VTFT with post, cap, and aligned gate

1. A thin film transistor comprising:

a substrate;

a post on the substrate, the post having a height dimension extending away from the substrate to a top, the post having an edge along the height dimension;

a cap on the top of the post, the cap covering the top of the post, the cap extending to a distance beyond the edge of the post to define a reentrant profile;

a conformal conductive gate layer on the edge of the post in the reentrant profile and not over the cap, the conformal conductive gate layer including a portion that extends along the substrate;

a conformal insulating layer on the gate layer in the reentrant profile;

a conformal semiconductor layer on the insulating layer in the reentrant profile;

a first electrode located in contact with a first portion of the semiconductor layer over the cap; and

a second electrode located in contact with a second portion of the semiconductor layer not over the post.

2. The transistor of claim 1 , wherein the post is a structural polymer post.

3. The transistor of claim 2 , wherein the post comprises an epoxy resin or polyimide.

4. The transistor of claim 1 , wherein the cap is an inorganic material cap.

5. The transistor of claim 1 , wherein the post is a conductive material post.

6. The transistor of claim 5 , wherein the conductive material post is a metal post.

7. The transistor of claim 1 , wherein the cap is a conductive material cap.

8. The transistor of claim 1 further comprising:

a conformal dielectric layer on the cap, the edges of the post, and at least a portion of the substrate, the conformal dielectric layer being located at least between the conformal conductive gate layer and the post.

9. The transistor of claim 1 , the post having another edge along the height dimension, the cap extending beyond the other edge of the post to define a second reentrant profile, and further comprising:

a third electrode located in contact with a third portion of the semiconductor layer over the substrate and not over the post, and adjacent to the other edge in the second reentrant profile.

10. The transistor of claim 1 , wherein the first electrode and the second electrode are transparent conductive oxides.

11. The transistor of claim 1 , wherein the conformal conductive gate layer includes a portion that extends along the substrate beyond the distance that the cap extends beyond the edge of the post.

12. The transistor of claim 1 , wherein the conformal conductive gate layer includes a portion that extends along the substrate but does not extend beyond the distance that the cap extends beyond the edge of the post.

13. The transistor of claim 1 , wherein the conformal conductive gate layer includes a portion that extends along the substrate to the distance that the cap extends beyond the edge of the post.

14. The transistor of claim 1 , wherein the second electrode located in contact with a second portion of the semiconductor layer not over the post is over a portion of conformal conductive gate layer that extends along the substrate.

15. The transistor of claim 1 , further comprising another conductive material layer positioned at least under a portion of the post and in electrical contact with the conformal conductive gate layer.

16. The transistor of claim 15 , wherein the conductive material layer and the cap are vertically aligned and have the same pattern within the area of the transistor.

17. The transistor of claim 1 , wherein the cap includes a material that blocks more than 80% of light at wavelengths less than 400 nanometers.

18. The transistor of claim 1 , wherein the conformal conductive gate layer includes a material that blocks more than 80% of light at wavelengths less than 400 nanometers.