A device includes a first conductive via plug, a first electrode, a storage element, a second electrode, a spacer, a barrier structure, a first dielectric layer. The first electrode is over the first conductive via plug. The storage element is over the first electrode. The second electrode is over the storage element. The spacer has a bottom portion extending along a top surface of the first electrode and a standing portion extending from the bottom portion and along a sidewall of the second electrode. The barrier structure extends from the bottom portion of the spacer and along a sidewall of the standing portion of the spacer. The first dielectric layer is substantially conformally over the spacer and the barrier structure.