Ferroelectric memory and non-volatile memory cell for same

• US 5,541,870 A
• Filed: 10/28/1994
• Issued: 07/30/1996
• Est. Priority Date: 10/28/1994
• Status: Expired due to Term

• Current Assignee: Symetrix Corporation
• Original Assignee: Olympus Optical Corporation Limited (Olympus Corporation), Symetrix Corporation
• Inventors: Mihara, Takashi, Paz de Araujo, Carlos A., Watanabe, Hitoshi, McMillan, Larry D., Yoshimori, Hiroyuki
• Primary Examiner(s): Nelms, David C.
• Assistant Examiner(s): MAI, SON LUU
• Application Number:
  US08/330,989
• Time in Patent Office: 641 Days
• Field of Search: 365/145, 365/149, 365/117, 257/295
• US Class Current: 365/145
• CPC Class Codes: G11C 11/22 using ferroelectric elements
• CPC Class Codes: H10B 53/00 Ferroelectric RAM [FeRAM] devices comprising ferroelectric memory capacitors

Abstract

A non-volatile integrated circuit memory in which the memory cell includes a first transistor gate overlying a first channel region, a ferroelectric material overlying a second channel region, and a second transistor gate overlying a third channel region. The channel regions are connected in series, and preferably are contiguous portions of a single semiconducting channel. The firm channel is connected to a plate voltage that is 20% to 50% of the coercive voltage of the ferroelectric material. A sense amplifier is connected to the third channel region via a bit line. The rise of the bit line after reading a logic "1" state of the cell is prevented from disturbing the ferroelectric material by shutting off the third channel before the sense amplifier rises.

Claims

1. A memory cell for a non-volatile integrated circuit memory, said memory cell comprising:

first transistor means, including a first semiconducting channel region, for effecting transistor action in said first semiconducting channel region to control current flow through said first semiconducting channel region;

ferroelectric transistor means, including a second semiconducting channel region, for effecting transistor action in said second semiconducting channel region to control current flow through said second semiconducting channel region, said ferroelectric transistor means further including a ferroelectric material having a first polarization state and a second polarization state and a ferroelectric gate means for controlling said polarization state of said ferroelectric material; and

second transistor means, including a third semiconducting channel region, for effecting transistor action in said third semiconducting channel region to control current flow through said third semiconducting channel region;

wherein said first, second, and third semiconducting channel regions are connected in series.

2. A memory cell as in claim 1 wherein said first, second and third channel regions are contiguous portions of a single semiconducting channel region.

3. A memory cell as in claim 2 wherein said memory cell is formed on and in a semiconductor substrate having a first doped region doped with a first type of dopant and a second doped region doped with a second type of dopant, and said first, second, and third semiconducting channel regions are contiguous portions of said first doped region.

4. A memory cell as in claim 3 wherein said second doped region comprises first and second noncontiguous portions, said first portion located adjacent said first semiconducting channel region and said second portion adjacent said third semiconducting channel region.

5. A memory cell as in claim 1 wherein said first transistor means further comprises a first transistor gate and said second transistor means further comprises a second transistor gate.

6. A memory as in claim 5 wherein said ferroelectric material overlies at least a portion of said first transistor gate and said second transistor gate.

7. A memory as in claim 6 and further including an isolation layer between said ferroelectric material and said first transistor gate and between said ferroelectric material and said second transistor gate.

8. A memory as in claim 7 wherein said isolation layer comprises a material selected from the group comprising silicon dioxide and Si₃ N₄.

9. A memory as in claim 5 wherein said ferroelectric material directly contacts said first transistor gate and said second transistor gate.

10. A memory cell as in claim 5 wherein said first, second and third channel regions are contiguous portions of a single semiconducting channel.

11. A memory cell as in claim 10 wherein said memory cell is formed on and in a semiconductor substrate having a first doped region doped with a first type of dopant and a second doped region doped with a second type of dopant, and said first, second, and third semiconducting channel regions are contiguous portions of said first doped region.

12. A memory cell as in claim 1 wherein said first transistor means comprises a first transistor, said ferroelectric means comprises a ferroelectric transistor, and said second transistor means comprises a second transistor.

13. A memory cell as in claim 12 wherein said first transistor comprises a first MOS transistor, said second transistor comprises a second MOS transistor, and said ferroelectric transistor comprises a ferroelectric FET.

14. A memory cell as in claim 13 wherein:

said first MOS transistor includes a first source/drain and a second source/drain;

said second MOS transistor includes a first source/drain and a second source drain; and

said ferroelectric FET includes a first source/drain and a second source/drain; and

wherein said second source/drain of said first MOS transistor is connected to the first source/drain of said ferroelectric FET, and said first source/drain of said MOS second transistor is connected to the second source/drain of said ferroelectric FET.

15. A ferroelectric memory device comprising:

a substrate, a channel region in said substrate, a first conducting gate overlying at least a first portion of said channel region, a second conducting gate overlying at least a second portion of said channel region, a ferroelectric material overlying at least a third portion of said channel region between said first and second conducting gates, and a ferroelectric gate overlying at least a portion of said ferroelectric material.

16. A non-volatile integrated circuit memory comprising a plurality of bit lines, a plurality of word lines, a plurality of memory cells, a source of a plate voltage, row address means for applying signals to selected ones of said memory cells via said word lines, column address means for applying signals to selected ones of said memory cells via said bit lines, and data in/out means for applying data signals to and receiving data signals from said memory cells, each memory cell comprising:

first transistor means, including a first semiconducting channel region, for effecting transistor action in said first semiconducting channel region to control current flow through said first semiconducting channel region;

ferroelectric transistor means, including a second semiconducting channel region, for effecting transistor action in said second semiconducting channel region to control current flow through said second semiconducting channel region, said ferroelectric transistor means further including a ferroelectric material capable of existing in a first polarization state and a second polarization state and a ferroelectric gate means for controlling said polarization state of said ferroelectric material; and

second transistor means, including a third semiconducting channel region, for effecting transistor action in said third semiconducting channel region to control current flow through said third semiconducting channel region;

wherein said first, second, and third semiconducting channel regions are connected in series, each one of said word lines is electrically connected to said first transistor means and said second transistor means in one of said memory cells, said source of a plate voltage is electrically connected to said first semiconducting channel region in each of said memory cells, and each one of said bit lines is electrically connected to said third semiconducting channel in one of said memory cells.

17. A memory as in claim 16 wherein, in each of said memory cells, said first, second and third channel regions are contiguous portions of a single semiconducting channel.

18. A memory cell as in claim 17 wherein said first transistor means comprises a first transistor, said ferroelectric means comprises a ferroelectric transistor, and said second transistor means comprises a second transistor.

19. A memory as in claim 18 wherein:

said first transistor includes a first source/drain and a second source/drain;

said second transistor includes a first source/drain and a second source drain; and

said ferroelectric transistor includes a first source/drain and a second source/drain; and

wherein said first source/drain of said first transistor is connected to said source of a plate voltage, said second source/drain of said first transistor is connected to the first source/drain of said ferroelectric transistor, said first source/drain of said second transistor is connected to the second source/drain of said ferroelectric transistor, and said second source/drain of said second transistor is connected to said bit line connected to said memory cell.

20. A memory as in claim 16 wherein said memory further includes a sense amplifier electrically connectable to at least one of said bit lines, and a source of a reference voltage electrically connected to said sense amplifier, and wherein said reference voltage is less than said plate voltage.

21. A memory as in claim 16 wherein said plate voltage is from 20% to 50% of the coercive voltage of said ferroelectric material.

22. A memory as in claim 16 wherein said plate voltage is 0.5 volts or less.

23. A memory cell for a non-volatile integrated circuit memory, said memory cell comprising:

a semiconducting substrate;

a first doped region formed in said substrate, said doped region including a first portion, a second portion and a third portion connected in series;

a first conductor overlying said first portion of said first doped region;

a second conductor overlying said third portion of said first doped region;

a first insulator between said first conductor and said first portion of said first doped region and a second insulator between said second conductor and said third portion of said first doped region;

a ferroelectric member, a first portion of which overlies said first conductor, a second portion of which overlies said second portion of said first doped region, and a third portion of which overlies said second conductor; and

a third conductor overlying said ferroelectric member.

24. A memory cell as in claim 23 and further including a third insulator between said first portion of said ferroelectric member and said first conductor and a fourth insulator between said third portion of said ferroelectric member and said second conductor.

25. A memory cell as in claim 24 wherein said first and second conductors comprise polysilicon and said third and fourth insulation layers comprise silicon dioxide.

26. A memory cell as in claim 23 and further including an isolation layer between said first portion of said ferroelectric member and said first conductor and between said third portion of said ferroelectric member and said second conductor.

27. A memory cell as in claim 26 wherein said isolation layer comprises Si₃ N₄.

28. A memory cell as in claim 26 wherein said isolation layer comprises silicon dioxide.

29. A memory cell as in claim 23 wherein said ferroelectric member directly contacts said first conductor and said second conductor.

30. A memory cell as in claim 23 wherein said ferroelectric member directly contacts said second portion of said first doped region.

31. A memory cell as in claim 23 and further including a second doped region formed in said substrate, said second doped region being doped with a different type of dopant than said first doped region, said second doped region including first and second non-contiguous portions, said first portion of said second doped region contacting said first portion of said first doped region and said second portion of said second doped region contacting said third portion of said first doped region.

32. A memory cell for a non-volatile integrated circuit memory, said memory cell comprising:

a first pass gate transistor;

a second pass gate transistor; and

a ferroelectric transistor electrically connected between said first pass gate transistor and said second pass gate transistor.

33. A memory cell as in claim 32 wherein each of said pass gate transistors include a first source/drain and a second source/drain, and said ferroelectric transistor is electrically connected between one of the source/drains of said first pass gate transistor and one of the source/drains of said second pass gate transistor.

34. A non-volatile integrated circuit memory comprising a plurality of bit lines, a plurality of word lines, a plurality of memory cells, a source of a plate voltage, row address means for applying signals to selected ones of said memory cells via said word lines, column address means for applying signals to selected ones of said memory cells via said bit lines, and data in/out means for applying data signals to and receiving data signals from said memory cells, each memory cell comprising:

a first pass gate transistor;

a second pass gate transistor; and

a ferroelectric transistor electrically connected between said first pass gate transistor and said second pass gate transistor;

wherein each one of said word lines is electrically connected to said first pass gate transistor and said second pass gate transistor in one of said memory cells, said source of a plate voltage is electrically connected to said first pass gate transistor in each of said memory cells, and each one of said bit lines is electrically connected to said second pass gate transistor in each of said memory cells.

35. A memory as in claim 34 wherein said memory further includes a sense amplifier electrically connectable to at least one of said bit lines, and a source of a reference voltage electrically connected to said sense amplifier, and wherein said reference voltage is less than said plate voltage.

36. A memory as in claim 34 wherein said plate voltage is from 20% to 50% of the coercive voltage of said ferroelectric material.

37. A memory as in claim 34 wherein said plate voltage is 0.5 volts or less.

38. A ferroelectric memory comprising:

a memory cell including a ferroelectric device having a first logic state and a second logic state;

a bit line;

a sense amplifier;

first connecting means for electrically connecting said ferroelectric device to said bit line;

second connecting means for electrically connecting said bit line to said sense amplifier; and

timing means connected to said first and second connecting means for;

causing said first connecting means to connect said ferroelectric device to said bit line for a sufficient time to allow said bit line to assume a first voltage determined by the logic state of said ferroelectric device, causing said second connecting means to connect said sense amplifier to said bit line, and causing said first connecting means to disconnect said ferroelectric device from said bit line before said sense amplifier drives said bit line to a second voltage indicative of the logic state of said ferroelectric device.

39. A memory as in claim 38 wherein said first connecting means comprises a transistor means.

40. A memory as in claim 38 wherein said first voltage has a value of less than 50% of the coercive voltage of said ferroelectric device.

41. A memory as in claim 38 wherein said first voltage is 0.5 volts or less.