Systems and methods for multi-color LED pixel unit
A micro multi-color LED device includes two or more LED structures for emitting a range of colors. The two or more LED structures are vertically stacked to combine light from the two more LED structures vertically, and/or horizontally and reflected upward via some reflective structures. In some embodiments, each LED structure is connected to a pixel driver and/or a common electrode. The LED structures are bonded together through bonding layers. In some embodiments, planarization layers enclose each of the LED structures or the micro multi-color LED device. In some embodiments, one or more of reflective layers, refractive layers, micro-lenses, spacers, and reflective cup structures are implemented in the device to improve the LED emission efficiency. A display panel comprising an array of the micro tri-color LED devices has a high resolution and a high illumination brightness.
1. A micro-LED pixel unit, comprising,
a semiconductor substrate;
a light emitting region, formed on the semiconductor substrate, including a plurality of color LED structures including a top color LED stacked on top of a lower color LED structure, a bottom of each of the plurality of color LED structures being connected to a corresponding bonding metal layer in the light emitting region, wherein each of the plurality of color LED structures includes a light emitting layer and a reflective layer at a bottom of the light emitting layer;
a top electrode layer, covering each of the plurality of color LED structures and electrically contacting with the top color LED structure and the lower color LED structure of each of the plurality of color LED structures, wherein the semiconductor substrate is electrically connected with each of the plurality of color LED structures; and
a reflective cup, surrounding the light emitting region, light emitted from sidewalls of the light emitting layer of each of the plurality of color LED structures in a horizontal direction arriving at and being reflected upward by the reflective cup, a top of the reflective cup being higher than a top of the light emitting region.
2. The micro-LED pixel unit according to claim 1 , further comprising a micro-lens formed above the light emitting region.
3. The micro-LED pixel unit according to claim 2 , wherein the top of the reflective cup is higher than a top of the micro-lens.
4. The micro-LED pixel unit according to claim 2 , further comprising a refractive structure at a bottom of the micro-lens and formed between the reflective cup and the light emitting region.
5. The micro-LED pixel unit according to claim 2 , wherein a lateral dimension of the micro-lens is not less than a lateral dimension of the light emitting region.
6. The micro-LED pixel unit according to claim 2 , wherein the reflective cup has a top opening area and a lateral dimension of the micro-lens is less than a lateral dimension of the top opening area.
7. The micro-LED pixel unit according to claim 1 , further comprising a bottom dielectric layer formed between a bottom of the reflective cup and the semiconductor substrate.
8. The micro-LED pixel unit according to claim 1 , further comprising a top conductive layer formed on a top of the light emitting region, and the top conductive layer is electrically connected with the reflective cup.
9. The micro-LED pixel unit according to claim 1 , wherein each of the plurality of color LED structures includes a bottom conductive contact layer and a top conductive contact layer, and the light emitting layer is formed between the bottom conductive contact layer and the top conductive contact layer; and wherein
the bottom conductive contact layer is electrically connected with the semiconductor substrate through the reflective structure and corresponding the bonding metal layer by a contact via, and
a top surface of the top conductive contact layer of a top color LED structure is in contact with the top electrode layer, and an edge of the top conductive contact layer of a color LED structure under the top color LED structure is in contact with the top electrode layer.
10. The micro-LED pixel unit according to claim 1 , wherein a bottom of the light emitting region is electrically connected with the semiconductor substrate.
11. The micro-LED pixel unit according to claim 1 , wherein the semiconductor substrate is an IC substrate.
12. The micro-LED pixel unit according to claim 1 , wherein the reflective cup is a stair-shaped reflective cup forming a cavity encompassing the light emitting region.
13. The micro-LED pixel unit according to claim 12 , wherein an inner sidewall of the cavity includes a plurality of inclined surfaces.
14. The micro-LED pixel unit according to claim 13 , wherein angles of the plurality of inclined surfaces relative to surface of the semiconductor substrate from bottom to top of the cavity become smaller.
15. The micro-LED pixel unit according to claim 13 , wherein sub-cavities formed by the plurality of inclined surfaces have different dimensions in a horizontal direction.
16. The micro-LED pixel unit according to claim 15 , wherein inner sidewalls of the sub-cavities are not arranged in a same plane.
17. The micro-LED pixel unit according to claim 15 , wherein heights of the sub-cavities are different.
18. The micro-LED pixel unit according to claim 15 , wherein a height of a sub-cavity in the middle of the cavity is less than heights of other sub-cavities.
19. The micro-LED pixel unit according to claim 15 , wherein a height of a sub-cavity at a top of the cavity is larger than a height of a sub-cavity at a bottom of the cavity.
20. The micro-LED pixel unit according to claim 12 , wherein the cavity includes a plurality of sub-cavities, and each of the plurality of color LED structures is in a respectively different one of the sub-cavities.
21. The micro-LED pixel unit according to claim 1 , wherein a material of the reflective cup comprises metal.