Method for reading and restoring data in a data storage element

• US 5,579,257 A
• Filed: 08/31/1995
• Issued: 11/26/1996
• Est. Priority Date: 08/31/1995
• Status: Expired due to Term

• Current Assignee: Freescale Semiconductor, Inc. (NXP Semiconductors NV)
• Original Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Inventors: Tai, Jy-Der D.
• Primary Examiner(s): Nelms, David C.
• Assistant Examiner(s): Hoang, Huan
• Application Number:
  US08/522,477
• Time in Patent Office: 453 Days
• Field of Search: 365/145, 365/149, 365/117
• US Class Current: 365/145
• CPC Class Codes: G11C 11/22 using ferroelectric elements

Abstract

A method for reading and restoring data in a FERAM (10) is provided. The FERAM (10) comprises a FET (11) and a ferroelectric capacitor (12). The FET (11) has a gate connected to a word line (14), a source coupled to a plate line (15) via the ferroelectric capacitor (12), and a drain connected to a bit line (16). The reading process begins by placing a predetermined amount of charge in a bit line capacitor (17), which in turn charges the ferroelectric capacitor (12) after the FET (11) is switched on, resulting in a voltage drop determined by data stored in the FERAM (10) at the bit line (16). A sense amplifier (18) adjusts the voltage at the bit line (16) accordingly to read data from the FERAM (10). Applying a voltage at the plate line (15) and switching the FET (11) off restore the data to the FERAM (10).

Claims

1. A method for reading and restoring data in a data storage element, comprising the steps of:

providing the data storage element having a switch and a capacitor with polarization retention, wherein the switch has a control electrode coupled for receiving control signals, a first current conducting electrode coupled via the capacitor with polarization retention for receiving restoration signals, and a second current conducting electrode coupled for transmitting data;

providing data in the data storage element;

placing the switch in a non-conductive state;

applying a first restoration signal to the first current conducting electrode of the switch via the capacitor with polarization retention;

applying a charging voltage to the second current conducting electrode of the switch;

removing the charging voltage applied to the second current conducting electrode of the switch;

placing the switch in a conductive state;

applying a data value voltage to the second current conducting electrode of the switch in response to a voltage at the second current conducting electrode of the switch to read data from the data storage element;

applying a second restoration signal to the first current conducting electrode of the switch via the capacitor with polarization retention; and

placing the switch in the non-conductive state to restore data in the data storage element.

2. The method for reading and restoring data in a data storage element as claimed in claim 1, wherein the step of providing the data storage element further includes providing a word line coupled to the control electrode of the switch, a plate line coupled to the first current conducting electrode of the switch via the capacitor with polarization retention, and a bit line coupled to the second current conducting electrode of the switch.

3. The method for reading and restoring data in a data storage element as claimed in claim 1, wherein the step of providing the data storage element includes providing an n-channel insulated gate field effect transistor serving as the switch and providing a ferroelectric capacitor serving as the capacitor with polarization retention, wherein the n-channel insulated gate field effect transistor has a gate electrode serving as the control electrode of the switch, a source electrode serving as the first current conducting electrode of the switch, and a drain electrode serving as the second current conducting electrode of the switch.

4. The method for reading and restoring data in a data storage element as claimed in claim 1, wherein the step of providing data in the data storage element includes the steps of:

applying the first restoration signal to the first current conducting electrode of the switch via the capacitor with polarization retention;

applying a data storing voltage to the second current conducting electrode of the switch;

placing the switch in a conductive state;

applying the second restoration signal to the first current conducting electrode of the switch via the capacitor with polarization retention; and

placing the switch in a non-conductive state to store data in the data storage element.

5. The method for reading and restoring data in a data storage element as claimed in claim 4, wherein the step of applying a data storing voltage includes applying a voltage determined by the data to be stored in the data storage element.

6. The method for reading and restoring data in a data storage element as claimed in claim 1, wherein the step of placing the switch in a non-conductive state includes applying a first control signal to the control electrode of the switch.

7. The method for reading and restoring data in a data storage element as claimed in claim 1, wherein the step of applying a second restoration signal includes applying the first restoration signal.

8. A method for reading and restoring data in a ferroelectric memory cell, comprising the steps of:

providing the ferroelectric memory cell having a word line, a plate line, a bit line, a field effect transistor, and a ferroelectric capacitor, wherein the field effect transistor has a gate electrode coupled to the word line, a source electrode coupled to the plate line via the ferroelectric capacitor, and a drain electrode coupled to the bit line;

writing data into the ferroelectric memory cell;

placing the field effect transistor in a non-conductive state;

applying a first restoration signal to the plate line;

charging the bit line;

placing the field effect transistor in a conductive state;

applying a data value voltage to the bit line in response to a potential at the bit line to read data from the ferroelectric memory cell;

applying a second restoration signal to the plate line; and

placing the field effect transistor in the non-conductive state to restore data in the ferroelectric memory cell.

9. The method for reading and restoring data in a ferroelectric memory cell as claimed in claim 8, wherein the step of providing the ferroelectric memory cell includes providing an n-channel insulated gate field effect transistor serving as the field effect transistor, wherein the n-channel insulated gate field effect transistor has a threshold voltage.

10. The method for reading and restoring data in a ferroelectric memory cell as claimed in claim 9, wherein the step of placing the field effect transistor in a non-conductive state includes applying a voltage lower than the threshold voltage of the n-channel insulated gate field effect transistor to the word line.

11. The method for reading and restoring data in a ferroelectric memory cell as claimed in claim 8, wherein the step of applying a first restoration signal includes applying a ground voltage to the plate line.

12. The method for reading and restoring data in a ferroelectric memory cell as claimed in claim 8, wherein the step of applying a second restoration signal includes applying a supply voltage to the plate line.

13. The method for reading and restoring data in a ferroelectric memory cell as claimed in claim 8, wherein the step of charging the bit line includes the steps of:

applying a charging voltage to the bit line; and

removing the charging voltage applied to the bit line.

14. The method for reading and restoring data in a ferroelectric memory cell as claimed in claim 8, wherein the step of applying a data value voltage to the bit line in response to a potential at the bit line includes the steps of:

providing a predetermined reference potential;

applying a ground voltage to the bit line in response to the potential at the bit line lower than the predetermined reference potential; and

applying a supply voltage to the bit line in response to the potential at the bit line higher than the predetermined reference potential.

15. A method for reading and restoring data in a ferroelectric memory cell, comprising the steps of:

providing the ferroelectric memory cell having a word line, a plate line, a bit line, a complementary bit line, a first field effect transistor, a second field effect transistor, a first ferroelectric capacitor, and a second ferroelectric capacitor, wherein a gate electrode of the first field effect transistor and a gate electrode of the second field effect transistor are coupled to the word line, a source electrode of the first field effect transistor and a source electrode of the second field effect transistor are coupled to the plate line via the first ferroelectric capacitor and the second ferroelectric capacitor, respectively, and a drain electrode of the first field effect transistor and a drain electrode of the second field effect transistor are coupled to the bit line and the complementary bit line, respectively;

writing data into the ferroelectric memory cell;

placing the first and second field effect transistors in a non-conductive state;

applying a first restoration signal to the plate line;

charging the bit line and the complementary bit line;

placing the first and second field effect transistors in a conductive state;

applying a first data value voltage to the bit line and applying a second data value voltage to the complementary bit line in response to a potential at the bit line higher than a potential at the complementary bit line to read a first logical value from the ferroelectric memory cell;

applying the second data value voltage to the bit line and applying the first data value voltage to the complementary bit line in response to a potential at the bit line lower than a potential at the complementary bit line to read a second logical value complementary to the first logical value from the ferroelectric memory cell;

applying a second restoration signal to the plate line; and

placing the first and second field effect transistors in the non-conductive state to restore data in the ferroelectric memory cell.

16. The method for reading and restoring data in a ferroelectric memory cell as claimed in claim 15, wherein the step of providing the ferroelectric memory cell includes providing a first n-channel insulated gate field effect transistor having a first threshold voltage serving as the first field effect transistor and providing a second n-channel insulated gate field effect transistor having a second threshold voltage serving as the second field effect transistor.

17. The method for reading and restoring data in a ferroelectric memory cell as claimed in claim 16, wherein the step of placing the first and second field effect transistors in a conductive state includes applying a voltage higher than the first and second threshold voltages to the word line.

18. The method for reading and restoring data in a ferroelectric memory cell as claimed in claim 15, wherein the step of charging the bit line and the complementary bit line includes the steps of:

applying a charging voltage to the bit line and the complementary bit line; and

removing the charging voltage applied to the bit line and the complementary bit line.

19. The method for reading and restoring data in a ferroelectric memory cell as claimed in claim 15, wherein the step of applying a charging voltage includes applying a supply voltage to the bit line and the complementary bit line.

20. The method for reading and restoring data in a ferroelectric memory cell as claimed in claim 15, wherein the step of applying a first data value voltage to the bit line and applying a second data value voltage to the complementary bit line in response to a potential at the bit line higher than a potential at the complementary bit line includes applying a supply voltage to the bit line and applying a ground voltage to the complementary bit line.