Vertical gate transistors in pass transistor logic decode circuits

• US 6,222,788 B1
• Filed: 05/30/2000
• Issued: 04/24/2001
• Est. Priority Date: 05/30/2000
• Status: Expired due to Term

• Current Assignee: Micron Technology, Inc.
• Original Assignee: Micron Technology, Inc.
• Inventors: Ahn, Kie Y., Forbes, Leonard
• Primary Examiner(s): NGUYEN, TAN
• Application Number:
  US09/580,860
• Time in Patent Office: 329 Days
• Field of Search: 365/230.06, 365/230.02, 365/185.05, 365/185.1, 257/314, 257/315, 257/316, 257/317, 257/318, 257/302
• US Class Current: 365/230.06
• CPC Class Codes: G11C 8/10 Decoders
• CPC Class Codes: H01L 21/823437 with a particular manufacturing method of the gate conductors, e.g. particular materials, shapes
• CPC Class Codes: H01L 21/823462 with a particular manufacturing method of the gate insulating layers, e.g. different gate insulating layer thicknesses, particular gate insulator materials or particular gate insulator implants
• CPC Class Codes: H01L 29/7831 with multiple gate structure FinFETs or MuGFETs H01L29/7855, thin film transistors H01L29/78645

Abstract

Systems and methods are provided for vertical gate transistors in static pass transistor decode circuits. The vertical gate transistors have multiple vertical gates which are edge defined such that only a single transistor is required for multiple logic inputs. Thus a minimal surface area is required for each logic input. The novel decode circuits of the present invention include an address decoder for a memory device. The decode circuit includes a number of address lines and a number of output lines. The address lines and the output lines form an array. A number logic cells that disposed at the intersections of output lines and address lines. According to the teachings of the present invention each logic cell includes a source region and a drain region in a horizontal substrate. A depletion mode channel region separates the source and the drain regions. A number of vertical gates are located above different portions of the depletion mode channel region. At least one of the vertical gates is located above a first portion of the depletion mode channel region and is separated from the channel region by a first thickness insulator material. At least one of the vertical gates is located above a second portion of the channel region and is separated from the channel region by a second thickness insulator material. According to the present invention, there is no source nor drain region associated with each input and the gates have sub-lithographic horizontal dimensions by virtue of being edge defined vertical gates.

Claims

1. An address decoder for a memory device, comprising:

a number of address lines;

a number of output lines;

wherein the address lines, and the output lines form an array; and

a number logic cells that are disposed at the intersections of output lines and address lines, wherein each of the logic cells includes;

a source region in a horizontal substrate;

a drain region in the horizontal substrate;

a depletion mode channel region separating the source and the drain regions;

a number of vertical gates located above different portions of the depletion mode channel region;

wherein at least one of the vertical gates is located above a first portion of the depletion mode channel region and is separated from the channel region by a first thickness insulator material; and

wherein at least one of the vertical gates is located above a second portion of the channel region and is separated from the channel region by a second thickness insulator material.

2. The address decoder of claim 1, wherein the vertical gate located above a first portion of the channel region is parallel to the vertical gate located above a second portion of the channel region and separated therefrom by an intergate dielectric.

3. The address decoder of claim 1, wherein the number of vertical gates each have a horizontal width of approximately 100 nanometers (nm).

4. The address decoder of claim 1, wherein the first thickness insulator material is approximately 33 Angstroms (Å

), and wherein the second thickness insulator material is approximately 100 Angstroms (Å

).

5. The address decoder of claim 1, wherein the first thickness insulator material, the second thickness insulator material, and the intergate dielectric include silicon dioxide (SiO₂).

6. The address decoder of claim 1, wherein the number of vertical gates have a vertical height of approximately 500 nanometers (nm).

7. The address decoder of claim 1, wherein the depletion mode channel region separating the source and the drain regions is controlled by a potential range of less than 0.5 Volts applied to at least one of the number of vertical gates.

8. A decode circuit for a semiconductor memory, comprising:

a number of logic cells having a source region, a drain region, and a horizontal depletion mode channel therebetween, wherein each logic cell includes;

a first vertical gate separated from a first portion of the depletion mode channel region by a first oxide thickness; and

a second vertical gate separated from a second portion of the depletion mode channel region by a second oxide thickness, wherein the first vertical gate is formed opposing the second vertical gate;

a number of address lines coupled to the gates of the number of logic cells; and

a number of output lines coupled to the drain region of the number of logic cells.

9. The decode circuit of claim 8, wherein the first vertical gate and the second vertical gate each have a horizontal width which has sub-lithographic dimensions.

10. The decode circuit of claim 8, wherein the first vertical gate and the second vertical gate are logic inputs such that a minimal area in the transistor is used for each logic input.

11. The decode circuit of claim 8, wherein the first vertical gate includes an active input for the transistor, and wherein the first oxide thickness is less than 50 Angstroms (Å

).

12. The decode circuit of claim 8, wherein the second vertical gate includes a passing line, and wherein the second oxide thickness is less than 150 Angstroms (Å

).

13. The decode circuit of claim 8, wherein only the first vertical gate is able to control conduction in the depletion mode channel region.

14. The decode circuit of claim 8, wherein the transistor includes a NAND gate transistor, and wherein a both the first vertical gate and the second vertical gate control conduction in the depletion mode channel region.

15. A decode circuit for a semiconductor memory, comprising:

a number of logic cells having a source region, a drain region, and a horizontal depletion mode channel therebetween, wherein each logic cell includes;

a first vertical gate located above a first portion of the depletion mode channel region and separated from the depletion mode channel region by a first oxide thickness;

a second vertical gate located above a second portion of the depletion mode channel region and separated from the depletion mode channel region by a second oxide thickness, and

a third vertical gate located above a third portion of the depletion mode channel region and separated from the depletion mode channel region by the second oxide thickness;

a number of address lines coupled to the gates of the number of logic cells; and

a number of output lines coupled to the drain region of the number of logic cells.

16. The decode circuit of claim 15, wherein the second and the third vertical gates are parallel to and on opposing sides of the first vertical gate.

17. The decode circuit of claim 15, wherein the first vertical gate includes an active input and wherein the second and the third vertical gates include passing lines.

18. The logic gate transistor of claim 15, wherein first vertical gate includes a passing line and wherein the second and the third vertical gates include active inputs.

19. The decode circuit of claim 15, wherein an operating voltage applied to the first vertical gate cannot control conduction in the depletion mode channel region, and wherein the operating voltage applied to the second and the third vertical gates controls conduction in the depletion mode channel region.

20. The decode circuit of claim 15, wherein the second oxide thickness is less than the first oxide thickness.

21. The decode circuit of claim 15, wherein the first vertical gate, the second vertical gate, and the third vertical gate include polysilicon gates which are separated from one another by silicon dioxide (SiO₂).

22. The decode circuit of claim 15, wherein the first vertical gate, the second vertical gate, and the third vertical gate each have a horizontal width which is sub-lithographic in dimension such that a minimal area of the logic gate transistor is needed for each gate.

23. The decode circuit of claim 15, wherein the first oxide thickness and the second oxide thickness are approximately the same thickness such that the first, the second, and the third vertical gate each control conduction in the depletion mode channel region.

24. A memory address decoder, comprising:

a number of static pass transistors, wherein each of the static pass transistors includes;

a horizontal substrate, wherein the substrate includes a source region, a drain region, and a depletion mode channel region separating the source and the drain region;

a first vertical gate separated from a first portion of the depletion mode channel region by a first oxide thickness; and

a second vertical gate separated from a second portion of the depletion mode channel region by a second oxide thickness, wherein the second vertical gate is parallel to the first vertical gate; and

a number of address lines coupled to the gates of the number of static pass transistors; and

a number of output lines coupled to the drain region of the number of static pass transistors.

25. The memory address decoder of claim 24, wherein the vertical gates in each static pass transistor are multiple logic inputs such that the memory address decoder conserves surface space by having multiple logic inputs per static pass transistor.

26. The memory address decoder of claim 24, wherein each static pass transistor includes a NAND logic cell.

27. The memory address decoder of claim 24, wherein each static pass transistor includes an n-type depletion mode channel region.

28. The memory address decoder of claim 24, wherein the first vertical gate in each logic cell includes an active input and wherein the second vertical gate in each logic cell includes a passing line.

29. The memory address decoder of claim 24, wherein the first vertical gate and the second vertical gate are each edge defined such that each vertical gate has a horizontal width which has sub-lithographic dimensions.

30. The memory address decoder of claim 24, wherein the first oxide thickness is less than 50 Angstroms (Å

), and wherein the second oxide thickness is less than 150 Angstroms (Å

).

31. A memory device, comprising:

an array of memory cells;

a decode circuit coupled to the array of memory cells, wherein the decode circuit includes a plurality of logic cells, and wherein each logic cell includes;

a horizontal substrate, wherein the substrate includes a source region, a drain region, and a depletion mode channel region separating the source and the drain region;

a first vertical gate located above a first portion of the depletion mode channel region and separated from the depletion mode channel region by a first oxide thickness;

a second vertical gate located above a second portion of the depletion mode channel region and separated from the depletion mode channel region by a second oxide thickness, and

a third vertical gate located above a third portion of the depletion mode channel region and separated from the depletion mode channel region by the second oxide thickness; and

at least one sense amplifier, wherein the at least one sense amplifier couples to the plurality of logic cells.

32. The memory device of claim 31, wherein the first oxide thickness and the second oxide thickness have different thicknesses, wherein one oxide thickness is less than the other such that the vertical gates over a lesser oxide thickness control conduction in the depletion mode channel region.

33. The memory device of claim 32, wherein the vertical gates over a greater oxide thickness have a minimal or no effect on conduction in the depletion mode channel region.

34. The memory device of claim 31, wherein the first oxide thickness and the second oxide thickness are approximately equal such that all of the vertical gates control conduction in the depletion mode channel region.

35. The memory device of claim 31, wherein each of the logic cells are NAND logic cells.

36. The memory device of claim 31, wherein the vertical gates in each logic cell are multiple logic inputs such that the memory device conserves surface space by having multiple logic inputs per logic cell.

37. An electronic system, comprising:

a processor; and

a memory device coupled to the processor, wherein the memory device includes a decode circuit, the decode circuit having a plurality of logic cells, and wherein each logic cell includes;

a horizontal substrate, wherein the substrate includes a source region, a drain region, and a depletion mode channel region separating the source and the drain region;

a number of vertical gates located above different portions of the depletion mode channel region;

wherein at least one of the vertical gates is located above a first portion of the depletion mode channel region and is separated from the channel region by a first oxide thickness; and

wherein at least one of the vertical gates is located above a second portion of the channel region and is separated from the channel region by a second oxide thickness.

38. The electronic system of claim 37, wherein the number of vertical gates located above different portions of the depletion mode channel region include parallel polysilicon vertical gates separated by a silicon dioxide (SiO2) intergate dielectric such that the number of vertical gates make up a number of logic inputs for each logic cell.

39. The electronic system of claim 38, wherein the intergate dielectric has a thickness which is approximately equal to the first oxide thickness.

40. The electronic system of claim 37, wherein the first vertical gate includes a passing line and the second and the third vertical gates include active inputs.

41. The electronic system of claim 37, wherein the number of vertical gates include edge defined vertical gates such that each vertical gate has a horizontal width which is sub-lithographic in dimension.

42. The electronic system of claim 37, wherein the second and the third vertical gates separated from the depletion mode channel region by a second oxide thickness includes a second oxide thickness which is less than the first oxide thickness such that the second and the third vertical gates control conduction in the depletion mode channel region.

43. The electronic system of claim 37, wherein an independent operating voltage is applied to each of the number of vertical gates.

44. The electronic system of claim 43, wherein an operating voltage range of approximately between 0.0 and −

0.6 Volts applied the second and the third vertical gates controls the conduction in the depletion mode channel region.

45. A method for forming a decode circuit, comprising:

forming a number of address lines;

forming a number of output lines;

forming a number of logic cells having gates coupled to the address lines and drain regions coupled to the output lines, wherein forming the number of logic cells includes;

forming a source region and a drain region in a horizontal substrate;

forming a depletion mode channel in the horizontal substrate between the source and the drain regions;

forming a number of vertical gates above different portions of the depletion mode channel;

wherein forming a number of vertical gates includes forming at least one of the vertical gates separated from the depletion mode channel by a first oxide thickness (t1); and

wherein forming a number of vertical gates includes forming at least one of the vertical gates separated from the depletion mode channel region by a second oxide thickness (t2).

46. The method of claim 45, wherein forming a number of vertical gates above different portions of the depletion mode channel includes forming a number of edge defined vertical gates such that each vertical gate has a horizontal width which is sub-lithographic in dimension.

47. The method of claim 45, wherein forming a number of vertical gates above different portions of the depletion mode channel includes forming a number of logic inputs for the static pass transistor.

48. The method of claim 45, wherein forming the number of logic cells includes forming a NAND logic cells.

49. The method of claim 45, wherein forming at least one of the vertical gates separated from the depletion mode channel by a first oxide thickness (t1) includes forming at least one of the vertical gates as an active input for the number of logic cells such that the at least one of the vertical gates separated from the depletion mode channel by a first oxide thickness (t1) controls conduction in the depletion mode channel.

50. The method of claim 49, wherein forming at least one of the vertical gates separated from the depletion mode channel by a first oxide thickness (t1) includes forming a first oxide thickness of less than 50 Angstroms (Å

).

51. The method of claim 45, wherein forming at least one of the vertical gates separated from the depletion mode channel by a second oxide thickness (t2) includes forming at least one of the vertical gates as a passing line such that the at least one of the vertical gates separated from the depletion mode channel by a second oxide thickness (t2) has a minimal or no control over conduction in the depletion mode channel.

52. The method of claim 51, wherein forming at least one of the vertical gates separated from the depletion mode channel by a second oxide thickness (t1) includes forming a second oxide thickness of less than 150 Angstroms (Å

).

53. A method for forming a memory address decoder, comprising:

forming a number of logic cells, wherein forming a number of logic cells includes;

forming a source region and a drain region in a horizontal substrate;

forming a depletion mode channel between the source and the drain regions;

forming a first vertical gate located above a first portion of the depletion mode channel and separated from the depletion mode channel by a first oxide thickness;

forming a second vertical gate located above a second portion of the depletion mode channel and separated from the depletion mode channel by a second oxide thickness; and

forming a third vertical gate located above a third portion of the depletion mode channel and separated from the depletion mode channel by the second oxide thickness.

54. The method of claim 53, wherein forming the second and the third vertical gates includes forming the second and the third vertical gates as active inputs for the logic gate transistor such that the second and the third vertical gates control conduction in the depletion mode channel.

55. The method of claim 53, wherein forming the first vertical gate includes forming a passing line such that the first vertical gate has a minimal or no control over conduction in the depletion mode channel.

56. The method of claim 53, wherein forming a first vertical gate separated from the depletion mode channel by a first oxide thickness and forming a second and a third vertical gate separated from the depletion mode channel by a second oxide thickness includes forming a first oxide thickness which has a thickness greater than the second oxide thickness.

57. The method of claim 53, wherein forming the first, the second, and the third vertical gates includes forming edge defined polysilicon gates which are separated from one another by silicon dioxide (SiO₂).

58. The method of claim 57, wherein forming the edge defined polysilicon gates includes forming edge defined polysilicon gates to have a sub-lithographic horizontal width.

59. The method of claim 53, wherein forming a first vertical gate separated from the channel region by a first oxide thickness includes forming a first oxide thickness of approximately 33 Angstroms (Å

), and wherein forming a second and a third vertical gate separated from the channel region by a second oxide thickness includes forming a second oxide thickness of approximately 100 Angstroms (Å

).

60. A method for operating a decode circuit, comprising:

applying a number of address signals to a number of logic cells, wherein applying a number of address signals to the number of logic cells includes applying a potential to a number of vertical gates located above different portions of a horizontal depletion mode channel, wherein at least one of the vertical gates is separated from the depletion mode channel by a first oxide thickness, and wherein at least one of the vertical gates is separated from the depletion mode channel by a second oxide thickness; and

sensing a conduction level through the depletion mode channel for decoding a row line.

61. The method of claim 60, wherein applying a potential to the number of vertical gates includes applying the potential to a number of active inputs for each logic cell.

62. The method of claim 61, wherein applying the potential to the number of active inputs controls conduction in the depletion mode channel such that each logic cell functions as a NAND gate.

63. The method of claim 61, wherein applying the potential to the number of active inputs includes applying a negative potential of approximately −

0.6 Volts to at least one of the active inputs such that the active input turns off conduction in the depletion mode channel.

64. The method of claim 60, wherein applying a potential to the number of vertical gates includes applying the potential to a number of passing lines.

65. A method for operating a memory decode circuit, comprising:

addressing a number of logic cells, wherein addressing a number of logic cells includes using a number of vertical gates located above a horizontal depletion mode channel between a single source region and a single drain region to provide an applied potential above the depletion mode channel, wherein at least one of the vertical gates is separated from the depletion mode channel by a first oxide thickness, and wherein at least one of the vertical gates is separated from the depletion mode channel by a second oxide thickness vertical;

using at least one of the number of vertical gates as a passing line such that a potential on the passing line does not effect conduction in the depletion mode channel; and

using at least two of the number of vertical gates as a number of active inputs such that the active inputs control conduction in the depletion mode channel for decoding a row line.

66. The method of claim 65, wherein the method further includes independently applying potential values to the number of vertical gates.

67. The method of claim 66, wherein independently applying potential values to the number of vertical gates includes performing a logic function.

68. The method of claim 67, wherein performing a logic function includes performing a NAND logic function.

69. The method of claim 65, wherein using at least two of the number of vertical gates as a number of active inputs such that the active inputs control conduction in the depletion mode channel for decoding a row line includes applying a negative potential to the active inputs of approximately −

0.6 Volts to turn off conduction in the depletion mode channel region.

70. The method of claim 65, wherein using at least one of the number of vertical gates as a passing line includes using at least one of the number of vertical gates separated from the depletion mode channel by the second oxide thickness as the passing line, wherein the second oxide thickness is greater than the first oxide thickness.

71. The method of claim 65, wherein the method further includes sensing a conduction level through the horizontal depletion mode channel for decoding a redundant row line.

72. The method of claim 65, wherein using a number of vertical gates located above a horizontal depletion mode channel between a single source region and a single drain region to provide an applied potential above the depletion mode channel includes using a number of edged defined vertical gates such that the vertical gates have a horizontal width which is sub-lithographic in dimension.

73. The method of claim 72, wherein using a number of edged defined vertical gates such that the vertical gates have a horizontal width which is sub-lithographic in dimension includes using less than one MOSFET for a number of logic inputs in each logic cell of the memory decode circuit.