Ferroelectric memories and method of activating the same

Claim 2

A ferroelectric memory comprising a thin plate formed of a ferroelectric material, cut perpendicularly to its ferroelectric axis and metallized directly on its two larger faces perpendicular to said axis, means for applying, at will, a preparation or erasing voltage between these two faces in order to polarize all the ferroelectric domains in the same direction, a load resistor connectable across the two metallized faces of the plate, means for concentrating the spot of a laser beam directly on one of the two metallized faces constituting an active face of the plate and to scan said active face point by point with this spot, said laser being used both for writing and reading information on the active face of said memory and means for detecting the flow and direction of a current in said load resistor when it is connected across the two metallized faces, said memory including means for applying, during writing, a voltage of zero value, the energy introduced by the laser beam at each point of the active face of said plate being at least equal to a given value during writing, this energy being adapted to create a polarization gradient for generating an electric field adapted to produce an irreversible switching of the polarization of the domain situated under said point, this energy introduced by the laser beam having a value substantially less on reading.

Claim 3

The memory according to claim 1, comprising control means for the time of application, at each point of said active face, of the spot of the laser beam having a given intensity, these control means being arranged to enable adjustment of the time of application so that this time of application is substantially greater on writing than on reading, the time of application of the spot of the laser beam on writing being at least equal to a value t which is a function of said given intensity.

Claim 4

The memory according to claim 1, comprising attenuation means for attenuating the intensity of the laser beam on reading.

Claim 5

The memory according to claiM 1, wherein the means for concentrating the spot of the laser beam directly on the active surface of said plate comprise a microscope.

Claim 6

The memory according to claim 1, wherein the metal covering said active face of the plate comprises a layer of chromium whose squared resistance is equal to 377 ohms.

Claim 7

The ferroelectric memory according to claim 1, wherein said ferroelectric material is selected from the group comprising the following materials: triglycine sulfate, lead zircotitanate and triglycine seleniate.

Claim 8

The memory according to claim 1, comprising a resistance of high value with respect to the value of the load resistor, this resistance being connected between the metallized faces of the plate.

Claim 9

A ferroelectric memory comprising a thin plate formed of a ferroelectric material and metallized directly on its two large faces, means for applying, at will, an erasing voltage between these two faces in order to polarize all the domains in the same direction, means for concentrating the spot of a laser beam directly on one of the two metallized faces of the plate and to scan said face point by point with this spot, and means for reading information written on said memory, comprising means for applying between said two faces on writing, a voltage of zero value, the energy introduced by the spot of the laser beam at each point of said face of the plate being at least equal to a given value, this energy being adapted to create a polarization gradient for generating an electric field adapted to produce an irreversible switching of the polarization of the domain situated under said point.

Claim 10

A ferroelectric memory comprising a thin plate formed of a ferroelectric material and metallized directly on its two large faces, means for applying, at will, an erasing voltage between these two faces in order to polarize all the domains in the same direction, means for concentrating the spot of a laser beam directly on one of the two metallized faces of the plate and to scan said face point by point with this spot, and means for reading information written on said memory, comprising means for applying between said two faces on writing, a voltage of zero value, the energy introduced by the spot of the laser beam at each point of said face of the plate being at least equal to a given value, this energy being adapted to create a polarization gradient for generating an electric field adapted to produce an irreversible switching of the polarization of the domain situated under said point.

Claim 11

The memory according to claim 8, wherein said ferroelectric material is bismuth titanate.

Claim 12

A ferroelectric memory device which includes, in combination, a thin plate made of a ferroelectric material cut at right angles to its ferroelectric axis and metallized directly on its two larger faces perpendicular thereto, means for applying at will across said two faces a first or a second voltage, a load resistor connectable across the two metallized faces of the plate, means for focusing the spot of a laser beam of desired intensity to reach a focus directly on one of the two metallized faces constituting an active face of the plate and for scanning said active face of the plate with said spot, said laser beam being utilized both for writing and reading information on said memory device, means capable of occluding when desired said laser spot during writing, and means for detecting the flow and direction of a current through said resistor when the same is connected across said two faces, the desired intensity of the laser beam being selected in order to produce, on reading, a reversible switching of the polarization of the domains, and an irreversible switching of the polarization of the domains when said laser spot is unoccluded.

Claim 13

A ferroelectric memory device which includes, in combination, a thin plate made of a ferroelectric material cut at right angles to its ferroelectric axis and metallized directly on its two larger faces perpendicular thereto, means for applying at will across said two faces a first or a second voltage, a load resistor connectable across the two metallized faces of the plate, means for focusing the spot of a laser beam of desired intensity to reach a focus directly on one of the two metallized faces constituting an active face of the plate and for scanning said active face of the plate with said spot, said laser beam being utilized both for writing and reading information on said memory device, means capable of occluding when desired said laser spot during writing, and means for detecting the flow and direction of a current through said resistor when the same is connected across said two faces, the desired intensity of the laser beam being selected in order to produce, on reading, a reversible switching of the polarization of the domains, and an irreversible switching of the polarization of the domains when said laser spot is unoccluded.

Claim 14

A ferroelectric memory device including a thin plate of a ferroelectric material cut at right angles to its ferroelectric axis and metallized directly on its two larger faces perpendicular thereto, means for applying across said two faces a preparation voltage, a load resistor connectable across the two metallized faces of the plate, means for focusing the spot of a laser beam to reach a focus directly on one of the two metallized faces constituting an active face of the plate and for scanning said active face of the plate with said spot, said laser being utilized both for writing and reading information on the memory device, means for occluding said laser spot during writing, means for detecting the flow and direction of a current through said load resistor when it is connected between the two metallized faces and means for applying between said faces, during writing, a voltage of zero value or of the same sense as the preparation voltage, the energy brought by the spot of the laser beam on each point of the active face of the plate having, during writing, a value which is at least equal to a given value, this energy being adapted to cReate a polarization gradient for generating an electric field adapted to produce an irreversible switching of the polarization of the domain situated under said point, said energy brought by the spot of the laser beam to each point of the active face of the plate having a value, during reading, which is much less than the value of said energy during writing.

Claim 15

A ferroelectric memory device including a thin plate of a ferroelectric material cut at right angles to its ferroelectric axis and metallized directly on its two larger faces perpendicular thereto, means for applying across said two faces a preparation voltage, a load resistor connectable across the two metallized faces of the plate, means for focusing the spot of a laser beam to reach a focus directly on one of the two metallized faces constituting an active face of the plate and for scanning said active face of the plate with said spot, said laser being utilized both for writing and reading information on the memory device, means for occluding said laser spot during writing, means for detecting the flow and direction of a current through said load resistor when it is connected between the two metallized faces and means for applying between said faces, during writing, a voltage of zero value or of the same sense as the preparation voltage, the energy brought by the spot of the laser beam on each point of the active face of the plate having, during writing, a value which is at least equal to a given value, this energy being adapted to cReate a polarization gradient for generating an electric field adapted to produce an irreversible switching of the polarization of the domain situated under said point, said energy brought by the spot of the laser beam to each point of the active face of the plate having a value, during reading, which is much less than the value of said energy during writing.

Claim 16

A ferroelectric memory comprising a thin plate formed of a ferroelectric material, cut perpendicularly to its ferroelectric axis and metallized directly on its two larger faces perpendicular to said axis, means for applying, at will, a preparation or erasing voltage between these two faces in order to polarize all the ferroelectric domains in the same direction, a load resistor connectable across the two metallized faces of the plate, means for concentrating the spot of a laser beam directly on one of the two metallized faces constituting an active face of the plate and to scan said active face point by point with this spot, said laser being used both for writing and reading information on the active face of said memory and means for detecting the flow and direction of a current in said load resistor when it is connected across the two metallized faces, said memory further including means for applying, during writing, a voltage of zero value or of the same sense as the erasing voltage, the energy introduced by the laser beam at each point of the active face of said plate being at least equal to a given value during writing, this energy being adapted to create a polarization gradient for generating an electric field adapted to produce an irreversible switching of the polarization of the domain situated under said point, this energy introduced by the laser beam having a value substantially less on reading; and wherein the energy introduced by the laser beam at each point of the active face of said plate on reading is adapted to generate a polarization gradient for creating an electric field adapted to produce a reversible switching of the polarization of the domain beneath said point.

Claim 17

A ferroelectric memory comprising a thin plate formed of a ferroelectric material, cut perpendicularly to its ferroelectric axis and metallized directly on its two larger faces perpendicular to said axis, means for applying, at will, a preparation or erasing voltage between these two faces in order to polarize all the ferroelectric domains in the same direction, a load resistor connectable across the two metallized faces of the plate, means for concentrating the spot of a laser beam directly on one of the two metallized faces constituting an active face of the plate and to scan said active face point by point with this spot, said laser being used both for writing and reading information on the active face of said memory and means for detecting the flow and direction of a current in said load resistor when it is connected across the two metallized faces, said memory further including means for applying, during writing, a voltage of zero value or of the same sense as the erasing voltage, the energy introduced by the laser beam at each point of the active face of said plate being at least equal to a given value during writing, this energy being adapted to create a polarization gradient for generating an electric field adapted to produce an irreversible switching of the polarization of the domain situated under said point, this energy introduced by the laser beam having a value substantially less on reading; and wherein the energy introduced by the laser beam at each point of the active face of said plate on reading is adapted to generate a polarization gradient for creating an electric field adapted to produce a reversible switching of the polarization of the domain beneath said point.

Claim 18

A ferroelectric memory comprising a thin plate formed of a ferroelectric material, cut perpendicularly to its ferroelectric axis and metallized directly on its two larger faces perpendicular to said axis, means for applying, at will, a preparation or erasing voltage between these two faces in order to polarize all the ferroelectric domains in the same direction, a load resistor connectable across the two metallized faces of the plate, means for concentrating the spot of a laser beam directly on one of the two metallized faces constituting an active face of the plate and to scan said active face point by point with this spot, said laser being used both for writing and reading information on the active face of said memory and means for detecting the flow and direction of a current in said load resistor when it is connected across the two metallized faces, said memory including means for applying, during writing, a voltage of the same sense as the erasing voltage, the energy introduced by the laser beam at each point of the active face of said plate being at least equal to a given value during writing, this energy being adapted to create a polarization gradient for generating an electric field adapted to produce an irreversible switching of the polarization of the domain situated under said point, this energy introduced by the laser beam having a value substantially less on reading.

Claim 19

A ferroelectric memory comprising a thin plate formed of a ferroelectric material, cut perpendicularly to its ferroelectric axis and metallized directly on its two larger faces perpendicular to said axis, means for applying, at will, a preparation or erasing voltage between these two faces in order to polarize all the ferroelectric domains in the same direction, a load resistor connectable across the two metallized faces of the plate, means for concentrating the spot of a laser beam directly on one of the two metallized faces constituting an active face of the plate and to scan said active face point by point with this spot, said laser being used both for writing and reading information on the active face of said memory and means for detecting the flow and direction of a current in said load resistor when it is connected across the two metallized faces, said memory including means for applying, during writing, a voltage of the same sense as the erasing voltage, the energy introduced by the laser beam at each point of the active face of said plate being at least equal to a given value during writing, this energy being adapted to create a polarization gradient for generating an electric field adapted to produce an irreversible switching of the polarization of the domain situated under said point, this energy introduced by the laser beam having a value substantially less on reading.

Claim 20

A ferroelectric memory comprising a thin plate formed of a ferroelectric material and metallized directly on its two large faces, means for applying, at will, an erasing voltage between these two faces in order to polarize all the domains in the same direction, means for concentrating the spot of a laser beam directly on one of the two metallized faces of the plate and to scan said face point by point with this spot, and means for reading information written on said memory, comprising means for applying between said two faces on writing, a voltage of tHe same sense as the erasing voltage, the energy introduced by the spot of the laser beam at each point of said face of the plate being at least equal to a given value, this energy being adapted to create a polarization gradient for generating an electric field adapted to produce an irreversible switching of the polarization of the domain situated under said point.

Claim 21

A ferroelectric memory comprising a thin plate formed of a ferroelectric material and metallized directly on its two large faces, means for applying, at will, an erasing voltage between these two faces in order to polarize all the domains in the same direction, means for concentrating the spot of a laser beam directly on one of the two metallized faces of the plate and to scan said face point by point with this spot, and means for reading information written on said memory, comprising means for applying between said two faces on writing, a voltage of tHe same sense as the erasing voltage, the energy introduced by the spot of the laser beam at each point of said face of the plate being at least equal to a given value, this energy being adapted to create a polarization gradient for generating an electric field adapted to produce an irreversible switching of the polarization of the domain situated under said point.