New Measurement Technique for Sub-Bandgap Impact Ionization Current by Transient Characteristics of Partially Depleted SOI MOSFETs

We have developed a novel, sensitive measurement technique for the sub-bandgap impact ionization current in scaled metal-oxide-semiconductor field effect transistors (MOSFETs). In this technique, partially depleted silicon on insulator MOSFETs is utilized where the floating body potential is gradually charged by the impact ionization current. The transient increase of the body potential causes a decrease in the threshold voltage due to the body effect, resulting in a transient increase in the drain current. The impact ionization current is derived from the transient increase in the body potential. The derived impact ionization current is in good agreement with the direct current measurement. Furthermore, the new measurement technique is very sensitive even in the sub-bandgap region and measurements of less than 50 fA are demonstrated.