Thin film transistor compositions, and methods relating thereto
View Patent ↗A process for forming at least one transistor on a substrate is described. The substrate comprises a polyimide and a nanoscopic filler. The polyimide is derived substantially or wholly from rigid rod monomers and the nanoscopic filler has an aspect ratio of at least 3:1. The substrates of the present disclosure are particularly well suited for thin film transistor applications, due at least in part to high resistance to hygroscopic expansion and relatively high levels of thermal and dimensional stability.
1. A composite comprising a semiconductor material supported by a passivating layer, the passivating layer supported by a substrate, the substrate, comprising:
a) a polyimide in an amount from 40 to 95 weight percent of the layer, the polyimide being derived from:
i) at least one aromatic dianhydride, at least 85 mole percent of said aromatic dianhydride being a rigid rod type dianhydride, and
ii)at least one aromatic diamine, at least 85 mole percent of said aromatic diamine being a rigid rod type diamine; and
b) a filler that:
a) is less than 800 nanometers in at least one dimension;
b) has an aspect ratio greater than 3:1;
c) is less than the thickness of the film in all dimensions; and
d) is present in an amount from 5 to 60 weight percent of the total weight of the film,
the substrate having a thickness from 8 to 150 microns.
2. A composite according to claim 1 , wherein the passivating layer comprises silicon dioxide or aluminum nitride.
3. A composite according to claim 1 , wherein the passivating layer has a thickness of less than 20 nanometers.
4. A composite according to claim 1 , wherein the passivating layer is deposited on both surfaces of the substrate.
5. A composite according to claim 1 , wherein the substrate comprises a metal layer having a thickness of less than 50 nanometers on the side thereof remote from the semiconductor material.
6. A composite according to claim 5 , wherein the metal layer has walls defining apertures extending through the metal layer.
7. A composite according to claim 6 , wherein the metal layer comprises chromium.
8. A composite according to claim 1 , wherein a layer of dielectric material is located over the metal layer and under the semiconductor material.
9. A composite according to claim 8 , wherein the layer of dielectric material comprises silicon nitride.
10. A composite according to claim 1 , wherein the semiconductor material comprises amorphous silicon.
11. A composite according to claim 10 , wherein the semiconductor material further comprises a layer of n-type silicon on the amorphous silicon.
12. A composite according to claim 11 , further comprising a patterned layer of metal located on the n-type silicon, wherein the n-type silicon defines a complementary pattern to the pattern of the metal so that the n-type silicon is only under the metal pattern.
13. A composite according to claim 1 , wherein the filler is smaller than 600 nm in at least one dimension.
14. A composite according to claim 1 , wherein the filler comprises acicular titanium dioxide.
15. A composite according to claim 1 , wherein:
a) the rigid rod type dianhydride is selected from a group consisting of 3,3′,4,4′-biphenyl tetracarboxylic dianhydride (BPDA), pyromellitic dianhydride (PMDA), and mixtures thereof;
and
b) the rigid rod type diamine is selected from 1,4-diaminobenzene (PPD), 4,4′-diaminobiphenyl, 2,2′-bis(trifluoromethyl) benzidene (TFMB), 1,5-naphthalenediamine, 1,4-naphthalenediamine, and mixtures thereof.