Semiconductor device having buried gate structure and method of fabricating the same

A method of fabricating a semiconductor device, the method comprising:

• forming a first trench extending in a first direction in a substrate;
• forming a lower active gate insulating material filling a lower portion of the first trench;
• forming a semiconductor pattern on the lower active gate insulating material;
• forming a device isolation region defining an active region in the substrate, the active region extends in a second direction crossing the first direction;
• forming an upper active gate trench in the active region;
• and
• forming an upper active gate structure in the upper active gate trench.

A method of fabricating a semiconductor device, the method comprising:

• forming a device isolation region defining an active region in a substrate;
• forming an upper active gate trench and a lower active gate tunnel in the active region, the upper active gate trench and the lower active gate tunnel are separated vertically;
• forming a field gate trench in the device isolation region;
• forming an upper active gate structure in the upper active gate trench;
• forming a lower active gate structure in the lower active gate tunnel;
• and
• forming a field gate structure in the field gate trench.