Ferroelectric memory device, method for driving ferroelectric memory device, and electronic equipment
A ferroelectric memory device includes: a memory cell having a ferroelectric capacitor connected between a plate line and a bit line; a first node connected to the bit line through a charge transfer MISFET; a potential generation circuit that has a first capacitor having a first terminal connected to the first node and a first switching MISFET connected to a second terminal of the first capacitor, and is capable of setting the first node to a negative potential; and a sense amplifier connected to the second terminal of the first capacitor. When reading a charge stored in the ferroelectric capacitor, the potential generation circuit sets the first node at a negative potential and then sets the first switching MISFET to an off state, thereby setting the second terminal of the first capacitor to a floating state, and the sense amplifier amplifies a potential on the second terminal of the first capacitor in the floating state.
1. A ferroelectric memory device comprising:
a memory cell having a ferroelectric capacitor connected between a plate line and a bit line;
a first node connected to the bit line through a charge transfer MISFET;
a potential generation circuit that has a first capacitor having a first terminal connected to the first node and a first switching MISFET connected to a second terminal of the first capacitor, and is capable of setting the first node to a negative potential; and
a sense amplifier connected to the second terminal of the first capacitor,
wherein, when reading a charge stored in the ferroelectric capacitor, the potential generation circuit sets the first node at a negative potential and then sets the first switching MISFET to an off state, thereby setting the second terminal of the first capacitor to a floating state, and the sense amplifier amplifies a potential on the second terminal of the first capacitor in the floating state.
2. A ferroelectric memory device according to claim 1 , wherein the first switching MISFET is connected between a ground potential and the second terminal of the first capacitor, and the potential generation circuit has a second switching MISFET connected between a power supply potential and the second terminal of the first capacitor.
3. A ferroelectric memory device according to claim 2 , wherein, by setting the first and second switching MISFETs from OFF and ON states to ON and OFF states, respectively, the first node is set to a negative potential; and by setting the first and second switching MISFETs to OFF and OFF states, respectively, the second terminal of the first capacitor is set to a floating state.
4. A ferroelectric memory device according to claim 1 , wherein the potential generation circuit has a first inverter, and a second capacitor connected between an output of the first inverter and the first node.
5. A ferroelectric memory device according to claim 1 , comprising a source follower circuit between the second terminal of the first capacitor and the sense amplifier.
6. A ferroelectric memory device according to claim 5 , wherein the source follower circuit has a first MISFET that has a gate electrode connected to the second terminal of the first capacitor and is connected between the power supply potential and the sense amplifier, and a second MISFET that has a gate electrode connected to the first node and is connected between the ground potential and the sense amplifier.
7. A ferroelectric memory device according to claim 1 , comprising a threshold potential generation circuit that is connected to a gate electrode of the charge transfer MISFET.
8. A ferroelectric memory device according to claim 1 , wherein the charge transfer MISFET is a p-channel type MISFET.
9. A ferroelectric memory device according to claim 1 , comprising a control circuit that is connected between the bit line and a gate electrode of the charge transfer MISFET, and controls the potential to be applied to the gate electrode according to the potential on the bit line.
10. A ferroelectric memory device according to claim 9 , wherein the control circuit has a second inverter that is connected between the bit line and the gate electrode of the charge transfer MISFET, the second inverter having an input section connected to the bit line through a third capacitor, and an output section connected to a gate electrode of the charge transfer MISFET through a fourth capacitor.
11. An electronic equipment comprising the ferroelectric memory device recited in claim 1 .
12. A method for driving a ferroelectric memory device that has a memory cell having a ferroelectric capacitor connected between a plate line and a bit line, a first node connected to the bit line through a charge transfer MISFET, a potential generation circuit that has a first capacitor having a first terminal connected to the first node and a switching MISFET connected to a second terminal of the first capacitor, and a sense amplifier connected to the second terminal of the first capacitor, the method comprising the steps of:
1) changing the potential on the second terminal of the first capacitor from a high potential level to a low potential level to set the first node to a negative potential;
2) setting the switching MISFET to an off state, after the step 1);
3) changing the potential on the plate line from a low potential level to a high potential level to transfer a charge stored in the ferroelectric capacitor to the first node through the charge transfer MISFET, after the step 1); and
amplifying the potential on the second terminal of the first capacitor by the sense amplifier, after the step 2), thereby conducting a readout operation.