Ferroelectric capacitor and ferroelectric memory

1. A ferroelectric capacitor comprising:

a first capacitor and a second capacitor having the first electrodes (storage node electrodes) connected to each other and drawing the same hysteresis curve, the second electrodes of these first and second capacitors are connected to a first plate line and a second plate line, respectively and the potentials of these plate lines are set so as to polarize the first capacitor and the second capacitor in opposite directions to each other with respect to the first electrodes so as to read out residual capacitance which remains in the first capacitor and the second capacitor when a voltage is applied to a second electrode.

2. A ferroelectric capacitor according to claim 1 , wherein said ferroelectric capacitor is formed in a sandwiching structure in which a ferroelectric layer is sandwiched between said first electrodes which are a common electrode connected to one of the source and drain of a select transistor and the second electrodes which are first and the second individual electrodes connected to the first and the second plate line, respectively.

3. A ferroelectric capacitor according to claim 2 , wherein the first and the second ferroelectric film are made of any one of PZT and SBT.

4. A ferroelectric capacitor according to claim 2 , wherein the first electrode is made of two layer structure film of iridium and iridium oxide.

5. A ferroelectic capacitor according to claim 4 , wherein the second individual electrode is made of two layer structure film of iridium and iridium oxide.

6. A ferroelectric memory comprising a select transistor and a ferroelectric capacitor characterized in that the ferroelectric capacitor includes a dummy capacitor and a memory capacitor the first electrodes (storage node electrodes) of which are connected to one of the source and drain of the select transistor and which draw the same hysteresis curve, the second electrodes of the dummy capacitor and the memory capacitor are connected to a first plate line and a second plate line, respectively, and the potentials of these plate lines are set so as to polarize the dummy capacitor and the memory capacitor in opposite directions to each other with respect to the first electrode so as to read out residual capacitance which remains in the dummy capacitor and the memory capacitor when a voltage is applied to a second electrode.

7. A ferroelectric memory according to claim 6 , wherein said ferroelectric capacitor is formed in a sandwiching structure in which a ferroelectric layer is sandwiched between said first electrodes which are a common electrode connected to one of the source and drain of said select transistor and the second electrodes which are first and second individual electrodes connected to the first and the second plate line, respectively.

8. A ferroelectric memory according to claim 7 , wherein the first and the second ferroelectric film are made of any one of PZT and SBT.

9. A ferroelectric memory according to claim 8 , wherein the second individual electrode is made of two layer structure film of iridium and iridium oxide.

10. A ferroelectric memory according to claim 8 , wherein the second individual electrode is made of two layer structure film of iridium and iridium oxide.

11. A ferroelectric memory according to claim 6 , wherein polarization directions of said dummy capacitor and said memory capacitor are set to opposite direction to each other at a memory writing operation.

12. A ferroelectric memory structured MFSFET comprising:

source/drain layers formed on the surface of a semiconductor substrate and a first gate electrode formed between the source/drain regions through a gate insulating film of a first ferroelectric film; a second ferroelectric film formed on the first gate electrode; and second and third gate electrodes formed on the second ferroelectric film having equal areas, wherein the second and third electrodes are held at predetermined potentials so that the ferroelectric film corresponding to the second and third electrodes holds their polarization in opposite directions to each other.

13. A ferroelectric memory according to claim 12 , wherein said second gate electrode and said third gate electrode are given electric potentials so as to polarize ferroelectric layers below the second and third gate electrodes in opposite directions to each other at a memory write operation.

14. A ferroelectric memory according to claim 12 , wherein the first and the second ferroelectric film are made of any one of PZT and SBT.

15. A ferroelectric memory according to claim 12 , wherein the first electrode is made of two layer structure film of iridium and iridium oxide.

16. A ferroelectric memory according to claim 12 , wherein the second individual electrode is made of two layer structure film of iridium and iridium oxide.

17. A method of writing to and reading from a ferroelectric memory comprising a select transistor and ferroelectric capacitors, said ferroelectric memory is further characterized by that said ferroelectric capacitors include a dummy capacitor and a memory capacitor the first electrodes (storage node electrodes) of which are connected to one of the source and drain of the select transistor and which draw the same hysteresis curve, and that said second electrodes of the dummy capacitor and the memory capacitor are connected to a first plate line and a second plate line, respectively;

including:

a step of setting electric potentials of said first plate line and said second plate line so as to polarize said dummy capacitor and said memory capacitor in opposite directions at a memory write operation, and

a step of reading out residual capacitance which remains in the dummy capacitor and the memory capacitor when a voltage is applied to a second electrode.

18. A method of reading from and writing to a ferroelectric memory according to claim 17 , wherein the step of reading out includes steps of:

a step of giving a read out preparation electric potential to said first plate line; and

a step of giving a read out electric potential to said second plate line.