Influence of the floating substrate potential on the characteristics of ESFI MOS transistors

A model is proposed to explain the anomalous current-voltage characteristics of ESFI MOS transistors. Due to the floating state the substrate potential of the ESFI transistor is increasing with increasing majority carrier current flowing through the substrate to source. In the region of multiplication by avalanche that effect will get quite pronounced. The change of substrate potential yields a change of the threshold voltage hereby increasing the drain current and resulting a bend in the I_D(U_D) curves. The assumptions of the model have been justified by additional experiments as with illumination of light or increased temperatures. Based on the physical model a computer program was developed to simulate the I_D(U_D) characteristics of ESFI MOS transistors of the enhancement type, resulting good agreement between measured and simulated characteristics.