Gapless microlens array and method of fabrication
A microlens array with reduced or no empty space between individual microlenses and a method for forming the same. The microlens array is formed by patterning a first set of microlens precursors in a checkerboard pattern on a substrate. The first set of microlens precursors is reflowed and cured into first microlenses impervious to subsequent reflows. Then, a second set of microlens precursors is patterned in spaces among the first microlenses, reflowed and cured into second microlenses. The reflows and cures can be conducted under different conditions, and the microlenses may be differently sized. The conditions of the reflows can be chosen to ensure that the focal lengths of microlenses are optimized for maximum sensor signal.
1. A method of forming an imaging device, comprising:
providing a pixel cell array having at least one photosensor asymmetrically formed such that said at least one photosensor is spaced unequally from surrounding photosensors;
patterning a first set of microlens precursors onto a substrate formed over said pixel cell array;
reflowing the first set of microlens precursors under first reflow conditions;
curing the first set of microlens precursors to form first microlenses;
patterning a second set of microlens precursors onto the substrate;
reflowing the second set of microlens precursors; and
curing the second set of microlens precursors to form second microlenses,
wherein the second microlenses are each positioned in a space among the first microlenses and have a shifted focal point that coincides with a photosensitive region of said at least one asymmetrically formed photosensor.
2. The method of claim 1 , wherein said reflowing the second set of microlens precursors comprises reflowing the second set of microlens precursors under reflow conditions that are different than said first reflow conditions.
3. The method of claim 2 , wherein said first and second reflow conditions are chosen to create a focal length in said first microlenses substantially equal to a focal length in said second microlenses.
4. The method of claim 2 , wherein said first and second reflow conditions are chosen to create a focal length in said first microlenses corresponding to a first wavelength of light and to create a focal length in said second microlenses corresponding to a second wavelength of light.
5. The method of claim 1 , wherein said patterning the first set of microlens precursors comprises patterning the first set of microlens precursors into a first plurality of portions arranged in a checkerboard pattern, the checkerboard pattern including spaces between said portions.
6. The method of claim 5 , wherein said patterning the second set of microlens precursors comprises patterning the second set of microlens precursors into a second plurality of portions in a complementary checkerboard pattern filling in said spaces between the plurality of portions of the first set of microlens precursors.
7. The method of claim 2 , wherein said second plurality of portions comprise portions having a size no smaller than the size of the portions in the first plurality of patterns.
8. The method of claim 1 , further comprising:
patterning a third set of microlens precursors onto the substrate;
reflowing the third set of microlens precursors; and
curing the third set of microlens precursors to form third microlenses.
9. The method of claim 8 , wherein the patterning and reflow conditions of said first set, second set, and third set of microlens precursors create a microlens array having at least approximately no space between adjacent microlenses.