Power mos current sensefet temperature drift study and improvement by the help of 3D simulations

A sensefet monitoring is used for overload, open-load detection and load current analog feedback. The sensefet matching properties to the main power mos represent the main quality factor of the device. Its current should be proportional to the main power one, maintaining the same coefficient over the entire temperature and biasing working range. In this work the effects of the edge cells layout and process are analyzed by the help of 3D device simulations. The causes for the real to theoretical ratio mismatch and the drift behavior versus the temperature are put into evidence. The corrective actions allow to reach 1÷2% of drift in the range -40°C to 150°C. Only technological considerations are here faced, concerning the construction and optimization of the structure.