the ferroelectric capacitor.

Claim 39

Dependent Claim 135 words

Apparatus for determining a polarization state of a ferroelectric capacitor memory cell exhibiting a hysteresis characteristic, comprising: means for applying a word line signal to access the cell; means for applying a drive line voltage to one plate of the ferroelectric capacitor of the memory cell, said drive line voltage having a first polarity pulse followed by a second different polarity pulse; means for generating a first ferroelectric capacitor readout signal on a bit line in response to the first polarity pulse; means for generating a second ferroelectric capacitor readout signal on the bit line in response to the second polarity pulse; and means for combining together electrical charges representative of the first and second readout signals to determine a resultant first or second polarity that corresponds to the polarization state of the ferroelectric capacitor.

Claim 40

Dependent Claim 26 words

The apparatus of claim 34, further including a comparator for comparing the resultant first or second polarity with a reference voltage to determine the polarization state.

Claim 41

Dependent Claim 13 words

The apparatus of claim 35, further including a zero volt reference voltage generator.

Claim 42

Dependent Claim 11 words

The apparatus of claim 35, further including a nonzero reference voltage.

Annuity Stage	Window Opens	Payment Deadline	Surcharge Period Until	Estimated Fee	Status
3.5 Years (Year 4)	1996-11-15	1997-05-17	1997-11-16	$2000.00	Window Closed / Lapsed
7.5 Years (Year 8)	2000-11-15	2001-05-17	2001-11-16	$3760.00	Window Closed / Lapsed
11.5 Years (Year 12)	2004-11-15	2005-05-17	2005-11-16	$7700.00	Window Closed / Lapsed

Nondestructive reading of a ferroelectric capacitor

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