Fully depleted double-gate MSDRAM cell with additional nonvolatile functionality

We demonstrate a new fully depleted (FD) double-gate (DG) MSDRAM cell, which features SONOS type storage node at the back-gate (control-gate). This single-transistor cell, based on the meta-stable dip (MSD) hysteresis effect, can also be operated in non-volatile memory (NVM) mode. The NVM functionality is achieved by Fowler–Nordheim tunneling hole injection into the nitride storage node; the injected holes induce a permanent inversion layer in silicon body. The proposed device shows a large current ratio between ‘1’ and ‘0’ states (∼103) and a wide memory window (∼3 V). The effect of the NVM functionality on the MSD hysteresis was investigated and combined with the effect of the control-gate bias. The SONOS charging can be used for replacing the second gate (i.e. enabling single-gate MSDRAM) or for achieving ‘unified’ memory operation.

► A fully depleted SONOS-type 1T-DRAM cell based on MSD hysteresis was experimentally demonstrated.
► The SONOS storage node enables additional nonvolatile memory functionalities.
► The device features large memory window, low-power operation, and long retention time.
► The non-volatile positive charge stored in SONOS enables single-gate operation of the MSDRAM cell.
► This ’unified’ memory can be operated in either 1T-DRAM mode or EEPROM mode.