The effects on the electrical properties of electron-cyclotron-resonance (ECR) nitride films grown at room temperature with different SiH4/N2 gas ratios from 7 sccm/43 sccm to 2 sccm/48 sccm are systematically investigated. Superior properties of the films with low bulk trap density 8×1017 cm-3, small trap cross section, high breakdown strength 12.12 MV/cm, and near-stoichiometric refractive index 2.0 are obtained when the gas ratio SiH4/N2 is 5 sccm/45 sccm, the microwave power is 210 W, and the chamber pressure is 0.5 mTorr. With the microwave power, total gas flow rate, and total pressure unchanged, the decrease in SiH4/N2 ratio lower than 5/45 results in larger trap density and some lower breakdown strength. On the other side, increasing SiH4/N2 ratio results in higher hydrogen content, lower breakdown strength, and films which are easily degraded during consecutive voltage sweep. High microwave power will eliminate the weak bonds and strengthen the electrical stability of the high SiH4/N2 ratio film.