System and method for the fluidic assembly of emissive displays

Patent metadata

Field	Value
Publication number	US-10418527-B2
Application number	US-201715412731-A
Country	US
Kind code	B2
Filing date	Jan 23, 2017
Priority date	Oct 31, 2014
Publication date	Sep 17, 2019
Grant date	Sep 17, 2019

Abstract

Fluidic assembly methods are presented for the fabrication of emissive displays. An emissive substrate is provided with a top surface, and a first plurality of wells formed in the top surface. Each well has a bottom surface with a first electrical interface. Also provided is a liquid suspension of emissive elements. The suspension is flowed across the emissive substrate and the emissive elements are captured in the wells. As a result of annealing the emissive substrate, electrical connections are made between each emissive element to the first electrical interface of a corresponding well. A eutectic solder interface metal on either the substrate or the emissive element is desirable as well as the use of a fluxing agent prior to thermal anneal. The emissive element may be a surface mount light emitting diode (SMLED) with two electrical contacts on its top surface (adjacent to the bottom surfaces of the wells).

First claim

We claim:

1. A fluidic assembly method for the fabrication of emissive displays, the method comprising: providing an emissive substrate with a top surface, a first plurality of wells formed in the top surface, each well comprising a bottom surface with a first electrical interface, and a matrix of column and row traces forming a first plurality of column/row intersections, where each column/row intersection is associated with a corresponding well; providing a liquid suspension of light emitting diodes (LEDs), with each LED having a post, made from an insulator material, extending from a surface; flowing the liquid suspension across the emissive substrate top surface; capturing the LEDs in the wells, oriented so that the posts are exposed and extending out of well openings in the emissive substrate top surface; annealing the emissive substrate; and, in response to the annealing, electrically connecting each LED to the first electrical interface of a corresponding well, wherein flowing the liquid suspension across the substrate top surface includes flipping the orientation of inverted LEDs, from a post-down to a post-up orientation, in response to drag forces resulting from a moment of force about an LED surface edge creating a fixed point of rotation with respect to a substrate surface.

2. The method of claim 1 wherein electrically connecting each LED includes connecting each LED to the first electrical interface without the formation of overlying metal layers, additional conductive traces, or wire bonding on the substrate subsequent to annealing.

3. The method of claim 1 further comprising:
engaging an auxiliary mechanism for distributing the LEDs selected from the group consisting of a brush (rotating or non-rotating), wiper, rotating cylinder, pressurized fluid, and mechanical vibration; and,
wherein capturing the LEDs in the wells includes capturing the LEDs in response to the auxiliary mechanism engaging elements selected from the group consisting of the LEDs in the suspension and the emissive substrate top surface.

4. The method of claim 3 wherein providing the emissive substrate includes providing an emissive substrate having a length and a width;
wherein engaging the auxiliary mechanism includes engaging a brush, having a rotation axis and brush length at least equal to the emissive substrate width, as follows:
in a first pass, translating the brush length across the emissive substrate length in the first direction;
simultaneously with the first pass of brush translation, rotating the brush to create a first local variance in liquid suspension velocity.

5. The method of claim 4 wherein engaging the auxiliary mechanism includes:
rotating the brush at a rate in a range of 120 to 300 revolutions per minute (RPM); and,
translating the brush at a speed in a range of 3 to 10 centimeter per second (cm/s).

6. The method of claim 1 wherein providing the emissive substrate includes providing wells with solder-coated first electrical interfaces.

7. The method of claim 1 wherein flowing the suspension across the emissive substrate top surface includes creating a maximum local density of LEDs in the liquid suspension in a range of 0.3 to 0.8 monolayers.

8. The method of claim 1 wherein providing the liquid suspension of emissive elements includes providing vertical LEDs having a bottom surface with a first electrical contact and a top surface with a second electrical contact, with the post extending from the LED top surface;
wherein capturing the LEDs in the wells includes capturing the vertical LED bottom surface directly overlying a corresponding well bottom surface; and,
wherein electrically connecting each LED first electrical interface in the corresponding well includes electrically connecting each vertical LED first electrical contact to a corresponding well first electrical interface.

9. The method of claim 1 wherein electrically connecting each LED includes electrically connecting each LED to the first electrical interface of a corresponding well without the application of external pressure on the LED.

10. The method of claim 1 wherein capturing the LEDs in the wells includes surface orienting the LED first electrical contacts directly overlying the well bottom surfaces in response to the LED posts.

11. The method of claim 1 wherein providing the emissive substrate includes each well comprising a bottom surface with both the first electrical interface and a second electrical interface;
wherein providing the liquid suspension of LEDs includes providing surface mount LEDs having a bottom surface and a top surface, with a first electrical contact and a second electrical contact formed on the top surface, and with the post extending from the LED bottom surface;
wherein capturing the LEDs in the wells includes capturing each surface mount LED top surface directly overlying a corresponding well bottom surface; and,
wherein electrically connecting each LED to the first electrical interface in the corresponding well in response to the annealing includes electrically connecting each surface mount LED first electrical contact to a corresponding well first electrical interface and each surface mount LED second electrical contact to a corresponding well second electrical interface.

12. The method of claim 1 wherein providing the liquid suspension of LEDs comprises providing a suspension including a solder fluxing agent.

13. The method of claim 1 further comprising:
subsequent to capturing the LEDs in the wells and prior to annealing the substrate, filling the LED populated wells with a solder fluxing agent.

14. The method of claim 1 further comprising:
simultaneously with capturing the LEDs in the wells, collecting uncaptured LEDs; and,
resuspending the collected LEDs in a liquid suspension for subsequent emissive display fabrication.

15. The method of claim 1 further comprising:
forming a plurality of color modifiers overlying exposed surfaces of a corresponding plurality of LEDs.

16. The method of claim 1 further comprising:
forming a plurality of light diffusers overlying a corresponding plurality of LEDs.

17. The method of claim 1 wherein providing the liquid suspension of LEDs includes providing a liquid selected from the group consisting of alcohols, polyols, ketones, halocarbons, and water.

18. The method of claim 1 wherein providing the liquid suspension of LEDs includes providing LEDs having a solder-coated electrical contacts.

19. A fluidic assembly method for the fabrication of emissive displays, the method comprising:
providing an emissive substrate with a top surface, a first plurality of wells formed in the top surface, each well comprising a bottom surface with a first electrical interface and sidewalls formed about orthogonal to the bottom surface, and a matrix of column and row traces forming a first plurality of column/row intersections, where each column/row intersection is associated with a corresponding well;
providing a liquid suspension of vertical light emitting diodes (LEDs) having a bottom surface with a first electrical contact, a top surface with a second electrical contact, and a post made from an insulator material extending from the vertical LED top surface;
flowing the liquid suspension across the emissive substrate top surface;
capturing the vertical LEDs bottom surfaces directly overlying corresponding well bottom surfaces;
annealing the emissive substrate;
in response to the annealing, electrically connecting each vertical LED first electrical contact to the first elect

Assignees

• Elux Inc

Inventors

• Sasaki Kenji
• Schuele Paul J
• Ulmer Kurt
• Lee Jong-Jan

Classifications

• H10W90/00

  Package configurations · CPC title

• H10W72/0198

  batch processes · CPC title

• H01L2933/0066

  Electricity · mapped topic

• H01L33/62

  Electricity · mapped topic

• H01L25/0753

  Electricity · mapped topic