Transistor structures having a transparent channel

• US 7,189,992 B2
• Filed: 11/27/2002
• Issued: 03/13/2007
• Est. Priority Date: 05/21/2002
• Status: Expired due to Term

• Current Assignee: Oregon State University (Oregon University System)
• Original Assignee: Oregon State University (Oregon University System)
• Inventors: Wager, John F. III, Hoffman, Randy L.
• Primary Examiner(s): RICHARDS, N DREW
• Application Number:
  US10/307,162
• Publication Number:
  US 20030218221A1
• Time in Patent Office: 1,567 Days
• Field of Search: 257/43, 257/613, 438/85, 438/104
• US Class Current: 257/43
• CPC Class Codes: H01L 29/02 Semiconductor bodies ; Multistep manufacturing processes therefor
• CPC Class Codes: H01L 29/45 Ohmic electrodes
• CPC Class Codes: H01L 29/4908 for thin film semiconductor, e.g. gate of TFT
• CPC Class Codes: H01L 29/66969 of devices having semiconductor bodies not comprising group 14 or group 13/15 materials comprising selenium or tellurium in uncombined form other than as impurities in semiconductor bodies of other materials, comprising cuprous oxide or cuprous iodide H01L21/02365
• CPC Class Codes: H01L 29/7869 having a semiconductor body comprising an oxide semiconductor material, e.g. zinc oxide, copper aluminium oxide, cadmium stannate

Abstract

Enhancement mode, field effect transistors wherein at least a portion of the transistor structure may be substantially transparent. One variant of the transistor includes a channel layer comprising a substantially insulating, substantially transparent, material selected from ZnO or SnO₂. A gate insulator layer comprising a substantially transparent material is located adjacent to the channel layer so as to define a channel layer/gate insulator layer interface. A second variant of the transistor includes a channel layer comprising a substantially transparent material selected from substantially insulating ZnO or SnO₂, the substantially insulating ZnO or SnO₂ being produced by annealing. Devices that include the transistors and methods for making the transistors are also disclosed.

Claims

1. A field effect transistor, comprising:

a channel layer comprising a substantially insulating, substantially transparent, material selected from ZnO or SnO₂, wherein the channel layer comprising ZnO is vapor deposited;

a gate insulator layer comprising a substantially transparent material and being located adjacent to the channel layer so as to define a channel layer/gate insulator layer interface;

a source that can inject electrons into the channel layer for accumulation at the channel layer/gate insulator layer interface; and

a drain that can extract electrons from the channel layer;

wherein the field effect transistor is configured for enhancement-mode operation, and exhibits an optical transmission through the field effect transistor of at least about 70% in the visible portion of the electromagnetic spectrum.

2. The transistor according to claim 1, wherein the channel layer/gate insulator layer interface defines an electron conducting channel between the source and the drain.

3. The transistor according to claim 1, wherein the field effect transistor comprises a thin film transistor.

4. The transistor according to claim 1, wherein the channel layer material is a different material from the gate insulator layer material.

5. The transistor according to claim 1, wherein the transistor is a surface-channel transistor.

6. The transistor according to claim 1, further comprising a gate electrode and a substrate, and wherein the source, drain, gate electrode, and substrate are each made from a substantially transparent material.

7. The transistor according to claim 1, further comprising a gate electrode and a substrate, and wherein at least one of the source, drain, gate electrode, or substrate is made from an opaque material.

8. The transistor according to claim 1, wherein the gate insulator layer comprises Al₂O₃/TiO₂.

9. The transistor according to claim 6, wherein the gate insulator layer comprises Al₂O₃/TiO₂ or Al₂O₃;

the source, drain, and gate electrode each comprise indium-tin oxide; and

the substrate comprises glass.

10. The transistor according to claim 1, wherein the channel layer/gate insulator layer interface defines a discrete material boundary.

11. The transistor according to claim 1, wherein the optical transmission is at least about 90% in the visible portion of the electromagnetic spectrum.

12. The transistor according to claim 1, wherein the channel layer is not ion implanted.

13. The transistor according to claim 1, wherein the channel layer comprises undoped ZnO.

14. The transistor according to claim 1, wherein at least one of the source or the drain comprises a material selected from indium-tin oxide, LaB₆, or ZnO:

Al.

15. The transistor according to claim 1, wherein the channel layer material exhibits a bandgap of less than about 5 eV.

16. The transistor according to claim 1, wherein the ZnO or SnO₂ has a reduced oxygen vacancy concentration.

41. An optoelectronic display device comprising at least one display element coupled to a switch comprising an enhancement-mode, field effect transistor according to claim 1.

42. The optoelectronic display device of claim 41, wherein the device comprises an active-matrix liquid-crystal display.

45. A substantially transparent, dynamic random-access memory cell, comprising a substantially transparent capacitor coupled to an enhancement-mode, field effect transistor according to claim 1.

47. A substantially transparent logic inverter, comprising a load device coupled to an enhancement-mode, field effect transistor according to claim 1.

49. An amplifier comprising an enhancement-mode, field effect transistor according to claim 1.

54. The transistor according to claim 6, wherein the channel layer comprises undoped ZnO.

58. The transistor according to claim 1, wherein the channel layer comprises SnO₂.

60. The transistor according to claim 1, wherein the channel layer/gate insulator layer interface has an effective electron mobility of about 0.05 cm²V⁻

1s<sup>−

1</sup> to about 20 cm²V<sup>−

1</sup>s<sup>−

1</sup>.

61. The transistor according to claim 1, wherein the channel layer comprises ZnO.

63. The transistor according to claim 60, wherein the channel layer comprises ZnO.

64. The transistor according to claim 61, wherein the channel layer/gate insulator layer interface has an effective electron mobility of at least about 0.05 cm²V⁻

1s<sup>−

1</sup>.

65. The transistor according to claim 1, wherein the channel layer comprising ZnO comprises a chemical vapor deposited channel layer or a sputtered channel layer.

17. A field effect transistor, comprising:

a channel layer comprising a substantially transparent material selected from substantially insulating ZnO or substantially insulating SnO₂, the substantially insulating SnO₂ being produced by annealing and the substantially insulating ZnO being vapor deposited and the resulting ZnO layer undergoes annealing;

a gate insulator layer located adjacent to the channel layer;

a source;

a drain; and

a gate electrode;

wherein the field effect transistor is configured for enhancement-mode operation, and exhibits an optical transmission through the field effect transistor of at least about 70% in the visible portion of the electromagnetic spectrum.

18. The transistor according to claim 17, wherein the gate insulator layer comprises a substantially transparent material.

19. The transistor according to claim 18, wherein the gate insulator layer comprises Al₂O₃/TiO₂.

20. The transistor according to claim 17, further comprising a substrate, wherein the source, drain, gate electrode, and substrate are each made from a substantially transparent material.

21. The transistor according to claim 17, further comprising a substrate, and wherein at least one of the source, drain, gate electrode, or substrate is made from an opaque material.

22. The transistor according to claim 17, wherein the field effect transistor comprises a thin film transistor.

23. The transistor according to claim 17, wherein the channel layer comprises insulating ZnO fabricated by annealing a ZnO film for about 1 to about 5 minutes at a temperature of about 300 to about 1000°

C. in a substantially oxidative or inert atmosphere.

24. The transistor according to claim 23, wherein the gate insulator layer comprises Al₂O₃/TiO₂ or Al₂O₃;

the source, drain, and gate electrode each comprise indium-tin oxide; and

the substrate comprises glass.

25. The transistor according to claim 17, wherein the channel layer is interposed between the gate insulator layer and the source and drain.

26. The transistor according to claim 17, wherein the channel layer and the gate electrode are disposed, respectively, on opposing surfaces of the gate insulator layer.

27. The transistor according to claim 17, wherein the channel layer is not ion implanted.

28. The transistor according to claim 17, wherein the channel layer comprises undoped ZnO.

29. The transistor according to claim 17, wherein at least one of the source and the drain comprises a material selected from indium-tin oxide, LaB₆, or ZnO:

Al.

30. The transistor according to claim 17, wherein the channel layer material exhibits a bandgap of less than about 5 eV.

31. The transistor according to claim 17, wherein the channel layer is not interposed between the gate insulator layer and the source and drain.

32. The transistor according to claim 17, further comprising a substrate, and wherein the gate electrode is disposed adjacent to the substrate.

33. The transistor according to claim 17, wherein the annealed ZnO or SnO₂ has a lower oxygen vacancy concentration relative to ZnO or SnO₂ that has not been annealed.

43. An optoelectronic display device comprising at least one display element coupled to a switch comprising an enhancement-mode, field effect transistor according to claim 17.

44. The optoelectronic display device of claim 43, wherein the device comprises an active-matrix liquid-crystal display.

46. A substantially transparent, dynamic random-access memory cell, comprising a substantially transparent capacitor coupled to an enhancement-mode, field effect transistor according to claim 17.

48. A substantially transparent logic inverter, comprising a load device coupled to an enhancement-mode, field effect transistor according to claim 17.

50. An amplifier comprising an enhancement-mode, field effect transistor according to claim 17.

55. The transistor according to claim 23, wherein the channel layer comprises undoped ZnO.

57. The transistor according to claim 23, wherein the annealing occurs at a temperature of about 700°

C. to about 800°

C. in an Ar or O₂ atmosphere.

66. The transistor according to claim 17, wherein the substantially insulating ZnO is chemical vapor deposited or sputtered.

34. A thin film transistor comprising:

a discrete channel layer comprising an inorganic, substantially insulating ZnO or SnO₂ material, wherein the channel layer comprising ZnO is produced by vapor deposition; and

a gate insulator layer located adjacent to the channel layer,

wherein the combined channel layer and gate insulator layer construct exhibits an optical transmission through the construct of at least about 90% in the visible portion of the electromagnetic spectrum, and is configured for enhancement-mode operation.

35. The transistor according to claim 34, wherein the combined channel layer and gate insulator layer construct exhibits an optical transmission through the construct of at least about 95% in the visible portion of the electromagnetic spectrum.

36. The transistor according to claim 35, wherein the channel layer comprises insulating ZnO.

62. The transistor according to claim 34, wherein the channel layer comprises SnO₂.

78. The transistor according to claim 34, further comprising a gate electrode, a substrate, a source, and a drain, and wherein at least one of the source, drain, gate electrode, or substrate is made from an opaque material.

79. The transistor according to claim 34, wherein the ZnO or SnO₂ has a reduced oxygen vacancy concentration.

80. The transistor according to claim 34, wherein the gate insulator layer comprises Al₂O₃/TiO₂.

37. A method for operating a field effect transistor, comprising:

providing a field effect transistor that includes (i) a channel layer comprising a substantially insulating, substantially transparent material selected from ZnO or SnO₂, wherein the ZnO is produced by vapor deposition;

(ii) a gate insulator layer located adjacent to the channel layer so as to define a channel layer/gate insulator layer interface (iii) a source;

(iv) a drain; and

(v) a gate electrode, wherein the field effect transistor exhibits an optical transmission through the field effect transistor of at least about 70% in the visible portion of the electromagnetic spectrum; and

applying a positive voltage to the gate electrode to effect a flow of electrons at the channel layer/gate insulator layer interface, wherein in the absence of an applied positive voltage substantially no current flow occurs.

38. The method according to claim 37, wherein the gate insulating layer comprises a substantially transparent material.

39. The method according to claim 37, wherein the electrons flowing at the channel layer/gate insulator layer interface have an effective mobility of about 0.05 cm²V⁻

1 s<sup>−

1</sup> to about 20 cm² V<sup>−

1</sup> s<sup>−

1</sup>

40. The method according to claim 37, wherein a voltage of about 5 to about 40 V is applied to the gate electrode and the drain.

59. The method according to claim 37, wherein the channel layer comprises SnO₂.

67. The method of claim 37, wherein the ZnO is produced by chemical vapor deposition or sputtering.

51. A microelectronic construct, comprising:

a continuous channel layer film comprising a substantially insulating material selected from ZnO or substantially transparent SnO₂, wherein the channel layer comprising ZnO is produced by vapor deposition and the channel layer comprising SnO₂ exhibits an optical transmission of at least about 70% in the visible portion of the electromagnetic spectrum; and

a plurality of patterned gate insulator layers, sources, and drains arranged so that each gate insulator layer, source and drain forms, along with the continuous channel layer film, a discrete electrical device, wherein the gate insulator layer is located adjacent to the continuous channel layer film so as to define a channel layer/gate insulator layer interface.

52. The microelectronic construct according to claim 51, wherein the continuous channel layer film is not patterned.

53. The microelectronic construct according to claim 51, wherein the continuous channel layer film comprises a substantially transparent material, and the gate insulator layer comprises a substantially transparent material.

56. The microelectronic construct according to claim 51, wherein the channel layer comprises undoped ZnO.

68. The microelectronic construct according to claim 51, wherein the channel layer comprising ZnO is produced by chemical vapor deposition or sputtering.

69. A field effect transistor, comprising:

a channel layer comprising a substantially insulating material comprising ZnO, wherein the channel layer comprising ZnO is vapor deposited;

a gate insulator layer comprising a substantially transparent material and being located adjacent to the channel layer so as to define a channel layer/gate insulator layer interface;

a source that can inject electrons into the channel layer for accumulation at the channel layer/gate insulator layer interface; and

a drain that can extract electrons from the channel layer;

wherein the field effect transistor is configured for enhancement-mode operation and the channel layer exhibits an optical transmission of at least about 50% across the visible portion of the electromagnetic spectrum.

70. The transistor according to claim 69, wherein the channel layer exhibits an optical transmission of at least about 70% across the visible portion of the electromagnetic spectrum.

71. A field effect transistor, comprising:

a channel layer comprising a substantially insulating, substantially transparent, material selected from ZnO or SnO₂, wherein the channel layer comprising ZnO is vapor deposited;

a gate insulator layer comprising a substantially transparent material and being located adjacent to the channel layer so as to define a channel layer/gate insulator layer interface;

a source that can inject electrons into the channel layer for accumulation at the channel layer/gate insulator layer interface; and

a drain that can extract electrons from the channel layer;

wherein the field effect transistor is configured for enhancement-mode operation, and at least one of the source or the drain comprises a material selected from indium-tin oxide, LaB₆, or ZnO;

Al.

72. A field effect transistor, comprising:

a channel layer comprising a substantially transparent material selected from substantially insulating ZnO or substantially insulating SnO2, the substantially insulating SnO₂ being produced by annealing and the substantially insulating ZnO being vapor deposited and the resulting ZnO layer undergoes annealing;

a gate insulator layer located adjacent to the channel layer;

a source;

a drain; and

a gate electrode;

wherein the field effect transistor is configured for enhancement-mode operation, and at least one of the source or the drain comprises a material selected from indium-tin oxide, LaB₆, or ZnO;

Al.

73. A method for operating a field effect transistor, comprising:

providing a field effect transistor that includes (i) a channel layer comprising a substantially insulating, substantially transparent material selected from ZnO or SnO₂, wherein the ZnO is produced by vapor deposition;

(ii) a gate insulator layer located adjacent to the channel layer so as to define a channel layer/gate insulator layer interface (iii) a source;

(iv) a drain; and

(v) a gate electrode; and

applying a positive voltage to the gate electrode to effect a flow of electrons having an effective mobility of about 0.05 cm²V<sup>−

1</sup>s<sup>−

1</sup> to about 20 cm²V<sup>−

1</sup>s<sup>−

1</sup> at the channel layer/gate insulator layer interface, wherein in the absence of an applied positive voltage substantially no current flow occurs.

74. A field effect transistor, comprising:

a channel layer comprising a substantially insulating, substantially transparent, material selected from ZnO or SnO₂, wherein the channel layer comprising ZnO is vapor deposited;

a gate insulator layer comprising a substantially transparent material and being located adjacent to the channel layer so as to define a channel layer/gate insulator layer interface having an effective electron mobility of about 0.05 cm²V<sup>−

1</sup>s<sup>−

1</sup> to about 20 cm²V<sup>−

1</sup>s<sup>−

1</sup>;

a source that can inject electrons into the channel layer for accumulation at the channel layer/gate insulator layer interface; and

a drain that can extract electrons from the channel layer;

wherein the field effect transistor is configured for enhancement-mode operation.

75. A field effect transistor, comprising:

a channel layer comprising a substantially insulating, substantially transparent ZnO material, wherein the channel layer comprising ZnO is vapor deposited;

a gate insulator layer comprising a substantially transparent material and being located adjacent to the channel layer so as to define a channel layer/gate insulator layer interface;

a source that can inject electrons into the channel layer for accumulation at the channel layer/gate insulator layer interface; and

a drain that can extract electrons from the channel layer;

wherein the field effect transistor is configured for enhancement-mode operation.

76. The transistor according to claim 75, wherein the ZnO material comprises undoped ZnO.

77. The transistor according to claim 75, further comprising a gate electrode and a substrate, and wherein at least one of the source, drain, gate electrode, or substrate is made from an opaque material.