Devices including vertical transistors, and related methods

1. A device, comprising:

vertically oriented pillars each comprising at least one oxide semiconductor material, at least one of the vertically oriented pillars wider in a first lateral direction at a lower portion thereof than at an upper portion thereof and wider in a second lateral direction at the upper portion thereof than at the lower portion thereof;

electrically conductive lines vertically underlying the vertically oriented pillars and extending in the first lateral direction;

gate dielectric material adjacent sidewalls of the vertically oriented pillars and upper surfaces of the electrically conductive lines; and

gate electrodes horizontally adjacent the gate dielectric material.

2. The device of claim 1 , wherein the gate electrodes extend in the second lateral direction.

3. The device of claim 1 , wherein the at least one oxide semiconductor material comprises a composite semiconductor material comprising at least two oxide semiconductor materials.

4. The device of claim 1 , wherein the at least one oxide semiconductor material comprises three oxide semiconductor materials.

5. The device of claim 1 , wherein the at least one oxide semiconductor material comprises:

a first oxide semiconductor material;

a second oxide semiconductor material; and

a third oxide semiconductor material comprising substantially the same material composition as the first oxide semiconductor material, the second oxide semiconductor material horizontally between the first oxide semiconductor material and the third oxide semiconductor material.

6. The device of claim 1 , wherein the at least one oxide semiconductor material comprises:

a first oxide semiconductor material; and

a second oxide semiconductor material neighboring the first oxide semiconductor material and comprising the same elements as the first oxide semiconductor material, the second oxide semiconductor material comprising a different atomic percent of one or more elements than the first oxide semiconductor material.

7. The device of claim 1 , wherein the at least one oxide semiconductor material comprises an unetched oxide semiconductor material.

8. The device of claim 1 , wherein an angle of the sidewalls of the vertically oriented pillars is different in the first lateral direction than in the second lateral direction.

9. The device of claim 1 , wherein the sidewalls of the vertically oriented pillars are oriented at an angle of from about 2° to about 5°.

10. The device of claim 1 , wherein a thickness of the gate electrodes is within a range of from about 5 nm to about 15 nm.

11. A method of forming a device, the method comprising:

forming, on sidewalls of a sacrificial material, a gate dielectric material extending in a first lateral direction, the sacrificial material wider in the first lateral direction at a lower portion of the sacrificial material than at an upper portion of the sacrificial material;

forming a gate electrode on sidewalls of the gate dielectric material; and

replacing the sacrificial material with an oxide semiconductor material to form an oxide semiconductor material wider in the first lateral direction at a lower portion thereof than at an upper portion thereof and wider in a second lateral direction at the upper portion thereof than at the lower portion thereof.

12. The method of claim 11 , further comprising forming the sacrificial material to comprise silicon, a carbon-containing material, polysilicon, or silicon nitride.

13. The method of claim 11 , wherein replacing the sacrificial material with an oxide semiconductor material comprises:

selectively removing the sacrificial material to form openings; and

forming the oxide semiconductor material by atomic layer deposition to fill the openings with the oxide semiconductor material.

14. The method of claim 11 , wherein replacing the sacrificial material with an oxide semiconductor material comprises forming an oxide semiconductor material comprising a composite structure.

15. The method of claim 11 , wherein replacing the sacrificial material with an oxide semiconductor material comprises forming an oxide semiconductor material comprising a second oxide semiconductor material disposed between a first oxide semiconductor material and a third oxide semiconductor material comprising substantially the same material composition as the first oxide semiconductor material.

16. The method of claim 11 , wherein forming an oxide semiconductor material comprises forming the oxide semiconductor material to have a vertical height larger than a vertical height of the gate electrode.

17. A device, comprising:

a vertically oriented pillar comprising:

an unetched composite oxide semiconductor material comprising:

a first oxide semiconductor material; and

a second oxide semiconductor material neighboring the first oxide semiconductor material and having a different material composition than the first oxide semiconductor material;

wherein a lower portion of the unetched composite oxide semiconductor material has a greater width than an upper portion thereof in a first lateral direction; and

wherein the upper portion of the unetched composite oxide semiconductor material has a greater width than the lower portion thereof in a second lateral direction;

a gate dielectric material on sidewalls of the vertically oriented pillar; and

a gate electrode on at least a portion of the gate dielectric material.

18. The device of claim 17 , wherein the unetched composite oxide semiconductor material further comprises a third oxide semiconductor material neighboring the second oxide semiconductor material on a side of the second oxide semiconductor material opposite the first oxide semiconductor material.

19. The device of claim 17 , wherein an upper surface of the unetched composite oxide semiconductor material extends vertically higher than an upper surface of the gate electrode a distance within a range of from about 5 nm to about 10 nm.