Nanosheet capacitor

1. A method for forming a capacitive device, the method comprising:

forming a buffer layer on a substrate;

forming a nanosheet stack on the buffer layer, wherein the nanosheet stack includes alternating layers of a first semiconductor material and a second semiconductor material;

removing portions of the nanosheet stack and the buffer layer to form a first fin and a second fin;

depositing a first insulator layer on the substrate;

implanting ions in the first fin and the second fin and annealing to form a first electrode and a second electrode;

removing the first insulator layer;

removing portions of the buffer layer in the first electrode and the second electrode to form a void between the first electrode and the substrate and a void between the second electrode and the substrate;

depositing a second insulator layer on the substrate and in the void under the first electrode and the void under the second electrode; and

forming a first metallic conductive contact on a basal end of the first electrode and a second metallic conductive contact on a basal end of the second electrode.

2. The method of claim 1 , wherein the buffer layer includes a semiconductor material.

3. The method of claim 1 , wherein the buffer layer includes a semiconductor dissimilar from the substrate.

4. The method of claim 1 , wherein the first conductive contact is formed by:

removing portions of the second insulator layer to form a cavity that exposes portions of the first electrode; and

depositing a conductive material in the cavity.

5. The method of claim 1 , wherein the first electrode is arranged substantially in parallel with the second electrode.

6. The method of claim 1 , wherein the first semiconductor material includes silicon germanium.

7. The method of claim 1 , wherein the second semiconductor material includes silicon.

8. A method for forming a capacitive device, the method comprising:

forming a buffer layer on a substrate;

forming a nanosheet stack on the buffer layer, wherein the nanosheet stack includes alternating layers of a first semiconductor material and a second semiconductor material;

removing portions of the nanosheet stack and the buffer layer to form a first fin and a second fin;

depositing a first insulator layer on the substrate;

implanting ions in the first fin and the second fin and annealing to form a first electrode and a second electrode;

removing the first insulator layer;

removing portions of the buffer layer in the first electrode and the second electrode to form a void between the first electrode and the substrate and a void between the second electrode and the substrate;

depositing a second insulator layer on the substrate and in the void under the first electrode and the void under the second electrode; and

growing a first crystalline conductive contact on a basal end of the first electrode and a second crystalline conductive contact on a basal end of the second electrode.

9. The method of claim 8 , wherein the buffer layer includes a semiconductor material.

10. The method of claim 8 , wherein the buffer layer includes a semiconductor dissimilar from the substrate.

11. The method of claim 8 , wherein the first crystalline conductive contact is formed by:

removing portions of the second insulator layer to form a cavity that exposes portions of the first electrode; and

growing a crystalline material in the cavity.

12. The method of claim 8 , wherein the first electrode is arranged substantially in parallel with the second electrode.

13. The method of claim 8 , wherein the first semiconductor material includes silicon germanium.

14. The method of claim 8 , wherein the second semiconductor material includes silicon.

15. A capacitive device comprising:

a first electrode comprising a nanosheet stack;

a second electrode comprising a nanosheet stack, the second electrode arranged substantially parallel to the first electrode;

a first conductive contact arranged on a basal end of the first electrode; and

a second conductive contact arranged on a basal end of the second electrode,

wherein the nanosheet stack includes alternating layers of a first semiconductor material and a second semiconductor material.

16. The device of claim 15 , further comprising an insulator layer arranged between a substrate and the first electrode.

17. The device of claim 15 , wherein the first conductive contact includes a metallic material.