Thermally managed LED arrays assembled by printing

• US 9,765,934 B2
• Filed: 05/15/2012
• Issued: 09/19/2017
• Est. Priority Date: 05/16/2011
• Status: Active Grant

• Current Assignee: Board of Trustees of The University of Illinois, Northwestern University
• Original Assignee: Board of Trustees of The University of Illinois, Northwestern University
• Inventors: Rogers, John A., Kim, Hoon-Sik, Huang, Yonggang
• Primary Examiner(s): SAYADIAN, HRAYR
• Application Number:
  US13/472,165
• Publication Number:
  US 20120320581A1
• Time in Patent Office: 1,953 Days
• Field of Search: 362235, 36224902, 257 88, 257E33059, 438 28
• CPC Class Codes: F21K 9/00 Light sources using semiconductor devices as light-generating elements, e.g. using light-emitting diodes [LED] or lasers
• CPC Class Codes: F21V 29/70 characterised by passive heat-dissipating elements, e.g. heat-sinks
• CPC Class Codes: F21Y 2105/10 comprising a two-dimensional array of point-like light-generating elements
• CPC Class Codes: F21Y 2105/12 characterised by the geometrical disposition of the light-generating elements, e.g. arranging light-generating elements in differing patterns or densities
• CPC Class Codes: F21Y 2115/10 Light-emitting diodes [LED]
• CPC Class Codes: H01L 21/568 Temporary substrate used as encapsulation process aid H01L21/4832 and H01L21/566 take precedence
• CPC Class Codes: H01L 2224/24137 the bodies being arranged next to each other, e.g. on a common substrate
• CPC Class Codes: H01L 2224/73267 Layer and HDI connectors
• CPC Class Codes: H01L 24/24 of an individual high density interconnect connector
• CPC Class Codes: H01L 24/82 by forming build-up interconnects at chip-level, e.g. for high density interconnects [HDI] interconnection structure between a plurality of semiconductor chips H01L23/5389
• CPC Class Codes: H01L 25/0753 the devices being arranged next to each other
• CPC Class Codes: H01L 2924/00 Indexing scheme for arrangements or methods for connecting or disconnecting semiconductor or solid-state bodies as covered by H01L24/00
• CPC Class Codes: H01L 2924/12041 LED
• CPC Class Codes: H01L 2924/12042 LASER
• CPC Class Codes: H01L 2924/12043 Photo diode
• CPC Class Codes: H01L 2924/13063 Metal-Semiconductor Field-Effect Transistor [MESFET]
• CPC Class Codes: H01L 2924/13091 Metal-Oxide-Semiconductor Field-Effect Transistor [MOSFET]
• CPC Class Codes: H01L 2924/1461 MEMS
• CPC Class Codes: H01L 2924/15788 Glasses, e.g. amorphous oxides, nitrides or fluorides
• CPC Class Codes: H01L 2924/181 Encapsulation
• CPC Class Codes: H01L 2924/351 : Thermal stress
• CPC Class Codes: H01L 33/647 : the elements conducting electric current to or from the semiconductor body
• CPC Class Codes: H05K 1/0201 : Thermal arrangements, e.g. for cooling, heating or preventing overheating
• CPC Class Codes: H05K 1/16 : incorporating printed electric components, e.g. printed resistor, capacitor, inductor

Abstract

Provided herein are electronic devices including arrays of printable light emitting diodes (LEDs) having device geometries and dimensions providing enhanced thermal management and control relative to conventional LED-based lighting systems. The systems and methods described provide large area, transparent, and/or flexible LED arrays useful for a range of applications in microelectronics, including display and lightning technology. Methods are also provided for assembling and using electronic devices including thermally managed arrays of printable light emitting diodes (LEDs).

Claims

1. An electronic device comprising:

a substrate; and

an array of light emitting diodes (LEDs) supported by said substrate, said array of LEDs comprising;

a plurality of printable LEDs, wherein each LED in said array of LEDs is a unitary structure having one or more lateral dimensions less than or equal to 1000 μ

m and a thickness dimension less than or equal to 50 μ

m, and wherein a spacing between adjacent LEDs in said array of LEDs is greater than or equal to at least one lateral dimension of the adjacent LEDs in said array; and

a plurality of electrical interconnects, wherein each LED in said array of LEDs is positioned in electrical communication and thermal communication with at least two of said plurality of electrical interconnects, wherein each of said electrical interconnects physically connects two LEDs and has lateral dimensions and an average thickness large enough such that the electrical interconnects act as a heat sink to provide dissipation of heat from said array of LEDs at a rate greater than or equal to 5 μ

J s<sup>−

1</sup> at room temperature.

2. The electronic device of claim 1, wherein said lateral dimensions and said average thickness of said electrical interconnects are large enough to provide heat dissipation from each of said LEDs in said array during operation at a rate selected over the range of 5 μ

J s<sup>−

1</sup> to 100 J s<sup>−

1</sup>.

3. The electronic device of claim 1, wherein said lateral dimensions and said thickness of said electrical interconnects are large enough to provide a maximum temperature of each of said LEDs in said array less than or equal to 373 K for a power consumption equal to or greater than 5 μ

W.

4. The electronic device of claim 1, wherein each of said electrical interconnects of said array has an average heat capacity equal to or greater than 7.3×

10<sup>−

11</sup> J/K.

5. The electronic device of claim 1, wherein an average thermal conductivity of each of said electrical interconnects is a factor of 0.4 to 50 of an average thermal conductivity of each of said LEDs.

6. The electronic device of claim 1, wherein said array has a density of said LEDs less than or equal to 100 LEDs mm⁻

2.

7. The electronic device of claim 1, wherein said array has an average spacing between adjacent LEDs selected over the range of 10 μ

m to 100 μ

m.

8. The electronic device of claim 1, wherein each of said LEDs in said array has average lateral dimensions selected over the range of 10 μ

m to 1 mm.

9. The electronic device of claim 1, wherein each of said LEDs in said array has an average thickness dimension selected over the range of 500 nm to 50 μ

m.

10. The electronic device of claim 1, wherein each of said electrical interconnects has an average thickness greater than or equal to 10 nm.

11. The electronic device of claim 1, wherein each of said electrical interconnects has lateral dimensions selected over the range of 10 μ

m to 10 cm.

12. The electronic device of claim 1, wherein each LED independently comprises a single crystalline inorganic semiconductor.

13. The electronic device of claim 1, further comprising an encapsulating layer provided on at least a portion of said array.

14. The electronic device of claim 1, wherein the spacing between adjacent LEDs in said array of LEDs is greater than or equal to 2 μ

m.

25. The electronic device of claim 1, the plurality of printable LEDs being an array thereof with a density of 81 to 100 LEDs mm⁻

2.

26. The electronic device of claim 1, each the plurality of electrical interconnects having a length greater than a separation distance between the two LEDs each electrical interconnect is connecting.

27. The electronic device of claim 26, at least some of the plurality of electrical interconnects having at least one orthogonal portion.

28. The electronic device of claim 1, each of the plurality of printable LEDs having electrical contacts at opposing corners thereof.

29. The electronic device of claim 1, further including a polymer encapsulating the printable LEDs except at the location of electrical contacts of the plurality of printable LEDs.

30. The electronic device of claim 29, the polymer including positively sloped sidewalls proximate the location of the electrical contacts.

31. The electronic device of claim 28, the electrical contacts having a width, at least at the location of the electrical contacts, greater than a width of the electrical contacts.

32. The electronic device of claim 1, an average thermal conductivity of each of the electrical interconnects being a factor of 0.44 to 1.54 of the average thermal conductivity of the plurality of printable LEDs.

15. A method of making an electronic device, the method comprising the steps of:

providing a substrate;

assembling a plurality of printable LEDs onto said substrate by transfer printing said printable LEDs onto a receiving surface of said substrate, thereby making an array of LEDs, wherein each LED is a unitary structure having one or more lateral dimensions less than or equal to 1000 μ

m and a thickness dimension less than or equal to 50 μ

m and wherein a spacing between adjacent LEDs in said array of LEDs is greater than or equal to at least one lateral dimension of the adjacent LEDs in said array of LEDs; and

providing a plurality of electrical interconnects to said array of LEDs, wherein each LED in said array of LEDs is positioned in electrical communication and thermal communication with two or more of said plurality of electrical interconnects, wherein each of said electrical interconnects physically connects two LEDs and has lateral dimensions and an average thickness large enough such that the electrical interconnects act as a heat sink to provide dissipation of heat from said array of LEDs at a rate greater than or equal to 5 μ

J s<sup>−

1</sup> at room temperature, thereby making said electronic device.

16. The method of claim 15 further comprising providing a polymer encapsulating layer that completely or partially encapsulates said printable LEDs, said electrical interconnects or both.

17. The method of claim 15, wherein the step of assembling a plurality of printable LEDs onto said substrate is achieved using dry contact transfer printing.

18. The method of claim 15, further comprising the steps of:

providing a photosensitive prepolymer layer over said array of LEDs, thereby encapsulating said array of LEDs;

exposing portions of said photosensitive prepolymer layer to electromagnetic radiation, wherein said electromagnetic radiation passes through said substrate and portions of said array of LEDs, thereby forming developed portions and undeveloped portions of said photosensitive prepolymer layer; and

removing said undeveloped portions of said photosensitive prepolymer layer, thereby exposing portions of each LED in said array of LEDs.

33. The method of claim 15, the plurality of printable LEDs being assembled in an array thereof with a density of 81 to 100 LEDs mm⁻

2.

34. The method of claim 15, each the plurality of electrical interconnects having a length greater than a separation distance between the two LEDs each electrical interconnect is connecting.

35. The method of claim 34, at least some of the plurality of electrical interconnects having at least one orthogonal portion.

36. The method of claim 15, each of the plurality of printable LEDs having electrical contacts at opposing corners thereof.

37. The method of claim 15, further including forming a polymer encapsulating the printable LEDs except at the location of electrical contacts of the plurality of printable LEDs.

38. The method of claim 37, the polymer including positively sloped sidewalls proximate the location of the electrical contacts.

39. The method of claim 36, the electrical contacts having a width, at least at the location of the electrical contacts, greater than a width of the electrical contacts.

40. The method of claim 15, an average thermal conductivity of each of the electrical interconnects being a factor of 0.44 to 1.54 of the average thermal conductivity of the plurality of printable LEDs.

19. A method of generating electromagnetic radiation, the method comprising the steps of:

providing an electronic device comprising;

a substrate; and

an array of light emitting diodes (LEDs) supported by said substrate, said array of LEDs comprising;

a plurality of printable LEDs, wherein each LED in said array of LEDs is a unitary structure having one or more lateral dimensions less than or equal to 1000 μ

m and a thickness dimension less than or equal to 50 μ

m, and wherein a spacing between adjacent LEDs in said array of LEDs is greater than or equal to at least one lateral dimension of the adjacent LEDs in said array; and

a plurality of electrical interconnects, wherein each LED in said array of LEDs is positioned in electrical communication and thermal communication with at least two of said plurality of electrical interconnects, wherein each of said electrical interconnects physically connects two LEDs and has lateral dimensions and an average thickness large enough such that the electrical interconnects act as a heat sink to provide dissipation of heat from said array of LEDs at a rate greater than or equal to 5 μ

J s<sup>−

1</sup> at room temperature; and

providing a voltage across two or more of said plurality of electrical interconnects, thereby generating electromagnetic radiation from at least a portion of said array of LEDs.

20. The method of claim 19, wherein each of said electrical interconnects has an average thickness greater than or equal to 300 nm.

21. The method of claim 19, wherein said step of providing an electronic device comprises assembling said LED array on said substrate using a dry transfer contact printing method.

22. An electronic device comprising:

a substrate; and

an array of light emitting diodes (LEDs) supported by said substrate, said array of LEDs comprising;

a plurality of printable LEDs, wherein each LED in said array of LEDs is a unitary structure having one or more lateral dimensions less than or equal to 1000 μ

m and a thickness dimension less than or equal to 50 μ

m, and wherein a spacing between adjacent LEDs in said array of LEDs is greater than or equal to 10 μ

m; and

a plurality of electrical interconnects, wherein each LED in said array of LEDs is positioned in electrical communication with at least two of said plurality of electrical interconnects, wherein each of said electrical interconnects physically connects two LEDs and is characterized by lateral dimensions and an average thickness such that the electrical interconnects act as a heat sink to provide dissipation of heat from said array of LEDs at a rate greater than or equal to 5 μ

J s<sup>−

1</sup> at room temperature.

23. A method of making an electronic device, the method comprising the steps of:

providing a substrate;

assembling a plurality of printable LEDs onto said substrate by transfer printing said printable LEDs onto a receiving surface of said substrate, thereby making an array of LEDs, wherein each LED is a unitary structure having one or more lateral dimensions less than or equal to 1000 μ

m and a thickness dimension less than or equal to 50 μ

m and wherein a spacing between adjacent LEDs in said array of LEDs is greater than or equal to 10 μ

m; and

providing a plurality of electrical interconnects to said array of LEDs, wherein each LED in said array of LEDs is positioned in electrical communication with two or more of said plurality of electrical interconnects, wherein each of said electrical interconnects physically connects two LEDs and is characterized by lateral dimensions and an average thickness, thereby making said electronic device such that the electrical interconnects act as a heat sink to provide dissipation of heat from said array of LEDs at a rate greater than or equal to 5 μ

J s<sup>−

1</sup> at room temperature.

24. A method of generating electromagnetic radiation, the method comprising the steps of:

providing an electronic device comprising;

a substrate; and

an array of light emitting diodes (LEDs) supported by said substrate, said array of LEDs comprising;

a plurality of printable LEDs, wherein each LED in said array of LEDs is a unitary structure having one or more lateral dimensions less than or equal to 1000 μ

m and a thickness dimension less than or equal to 50 μ

m, and wherein a spacing between adjacent LEDs in said array of LEDs is greater than or equal to 10 μ

m; and

a plurality of electrical interconnects, wherein each LED in said array of LEDs is positioned in electrical communication with at least two of said plurality of electrical interconnects, wherein each of said electrical interconnects physically connects two LEDs and is characterized by lateral dimensions and an average thickness such that the electrical interconnects act as a heat sink to provide dissipation of heat from said array of LEDs at a rate greater than or equal to 5 μ

J s<sup>−

1</sup> at room temperature; and

providing a voltage across two or more of said plurality of electrical interconnects, thereby generating electromagnetic radiation from at least a portion of said array of LEDs.