Forming a metal-insulator diode and carbon memory element in a single damascene process is disclosed. A trench having a bottom and a sidewall is formed in an insulator. A first diode electrode is formed in the trench during a single damascene process. A first insulating region comprising a first insulating material is formed in the trench during the single damascene process. A second insulating region comprising a second insulating material is formed in the trench during the single damascene process. A second diode electrode is formed in the trench during the single damascene process. The first insulating region and the second insulating region reside between the first diode electrode and the second diode electrode to form a metal-insulator-insulator-metal (MIIM) diode. A region of carbon is formed in the trench during the single damascene process. At least a portion of the carbon is electrically in series with the MIIM diode.