The TID Characteristics of a Radiation Hardened Sense-Switch pFLASH Cell

In this paper, the total ionizing dose (TID) effects of the Sense-Switch pFLASH cell consisting of sense (T
₁
) and switch (T
₂
) co-floating gate pFLASH transistors fabricated with a 0.13 μm eFLASH technology are studied. Firstly, the impact of TID effects on the programming/erasing state's characteristics of T1and T
₂
transistors are mainly analyzed though Current-Voltage (I-V) and Transconductance-Voltage (Gm-V) curves. Secondly, the re-programming/erasing state's characteristics of the pFLASH device after TID irradiation, and its threshold voltage, sub-threshold swing, maximum transconductance and other parameters are thoroughly investigated. Lastly, it can be concluded that the threshold voltage of T
₁
and T
₂
transistors is mainly determined by the changes of floating gate charge (i.e., programming state: electron emission and hole injection; erasing state: electron injection and hole emission), trap charge concentration in oxide layers around floating gate (Not) and trap charge concentration in the interface trap of tunnel oxide (Nit). Meanwhile, the absolute values of the programming and erasing threshold voltage of T
₁
and T
₂
transistors decrease linearly with the cumulative dose, and the change rates are about 2.25 mV/rad (Si) and 1.45 mV/rad (Si), respectively. In addition, the charge change of floating gate under the ionizing radiation can be compensated by re-programming and re-erasing, but the charge of Nit and Not will increase with the increase of cumulative dose.