In some embodiments, an integrated circuit device includes a substrate and an interlevel-insulating layer on the substrate that has a hole therein that exposes the substrate. A unitary lower electrode of a capacitor is disposed on the substrate and has a contact plug portion thereof that is disposed in the hole. A dielectric layer is on the lower electrode and an upper electrode of the capacitor is on the dielectric layer. In other embodiments, an integrated circuit device includes a substrate and an interlevel-insulating layer on the substrate that has a hole therein that exposes the substrate. A barrier layer is disposed on the exposed portion of the substrate and on sidewalls of the interlevel-insulating layer. A contact plug is disposed in the hole on the barrier layer. A lower electrode of a capacitor is disposed on the contact plug and engages the contact plug at a boundary therebetween. A dielectric layer is on the lower electrode and an upper electrode of the capacitor is on the dielectric layer.