Two-step process for forming cured polymeric films for electronic device encapsulation
Methods for increasing the degree of curing and/or reducing the volatile photoinitiator concentration in cured polymeric film, and particularly in cured polymeric films in a multilayered thin film encapsulation stack are provided. Also provided are highly crosslinked and/or low-outgassing thin polymeric films and encapsulation stacks made using the methods.
1. A method of forming a polymeric film over an electronic device, the method comprising:
forming a cured polymeric film over the electronic device, wherein the cured polymeric film:
(a) is not fully cured; or
(b) comprises unreacted cure initiator molecules, fragments of cure initiator molecules, or a combination thereof; or
(c) both (a) and (b);
exposing the cured polymeric film to an ultraviolet plasma for a period sufficient to:
(i) increase the cure degree in the cured polymeric film; or
(ii) decrease the outgassing of fragments of cure initiator molecules from the cured polymeric film; or
(iii) both (i) and (ii).
2. The method of claim 1 , wherein the electronic device is an organic light-emitting diode.
3. The method of claim 1 , wherein the cure initiator molecules, fragments of cure initiator molecules, or a combination thereof are photoinitiator molecules, fragments of photoinitiator molecules, or a combination thereof.
4. The method of claim 3 , wherein forming the cured polymeric film comprises curing a composition comprising curable organic monomers by exposing the composition to ultraviolet light from a non-plasma source.
5. The method of claim 1 , wherein the polymeric film is an acrylate-based film.
6. The method of claim 1 , wherein the cured polymeric film is formed by curing a curable composition comprising:
a di(meth)acrylate monomer;
a multifunctional (meth)acrylate monomer; and
a photoinitiator.
7. The method of claim 6 , wherein the curable composition comprises:
64 mol. % to 98 mol. % di(meth)acrylate monomer;
1 mol. % to 26 mol. % tri(meth)acrylate monomer, tetra(meth)acrylate monomer, or a combination thereof; and
1 mol. % to 10 mol. % photoinitiator molecules.
8. The method of claim 1 , wherein exposing the cured polymeric film to the ultraviolet plasma occurs without the deposition of material onto the cured polymeric film.
9. The method of claim 1 , further comprising depositing an inorganic barrier layer over the cured polymeric film.
10. The method of claim 1 , wherein the cured polymeric film has a cure degree of no greater than 85% prior to exposing it to the ultraviolet plasma and a cure degree of at least 90% after exposing it to the ultraviolet plasma.
11. The method of claim 1 , wherein the electronic device is maintained at a temperature of at least 80° C. during the exposure to the ultraviolet plasma.
12. The method of claim 1 , wherein the polymeric film has a surface roughness of no greater than 10 nm rms.
13. The method of claim 1 , wherein the cured polymeric film comprises unreacted diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide, free diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide fragments, or a combination thereof.
14. The method of claim 1 , wherein exposing the cured polymeric film to the ultraviolet plasma reduces the outgassing of fragments of cure initiator molecules from the cured polymeric film by a factor of at least 10.
15. The method of claim 14 , wherein exposing the cured polymeric film to the ultraviolet plasma increases the cure degree for the cured polymeric film by at least 5%.