Integrated circuit devices and methods of manufacturing the same

An integrated circuit device comprising:

• a substrate including an active area;
• a bit line extending on the substrate in a first direction parallel to a top surface of the substrate and including a lower conductive pattern and an upper conductive pattern;
• a direct contact disposed between the active area of the substrate and the bit line;
• an electrically insulating spacer structure disposed on both sidewalls of the bit line to cover both sidewalls of the direct contact;
• and
• a semi-insulating field passivation layer, which extends between both sidewalls of the direct contact and the spacer structure and forms a hetero-interface with the direct contact, said hetero-interface including a quantum well within the field passivation layer;
• and
• wherein the quantum well within the field passivation layer is configured to induce an electron inversion layer within the direct contact, which increases the conductivity of the direct contact.