Capacitors including amorphous dielectric layers and methods of forming the same

1. A capacitor, comprising:

a lower electrode on a substrate;

a dielectric layer structure, including:

a first dielectric layer on the lower electrode, the first dielectric layer including a first crystalline metal oxide; and

a second dielectric layer on the first dielectric layer, the second dielectric layer including an amorphous metal oxide having a dielectric constant less than that of the first dielectric layer and greater than that of aluminum oxide; and

an upper electrode on the dielectric layer structure.

2. The capacitor of claim 1 , further comprising a third dielectric layer on the second dielectric layer, the third dielectric layer including a second crystalline metal oxide,

wherein the second dielectric layer has a dielectric constant less than that of the third dielectric layer.

3. The capacitor of claim 2 , wherein the first and second crystalline metal oxides include any one selected from the group consisting of titanium oxide, tantalum oxide, aluminum oxide, hafnium oxide and zirconium oxide.

4. The capacitor of claim 2 , wherein the second dielectric layer has a thickness less than respective thicknesses of the first and third dielectric layers.

5. The capacitor of claim 4 , wherein each of the first and third dielectric layers has a thickness of about 5 Å to about 150 Å, and the second dielectric layer has a thickness of about 3 Å to about 30 Å.

6. The capacitor of claim 1 , wherein the amorphous metal oxide includes lanthanum oxide or scandium oxide.

7. The capacitor of claim 1 , wherein each of the lower and upper electrodes includes any one selected from the group consisting of titanium, tungsten, tantalum, platinum, ruthenium, iridium, and an oxide thereof.

8. A method of forming a capacitor, the method comprising:

forming a lower electrode on a substrate;

forming a dielectric layer structure on the lower electrode, the dielectric layer structure including a first dielectric layer and a second dielectric layer sequentially stacked, the first dielectric layer containing a first metal oxide, and the second dielectric layer containing a second metal oxide having a dielectric constant less than that of the first metal oxide in a crystallized state and greater than that of aluminum oxide; and

forming an upper electrode on the dielectric layer structure.

9. The method of claim 8 , wherein forming the dielectric layer structure further includes forming a third dielectric layer on the second dielectric layer using a third metal oxide.

10. The method of claim 9 , wherein the third metal oxide includes a material substantially the same as the first metal oxide.

11. The method of claim 9 , wherein the second dielectric layer is formed to have a thickness that is less than respective thicknesses of the first and third dielectric layers.

12. The capacitor of claim 11 , wherein each of the first and third dielectric layers is formed to have a thickness of about 5 Å to about 150 Å, and the thickness of the second dielectric layer is formed to about 3 Å to about 30 Å.

13. The method of claim 9 , further comprising, after forming the upper electrode, performing a heat treatment or a plasma treatment on the dielectric layer structure to crystallize the first and third metal oxides.

14. The method of claim 8 , wherein the amorphous metal oxide includes lanthanum oxide or scandium oxide.

15. The capacitor of claim 8 , wherein each of the lower and upper electrodes is formed to include any one selected from the group consisting of titanium, tungsten, tantalum, platinum, ruthenium, iridium, an oxide thereof, and a nitride thereof.

16. A capacitor, comprising:

a crystallized metal oxide dielectric layer having a first dielectric constant; and

an amorphous metal oxide dielectric layer on the crystallized metal oxide dielectric layer, the amorphous metal oxide dielectric layer having a second dielectric constant that is less the first dielectric constant and is greater than a dielectric constant of aluminum oxide.

17. The capacitor of claim 16 wherein the crystallized metal oxide dielectric layer comprises a first crystallized metal oxide dielectric layer, the capacitor further comprising:

a second crystallized metal oxide dielectric layer on the amorphous metal oxide dielectric layer opposite the first crystallized metal oxide dielectric layer.

18. The capacitor of claim 17 wherein the first and second crystallized metal oxide dielectric layers each have a respective thickness of about 5 Å to about 150 Å, and wherein the amorphous metal oxide dielectric layer has a thickness of about 3 Å to about 30 Å.

19. The capacitor of claim 16 wherein the first dielectric constant is greater than a dielectric constant of SiN.

20. The capacitor of claim 16 wherein the amorphous metal oxide dielectric layer comprises lanthanum oxide or scandium oxide.