Comparative study of the radiation hardness of an analog CMOS pipeline, discrete MOS transistors and interface traps in MOS capacitors

The ZEUS experiment at HERA employs a custom made analog pipeline, manufactured with a 2 μm CMOS process. The standard transistor layout was not sufficiently radiation hard. After introducing thin oxide extension and guard bands, the pipeline worked after irradiation, up to 500 krad, with only minor performance degradation. The performance of the pipeline and of discrete transistors was studied before and after irradiation. Additionally, interface traps were investigated on MOS capacitors. All devices were made with the same process. The degradation of transistor parameters was related to changes in the parameters of the pipeline. Most effects in the circuit could be explained by the observed threshold voltage shift in the transistors. Interface trap densities were measured on MOS capacitors in the lower part of the silicon bandgap, obtained under different bias conditions during irradiation. The observed interface trap density is low. The threshold voltage shift is dominated by fixed oxide charges