An integrated circuit device includes a substrate having an active area therein, a bit line on the substrate, and a direct contact, which extends between the active area and the bit line and electrically couples the bit line to a portion of the active area. A spacer structure is also provided, which extends on sidewalls of the bit line and on sidewalls of the direct contact. A field passivation layer is provided, which extends between the sidewalls of the direct contact and the spacer structure. The spacer structure and the field passivation layer may include different materials, and the field passivation layer may directly contact the sidewalls of the direct contact. The field passivation layer can include nonstoichiometric silicon oxide SiOx, where 0.04≤x≤0.4, and may have a thickness of less than about 25 Å.