Bottom-gate and top-gate VTFTs on common structure

1. An electronic device comprising:

a substrate;

a top-gate transistor and a bottom-gate transistor sharing an insulating vertical-support-element located on the substrate, the vertical-support-element extending away from the substrate, the vertical-support-element having an outer surface including a first edge having a first reentrant profile and a second edge having a second reentrant profile;

wherein the top-gate transistor includes:

a first conformal semiconductor layer in contact with and conforming to the outer surface of the vertical-support-element in the first reentrant profile;

a first electrode located in contact with a first portion of the first conformal semiconductor layer over the top of and in contact with the vertical-support-element;

a second electrode located in contact with a second portion of the first conformal semiconductor layer over the substrate and not over the vertical-support-element, and adjacent to the first edge of the vertical-support-element, wherein the second electrode is in direct contact with the substrate, and wherein a third portion of the first conformal semiconductor layer between the first portion and the second portion of the first conformal semiconductor layer is in direct contact with the first edge of the vertical-support-element;

a first conformal dielectric layer in contact with and conforming to the first semiconductor layer in the first reentrant profile; and

a conformal conductive top-gate in contact with and conforming to the first conformal dielectric layer in the first reentrant profile;

wherein the first electrode and the second electrode define a first semiconductor channel of the top-gate transistor, and wherein the first conformal semiconductor layer, the first conformal dielectric layer and the conformal conductive top-gate maintain a shape of the first reentrant profile; and

wherein the bottom-gate transistor includes:

a conformal conductive bottom-gate in contact with and conforming to the outer surface of the vertical-support-element in the second reentrant profile;

a second conformal dielectric layer in the second reentrant profile and in contact with and conforming to the conformal conductive bottom-gate;

a second conformal semiconductor layer in the second reentrant profile and in contact with and conforming to the second conformal dielectric layer;

a third electrode located over the substrate and not over the vertical-support-element, and adjacent to the second edge, the third electrode in contact with the second semiconductor layer; and

a fourth electrode located over the top of the vertical-support-element and in contact with the second semiconductor layer;

wherein the third electrode and the fourth electrode define a second semiconductor channel of the bottom-gate transistor, and wherein the conformal conductive bottom-gate, the second conformal dielectric layer, and the second conformal semiconductor layer maintain a shape of the second reentrant profile;

wherein the conformal conductive top-gate, the third electrode, and the fourth electrode have a same material composition and thickness, and wherein the conformal conductive bottom-gate, the first electrode, and the second electrode have a same material composition and thickness.

2. The electronic device of claim 1 , wherein the conformal conductive top-gate, the third electrode, and the fourth electrode are parts of a single conductive material layer.

3. The electronic device of claim 2 , wherein the conductive material layer includes a conductive metal oxide.

4. The electronic device of claim 1 , wherein the conformal conductive bottom-gate, the first electrode, and the second electrode are parts of a single conductive material layer.

5. The electronic device of claim 1 , wherein the first dielectric and the second dielectric have a same material composition and thickness, and are two portions of a same layer.

6. The electronic device of claim 5 , wherein the material composition includes an insulating metal oxide.

7. The electronic device of claim 1 , wherein the vertical-support-element includes a polymer post and an inorganic material cap on top of the polymer post.

8. The electronic device of claim 1 , wherein the top-gate transistor and the bottom-gate transistor are n-type transistors.

9. The electronic device of claim 1 , wherein top-gate transistor and the bottom-gate transistor are metal oxide thin film transistors.

10. The electronic device of claim 1 , wherein the first semiconductor layer and the second semiconductor layer have the same material composition.

11. The electronic device of claim 1 , the first dielectric layer and the second dielectric layer each having a thickness, wherein the thickness of the first dielectric layer is greater than the thickness of the second dielectric layer.

12. The electronic device of claim 1 , wherein the first dielectric and the second dielectric are part of a common shared dielectric stack.

13. The electronic device of claim 12 , wherein the common shared dielectric stack includes a plurality of layers.

14. The electronic device of claim 13 , wherein each of the plurality of layers of the common shared dielectric stack has the same material composition.

15. The device of claim 13 , wherein one of the plurality of layers has a different pattern than another of the plurality of layers.

16. The electronic device of claim 1 , the top-gate transistor and the bottom-gate transistor being configured to operate as an enhancement-depletion-mode inverter in which the first electrode is electrically connected to the fourth electrode and the conformal conductive top-gate.

17. The electronic device of claim 1 , wherein the top-gate transistor is a load transistor configured to operate in a depletion mode, and the bottom-gate transistor is a drive transistor configured to operate in an enhancement mode.