A semiconductor device comprises a semiconductor substrate, and a pair of metal gates extends upwards from the semiconductor substrate. First and second channel regions are disposed between inner sidewalls of the pair of metal gates. First and second drain regions are disposed between the inner sidewalls of the pair of metal gates and are disposed directly over the first and second channel regions, respectively. First and second source regions are disposed between the inner sidewalls of the pair of metal gates directly below the first and second channel regions, respectively. A capacitor dielectric structure is disposed below the first and second source regions. A bottom capacitor electrode is disposed below the capacitor dielectric. The capacitor dielectric structure separates the first and second drain regions from the bottom capacitor electrode.