A New Method for Extracting the Radiation Induced Trapped Charge Density Along the STI Sidewall in the PDSOI NMOSFETs

The effects of the radiation-induced trapped charge in shallow trench isolation (STI) and buried oxide (BOX) on total ionizing radiation response of 0.13 μm partially-depleted silicon-on-insulator (PDSOI) NMOS technology are analyzed respectively. The positive trapped charge in the STI oxide, but not in the BOX, is responsible for the off-state leakage increase after ON bias radiation. A new method is proposed to calculate the surface charge density along the STI sidewall. This method takes into account the influences of the non-uniform electric field and the variable oxide thickness in the STI region. Moreover, the calculated non-uniform charge density along the STI sidewall is verified by three dimensional simulations. Even though there is charge-accumulation in the BOX, it shows minimal impact on the front-gate characteristics of the PDSOI devices in this 0.13 μm technology, except for the device with low body doping concentration. The positive charge trapped in BOX can induce significant threshold voltage shift in the RVT (regular Vth) I/O NMOSFET through coupling effect.