The effect of the operation voltage on the leakage current of SiO2/Si3N4/SiO2 (ONO) stack is investigated which is used for the inter-poly dielectric (IPD) of the floating gate (FG) type NAND flash memory. In this work, the field dependent charge trapping mechanism of ONO stack and the effect of the trapped charges on the electrical characteristics are examined. The leakage current density-electric field (J-E) and the capacitance-voltage (C-V) characteristics are measured for various test samples of ONO stack by varying the voltage sweep ranges. The charge trapping/detrapping mechanisms of ONO stack are observed as the range of the applied sweep voltage is increased and then decreased to a given voltage, which is corresponding to the given electric field. The numbers of trapped and detrapped charges are extracted from the difference of J-E curves using the same recursive voltage sweeps and the effects on the electrical characteristics of ONO stack are demonstrated. Moreover, the dominant trapping layer is also investigated by varying the thickness of ONO stack. (C) 2014 Elsevier Ltd. All rights reserved.