Effects of Gate Bias and Hydrogen Atmosphere on the Radiation Response of the MOSFET

摘要

Ionizing radiation produces hole-electron pairs in the oxide layers of metal-oxide-semiconductor (MOS) structures, generally resulting in a permanent or semi-permanent positive charge being trapped in the oxide. In the absence of a large electric field, recombination reduces the charge separation but net positive charge density results from the high diffusivity of the electrons relative to the holes and from the predominance of hole traps in the oxide, particularly near the Silicon/Silicon dioxide interface of silicon-based devices. The presence of an electric field during irradiation facilitates separation of the holes and electrons, thus reducing recombination and redistributing (or removing) the charge. The sensitivity of Metal Oxide Semiconductor Field Effect Transistor, (MOSFET) radiation sensors has been measured as a function of gate-to-source bias. The observed sensitivity-bias relation can be explained in terms of hole/electron recombination, charge trapping and charge transport in the oxide. To explain post-irradiation increases in the MOSFET readings, negative-charge trapping and detrapping in the oxide is proposed. The sensitivity of these MOSFETs has been found to be affected by the presence of hydrogen, indicating that hydrogen alters the trapping properties of the oxide. It may be possible to control the sensitivity of these sensors by controlling the hydrogen concentration at the time of hermetic packaging. Keywords: Holes (Electron deficiencies). Canada. (AW)