Subpixel light emitting diodes for direct view display and methods of making the same
A method includes transferring a first subset of the first LEDs from a first substrate to a first backplane to form first subpixels in pixel regions, transferring a first subset of the second LEDs to a second backplane and separating the first subset of the second LEDs from a second substrate to leave first vacancies on the second substrate, forming an additional electrically conductive material on a second subset of second LEDs located on the second substrate after transferring the first subset of the second LEDs to the second backplane, positioning the second substrate over the first backplane, such that the first subpixels are disposed in the first vacancies, and transferring the second subset of the second LEDs to a second subset of bonding structures on the first backplane to form second subpixels in the pixel regions, while a gap exists between the first subpixels and the second substrate.
1. A method of transferring light emitting diodes (LEDs), comprising:
providing first LEDs configured to emit first color light and located on a first substrate, and second LEDs configured to emit second color light different from the first color light and located on a second substrate;
transferring a first subset of the first LEDs to a first subset of bonding structures on a first backplane to form first subpixels in pixel regions and separating the first subset of the first LEDs from the first substrate;
transferring a first subset of the second LEDs to a second backplane and separating the first subset of the second LEDs from the second substrate to leave first vacancies on the second substrate;
forming an additional electrically conductive material on a second subset of second LEDs located on the second substrate after transferring the first subset of the second LEDs to the second backplane;
positioning the second substrate over the first backplane, such that the first subpixels are disposed in the first vacancies; and
transferring the second subset of the second LEDs to a second subset of bonding structures on the first backplane to form second subpixels in the pixel regions, while a gap exists between the first subpixels and the second substrate due to the presence of the additional electrically conductive material.
2. The method of claim 1 , wherein:
the step of transferring the first subset of the first LEDs to the first subset of bonding structures comprises forming a first solder layer on the first subset of the first LEDs, bonding the first solder layer to the first bonding structures, and separating the first subset of the first LEDs from the first substrate; and
the step of transferring the second subset of the second LEDs to the second subset of bonding structures comprises forming a second solder layer on the second subset of the second LEDs, bonding the second solder layer to the second bonding structures, and separating the second subset of the second LEDs from the second substrate.
3. The method of claim 2 , wherein:
bonding the first solder layer to the first bonding structures comprises a first laser bonding step;
separating the first subset of the first LEDs from the first substrate comprises a first laser lift off step which occurs before or after the first laser bonding step;
bonding the second solder layer to the second bonding structures comprises a second laser bonding step; and
separating the second subset of the second LEDs from the second substrate comprises a second laser lift off step which occurs before or after the second laser bonding step.
4. The method of claim 2 , wherein:
the first solder layer on the first subset of the first LEDs comprise first transfer structures;
the second solder layer on the second subset of the second LEDs comprise second transfer structures;
the first transfer structures extend from the first substrate by a first distance; and
the second transfer structures extend from the second substrate by a second distance that is greater than the first distance.
5. The method of claim 2 , wherein forming the additional electrically conductive material comprises forming the second solder layer which is thicker than the first solder layer.
6. The method of claim 2 , wherein forming the additional electrically conductive material comprises forming a second reflective layer on the second subset of second LEDs which is thicker than a first reflective layer on the first subset of first LEDs.
7. The method of claim 6 , further comprising:
forming a first portion of the second reflective layer on both the first and the second subsets of the second LEDs prior to transferring the first subset of the second LEDs to the second backplane; and
forming a second portion of the second reflective layer on the first portion of the second reflective layer located on the second subset of the second LEDs after transferring the first subset of the second LEDs to the second backplane.
8. The method of claim 2 , wherein forming the additional electrically conductive material comprises forming the second solder layer which is thicker than the first solder layer and forming a second reflective layer on the second subset of second LEDs which is thicker than a first reflective layer on the first subset of first LEDs.
9. The method of claim 2 , further comprising:
providing third LEDs configured to emit third color light different from the first and second color light and located on a third substrate;
transferring first and second subsets of the third LEDs to additional backplanes and separating the first and second subsets of the third LEDs from the third substrate to leave second vacancies on the third substrate;
forming another additional electrically conductive material on a third subset of third LEDs located on the third substrate after transferring the first and second subsets of the third LEDs to the additional backplanes;
positioning the third substrate over the first backplane, such that the first and the second subpixels are disposed in the second vacancies; and
transferring the third subset of the third LEDs to a third subset of bonding structures on the first backplane to form third subpixels in the pixel regions, while a gap exists between the first and the second subpixels and the third substrate due to the presence of the another additional electrically conductive material.
10. The method of claim 9 , wherein the step of transferring the third subset of the third LEDs to the third subset of bonding structures comprises forming a third solder layer on the third subset of the third LEDs, bonding the third solder layer to the third bonding structures, and separating the third subset of the third LEDs from the third substrate.
11. The method of claim 10 , wherein forming the other additional electrically conductive material comprises forming the third solder layer which is thicker than the first and the second solder layers.
12. The method of claim 10 , wherein forming the another additional electrically conductive material comprises forming a third reflective layer on the third subset of third LEDs which is thicker than a first reflective layer on the first subset of first LEDs and a second reflective layer on the second subset of second LEDs.
13. The method of claim 9 , wherein:
the first substrate comprises a first coupon diced from a first wafer on which the first LEDs are initially formed;
the second substrate comprises a second coupon diced from a second wafer on which the second LEDs are initially formed; and
the third substrate comprises a third coupon diced from a third wafer on which the third LEDs are initially formed.
14. The method of claim 9 , wherein a density of subpixels in the pixel region is lower than a density of the first LEDs located on the first substrate, is lower than a density of the second LEDs located on the second substrate, and is lower than a density of the third LEDs located on the third substrate.
15. The method of claim 9 , wherein:
the first LEDs are located on the first substrate in first pixel regions;
the second LEDs are located on the second substrate in second pixel regions;
the third LEDs are located on the third substrate in third pixel regions;
the first, second and third pixel regions have the same area and shape as the pixel regions on the first backplane; and
more LEDs are disposed in each of the first, second and third pixel regions than in the pixel regions on the first backplane.
16. The method of claim 15 , wherein at least two of the first, second, or third LEDs are disposed in each of the respective first, second or third pixel regions; and only one of each of the first, second, and third LEDs are disposed in each pixel region on the first backplane.
17. The method of claim 9 , wherein the first, second and third bonding structures extend from the first backplane by substantially the same distance.
18. The method of claim 1 , further comprising incorporating the first backplane into a direct view display device.