Total ionizing dose effect in 0.2 μm PDSOI NMOSFETs with shallow trench isolation

• A hump effect in the back gate characteristic curve is reported.
• Simple way to extract the sheet charge density along the STI sidewall is proposed.
• The electric field distributions in the STI and BOX are simulated.
• Charge trapped in STI is the main contributor to the off-state leakage.

This paper presents the total ionizing dose radiation performance of 0.2 μm PDSOI NMOS devices under different bias conditions. The hump effect is observed in the transfer characteristic of the back gate device instead of the front gate device after radiation. A STI bottom corner parasitic transistor model is proposed to explain this phenomenon. It also provides a simple way to extract the effective sheet charge density along the STI sidewall. Three-dimensional simulation was applied to explain the radiation effect. It shows that charge trapped in the shallow trench isolation, particularly at the bottom region of the trench oxide where the STI and the BOX are connected, is the dominant contributor to the off-state drain-to-source leakage current. The dimension of the transistor plays an important role on influencing the device’s performance after radiation. Larger off-state leakage current and radiation induced threshold voltage shift are reported in the narrow channel device than in the wide channel one. Different TID responses due to the STI process variation are also discussed.