DISCRETE DEVICES INCLUDING EAPROM TRANSISTOR AND NVRAM MEMORY CELL WITH EDGE DEFINED FERROELECTRIC CAPACITANCE, METHODS FOR OPERATING SAME, AND APPARATUS INCLUDING SAME

• US 20020001219A1
• Filed: 12/15/1999
• Published: 01/03/2002
• Est. Priority Date: 08/30/1999
• Status: Active Grant

• Current Assignee: Micron Technology, Inc.
• Original Assignee: Micron Technology, Inc.
• Inventors: AHN, KIE Y., NOBLE, WENDELL P., FORBES, LEONARD
• Granted Patent: US 6,337,805 B1
• Time in Patent Office: Days
• US Class Current: 365/145
• CPC Class Codes: G11C 11/005 comprising combined but independently operative RAM-ROM, RAM-PROM, RAM-EPROM cells
• CPC Class Codes: G11C 11/22 using ferroelectric elements
• CPC Class Codes: G11C 11/223 using MOS with ferroelectric gate insulating film
• CPC Class Codes: G11C 11/404 with one charge-transfer gate, e.g. MOS transistor, per cell
• CPC Class Codes: H10B 53/00 Ferroelectric RAM [FeRAM] devices comprising ferroelectric memory capacitors

Abstract

A memory cell includes a charge amplifier having a gate adjacent to a channel region coupling source and drain regions, a digitline coupled to one of the source and drain regions, a ground lead coupled to the other of the source and drain regions, a ferroelectric capacitor coupled to the gate, and a wordline coupled to the ferroelectric capacitor. Advantageously, the charge amplifier can be a CMOS transistor. Preferably, the gate is coupled to the ferroelectric capacitor by polysilicon, the junction formed at the gate has an intrinsic capacitance, and the capacitance of the ferroelectric capacitor is based on the magnitude of the intrinsic capacitance. Alternatively, the gate is coupled to the ferroelectric capacitor by polysilicon, the junction formed at the gate has an intrinsic capacitance, and the physical size of the ferroelectric capacitor is based on the magnitude of the intrinsic capacitance. In this case, the thickness of a ferroelectric material layer in the ferroelectric capacitor can be based on the magnitude of the intrinsic capacitance. A memory cell array, a memory module, and a processor based system can all be fabricated from this memory cell. Methods for reading data out of and writing data into the memory cell are also described.

Claims

1. A one transistor/one capacitor (1T/1C) memory cell comprising a ferroelectric capacitor operatively coupled to the gate electrode of a charge amplifier transistor.

2. The memory cell as recited in claim 1, wherein the ferroelectric capacitor has a surface area which is a predetermined percentage of the surface area of the gate electrode.

3. The memory cell as recited in claim 1, wherein the ferroelectric capacitor comprises an edge defined ferroelectric capacitor.

4. The memory cell as recited in claim 1, wherein the charge amplifier transistor comprises a CMOS transistor.

5. A memory cell comprising:

a charge amplifier comprising a gate adjacent to a channel region coupling source and drain regions;

a digitline coupled to one of the source and drain regions;

a source line coupled to the other of the source and drain regions;

a ferroelectric capacitor coupled to the gate; and

a wordline coupled to the ferroelectric capacitor.

6. The memory cell as recited in claim 5, wherein the charge amplifier comprises a transistor.

7. The memory cell as recited in claim 5, wherein the charge amplifier comprises a CMOS transistor.

8. The memory cell as recited in claim 5, wherein:

the gate is coupled to the ferroelectric capacitor by polysilicon;

the junction formed at the gate has an intrinsic capacitance; and

the capacitance of the ferroelectric capacitor is based on the magnitude of the intrinsic capacitance.

9. The memory cell as recited in claim 5, wherein:

the gate is coupled to the ferroelectric capacitor by polysilicon;

the junction formed at the gate has an intrinsic capacitance; and

the physical size of the ferroelectric capacitor is based on the magnitude of the intrinsic capacitance.

10. The memory cell as recited in claim 9, wherein the thickness of a ferroelectric material layer in the ferroelectric capacitor is based on the magnitude of the intrinsic capacitance.

11. A memory cell comprising:

a charge amplifier comprising a gate opposing a channel region coupling source and drain regions;

a digitline coupled to the drain region;

a source line coupled to the source region;

a ferroelectric capacitor, which stores data; and

a wordline coupled to the gate by the ferroelectric capacitor.

12. The memory cell as recited in claim 11, wherein the charge amplifier is a CMOS transistor.

13. The memory cell as recited in claim 11, wherein the ferroelectric capacitor has a surface area which is a predetermined percentage of surface area of the gate of the charge amplifier.

14. The memory cell as recited in claim 11, wherein:

the gate is coupled to the ferroelectric capacitor by polysilicon;

the junction formed at the gate has an intrinsic capacitance; and

the capacitance of the ferroelectric capacitor is based on the magnitude of the intrinsic capacitance.

15. The memory cell as recited in claim 11, wherein:

the gate is coupled to the ferroelectric capacitor by polysilicon;

the junction formed at the gate has an intrinsic capacitance; and

the physical size of the ferroelectric capacitor is based on the magnitude of the intrinsic capacitance.

16. The memory cell as recited in claim 11, wherein the ferroelectric capacitor is an edge defined ferroelectric capacitor.

17. The memory cell as recited in claim 16, wherein the edge defined ferroelectric capacitor comprises a dielectric layer of lead zirconate titanate (PZT).

18. The memory cell as recited in claim 11, wherein the ferroelectric capacitor comprises a dielectric layer of lead zirconate titanate (PZT).

19. The memory cell as recited in claim 18, wherein the PZT comprising the ferroelectric capacitor is of the form PbZr_xTi₁₋

xO₃ with x ranging between 0.4 and 0.53

45. The memory module as recited in claim 18, wherein the PZT comprising the ferroelectric capacitor is of the form PbZr_xTi₁₋

xO₃ with x ranging between 0.4 and 0.53

20. A one transistor/one capacitor (1T/1C) memory cell array, wherein each of the 1T/1C memory cells comprises a ferroelectric capacitor operatively coupled to the gate electrode of a charge amplifier transistor.

21. The memory cell array as recited in claim 20, wherein the charge amplifier transistor comprises a CMOS transistor.

22. The memory cell array as recited in claim 20, wherein the memory cell array comprises N rows by M columns of memory cells, and wherein the each of the M columns is defined by an associated digitline and an associated source line.

23. The memory cell array as recited in claim 20, wherein the surface area of the ferroelectric capacitor is a predetermined percentage of the surface area of the gate of the charge amplifier.

24. The memory cell array as recited in claim 23, wherein the ferroelectric capacitor is an edge defined ferroelectric capacitor.

25. The memory cell array as recited in claim 24, wherein the edge defined ferroelectric capacitor comprises a dielectric layer of lead zirconate titanate.

26. A memory cell array, comprising:

a plurality of memory cells organized as an array of rows and columns, at least one of the memory cells being a non-volatile memory cell comprising;

a charge transistor comprising a gate opposing a channel region coupling source and drain regions;

a digitline coupled to the drain region;

a source line coupled to the source region,

a ferroelectric capacitor coupled to the gate;

a wordline coupled to the ferroelectric capacitor; and

a sense amplifier coupled to the digitline of the at least one memory cell.

27. The memory cell array as recited in claim 26, wherein the ferroelectric capacitor has a surface area which is small relative to the surface area of the gate.

28. The memory cell array as recited in claim 26, wherein the ferroelectric capacitor comprises an edge defined ferroelectric capacitor.

29. The memory cell array as recited in claim 26, wherein data is written into the ferroelectric capacitor when the wordline and source line are asserted and data is read from the non-volatile memory cell when the wordline, the digitline and the source line are asserted.

30. The memory cell array as recited in claim 26, wherein an asserted source line comprises a grounded source line.

31. The memory cell array as recited in claim 26, wherein the charge amplifier amplifies the charge stored in the ferroelectric capacitor by at least one order of magnitude.

32. The memory cell array as recited in claim 26, wherein the charge amplifier amplifies the charge stored in the ferroelectric capacitor by a predetermined gain factor.

33. The memory cell array as recited in claim 26, wherein the charge amplifier comprises a transistor.

34. The memory cell array as recited in claim 33, wherein the transistor comprises a CMOS transistor.

35. A processor based system, comprising:

a processor; and

a memory cell array coupled to the processor, the memory cell array including a plurality of memory cells organized as an array of rows and columns, at least one of the memory cells being a non-volatile memory cell comprising;

a charge amplifier comprising a gate opposing a channel region coupling source and drain regions;

a digitline coupled to the drain region;

a source line coupled to the source region;

a ferroelectric capacitor coupled to the gate;

a wordline coupled to the ferroelectric capacitor; and

a sense amplifier coupled to the digitline of the at least one memory cell.

36. The processor based system as recited in claim 35, wherein the charge amplifier comprises a transistor.

37. The processor based system as recited in claim 35, wherein, under the control of the processor:

data is written into the ferroelectric capacitor when the wordline and the source line are both asserted; and

data is read out of the memory cell when the wordline, the digitline and the source line are asserted.

38. The processor based system as recited in claim 35, wherein ferroelectric capacitor comprises an edge defined ferroelectric capacitor.

39. The processor based system as recited in claim 35, wherein the ferroelectric capacitor comprises a dielectric layer of lead zirconate titanate (PZT).

40. The processor based system as recited in claim 39, wherein the PZT comprising the ferroelectric capacitor is of the form PbZr_xTi₁₋

xO₃ with x ranging between 0.4 and 0.53.

41. A memory module, comprising:

a substrate;

a plurality of memory chips mounted on the substrate, wherein one or more of the memory chips comprise a memory cell array fabricated on a semiconductor chip and communicating with a processor, said memory cell array comprising at least on non-volatile memory cell comprising a ferroelectric capacitor operatively coupled to the gate of a charge amplifier.

42. The memory module as recited in claim 41, wherein:

the gate is coupled to the ferroelectric capacitor by polysilicon;

the junction formed at the gate has an intrinsic capacitance; and

the capacitance of the ferroelectric capacitor is based on the magnitude of the intrinsic capacitance.

43. The memory module as recited in claim 41, wherein:

the gate is coupled to the ferroelectric capacitor by polysilicon;

the junction formed at the gate has an intrinsic capacitance; and

the physical size of the ferroelectric capacitor is based on the magnitude of the intrinsic capacitance.

44. The memory module as recited in claim 41, wherein the ferroelectric capacitor comprises a dielectric layer of lead zirconate titanate (PZT).

46. The memory module as recited in claim 41, wherein the non-volatile memory cell comprises:

the charge amplifier, which comprises the gate disposed adjacent to a channel region coupling source and drain regions;

a digitline coupled to drain region;

a source line coupled to the source region,

the ferroelectric capacitor coupled to the gate; and

a wordline coupled to the ferroelectric capacitor.

48. A method for reading information from a one transistor/one capacitor (1T/1C) memory cell having a charge amplifier including a gate disposed adjacent to a channel region coupling source and drain regions, a digitline coupled to drain region, a source line coupled to the source region, a ferroelectric capacitor coupled to the gate, and a wordline coupled to the ferroelectric capacitor, the method comprising:

grounding the source line;

asserting the wordline and digitline;

amplifying the charge on the ferroelectric capacitor; and

determining the resultant charge on the digitline.

49. The method as recited in claim 48, wherein the asserting step further comprises asserting the wordline at a voltage less than the coercive voltage of the ferroelectric capacitor.

50. The method as recited in claim 48, wherein the asserting step further comprises asserting the digitline which has been charged to a predetermined voltage value.

51. A method for writing information to a one transistor/one capacitor (1T/1C) memory cell having a charge amplifier including a gate disposed adjacent to a channel region coupling source and drain regions, a digitline coupled to drain region, a source line coupled to the source region, a ferroelectric capacitor coupled to the gate, and a wordline coupled to the ferroelectric capacitor, the method comprising:

asserting the source line; and

asserting the wordline to thereby apply a potential greater than the coercive voltage of the ferroelectric capacitor across the ferroelectric capacitor and the charge amplifier.

52. The method as recited in claim 51, wherein the asserted source line comprises a grounded source line.

53. A logic element, comprising:

N+1 source/drain regions;

N channels, each channel coupling adjacent ones of the N+1 source/drain regions;

N gates disposed adjacent to the N channels;

N ferroelectric capacitors, each of the N ferroelectric capacitors coupled to a respective one of the N gates;

a digitline couple to an end one of the N+1 source/drain regions; and

a source line coupled to the other end one of the N+1 source/drain regions.

54. The logic element as recited in claim 53, wherein the logic element is operated by assertion of all of the N gates.

55. The logic element as recited in claim 53, wherein the ferroelectric capacitors comprise edge defined ferroelectric capacitors.

56. The logic element as recited in claim 53, further comprising N wordlines, each of the N wordlines coupled to a respective one of the N ferroelectric capacitors, wherein the logic element is operated by assertion of all of the N wordlines coupled to respective N gates.