Semiconductor memory device and method of fabricating the same

A semiconductor memory device, comprising:

• a semiconductor substrate that includes a trench;
• a gate insulating layer disposed in the trench that covers bottom and inner side surfaces of the trench;
• a first gate electrode disposed in a lower portion of the trench, the first gate electrode including a first metal;
• a second gate electrode disposed in the trench and on the first gate electrode;
• and
• a barrier layer disposed between the first and second gate electrodes, the barrier layer including an oxynitride of the first metal,
• wherein the second gate electrode has a work-function that is less than the work-function of the first gate electrode.

A semiconductor memory device, comprising:

• a substrate that includes active regions surrounded by a device isolation layer, the active regions extending in a first direction;
• gate lines buried in trenches formed in an upper portion of the substrate, wherein the gate lines cross the active regions in a second direction that crosses the first direction and divide the active regions into first and second doped regions;
• and
• a bit line disposed on the gate lines that extends in a third direction that crosses both of the first and second directions,
• wherein each of the gate lines comprises:
• a first gate electrode disposed in a lower portion of the trench, wherein a top surface of the first gate electrode includes oxygen and nitrogen atoms;
• and
• a second gate electrode disposed on the first gate electrode.