Substrate bias dependence of subthreshold slopes in fully depleted silicon-on-insulator MOSFET's

Subthreshold slopes in submicrometer n-channel MOSFETs in depleted silicon-on-insulator (SOI) films were measured as a function of substrate bias and temperature, as well as drain bias. It is found that for low drain voltage, a simple capacitor model can explain the result. For large drain voltages, anomalously sharp threshold slopes are observed for very negative substrate biases, but the anomalous effects are greatly reduced with a more positive substrate bias. A qualitative model based on the charge state of the lower SOI interface is proposed to explain the dependence of the anomalous effects on substrate bias.>