Degradation Behavior and Mechanism of SONOS FLASH by Total Ionization Dose Effects

In this paper, the 2T SONOS FLASH is designed and fabricated based on 180 nm embedded FLASH process which includes one MOSFET and one SONOS FLASH transistor. The FLASH transistors are programmed and erased by band-to-band tunneling-induced hot electron and Fowler-Nordheim to realize different levels, and the mechanisms of the electrical degradation caused by radiation are investigated by the mid-gap technique. In order to clarify the degradation mechanism from the physical level, the first principle calculations are performed from the atomic and electronic term. The electric fields and the external environment are proved to play a crucial role in the charge loss. The higher electric fields can exacerbate the formation of the oxide charge, and the anti-radiation hardness can be achieved with oxygen-rich environment. The external field can efficiently change the electronic properties of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\alpha $ </tex-math></inline-formula>-SiO2 with oxygen vacancy and hydrogen. This study provides a novel perspective of electrical degradations on the SONOS FLASH unit in different levels from both the experiments and theoretical simulations, which can be helpful for the design of advanced computational chips in space.