We are investigating adaption of SOI pixel devices for future high energy<br />
physic(HEP) experiments. The pixel sensors are required to be operational in<br />
very severe radiation environment. Most challenging issue in the adoption is<br />
the TID (total ionizing dose) damage where holes trapped in oxide layers affect<br />
the operation of nearby transistors. We have introduced a second SOI layer -<br />
SOI2 beneath the BOX (Buried OXide) layer - in order to compensate for the TID<br />
effect by applying a negative voltage to this electrode to cancel the effect<br />
caused by accumulated positive holes. In this paper, the TID effects caused by<br />
Co gamma-ray irradiation are presented based on the transistor characteristics<br />
measurements. The irradiation was carried out in various biasing conditions to<br />
investigate hole accumulation dependence on the potential configurations. We<br />
also compare the data with samples irradiated with X-ray. Since we observed a<br />
fair agreement between the two irradiation datasets, the TID effects have been<br />
investigated in a wide dose range from 100~Gy to 2~MGy.