LIGHT EXTRACTION FOR MICRO-LEDS
Techniques disclosed herein relate to light extraction structures for micro-LED arrays. According to certain embodiments, a device includes an array of micro-LEDs characterized by a first pitch, and an array of micro-lenses on the array of micro-LEDs and characterized by a second pitch different from the first pitch. Each micro-lens in the array of micro-lenses corresponds to a respective micro-LED in the array of micro-LEDs. In some embodiments, the first pitch is greater than the second pitch such that a chief ray of light from each micro-LED in the array of micro-LEDs after passing through the corresponding micro-lens tilts in a respective direction towards a middle line of the device.
1 . A device comprising:
an array of micro-LEDs characterized by a first pitch; and
an array of micro-lenses on the array of micro-LEDs and characterized by a second pitch different from the first pitch, each micro-lens in the array of micro-lenses corresponding to a respective micro-LED in the array of micro-LEDs.
2 . The device of claim 1 , wherein each micro-lens in the array of micro-lenses is configured such that a chief ray of light from the corresponding micro-LED in the array of micro-LEDs after passing through the micro-lens propagates in a different respective direction.
3 . The device of claim 1 , wherein the first pitch is greater than the second pitch.
4 . The device of claim 3 , wherein a chief ray of light from each micro-LED in the array of micro-LEDs after passing through the corresponding micro-lens tilts in a respective direction towards a middle line of the device.
5 . The device of claim 1 , wherein:
the array of micro-LEDs includes a two-dimensional array of micro-LEDs;
the array of micro-lenses includes a two-dimensional array of micro-lenses; and
the first pitch and the second pitch are in a first dimension.
6 . The device of claim 5 , wherein:
the array of micro-LEDs is characterized by a third pitch in a second dimension;
the array of micro-lenses is characterized by a fourth pitch in the second dimension; and
the third pitch is different from the fourth pitch.
7 . The device of claim 6 , wherein the first pitch is different from the third pitch.
8 . The device of claim 6 , wherein the second pitch is different from the fourth pitch.
9 . The device of claim 1 , wherein the array of micro-lenses includes a dielectric material or an organic material.
10 . The device of claim 9 , wherein the dielectric material includes silicon oxide or silicon nitride.
11 . The device of claim 1 , wherein the array of micro-lenses includes an anti-reflective coating.
12 . The device of claim 1 , wherein the array of micro-lenses includes spherical micro-lenses or aspherical micro-lenses.
13 . The device of claim 1 , wherein each micro-lens in the array of micro-lenses is configured to collimate light from the corresponding micro-LED in the array of micro-LEDs.
14 . The device of claim 1 , wherein at least one of the first pitch or the second pitch varies across the device.
15 . The device of claim 1 , wherein the first pitch is lower than the second pitch.
16 . The device of claim 1 , wherein the first pitch is less than 10 μm.
17 . The device of claim 1 , wherein a linear dimension of each micro-lens in the array of micro-lenses is greater than a linear dimension of each micro-LED in the array of micro-LEDs.
18 . A method comprising:
depositing a polymer layer on a dielectric layer of a micro-LED array, the micro-LED array characterized by a first pitch between centers of adjacent micro-LEDs;
patterning the polymer layer to form a polymer pattern, wherein the polymer pattern in the polymer layer is characterized by a second pitch different from the first pitch; and
reflowing the polymer pattern to form a micro-lens array in the polymer layer, the micro-lens array characterized by a third pitch equal to the second pitch.
19 . The method of claim 18 , further comprising:
etching the micro-lens array in the polymer layer and the dielectric layer of the micro-LED array to form a micro-lens array in the dielectric layer,
wherein the polymer layer is characterized by an etch rate comparable to an etch rate of the dielectric layer.
20 . The method of claim 18 , wherein:
the polymer layer includes a photoresist layer; and
patterning the polymer layer comprises:
exposing the photoresist layer to exposure light through:
a gray-scale mask, wherein a light transmissivity profile of the gray-scale mask is complementary to a height profile of the micro-lens array in the polymer layer; or
a binary mask having a light transmissivity pattern corresponding to the polymer pattern in the polymer layer; and
developing the photoresist layer using a photoresist developer to remove exposed portions of the photoresist layer.