US Patent 8709889 Semiconductor memory device and manufacturing method thereof

A memory cell therein includes a first transistor and a capacitor and stores data corresponding to a potential held in the capacitor. The first transistor includes a pair of electrodes, an insulating film in contact with side surfaces of the electrodes, a first gate electrode provided between the electrodes with the insulating film provided between the first gate electrode and each electrode and whose top surface is at a lower level than top surfaces of the electrodes, a first gate insulating film over the first gate electrode, an oxide semiconductor film in contact with the first gate insulating film and the electrodes, a second gate insulating film at least over the oxide semiconductor film, and a second gate electrode over the oxide semiconductor film with the second gate insulating film provided therebetween. The capacitor is connected to the first transistor through one of the electrodes.