Gate structures and semiconductor devices including the gate structures

A gate structure comprising:

• a first conductive pattern;
• a first seed pattern on a lower surface and a portion of a sidewall of the first conductive pattern, wherein the first seed pattern includes a first material, and the first conductive pattern includes a second material that is different from the first material;
• a second conductive pattern that is in contact with an upper surface of the first conductive pattern and an uppermost surface of the first seed pattern;
• and
• a gate insulation pattern that is in contact with a sidewall of the second conductive pattern and a sidewall of the first seed pattern,
• wherein the first material has a first work function, and the second material has a second work function, and
• wherein the first work function is lower than the second work function.

A semiconductor device comprising:

• an active pattern on a substrate;
• a gate structure in an upper portion of the active pattern;
• a bit line structure on a central portion of the active pattern;
• a contact plug structure on each of opposite edge portions of the active pattern in a horizontal direction that is parallel with an upper surface of the substrate;
• and
• a capacitor on the contact plug structure,
• wherein the gate structure includes:
• a first conductive pattern;
• a first seed pattern on a lower surface and a first portion of a sidewall of the first conductive pattern, wherein the first seed pattern includes a first material, and the first conductive pattern includes a second material that is different from the first material;
• and
• a gate insulation pattern that is in contact with a second portion of the sidewall of the first conductive pattern and the first seed pattern,
• wherein the first material has a first work function, and the second material has a second work function, and
• wherein the first work function is lower than the second work function.