System and method for the selective harvest of emissive elements
A method is provided for the selective harvest of microLED devices from a carrier substrate. Defect regions are predetermined that include a plurality of adjacent defective microLED devices on a carrier substrate. A solvent-resistant binding material is formed overlying the predetermined defect regions and exposed adhesive is dissolved with an adhesive dissolving solvent. Non-defective microLED devices located outside the predetermined defect regions are separated from the carrier substrate while adhesive attachment is maintained between the microLED devices inside the predetermined defect regions and the carrier substrate. Methods are also provided for the dispersal of microLED devices on an emissive display panel by initially optically measuring a suspension of microLEDs to determine suspension homogeneity and calculate the number of microLEDs per unit volume. If the number of harvested microLED devices in the suspension is known, a calculation can be made of the number of microLED devices per unit of suspension volume.
1. A method for the selective harvest of micro light emitting diode (microLED) devices from a carrier substrate, the method comprising:
providing inorganic microLED devices attached to a carrier substrate with an adhesive;
predetermining defect regions, where each defect region includes a region selected from the group consisting of a plurality of adjacent defective microLED devices or process control structures;
forming a solvent-resistant binding material overlying the predetermined defect regions;
dissolving exposed adhesive with an adhesive dissolving solvent;
separating microLED devices located outside the predetermined defect regions from the carrier substrate; and, maintaining the adhesive attachment of microLED devices inside the predetermined defect regions to the carrier substrate.
2. The method of claim 1 further comprising:
inspecting the carrier substrate to locate defective microLED devices;
locating non-predetermined defect regions including a plurality of adjacent defective microLED devices; and,
wherein forming the solvent-resistant binding material includes forming the solvent-resistant binding material overlying the non- predetermined defect regions.
3. The method of claim 2 further comprising:
in response to inspecting, locating non-predetermined solitary defective microLED devices; and, using a laser trimming process to eject the solitary defective microLED devices.
4. The method of claim 2 wherein inspecting to locate defective microLED devices includes using an inspection process selected from the group consisting of optical comparison, electroluminescence, photoluminescence, or cathodoluminesence testing.
5. The method of claim 2 further comprising:
in response to separating the microLED devices from the carrier substrate, collecting functional microLED devices in a harvesting container.
6. The method of claim 5 further comprising:
applying an additional motivational force selected from the group consisting of fluid circulation, thermal energy, gravity, vibration, and combinations thereof; and,
wherein separating the microLED devices from the carrier substrate includes separating the microLED devices at least partially in response to the additional motivational force.
7. The method of claim 5 wherein collecting functional microLED devices in the harvesting container includes replacing the adhesive dissolving solvent with a fluid.
8. The method of claim 7 wherein collecting functional microLED devices in the harvesting container includes creating a suspension of functional microLED devices, having an average cross-sectional physical dimension s, and impurities in the fluid;
the method further comprising:
subsequent to collecting the functional microLED devices, filtering to remove impurities having a maximum cross-sectional physical dimension greater than t, where t>s.
9. The method of claim 8 wherein the filtering process is selected from the group consisting of mechanical mesh, elution, fractionation, or combinations thereof.
10. The method of claim 7 wherein collecting functional microLED devices in the harvest container includes creating a suspension of functional microLED devices, having an average cross-sectional physical dimension s, and impurities in the fluid;
the method further comprising:
filtering to remove impurities having a maximum cross-sectional physical dimension less than p, where p<s.
11. The method of claim 7 wherein replacing the adhesive dissolving solvent with the fluid includes exchanging the adhesive dissolving solvent with a filtering solution having a lower viscosity than the adhesive dissolving solvent; and,
the method further comprising:
filtering to remove impurities from the filtering solution.
12. The method of claim 7 wherein replacing the adhesive dissolving solvent with the fluid includes replacing the adhesive dissolving solvent with an assembly solution having a characteristic selected from the group consisting of a lower polarity than the adhesive dissolving solvent or a higher evaporation rate than the adhesive dissolving solvent.
13. The method of claim 12 wherein replacing the adhesive dissolving solvent with the fluid includes adding a surfactant to the assembly solution selected from the group consisting of anionic, cationic, non-ionic surfactants, or combinations thereof.
14. The method of claim 1 wherein dissolving exposed adhesive includes selectively exposing sections of the carrier substrate to the adhesive dissolving solvent; and,
wherein separating microLED devices from the carrier substrate includes separating microLED devices from the selectively exposed sections of the carrier substrate.
15. The method of claim 14 wherein selectively exposing sections of the carrier substrate to the solvent includes:
rotating the carrier substrate in a solvent bath;
exposing a radial section of the carrier substrate having a radius greater than dto the bath solvent; and,
wherein separating microLED devices from exposed sections of the carrier substrate includes separating microLED devices from the radial section of the carrier substrate.
16. The method of claim 1 wherein exposing the microLED devices to the adhesive dissolving solvent includes the adhesive dissolving solvent being selected from the group consisting of acetone, toluene, trichloroethane, N-methylpyrrolidone (NMP), xylene, cyclohexanone, butyl acetate, or combinations thereof.