STEPPED MICRO-LENS ON MICRO-LED
A light source includes a backplane including electrical circuits fabricated thereon, an array of micro-light emitting diodes (micro-LEDs) bonded to the backplane and configured to emit visible light, and an array of micro-lenses aligned with the array of micro-LEDs and configured to collimate the visible light emitted by the array of micro-LEDs. Each micro-lens of the array of micro-lenses has a plurality of discrete thickness levels. A pitch of the array of micro-lenses is equal to or less than about 5 μm, such as about 2 μm. The pitch of the array of micro-lenses can be the same as or different from the pitch of the array of micro-LEDs.
1 . A light source comprising:
a backplane including electrical circuits fabricated thereon;
an array of micro-light emitting diodes (micro-LEDs) bonded to the backplane and configured to emit visible light; and
an array of micro-lenses aligned with the array of micro-LEDs and configured to collimate the visible light emitted by the array of micro-LEDs, wherein each micro-lens of the array of micro-lenses has a plurality of discrete thickness levels.
2 . The light source of claim 1 , wherein a pitch of the array of micro-lenses is equal to or less than 5 μm.
3 . The light source of claim 1 , wherein the plurality of discrete thickness levels includes four or more discrete thickness levels.
4 . The light source of claim 1 , wherein:
each micro-LED of the array of micro-LEDs includes a semiconductor mesa structure that includes an active region configured to emit the visible light; and
a width of each micro-lens of the array of micro-lenses is greater than 1.3 times of a width of the active region.
5 . The light source of claim 1 , wherein the array of micro-lenses includes a dielectric material or a semiconductor material formed on or bonded to the array of micro-LEDs.
6 . The light source of claim 1 , wherein the array of micro-lenses is formed in a semiconductor epitaxial layer that is in physical contact with the array of micro-LEDs and has a same base semiconductor material as the array of micro-LEDs.
7 . The light source of claim 1 , wherein a perimeter of the micro-lens at each thickness level of the plurality of discrete thickness levels is characterized by a shape of a circle or a polygon.
8 . The light source of claim 1 , wherein the micro-lens approximates a spherical lens or an aspherical lens.
9 . The light source of claim 1 , further comprising an antireflective coating layer on the array of micro-lenses.
10 . The light source of claim 1 , wherein a pitch of the array of micro-lenses is different from a pitch of the array of micro-LEDs.
11 . A micro-light emitting diode (micro-LED) device comprising:
a backplane including electrical circuits fabricated thereon; and
an array of micro-LEDs bonded to the backplane, each micro-LED of the array of micro-LEDs including a semiconductor mesa structure and a micro-lens that are formed in a plurality of semiconductor epitaxial layers, wherein the micro-lens is characterized by a plurality of discrete thickness levels.
12 . The micro-LED device of claim 11 , wherein a pitch of the array of micro-LEDs is equal to or less than 5 μm.
13 . The micro-LED device of claim 11 , wherein the plurality of discrete thickness levels includes four or more discrete thickness levels and is characterized by a uniform or nonuniform thickness step.
14 . The micro-LED device of claim 11 , wherein a perimeter of the micro-lens at each thickness level of the plurality of discrete thickness levels is characterized by a shape of a circle, an oval, or a polygon.
15 . The micro-LED device of claim 11 , wherein the micro-lens approximates a spherical lens or an aspherical lens.
16 . The micro-LED device of claim 11 , wherein:
a center of the micro-lens aligns with a center of the semiconductor mesa structure; and
a width of the semiconductor mesa structure is equal to or larger than a width of the micro-lens.
17 . A method of fabricating an array of stepped micro-lenses, the method comprising:
depositing an etch mask layer on a lens material layer;
patterning the etch mask layer to form a first etch mask on the lens material layer, the first etch mask including a plurality of regions corresponding to centers of the array of stepped micro-lenses;
etching the lens material layer using the first etch mask to form a first step level of the array of stepped micro-lenses;
conformally depositing a spacer layer on surfaces of the lens material layer and the first etch mask;
etching the spacer layer using a first etch recipe to expose the lens material layer and form a second etch mask on the lens material layer; and
etching the lens material layer using the second etch mask and a second etch recipe to form a second step level for the array of stepped micro-lenses.
18 . The method of claim 17 , wherein conformally depositing the spacer layer includes performing a plurality of cycles of atomic layer deposition.
19 . The method of claim 17 , further comprising:
removing remaining etch mask materials on the array of stepped micro-lenses; and
depositing an antireflective coating layer on the array of stepped micro-lenses.
20 . The method of claim 17 , wherein:
the lens material layer includes one or more semiconductor epitaxial layers; and
the method comprises further etching the one or more semiconductor epitaxial layers to form a plurality of semiconductor mesa structures under the array of stepped micro-lenses.