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