We report bulk and interface charge densities in silicon nitride thin films deposited by plasma chemical vapor deposition from NH3-N-2-SiH4 Mixtures, at temperatures compatible with flexible plastic substrates. Bulk and interface charges are independently determined from measurements of flat band potential as a function of film thickness for a range of substrate temperatures and gas compositions. Increasing NH-SiH bond ratio in the deposited films (determined from infrared absorption) leads to a more positive interface charge and more negative bulk charge, and the trend in interface charge is consistent with a relation between charge and stress at the Si-SiNx interface. As substrate temperature is decreased from 250 to 50degreesC, the leakage is observed to decrease, the interface charge decreases, and the bulk charge changes from negative to net positive. (C) 2004 American Vacuum Society.